The cause of OCD is unknown. Both environmental and genetic factors are believed to play a role. Risk factors include a history of child abuse or other stress-inducing event. Drug-induced OCD Some medications and other drugs, such as methamphetamine or cocaine, can induce<unk>  (OCD) in people without previous symptoms. Some atypical antipsychotics (second-generation antipsychotics) such as olanzapine (Zyprexa) and clozapine (Clozaril) can induce OCD in people, particularly individuals with schizophrenia. Genetics There appear to be some genetic components of OCD causation, with identical twins more often affected than fraternal twins. Furthermore, individuals with OCD are more likely to have first-degree family members exhibiting the same disorders than matched controls. In cases in which OCD develops during childhood, there is a much stronger familial link in the disorder than with cases in which OCD develops later in adulthood. In general, genetic factors account for 45–65% of the variability in OCD symptoms in children diagnosed with the disorder. A 2007 study found evidence supporting the possibility of a heritable risk for OCD. A mutation has been found in the human serotonin transporter gene hSERT in unrelated families with OCD. A systematic review found that while neither allele was associated with OCD overall, in Caucasians the L allele was associated with OCD. Another meta-analysis observed an increased risk in those with the homozygous S allele, but found the LS genotype to be inversely associated with OCD. A genome-wide association study found OCD to be linked with SNPs near BTBD3 and two SNPs in DLGAP1 in a trio-based analysis, but no SNP reached significance when analyzed with case-control data. One meta-analysis found a small but significant association between a polymorphism in SLC1A1 and OCD. The relationship between OCD and COMT has been inconsistent, with one meta-analysis reporting a significant association, albeit only in men, and another meta analysis reporting no association. It has been postulated by evolutionary psychologists that moderate versions of compulsive behavior may have had evolutionary advantages. Examples would be moderate constant checking of hygiene, the hearth or the environment for enemies. Similarly, hoarding may have had evolutionary advantages. In this view, OCD may be the extreme statistical tail of such behaviors, possibly the result of a high number of predisposing genes. Brain structure and functioning Imaging studies have shown differences in the frontal cortex and subcortical structures of the brain in patients with OCD. There appears to be a connection between the OCD symptoms and abnormalities in certain areas of the brain, but that connection is not clear. Some people with OCD have areas of unusually high activity in their brain or low levels of a chemical called serotonin, which is a neurotransmitter that some nerve cells use to communicate with each other, and is thought to be involved in regulating many functions, influencing emotions, mood, memory and sleep. Autoimmune A controversial hypothesis is that some cases of rapid onset of OCD in children and adolescents may be caused by a syndrome connected to Group A streptococcal infections known as pediatric autoimmune neuropsychiatric disorders associated with streptococcal infections (PANDAS). OCD and tic disorders are hypothesized to arise in a subset of children as a result of a post-streptococcal autoimmune process. The PANDAS hypothesis is unconfirmed and unsupported by data, and two new categories have been proposed: PANS (pediatric acute-onset neuropsychiatric syndrome) and CANS (childhood acute neuropsychiatric syndrome). The CANS/PANS hypotheses include different possible mechanisms underlying acute-onset neuropsychiatric conditions, but do not exclude GABHS infections as a cause in a subset of individuals. PANDAS, PANS and CANS are the focus of clinical and laboratory research but remain unproven. Whether PANDAS is a distinct entity differing from other cases of tic disorders or OCD is debated. A review of studies examining anti-basal ganglia antibodies in OCD found an increased risk of having anti-basal ganglia antibodies in those with OCD versus the general population. Environment OCD may be more common in people who have been bullied, abused or neglected, and it sometimes starts after an important life event, such as childbirth or a bereavement. It has been reported in some studies that there is a connection between childhood trauma and<unk> -compulsive symptoms. More research is needed to understand this relationship better.
Obsessive–compulsive disorder
Obsessive–compulsive personality disorder
Conduct disorder
Major depressive disorder
Psychopathy
Anxiety disorder
Tourette syndrome
Eating disorder