The gut microbiome regulates a relationship with the brain known as the gut–microbiota–brain (GMB) axis. This interaction is influenced by immune cells, microbial metabolites and neurotransmitters. Recent findings show gut dysbiosis is prevalent in autism spectrum disorder (ASD) as well as attention deficit hyperactivity disorder (ADHD). There are previously established negative correlations among vitamin D, vitamin D receptor (VDR) levels and severity of ASD as well as ADHD. Both vitamin D and VDR are known to regulate homeostasis in the brain and the intestinal microbiome. This review summarizes the growing relationship between vitamin D/VDR signalling and the GMB axis in ASD and ADHD. We focus on current publications and summarize the progress of GMB in neurodevelopmental disorders, describe effects and mechanisms of vitamin D/VDR in regulating the microbiome and synoptically highlight the potential applications of targeting vitamin D/VDR signalling in neurodevelopment disorders. There has been increasing emphasis on the role of the microbiota in physiology, suggesting that the microbiota can be considered as another ‘human organ’. The gut microbiota is affected by intrinsic  and extrinsic  factors . There iDiagnostic and Statistical Manual (DSM-5) defines ASD diagnosis as reduced social-emotional reciprocity and nonverbal communication, whereas ADHD is characterized by hyperactivity and inattentiveness [The GMB axis describes the bidirectional relationship between the central nervous system (CNS) and gut microbiome, and this relationship is thought to be involved in neurodevelopmental disorders . GMB funnual DSM- defines Vitamin D and VDR have novel functions beyond their classical roles in bone development. VDR activates innate immunity and affects intestinal development patterns. In the adult, vitamin D has regulatory roles in mucosal immunity, host defense and inflammation via VDR. This interaction involves host factors and the gut microbiome –11. Vita2.13 to 1014 microorganisms, which collectively exceed the number of human cells in the entire body [An adult gut is inhabited by approximately 10ire body . The micire body . Mice moire body , Alzheimire body  and amyoire body .Bacteroides was associated with higher scores on Mullen's Early Learning Composite at age two [Clostridiales was associated with poorer communication scores in the Ages and Stages Questionnaire 3 , personal and social scores  at age three [Gut microbiota alterations may be associated with cognitive as well as social deficits. In a cohort of 89 one-year-olds, a relative overabundance of the genus  age two . Investige three .p = 0.003) compared with controls [et al. [The relationship between GI health and ASD individuals is growing. A longitudinal study of 124 children with ASD and 242 controls revealed that children with ASD had an increased incidence of constipation  increase in ASD risk following maternal infection during pregnancy . Notablysymptoms . The samsymptoms . IL-6 lesymptoms . IL-1β ierocytes . Biologierocytes .β, IL-6 and TNF-α are found elevated in the fetal brain and ASD symptoms result [Clostridium difficile, a pathogenic microbe [C. difficile remains subclinical, an increase in C. difficile composition is associated with atopic conditions in childhood C. difficile levels persisted when measured months later. Indeed, breast milk feeding for at least six months is protective against ASD [In mice, maternal administration of the viral mimic polyriboinosinic-polyribocytidylic acid (poly(I:C)) induces infection. In these offspring, IL-1s result . When vis result . An impo microbe , in the  microbe . While minst ASD . Vitamininst ASD  may contLactobacillus and Bifidobacterium) was administered to 13 ASD children (ages 3–12 years) to treat GI symptoms for a 19-week trial period. The Vibosome treatment showed significant improvement in GI complaints (p = 0.02) [n = 42; ages 2.5–8 years) for 12 months found that supplementation reduced behavioural irritability (p = 0.01) [n = 30) were given a prebiotic supplementation (B-GOS) to investigate the influence on stool and bowel movement as well as social behaviour scores in ASD individuals. The data were not reported, and researchers report no trend of GI discomfort reductions following B-GOS intervention [Bifidobacterium infantis plus prebiotic bovine colostrum product (BCP) mixture in ASD children  with constipation, diarrhoea and/or irritable bowel syndrome. Participants were treated with BCP only and the combination mixture of B. infantis plus BCP for 12 weeks. Overall, 75% (6/8) reported greater GI improvement with BCP only treatment compared with 25% (2/8) improvement via combination treatment. A reduced frequency of diarrhoea (BCP: p = 0.021 versus combination: p = 0.021) and normal stool consistency (BCP: p = 0.042 versus combination: p = 0.015) was observed in ASD individuals [n = 20) to ASD-diagnosed children (n = 18) rectified constipation, diarrhoea, indigestion and abdominal pain in ASD individuals for 18 weeks. After daily maintenance doses for seven to eight weeks, the study found that 80% children with ASD had decreased GI symptoms (p < 0.001) and reduced ASD severity (p = 0.002) [Some growing ideas to reduce GI irregularities and ASD severity including supplementation of probiotics or prebiotics and fecal microbiome transplant (FMT) have been examined in ASD clinical trials . Probiot = 0.02) . Anothern ages 3– years to = 0.01) . Howeverrvention . A growi= 0.002) . A follo= 0.002) . The FMTet al. hypothesized that altered microbiome composition and increased GI dysfunction may be present in ADHD children [pShannon = 0.036) in ADHD patients compared with controls while β diversity varied between patients and controls . At the family level, Bacteroidaceae was overabundant in ADHD patients. The authors suggested the genus Neisseria and elevated levels of Bacteroides spec. could be associated with juvenile ADHD [Bifidobacterium was abundant (p = 0.034) in the gut of ADHD individuals (n = 19) compared with healthy controls (n = 77). Additionally, a predicted enzyme involved in the synthesis of a dopamine precursor , cyclohexadienyl dehydratase (CDT) was significantly increased (p = 0.038) in ADHD patients compared with controls. Bifidobacterium abundance may contribute to the observed differences of CDT in a multiple regression analysis (p < 0.001). This finding suggests a hallmark of ADHD, diminished neural reward anticipation , may be correlated with overabundance of Bifidobacterium in the gut which was positively associated with elevated CDT levels [Ming children . The linile ADHD . ExternaT levels .n = 17; aged 7–12 years). There was no variability among treatment group and placebo in an ADHD scale (ADHD-IV-RS). The treatment group had significantly higher α diversity (p = 0.005) compared with controls, changes in Actinobacteria , reduced Bifidobacterium (adj p < 0.05) and an inverse relationship between Bifidobacterium and ADHD-IV-RS (p = 0.04) [Bifidobacterium involvement in ADHD as well as probiotics as a possible treatment.Studies regarding gut microbiome rebalance in ADHD are limited. A 10-week pilot study investigated the effects of a probiotic mixture  on fecal microbiome content in diagnosed ADHD children ( = 0.04) . These rin utero, may produce an ADHD-like phenotype [ADHD is also associated with inflammation dysregulation. In comparison to studies regarding ASD, many fewer studies have been performed correlating maternal infection and ADHD. However, one large cohort study found maternal genitourinary infection was associated with an increase in risk for ADHD (OR = 1.29). Pre-eclampsia was also implicated (OR = 1.19), and both together conveyed highest risk OR = 1.53) . Compari . Comparhenotype . Neonatehenotype . We were3.2, D3), and binds to the VDR in the cytoplasm. Bound VDR then associates with the retinoid X receptor, and the entire complex enters the nucleus to function as a transcription factor. The greater than 900 DNA sequences modulated by the VDR complex are called vitamin D response elements (VDRE) [2D3-regulated VDR-specific, Cyp24 hydroxylase gene. Indeed, approximately 3% of the mouse and human genomes are regulated directly or indirectly by the vitamin D endocrine system, further supporting the possibility of widespread effects of vitamin D and VDR in disease mechanisms [Vdr gene variation shapes gut microbiome and abundance of Parabacteroides affected by the VDR signalling in both human and mouse samples [The human body intakes vitamin D as cholecalciferol through fortified dairy and oily fish or through the conversion of 7-dehydrocholesterol by ultraviolet light . Once ins (VDRE) . Notablys (VDRE) ,61. VDR s (VDRE) . Target s (VDRE)  cathelics (VDRE) ,64, β-dechanisms –67. In tchanisms . Mice mochanisms , inhibitchanisms , and regchanisms . Further samples .ASD has been negatively correlated with maternal serum vitamin D concentration through many phases of development. Meta-analysis of eight studies found that an increase in autism-related traits and diagnosed ASD was correlated with decreased maternal serum vitamin D concentrations. Reductions in cognitive ability were most associated with low concentration in early-mid pregnancy . This asp = 0.041) in fok1, a VDR polymorphism, compared with 82 healthy controls. ASD individuals had decreased serum vitamin D levels which support the notion that VDR activity is strongly tied to serum vitamin D levels in ASD patients [Although correlation of maternal vitamin D concentration with ASD may diminish through third trimester, the molecule regains foremost importance during the early years of life. In the infant, serum vitamin D has been negatively correlated with ASD diagnosis  and ASD patients . Vitaminpatients ,81. Comp−1) and low (less than 38.4 nmol l−1) groups, the high concentration group showed a reduced incidence of hyperactivity–impulsivity symptoms  and total ADHD-like symptoms  when observed at age 4 [−1 increase in serum vitamin D at age 4–5 years [−1 versus 2.08 ± 0.42 ng ml−1, respectively) [The observed effect of maternal serum vitamin D concentration is varied in ADHD. In a cohort study, which stratified maternal serum vitamin D into high (greater than 50.7 nmol lat age 4 . A cohor–5 years . In a dictively) . On the ctively) , and a cctively) . The ten−1 from average has a 2.57 OR (95% CI = 1.09–6.04). Similarly, prospective studies show that low perinatal vitamin D concentrations increase risk of diagnosis later in life . This meta-analysis must be interpreted with caution, as removal of one study abolishes the correlation [p < 0.001) in ADHD children compared with controls . The results for these experiments suggest ADHD may have an effect on VDR levels.A stronger correlation exists between low serum vitamin D in the growing child and ADHD. Meta-analysis of available studies showed that concentration decreases of 6.75 ng mlrelation . Conside4.Gut microbiota controls neurobehaviour via modulating brain insulin sensitivity and metabolism of tryptophan, the precursor of serotonin . Increaset al [in vivo experiment linking maternal vitamin D and offspring TPH1/2 expression has been attempted.The BALB/c mice containing a loss-of-function mutation in TPH2 showed a 20% decrease in TPH2 mRNA and 28% fewer TPH2 immunolabelled neurons compared with TPH2 wild-type C57BL/6 J mice . Russo eet al  found thet al . To our TPH2 is also responsible for producing serotonin in the enteric nervous system (ENS) in the gut. Serotonergic neurons are the first to develop in the ENS where they direct the patterning of future neurons and neurotransmitter secretors . TPH2 knIn vitro, adding norepinephrine to culture of rat mesencephalic cells increased the differentiation of dopaminergic neurons [A hypothesis in the axis of ADHD is alteration of dopamine (DA) and norepinephrine function. DA functions in emotional response, reward, motivation, motor activity and attention, while norepinephrine is a an adrenergic neurotransmitter activating the sympathetic nervous system . Decreas neurons .Following release into the synaptic cleft, dopamine activity is terminated via breakdown by monoamine oxidase  or via rNorepinephrine is a second neurotransmitter implicated in ADHD pathogenesis. Analogous to the perturbation seen with DA, overactivity of the norepinephrine transporter (NET) causes rapid reuptake of NE into the presynaptic cytoplasm . An altein utero. Rats born to vitamin D-deficient mothers display grossly increased lateral ventricle volume and altered appearance of the dopaminergic substantia nigra [in utero between E12 and E15 which supports the correlation of maternal vitamin D deficiency in ADHD [In ADHD, alterations in neurodevelopment are evident ia nigra . VDR actia nigra . In rats in ADHD . DAT ove5.In humans, metabolites such as short-chain fatty acids (SCFA) are produced via bacterial fermentation in the colon , in contPropionate is the SCFAs most produced by ASD prevalent microorganisms ,121. SCFBacteroidetes, Bacteroides and Parabacteroides, with an increase in Akkermansia, Sutterella and Lachnospiraceae. The brains of mice colonized with ASD-associated microbiota display alternative splicing of ASD-relevant genes. Metabolome profiles of mice harbouring ASD microbiota  show distinct metabolites in the colon may modulate ASD behaviour. The metabolites taurine and 5-aminovaleric acid (5AV) (p = 0.0243) were significantly reduced in mice harbouring ASD microbiota compared with control germ-free mice. Metabolome profile differences between mice models may result from microbial metabolism [In order to understand gut microbiome contributions in developing ASD, researchers transplanted microbiota from ASD human donors to germ-free mice and found ASD microbiota may induce hallmark autistic behaviours. Mice colonized with microbiota from ASD human donors had a different microbial composition: a significant decrease in tabolism . This sttabolism , whereastabolism . Clinican = 23) and neurotypical children (n = 31) aged 11–12 years old found ASD children had higher levels of total SCFAs (136.6 ± 8.7 versus 111.1 ± 6.6 mmol kg−1) compared with neurotypical controls. Specifically, ASD individuals had higher concentrations of acetate, propionate, butyrate, isobutyrate, valerate and isovalerate compared with neurotypical children. Researchers concluded higher concentrations of fecal SCFAs in ASD may not be disastrous to the health of ASD participants [n = 23) had significantly higher levels of isopropanol (p = 0.022) in stool compared with healthy controls (n = 21) individuals aged 4–17 years old. High levels of isopropanol were hypothesized to cause GI disturbances like abdominal pain [Clostridium beijerinckii and C. aurantibutyricum convert acetone to isopropanol [n = 26) and healthy control (n = 24) and found significantly reduced levels of acetate, propionate and butyrate in ASD individuals [Multiple clinical trials found variation in fecal SCFA within ASD individuals. A clinical trial comparing the levels of fecal SCFAs between ASD children  at birth is suggested to increase ASD risk. PA is a propionate deficiency caused by reduced propionyl-CoA carboxylase (PCC) activity in the liver and other tissues. Interestingly, PA and ASD share most of their core symptoms and multiple case studies report ASD as a comorbidity to PA –138. HowBifidobacterium predicts ADHD by upregulating synthesis of phenylalanine, a precursor of dopamine, and decreases neural reward anticipation [n = 102), who exhibited increased kynurenine (+48.6%) and reduced serum KA (−11.2%) and XA levels (−12.5%) compared with healthy controls (n = 62) [Fez1, a gene in the nervous system, which leads to hyperactivity and impulsivity phenotypes [Fez1-KO mice. Furthermore, ADHD studies in metabolites are limited. It would be novel to identify the types and levels of metabolites in ADHD individuals.The SCFA levels associated with ADHD pathogenesis is largely unknown due to difficulty in identifying definite biomarkers. A pilot study investigated microbial differences in the microbiome between ADHD and neurotypical adolescent boys. The investigators found a significant difference between control and ADHD microbial composition. They also found a relative overabundance of cipation . A potencipation . These mcipation . VDR defcipation . These f(n = 62) . Limitatenotypes . This moOur research has shown that loss of intestinal epithelial VDR leads to an increase in butyrate-producing bacteria in intestinal inflammation . It may 6.VDR gene as well as low vitamin D in the serum. It is still unclear if reduction of vitamin D/VDR signalling in the intestinal lumen contributes to the low microbial diversity seen in the gut of ASD and ADHD individuals. We speculate that VDR may modify gut microbiota in ASD and ADHD through GMB axis, such as cytokines, neurotransmitters and SCFAs (ASD is characterized by a multitude of social deficits while ADHD is characterized by inattentiveness, impulsivity and hyperactivity . Howevernd SCFAs .Figure Gut microbial patterns in ASD individuals show decreased microbial diversity and some GI irregularities. Vitamin D supplementation reduced irritability in ASD individuals, yet the influence on GI dysfunction and microbial composition is limited. Additionally, the influence of vitamin D supplements via intestinal VDR should be explored to understand how VDR exerts influence in ASD. Immune activity in genetic ASD resembles immune activity in inflammatory bowel disease yet the influence of VDR in ASD immune activity is lacking. VDR may alter neurotransmitter activity in ASD via transcriptional regulation of tryptophan metabolism, the precursor of serotonin, yet the implications of VDR in serotonin activity are limited. Additionally, metabolites enhanced by VDR loss are unexplored in ASD cases. Fecal SCFAs concentrations are altered in ASD individuals yet inconsistencies among studies, suggest that factors, such as diet, age, location and/or cohort size may contribute to the observed differences. Characterization of abnormal SCFAs within ASD warrants further investigation.Bifidobacterium which acts as a functional target for dopamine. Its influence on the GI barrier is unexplored.There are indirect relationships linking VDR and ADHD via GMB axis. Activation of VDR drives the expression of a rate limiting step in dopamine production, tyrosine hydroxylase. VDR deficiency enhances tryptophan metabolites which are pronounced in the serum of some ADHD individuals. The gut microbiota in ADHD revealed an overabundance of Understanding of gut microbiota involvement in ASD and ADHD is growing. It is highly unlikely that the breadth of effects of vitamin D/VDR dysregulation is limited to just these two disorders. The interplay between brain development, gut microbiota and the VDR may be implicated in other CNS diseases.


Substance use disorders and insomnia are common in the general population, and particularly among adults with attention-deficit/hyperactivity disorder (ADHD). Here we investigated the relationship between insomnia, alcohol consumption and ADHD symptoms.n = 235, 41.3% males) and controls  completed a questionnaire assessing insomnia , alcohol consumption (Alcohol Use Disorders Identification Test), and current ADHD symptoms . The majority of the sample (95%) gave additional information about childhood ADHD symptoms , and information about lifetime occurrence of an internalizing disorder was included as part of background information.Adults with an ADHD diagnosis (Compared to controls, the ADHD group reported a higher frequency of insomnia, a higher quantity of consumed alcohol and a higher frequency of internalizing disorders. Current and childhood ADHD symptoms were more severe in those with than without insomnia. Scores on ADHD symptom scales were explained by the presence of insomnia and internalizing disorders, while the contribution from alcohol consumption was restricted to the control group.The high functional impact of insomnia, alcohol misuse and internalizing disorders is well known. The present study contributed by focusing on their relations to ADHD symptoms, and by showing that strong relations were not restricted to adults with a clinical ADHD diagnosis. By this, the results put a critical light on a categorical delineation between adults with an ADHD diagnosis and population selected controls, and call for further studies including dimensional metrics of ADHD symptoms and co-occurring problems. Attention-deficit/hyperactivity disorder (ADHD) is a neurodevelopmental disorder, characterized by symptoms of inattention and/or hyperactivity/impulsivity that are persistent across situations and time . ADHD inInsomnia is characterized by sleep loss due to problems initiating and maintaining sleep and/or early-morning awakening, with an inability to return to sleep. Insomnia is thus a sleep disorder with potentially high impact on the lives of those afflicted  are also common in adults with ADHD . Like inThe association between problematic alcohol use and insomnia is well established e.g., . Insomni1 where most of the participants in the ADHD group were recruited from a national registry of adults diagnosed in Norway from 1997 to May 2005. The diagnostic assessment was made by expert committees according to the ICD-10 research criteria  , includie DSM-IV .Alcohol consumption was assessed by self-reports on the Alcohol Use Disorder Identification Test AUDIT; . The scaThe 25-item version of WURS  was usedCurrent ADHD symptoms were assessed by the 18-item version of ASRS  addressiThe majority of the participants provided information about gender, age, education, work, if they had an ADHD diagnosis as a child and if they ever had experienced significant episodes of depression or anxiety. The latter was included as a measure of lifetime occurrence of an internalizing disorder, defined from a “yes” response on the following question: “Have you ever experienced significant anxiety or depression?”t-tests (with Levene test) and Chi-square tests when appropriate. The associations between the severity measure of alcohol consumption and the scores on the two symptom scales were included in a bivariate correlation analysis. Finally, a set of regression analyses were computed with each of the two ADHD symptom scales as the outcome variable. A preparatory step was included to identify background variables that should be included as control variables. Then a first set of regression analyses included only insomnia or alcohol consumption as independent variables, followed by a set of analyses including these two variables together with the control variables selected in the preparatory step. The results were calculated for the full sample and for each of the two groups.The SPSS software, version 25, was used for all statistical analyses. A set of explorative analyses included independent samples n = 235) and the control group (n = 184) were not significantly different regarding gender and age, but the ADHD group included fewer participants with the highest education than the control group and a lower percentage in active work participation  than without insomnia (n = 55). In the ADHD group, the proportion of participants reporting insomnia and internalizing disorders were similar among adults who reported that they had been diagnosed with ADHD during childhood and participants who had been diagnosed as adults, and the symptom scores were not significantly different between the two ADHD subgroups (p > 0.01).The ADHD  and the control group (p = 0.006). The differences were non-significant when comparing those with and without insomnia and when comparing alcohol consumption in those with and without internalizing disorders within each of the two groups. The differences were, however, statistically significant when the full sample was included in the analysis, both for insomnia  and internalizing disorders . The alcohol use was also more severe in the 27 adults with ADHD who reported a childhood diagnosis [15.59 (5.89)] than in adults with ADHD without such a diagnosis .n = 20) in the ADHD and 1.6% (n = 3) in the control group reporting drinking 10 or more units every time of drinking. The corresponding percentages for a frequency of at least 2–3 times a week were 57.2% for the ADHD group and 69% for the control group. Among those with insomnia, 46.9% in the ADHD and 24.6% in the control group reported drinking at least 5–6 units, with 10.8% (n = 17) in the ADHD and 3.8% (n = 2) in the control group reporting drinking 10 or more units every time of drinking. Among the 109 adults in the ADHD group with both insomnia and internalizing disorder, 11% reported alcohol consumption at the highest level.The difference between the ADHD and the control group was much higher for alcohol consumption quantity than for frequency of use, with 42.1% of the ADHD group and 21.1% of the control group drinking at least 5–6 units, with 8.5%  and the WURS scores  in the control group, and for none of the scales in the ADHD group . n = 3) with a very high quantity of alcohol consumption.The range of scores on the ASRS and the WURS were from 4–70 and 3–97, respectively. The ranges were wide in both the ADHD (8–70 and 12–97) and the control group (4–56 and 0–87), with significantly higher mean scores in the ADHD group on both scales and with significantly higher scores in adults with than without insomnia . StatistThe preparatory regression analysis, computed to select control variables to be included in the following analyses, identified statistically significant contributions from education and internalizing disorders. The first step of the analysis, including either insomnia (a) or severity of alcohol consumption (b) as the independent variable, showed that each variable contributed significantly to explain the two symptom scores, with insomnia contributing with as much as 20% explained variance in the full sample . When edThe present study showed a higher frequency of insomnia and a higher frequency and quantity of alcohol consumption in adults with ADHD than in adults selected from the general population. Participants with insomnia reported higher current (ASRS) and childhood (WURS) ADHD symptoms scores and a higher level of alcohol consumption than adults without insomnia. The presence of insomnia, the severity level of alcohol consumption and number of alcohol units consumed each time of drinking were associated with severity level of ADHD symptoms. When controlling for demographic variables and insomnia in a linear regression analysis, the severity of alcohol consumption contributed significantly to the ADHD symptom scores only in the control group, while insomnia and lifetime occurrence of internalizing disorder retained significant contributions in both groups.The high prevalence of insomnia and alcohol use in the ADHD group is expected from results in previous studies, showing a higher risk of both insomnia  and alcoThe results from the present study support arguments for a dimensional view on ADHD symptoms  and for The present study confirmed previous studies showing a female predominance both regarding reports of ADHD symptoms , insomniThe main strength of the present study is the inclusion of a clinically validated patient sample and a control sample randomly recruited from the Norwegian population without any formal exclusion criteria. We believe that this strengthens the validity and clinical utility of our findings. As already mentioned, there is a potential for some undiagnosed cases of ADHD being included in our control group and that adult onset cases may have different characteristics than cases identified in childhood. All cases and controls reported past and present ADHD symptom scores using the ASRS and WURS to screen for ADHD symptoms. Based on reported cut-off scores on these scales and an around 2% estimated prevalence rate of ADHD in the adult population , we beliThe results should, however, be viewed in light of several limitations. First of all, self-reports may have biased the results. Reports on alcohol use may for example be under-reported while mental health complaints like insomnia may be overrated. Furthermore, recall bias may have influenced the retrospective reports of childhood behavior on the WURS . The ASRThe present study indicated a strong impact of insomnia and the presence of lifetime internalizing disorders on core symptoms of ADHD, but the direction of the causality could not be stated from the available data. Although adults with an ADHD diagnosis showed signs of a higher quantum of alcohol consumption than controls, its impact on level of ADHD symptoms was restricted to the control group when insomnia and lifetime internalizing disorders were controlled. The present study should therefore inspire further studies on the role of co-existing problems along the full dimension of ADHD symptoms. Information from such studies are expected to improve our assessment and ability to target treatment programs for adults disturbed by symptoms associated with an ADHD diagnosis as well as in adults with problems like insomnia, AUD, depression and anxiety. The stronger association between alcohol consumption and ADHD related symptoms in the control group put a critical light on a categorical delineation between adults with a clinical ADHD diagnosis and controls.The data are not publicly available due to restrictions in the approval given by the Regional Committees for Medical and Health Research Ethics in Norway. The data that support the findings of this study are available on request from the corresponding author, AL.The studies involving human participants were reviewed and approved by the Norwegian Regional Committee for Medical and Health Research Ethics, RECWest [IRB #3 ]. The patients/participants provided their written informed consent to participate in this study.AL was responsible for the design and analyses, interpretation of results, and drafting the manuscript. DJ organized the data and commented on the design, results, and drafts of the manuscripts. JH contributed substantially as the head of the adult ADHD project and commented on the design, results, and drafts of the manuscript.The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.


Attention-deficit/hyperactivity disorder (ADHD) is one of the most common psychiatric diagnoses in childhood and adolescence. It is characterized by age-inappropriate levels of inattention, impulsivity, and hyperactivity and is associated with long-term academic, social, and mental health problems , 2. BothA range of nutrients have been linked to brain development and functioning, and diet may be a relevant factor in the high incidence and prevalence of mental disorders . As earlMajor dietary compounds proposed to be helpful in the treatment of ADHD include micronutrients, such as minerals and vitamins, and polyunsaturated fatty acids (PUFAs). Several studies have demonstrated reduced blood plasma levels of various minerals, such as magnesium, iron, and zinc in children with ADHD at group level, and their supplementation may reduce ADHD symptoms in individuals with respective deficiencies. However, evidence in support of this is lacking . The queThe role of omega-3 PUFAs in the pathophysiology and therapy of ADHD is controversial , 18. Sine.g. heterogeneity of design type, dosage, trial duration, or assessment of response. In the case of PUFAs, the mode of administration (fish or supplements), the type of PUFA employed (omega-3 or omega-6 or combination), and the ratio between DHA, EPA, and AA are likely to be important. An increase in the ratio between blood levels of omega-6 to omega-3 PUFAs has been suggested to be more significant in children with ADHD than the absolute concentrations of either  on children and adolescents with newly diagnosed ADHD were examined in a case–control study . Low adhCross-sectional investigations of the effects of micronutrients and diet usually focus on one or several compounds without regard to other lifestyle factors, such as physical activity or sedentary behavior. Recent studies have demonstrated the interrelationships between diet and lifestyle in ADHD. For example, children with ADHD were found to be almost twice as likely to show a reduced number of healthy behaviors . MoreoveThe gut microbiome appears to play an important role in the bidirectional communication between gut and brain (gut–brain axis). Gut microbiota composition and function have recently been associated with several mental and neurodevelopmental disorders . It has The role of food hypersensitivities in ADHD is a promising avenue worthy of further exploration. A systematic review of meta-analyses of double-blind placebo-controlled trials found no convincing evidence of therapeutic efficacy of artificial food color elimination, while the few-foods diet, which excludes many foods and additives, may offer new treatment options . The hypIn conclusion, unhealthy dietary patterns may precede a poor nutritional biochemistry status affecting ADHD behaviors, and the management of nutrition and diet should always be considered as an avenue towards improving ADHD symptoms. While several lines of evidence point to a potential role of micronutrients and diets in ADHD, a number of caveats need to be considered before any therapeutic recommendation can be made. Observational studies demonstrating associations between diet and micronutrient levels in people with ADHD and the presence or severity of symptoms do not allow any conclusions on causal relationships, since the preference for certain foods or dietary patterns may be a consequence of ADHD behaviors. While a role of single micronutrients in the treatment of ADHD at group level is not supported by current evidence, therapeutic benefits of supplementation may depend on pretreatment nutrient status and may be confined to individuals with specific micronutrient deficiencies. Potential severe adverse effects of micronutrient supplements need to be considered, especially when administered at supra-physiological doses over extended periods of time. Furthermore, the role of whole diets should be explored. Generally improved lifestyle choices may provide more substantial benefits to children with ADHD than dietary changes alone.The administration of an oligoantigenic diet with subsequent reintroduction of nutrients provides a more personalized approach to ADHD, which can reveal intolerances or allergies to foods and allows the assessment of their impact in ADHD. The high response rate to an oligoantigenic diet of approximately 60% found in several studies indicates that food intolerances may be important in the pathophysiology of ADHD. This intervention should therefore be considered in all children with ADHD. Individuals responding favorably to the diet should undergo an oral food challenge in order to identify individual food intolerances. Future investigations should use blinded designs and long-term outcome follow-up.The author confirms being the sole contributor of this work and has approved it for publication. The author declares that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.


Starting from 2013, the number of unvaccinated people alarmingly increased in Italy; therefore, in 2017 a new Vaccine National Plan was approved. Healthcare workers (HCWs), especially public health professionals , have an important role in informing and promoting vaccinations. In this context, the Italian Study Group of Hospital Hygiene of the Italian Society of Hygiene, Preventive Medicine and Public Health (GISIO-SItI) conducted a national survey to assess knowledge, attitude, and practices towards recommended vaccinations among PHPs. The survey was conducted during October 2019 with an anonymous questionnaire distributed to PHPs attending the 52° SItI National Congress. Overall, 57.1% of operators answered correctly to all seven recommended vaccinations, 12.8% reported to be vaccinated for all seven recommended vaccinations, while 30% were naturally immunized. A higher immunization coverage was reported for anti-hepatitis B (88.9%) and measles (86.1%), and 81.3% of the participants reported being offered the influenza vaccination during the 2018/2019 season. The majority of our sample indicated that hepatitis B (95%) and influenza (93.7%) were the recommended vaccines for HCWs, while less was known regarding varicella, pertussis, diphtheria, and tetanus boosters every 10 years. PHPs who were vaccinated (or who intended to be vaccinated) were more likely to recommend vaccinations to their patients and provided a reassuring example to those hesitant patients. Finally, this is the first study that identified good algorithms (using the techniques of machine learning as Random Forest and Deep Learning) to predict the knowledge of PHPs regarding recommended vaccinations with possible applications in other national and international contexts. Vaccines are considered one of the most effective and safest preventive measures at population level, followed by screening intervention ,2,3,4. NHaemophilus influenzae b invasive diseases, varicella, pneumococcal infections, measles, pertussis, influenza, and its corresponding complications [Decreasing immunization coverage caused the onset of cases or outbreaks of vaccine-preventable diseases (VPDs), such as ications ,11.Haemophilus influenza type b, pertussis, measles, mumps, rubella, and varicella (MMRV). The NPVP led to important policy changes, including the introduction of new vaccine recommendations (offered actively and free of charge) and the addition of new target populations, such as adults at a higher risk of infection and the elderly. However, further efforts are necessary to reach other vulnerable groups, including healthcare workers (HCWs) [In 2017, a new National Plan for Vaccine Prevention (NPVP) was approved in Italy , followes (HCWs) . In parts (HCWs) .In order to increase adherence to vaccination recommendations, information campaigns and communication strategies should be implemented. In this context, HCWs, especially public health professionals , have an important role in informing, advising and promoting vaccinations, contrasting vaccine safety fears, tackling vaccine hesitancy, and emphasizing the benefits and value of vaccines . AlthougIn Italy, several studies have been conducted on HCW vaccination coverage ,20,21,22The Italian Society of Hygiene, Preventive Medicine and Public Health (SItI), a group of more than 2000 PHPs, engages in promoting and protecting citizens’ health through vaccination, among other practices. Therefore, the Italian Study Group of Hospital Hygiene of the SItI (GISIO-SItI) conducted a national survey to assess knowledge, attitudes, and practices towards recommended vaccinations among PHPs.N = 2030), and assuming a response proportion of 50% [The survey was conducted in October 2019 with an anonymous questionnaire distributed during the 52° SItI National Congress, to PHPs that were a part of the SItI. A sample of at least 968 enrolled individuals would have been required to investigate the selected variables in the PHPs population examined. The sample was calculated by a sample size calculator, based on the reference population of SItI members  inferred by completion of the questionnaire, and they were not remunerated for their contribution. This questionnaire was accompanied by an information sheet that outlined the rationale for the study and explained that participation was voluntary, that the compilation took a few minutes, that they would have to deliver answers immediately and that full confidentiality and anonymity would be maintained. No personally identifiable information was collected in the questionnaire.The investigation was performed in accordance with the World Medical Association’s Declaration of Helsinki and did not include any experiment involving human or biological human samples, nor research on identifiable human data. Therefore, the study protocol received ethical and scientific approval by Department of Biomedical Science and Human Oncology, University of Bari Aldo Moro  with the number 0407_2019.N = 2) and attitude (N = 9) regarding the recommended vaccinations for HCWs and their immunization practices (N = 3). Three questions pertaining to attitudes were measured on a seven-point Likert scale with options from “strongly disagree” to “strongly agree.”The questionnaire consisted of multiple-choice questions divided into two sections. In the first part of the survey, there were seven questions about demographic and personal characteristics , professional setting, and occupation. The second part of the survey consisted of 14 questions about PHPs’ knowledge . The alpha values achieved were 0.975 and 0.972 for the pilot study and for the multicenter study, respectively. Data from the pilot were included in the final analysis.p-value < 0.05 was regarded as statistically significant.The information collected was entered into a database (Google forms) and analyzed using R version 3.6.3. . A descriptive analysis was performed considering demographic and professional characteristics of participants and answers provided by the sample. Data regarding conditions and behaviors were reported as the number and percentage of respondents; these variables were compared between the two groups “agreement” and “disagreement” using the Chi-squared test. A From 0–3 correct answers ;From 4–6 correct answers ;7 correct answers .In order to evaluate the possible influence on the variable “knowledge of recommended vaccinations for HCWs” (dependent variable), the results of seven responses on recommended vaccinations were grouped in one scored variable. The value of this variable was represented by the sum of the correct answers for each operator, assigning one point for each right question. Subsequently, ranges of scores were identified as follows:Sex of the respondents ;Age of the respondents;Length of practice;Professions of the HCWs ;Professional Setting ;Operative Units/Service ;Region of the HCWs ;Are you vaccinated or naturally immunized against Hepatitis B? ;Are you vaccinated or naturally immunized against Measles? ;Are you vaccinated or naturally immunized against Mumps? ;Are you vaccinated or naturally immunized against Rubella? ;Are you vaccinated or naturally immunized against Varicella? ;Are you aware of the existence of a structured protocol for the vaccination of HCWs where you work? ;I have no opinion on vaccinations (rating from 0–7);I believe that the risk of contracting a preventable vaccine disease and transmitting it to a patient is low (rating from 0–7);I believe that vaccinations by health professionals are a prerequisite for working in the health sector and being suitable for the job (rating from 0–7);It is better to acquire natural immunity to diseases rather than through vaccinations (rating from 0 to 7);I fear the possibility of adverse events resulting from vaccinations (rating from 0–7);Do you think it is necessary to implement the knowledge of health professionals about vaccinations? (rating from 0–7).Subsequently, the variables not related to knowledge of the recommended vaccinations were not considered . The result was the selection of 19 independent variables. Descriptive responses were coded to numbers  ,28 in orMachine learning algorithms, in particular those of Random Forest  and Deepn; Xnn not normalized: value of each variable at record n; Max(X): max value of each variable; Min (X): min value of each variable.The 1050 questionnaires collected were randomly mixed in order to test these algorithms. Then, all independent variables were normalized, to make the different units of measurement uniform and comparable, through the following formula :Xn = , the second part containing 30% of the data was subsequently used to evaluate the quality of the model (testing phase) .In order to run Deep Learning models, Rectified Linear Unit (ReLU) was used as the activation function. The “softmax” function at the output layer was used to better classify variables ,35 and tTo assess the accuracy of the developed models, confusion matrices were used between the predictive values of the models and the real values of the part of the testing dataset. The accuracy of the model was calculated by comparing the number of data correctly classified by the model compared to the real data as numerator and the number of data of the whole dataset as denominator.To evaluate the order of importance of the variables and related graphic processing, the permutation-based VI scores method  was usedLastly, an analysis was conducted to test the variables influencing the immunization status according to sex, age, profession, length of practice, occupation setting, operating unit, region, and presence of existing structured protocol for vaccination at their work structures. For this analysis, a Poisson regression model was applied.For the application of inferential statistics analysis, the Shapiro–Wilk test was applied; for the verification of normality, Wilcoxon Mann–Whitney, Kruskal–Wallis, Dunn post hoc, Fisher’s F, and Chi-squared tests were used. All statistical tests were two sided.Among the total of 2030 participants to National Congress SItI, 1050 PHPs agreed to participate and returned the survey for an overall response rate of 51.7%. The main demographic and professional characteristics of the study participants are displayed in Overall, 12.8% of PHPs reported being vaccinated for all seven recommended vaccinations, while 30% were naturally immunized. In particular, 2% were naturally immunized for Hepatitis B, 44.5% for Measles, 40.3% for Mumps, 37.9% for Rubella (39.2% of women), and 65.4% for Varicella. Overall, 81.3% (854/1050) of the participants were recommended to get influenza vaccination during the 2018/2019 season. Recommendations were mostly made by the Occupational medicine services  or by other colleagues  mainly through communication by the Health Authority .2 = 40.6, p < 0.0001; χ2=6.7, p = 0.009; χ2 = 28.7, p < 0.0001; χ2 = 173.6, p < 0.0001; χ2 = 191.9, p < 0.0001, respectively in five reasons). Full agreement response to adherence to anti-influenza vaccination were more frequently reported . The last reason showed the prevalence of disagreeing responses . In particular, 84.7% of enrolled PHPs considered anti-influenza vaccination an important tool to protect themselves and their patients.A total of 65.5% (688/1050) of PHPs reported a structured protocol for vaccination at their workplace, and 60% (768/1050) of the sample recommended vaccinations to their patients, according to new NPVP, during medical practice.p < 0.001). In the case of measles, mumps, rubella, and varicella, this difference was statistically significant both between vaccinated and unvaccinated and between naturally immunized and unvaccinated (p < 0.001).PHPs that were vaccinated against hepatitis B suggested vaccination more often than those who were not vaccinated  from 50.3–65.6%. The Random Forest model  had a better performance (73.6%) and was used to identify the order of importance of the 19 variables that had the greatest impact on the knowledge of HCWs regarding vaccinations. The most important variables influencing knowledge of recommended vaccinations were age (11.9%), length of practice (11.2%), region (10.9%), operating unit (6.9%), and profession (5%).The model highlighted that the knowledge of recommended vaccinations is higher at a younger age, it drops to the lowest point around 45 years, and then it rises slightly. Similarly, the knowledge is higher at minimum and maximum duration of practice, while it tends to drop for PHPs with intermediate duration of practice (about 25 years). The Italian northern regions seem to have greater knowledge than the Italian central and southern regions. PHPs engaged in epidemiology and biostatistics and public hygiene and health service had greater knowledge of vaccinations. Finally, physicians were more aware of these vaccinations.p-value < 0.0001).Inferential statistics tests on the above five variables were used in order to understand whether the simulation data corresponded to reality. No parametric tests were used because the distribution of the responses was not normal .Comparison between the respondents aged 23–38 years and the rest of the respondents confirmed that this age group was more aware of HCW recommended vaccinations . In particular Dunn’s post hoc test confirmed that 0–10 years of practice was more aware of HCW recommended vaccinations compared to 11–20 years , 21–30 years , and 30–40 years .Comparison between the respondents for the classes of length of practice  revealed a significant difference . In particular, through Dunn’s post hoc test, it was noted that the Northern Italian regions knew more about vaccinations than Central Italian Regions  and Southern Italian Regions .Comparison between geographical areas  revealed a significant difference  revealed statistically significant differences. In particular, with Dunn’s post hoc test, the public hygiene and health service OUs were found to have greater knowledge of the recommended vaccinations compared to all other OUs .For the Operating Units (OUs), the Kruskal–Wallis test . In particular, Dunn’s test highlighted how physicians were more aware of the recommended vaccinations than biologists  and nurses .Finally, regarding professions, the Kruskal–Wallis test confirmed the statistical significance of the results . Regarding Region, Northern Italy Regions are more aware of HCWs’ recommended vaccinations . Moreover, other variables influencing positively aware of HCW recommended vaccinations were the existence of a structured protocol for the vaccination of HCWs in the work structures , having less fear of adverse events resulting from vaccinations , and having done the vaccination against Hepatitis B .The Poisson Regression Model led to similar results of Random Forest Model. The younger age  and the less length of practice seems to influence more aware of HCW recommended vaccinations , profession , and presence of existing structured vaccination protocol in their work structures ;Anti-hepatitis B vaccination was associated with younger age  and older age ;Anti-measles vaccination was associated with male sex , profession , and operational units ;Anti-mumps vaccination was associated with older age , older age , profession , operational units , and presence of existing structured vaccination protocol in their work structures ;Anti-rubella vaccination was associated with female sex  and profession ;Anti-varicella vaccination was associated with female sex , region , and presence of existing structured vaccination protocol in their work structures ;Anti-diphtheria–tetanus–pertussis vaccination was associated with profession , older age , profession , and presence of existing structured vaccination protocol in their work structures .Anti-influenza vaccination was associated with male sex :Several surveys have been carried out worldwide on the knowledge, attitudes, and practices of HCWs in relation to vaccinations ,38,39, bAccording to our experience, referring to PHPs, 57.1% of the study sample was aware of all recommended vaccinations for HCWs (with a higher degree of knowledge in northern regions than in southern regions), unlike some other Italian studies that included all HCWs and reported lower values ,24.Younger PHPs and with fewer years of practice had more knowledge about recommended vaccinations; this may be due to the fact that less time had passed since obtaining their degree. Furthermore, consistent with other studies ,40, physOverall, the majority of our sample indicated that hepatitis B and influenza were recommended vaccines for HCWs, as reported in previous national investigations ,24, whilInadequate knowledge among PHPs may result in the transfer of false information to patients and the public. Therefore, it is important to continue implementing educational campaigns for PHPs, and in general for HCWs, on vaccination because they have been consistently identified as the most influential and trusted source of information on vaccine-preventable infectious disease ,41.In our study, only 12.8% of PHPs received all seven recommended vaccinations, and immunization status revealed inadequate vaccine coverage, i.e., below 95% for all recommended vaccinations examined. This result is not comforting, since, despite the significant impact of the media, PHPs have been identified as the most important source of information on vaccination for the general public; therefore, the willingness of health professionals to recommend immunization is crucial . PHPs amIn line with previous studies ,24,26, hConsistent with other studies , youngerRegarding measles and rubella, a reported high vaccination coverage was found in our survey, thanks to the National Plan of Measles and Congenital Rubella Elimination (PNEMoRC) 2010–2015, which strongly recommended vaccination of susceptible adults at risk of contracting and transmitting disease, such as health professionals . In factIn our study, women reported significantly higher vaccination coverage for rubella compared to men. This is consistent with the fact that, in Italy, rubella vaccination has been offered free of charge to women in adolescence and childbearing age since the seventies. In our sample, 39.2% (241/615) of women were naturally immunized towards rubella disease.Concerning influenza, it has been demonstrated that about 25% of HCWs contract the virus every year; thus, they can transmit the infection to patients, especially during the asymptomatic period . KnowledCompared to previous studies conducted in some European countries including Italy and targeted to HCWs ,24,49,50Our findings revealed that older workers had a higher likelihood to have been vaccinated for influenza, which is consistent with findings from other authors ,20, probOur study showed that most PHPs believe vaccinations are a prerequisite for eligibility to work in the healthcare sector (73.5%), and most reported the existence of a structured protocol for HCWs vaccination in their workplace (65.5%), which was associated with being vaccinated for hepatitis B, rubella, diphtheria–tetanus–pertussis, and influenza.Fortunately, only a minority of PHPs reported several reasons for not being vaccinated: they did not consider themselves at risk for VPDs, and they had uncertainty regarding vaccine safety, such as in other studies regarding HCWs . These bOn the other hand, the current Covid-19 pandemic and the great expectance for a vaccine  could reThe authors are aware of some potential limitations of this study. Firstly, the cross-sectional nature limits inferences on the directional causality of the associations observed in this study. Secondly, no information was given about no-responders  since they did not give their consent to participate to the survey. Therefore, the conclusion of the study might not be generalizable to all Italian PHPs. Thirdly, the information about vaccination status was self-reported rather than record-review. This might be prone to recall, declaration, or desirability biases; therefore, an over- or underestimation of coverage could occur. However, the fact that the survey maintained full confidentiality and anonymity may suggest that the responses were likely to be authentic, with minimal social desirability bias.Despite these potential biases, the wide response to the questionnaire (over 50% of the population) reduces the risk of the non-representativeness of the sample compared to the entire population. Finally, to our knowledge, this is the first study to identify good algorithms that are capable of predicting the knowledge of PHPs regarding recommended vaccinations, with possible applications in other national and international contexts. However, the algorithms can be improved with a higher degree of accuracy through more numerically conspicuous “training data” and consideration of other independent variables (sources of information about immunizations or data concerning socio-demographic characteristics). These considerations may be the basis for further research.Our study provides useful insights for learned societies, such as SItI, which are in charge of supporting the implementation of evidence-based national-level vaccination policies and improving the knowledge of vaccination among PHPs. PHPs could promote immunization by removing prejudices and including educational and implementation strategies to improve vaccine adhesion and confidence among people. Finally, the implementation of algorithms could represent an innovative tool to better target educational campaigns.


Attention-deficit/hyperactivity disorder (ADHD) is a neurodevelopmental disorder that has become increasingly prevalent worldwide. Its core symptoms, including difficulties regulating attention, activity level, and impulses, appear in early childhood and can persist throughout the lifespan. Current pharmacological options targeting catecholamine neurotransmissions have effectively alleviated symptoms in some, but not all affected individuals, leaving clinicians to implement trial-and-error approach to treatment. In this review, we discuss recent experimental evidence from both preclinical and human studies that suggest imbalance of excitation/inhibition (E/I) in the fronto-striatal circuitry during early development may lead to enduring neuroanatomical abnormality of the circuitry, causing persistence of ADHD symptoms in adulthood. We propose a model of precision medicine care that includes E/I balance as a candidate biomarker for ADHD, development of GABA-modulating medications, and use of magnetic resonance spectroscopy and scalp electrophysiology methods to monitor the effects of treatments on shifting E/I balance throughout the lifespan. AThere is emerging evidence that GABA and glutamate levels and their ratio contribute to the neurobiological etiology of ADHD and related neurodevelopmental disorders ,28. SeveResting-state GABA and glutamate concentrations in the frontal, striatal and premotor areas have been consistently reported as altered among children and adults with ADHD. Children with ADHD show reduced GABA concentrations in the motor cortices , striatuImportantly, GABA and glutamate concentrations are heavily influenced by the time of day, arousal state, and environmental changes ,45,46,47A synapse density [Spectral Slope: Not surprisingly, alterations in GABA inhibition are strongly implicated in abnormal neural oscillations marked by E/I imbalance. In neurophysiology studies, neural oscillation at gamma frequency range is highly correlated with GABA content in healthy and diseased individuals ,56. The  density . A large density ,61, whic density . Only tw density  found a  density . Thus, sLimitations: To date, there is no single genetic variant , neurocoEEG is a non-invasive, relatively low-cost method for measuring neural activity and therefore presents as a highly attractive method for measuring E/I in clinical patients. Moreover, many research EEG systems involve easy application of gel-free electrode caps, making it a feasible tool for use in outpatient settings. On the other hand, as with other neuroimaging methodologies, scalp electrophysiology is sensitive to artifact sources. In particular, muscle movement, cardiac signal, and power lines artifacts require data cleaning steps that may distort the original signal and introduce a degree of error. The use of multiple, repeated trials reduces part of this error, but continued biomarker development would benefit from confirmation with other methodologies . For insNeural E/I balance is critical to synaptic plasticity and neuronal growth and pruning. The maturation of the nervous system is shaped by activity-dependent tuning of synaptic connections and large-scale regional connections between neural networks. Within local networks in particular, GABA-releasing synapses sculpt neural connections in developing brains  and stabThe administration of stimulant medication is shown to normalize atypical brain connectivity measures among children with ADHD ,72,73,74Neuroimaging research is consistent with altered connectivity of brain networks in ADHD, particularly in the PFC and striatum . Recent Longitudinal studies indicate atypical long-term neural connectivity among individuals with ADHD. In a large, prospective study of youth, Kessler and colleagues  found thCatecholamine agonists are believed to increase the E/I ratio by increasing availability of excitatory neurotransmitters . HoweverGABA- and glutamate-modulators, such as arbaclofen, bumetanide, and tiagabine, have already been tested for treatment of neurodevelopmental disorders that frequently co-occur with ADHD, such as epilepsy , autism At the time of this writing, there are few published trials of GABAergic and glutamatergic treatments targeting ADHD symptoms. Long-term treatment of an oral GABA supplement, Gamalate@B6, has been reported to decrease hyperactivity and improve attention in adults with borderline to mild intellectual disability and coexisting ADHD . In anotWhile research on direct effects of GABAergic modulators on ADHD symptoms is limited, there is ample evidence to suggest that catecholamine-targeting stimulant medications may simultaneously affect GABAergic neurotransmission. For example, mouse brain slice research has shown that extracellular GABA in the striatum can be brought into dopaminergic axonal terminals by vesicular monoamine transporters ,114; wheThe literature reviewed here supports a model in which interactions among GABA, glutamate, and catecholamine neurotransmissions underlie E/I imbalance in the brains of very young children with ADHD. This imbalance likely propagates atypical neural development and network connectivity, leading to long-term ADHD symptom persistence and associated psychopathology. Structural and functional brain abnormalities reported among adolescents and adults with ADHD may be understood as a consequence of reduced synaptic signaling during experience-dependent stages of early neurodevelopment. However, due to the lack of prospective studies of E/I balance in infants who go on to develop ADHD, we cannot fully rule out that ADHD-like behaviors lead to E/I imbalance in later development. We find hope in reports that indicate this developmental cascade can be at least partially normalized by correction of E/I imbalance via administration of psychostimulant medications, even into adulthood. However, individual responses to stimulant and non-stimulant interventions vary considerably; thus, it remains a challenge for medical caregivers to predict treatment effectiveness without reliable biomarkers or clear demographic indicators . Precision medicine care depends upon two critical components: (1) availability of multiple treatment options; and (2) identification of reliable, valid biomarkers that map onto these available interventions. In ADHD, the first goal has at least partially been achieved. Multiple psychostimulant classes and non-stimulants exist, each offering slight variations in neurotransmitter targets, mechanisms, and duration of effect. However, side effects and tolerability restrict the impact and effectiveness of current treatments with few predictors of adverse events. The development of GABAergic and glutamatergic medications show promise for ADHD as well as other neurodevelopmental disorders, and merit continued investigation, particularly among children who do not tolerate stimulant medications well or non-responders. With respect to the second criteria for precision medicine, to date, traditional neuroimaging and genetic methods have thus far fallen short of identifying a reliable biomarker for ADHD. Despite some common trends, the genetic heterogeneity of ADHD and the fact that most individuals are not diagnosed until school age contributes to considerable variability in neural signatures among affected individuals. However, we believe that E/I imbalance, particularly in the frontal-striatal circuitry, may present a unifying, developmentally stable biomarker of ADHD. The challenge at this point will be to quantify E/I and test for short- and long-term associations with treatment response. We advocate for (1) the use of MR spectroscopy to measure effects of pharmacological treatment on excitatory and inhibitory neurotransmitters; and (2) characterization of changes in EEG 1/f spectral slope over the course of development, to serve as a normative comparison from which to quantify deviant trajectories associated with ADHD. These non-invasive, complementary approaches have both been used successfully in very young children as well as individuals with neurodevelopmental disorders. Most importantly, given the increasing prevalence of ADHD worldwide and its individual and societal impacts, these endeavors will be worth the financial and intellectual investment.


Background: The Child and Adolescent Dispositions Scale—parent rating (CADS-P) explores three emotional dispositions that may enlarge the probability of future externalizing problem behavior. The English version has proven its psychometric quality within a population-based sample of children and adolescents. The presents study investigates the German version of the CADS-P by examining a clinically referred sample of children with externalizing behavior problems.Methods:The sample included 132 children aged 4–11 years with a diagnosis of attention- deficit/hyperactivity disorder (ADHD) or oppositional defiant disorder (ODD). The factor structure of the CADS-P was evaluated using exploratory (EFA) and confirmatory factor analyses (CFA). Reliability was estimated using internal consistency . Validity was assessed through linear regression analyses, with symptoms of externalizing  and internalizing behavior problems  as criterion variables and the three CADS-P factor scores as predictors.Results:After eliminating eight items due to insufficient psychometric properties, EFA and CFA supported a three-factor solution for the German CADS-P. Cronbach's alpha coefficient exceeded α = 0.70 for all subscales. Mostly, as predicted, the CADS-P dimensions were associated with symptoms of ODD/CD and ADHD and symptoms of anxiety and depression.Conclusions:The present study provides evidence for the cross-cultural validity of the CADS- P in a non-English-Speaking country. Results show that the German version of the CADS-P is a reliable and valid parent questionnaire for assessing prosociality, negative emotionality and daring as emotional dispositions that may enlarge the probability to develop externalizing problem behavior.Trial Registration: The study was approved by the review board of the Medical Faculty of the University of Cologne (ID 09-123) and was pre-registered at ClinicalTrials.gov (ID: NCT01350986). Attention-deficit/hyperactivity disorder (ADHD), oppositional defiant disorder (ODD), and conduct disorder (CD) represent the most common forms of childhood disorders and can be subsumed under the term externalizing behavior problems. According to the Diagnostic and Statistical Manual of Mental Disorders (DSM-5) , which consists of 26 items , ADHD and other psychopathology in terms of external validity. In line with Lahey et al. , we assuClinicalTrials.gov (ID NCT01350986). To increase the sample size, an outpatient sample was additionally recruited at the Department of Child and Adolescent Psychiatry at the University Hospital of Cologne. The following inclusion criteria were applied to both samples: Child (a) aged 4–11 years, (b) attending a kindergarten, primary school, or special school, and (c) meeting the diagnostic criteria for ADHD or ODD according to DSM-IV-TR ; 82% were boys. Twenty percent of these children met the DSM-IV criteria for ADHD combined type, 7% for ADHD inattentive type, 21% for ODD, 43% for both ADHD combined type and ODD, and 9% for ADHD inattentive type and ODD. The diagnoses were generated on the basis of a structured interview using the German Diagnostic Checklists for ADHD and ODD, which assess the diagnostic criteria according to DSM-IV and ICD-10 . Additionally, data were available from 31 children of the outpatient population. Thus, the total clinical sample comprised 132 children with a mean age of 7.56 years  is a parent-rated questionnaire which was designed to assess children's emotional disposition toward sympathetic response to others , negative emotional response to threat, frustration and loss , and positive response to novelty and risk (daring). The original version of the CADS-P contains 26 items  for the adaptation of test of some cultures to others. Subsequently, the final wording of each one of the items was outlined in order to adapt them to the correct expression in German. Like the original questionnaire, the items were rated on a 4-point Likert scale ranging from 0  to 3 (very much). Subscale scores  and a total score were computed by averaging the associated item scores.The Symptom Checklist for Oppositional Defiant Disorder and Conduct Disorder—parent rating  is part of the German Diagnostic System DISYPS-II, and measures symptoms of ODD and CD according to DSM-IV-TR and ICD-10  is also part of the DISYPS-II and measures symptoms of ADHD according to DSM-IV and ICD- 10  , Mplus  fit statistic, where a p > 0.05 was considered to indicate adequate model fit. Second, we report the comparative fit index (CFI) and the Tucker-Lewis Index (TLI), with a suggested cut-off for acceptable fit of CFI/TLI > 0.90  were examined with regard to the total scale and the subscales. Values of 0.30 ≤rit≤ 0.50 were considered as moderate and values >0.50 as high  , suggesting that the factors represent different constructs and that a higher-order factor was not indicated.The fit statistics for the CFA are presented in ) Field, . An init) Field, , item 21) Field,  indicate) Field,  the RMSE) Field, ; the CFI) Field,  but not ) Field, . Standar) Field, . FactorsAll three factors of the modified CADS-P model (model II) demonstrated good internal consistencies see . Cronbact = −2.35, p < 0.05) and negative emotionality . However, in contrast to the proposed assumption, the symptoms were not significantly predicted by daring  were significantly predicted by prosociality . Additionally, symptoms of hyperactivity/impulsivity were significantly related to daring . As predicted by the model, symptoms of depression and anxiety, measured by the internalizing problems scale of the CBCL, were significantly related to negative emotionality β = −0.27, t = 2.19, p < 0.05).Symptoms of ADHD (inattention and hyperactivity/impulsivity—FBB/ADHS) were significantly related to negative emotionality, as predicted  in the study by Lahey et al. .'The datasets generated and analyzed during the current study are not publicly available due to obligation to secrecy toward the participants. Queries can be sent to the last author ( All procedures performed in studies involving human participants were in accordance with the ethical standards of the institutional and/or national research committee and with the 1964 Helsinki declaration and its later amendments or comparable ethical standards. Informed consent was obtained from all children included in the study. Written informed consent was obtained from their parents.TD performed the statistical analysis and drafted the manuscript. JT made substantial contributions to the analysis and interpretation of data. CH and MD designed and coordinated the study. DW was involved in drafting and revising the manuscript. All authors read and approved the final manuscript.The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.