since june 2002 , the finnish pediatric diabetes register and biobank has invited all pediatric patients diagnosed with diabetes in finland to participate in the register and the biobank . compared with the information provided by all the pediatric units in finland , the coverage of the register is 92% ( 25 ) . around 70% of the families participating in the register also provide blood samples for the biobank from the index case and/or the first - degree relatives as soon as possible after the diagnosis of the index case . the samples are analyzed for diabetes - related autoantibodies ( ica , iaa , gada , and antibodies to the islet antigen 2 molecule [ ia-2a ] ) and hla - dr - dqa1-dqb1 haplotypes ( 26 ) . families participating in the register receive a structured questionnaire ( supplementary data ) at the time of diagnosis of the index child . a diabetes nurse or doctor answers the questions regarding clinical status and degree of metabolic decompensation at diagnosis and assists the family with questions on the family history of diabetes . the total number of first - degree relatives ( parents and siblings ) is asked , but the number of second - degree relatives other than grandparents ( i.e. , siblings of parents ) is unknown . for parents , siblings , and grandparents , the diabetes status ( no , yes , or unknown ) and the diabetes type ( type 1 , type 2 , gestational , or other diabetes ) are asked separately , and families are asked to list any other relatives with type 1 diabetes . if the family is unsure of the diabetes type of a relative , the diabetes doctor or nurse classifies the disease according to the information provided by the family . for our analysis , however , parents with type 2 diabetes marked in the questionnaire were considered to have type 1 diabetes if autoantibodies other than iaa were detectable in their serum ( 8 of 2,916 , 0.3% ) . the legal guardians of the children and their siblings 18 years of age or older give informed written consent . the protocol has been approved by the ethics committee of the hospital district of helsinki and uusimaa . by october 2006 , the median age was 8.23 years ( range 016.98 ) , and 56.2% were male . we excluded children with age at diagnosis > 15 years , no information on their relatives in the register , or incomplete diabetes - associated autoantibody analyses by april 2007 . one child with an affected father and two affected brothers was excluded because a novel insulin gene mutation was recognized . we planned to exclude any autoantibody - negative children with diabetes occurring in three successive generations as suspected mody ( maturity - onset diabetes of the young ) cases . only the first child from any family to be diagnosed with diabetes and registered was included as an index case . the demographic characteristics of the children included in or excluded from the study did not differ . for most of the children ( 92.2% ) , the sample was drawn within 14 days . those with the serum sample taken > 30 days after the diagnosis ( 103 of 1,488 , 6.9% ) were excluded from the autoantibody analysis . we have shown that insulin antibody levels 1 month after the diagnosis correlate more strongly with the iaa titers at diagnosis than with insulin antibody levels 3 months later ( unpublished data ) , indicating that even insulin antibodies detected 30 days after the diagnosis reflect an autoimmune response rather than a response to exogenous insulin . 1 displays the grouping of the case subjects . for the analyses , the following categories were used . second , we used a classification into familial cases with affected first - degree relatives , familial with affected second - degree relatives , and familial with type 1 diabetes in both first- and second - degree relatives , as well as sporadic cases . third , a closer analysis of familial cases was performed according to who in the immediate family ( parent or sibling ) or extended family ( paternal or maternal second - degree relative ) had diabetes . grouping of the index case subjects according to who in the extended family was affected by type 1 diabetes . the dashed lines refer to the case subjects with affected relatives from more than one category of relatives . these case subjects are also included in the total number of each category of relatives . icas were analyzed with indirect immunofluorescense on human group 0 donor pancreas with 2.5 jdfu as the detection limit ( 27 ) . iaas , gadas , and ia-2as were quantified with specific radiobinding as - says ( 2830 ) . the cutoff limits for antibody positivity were determined as the 99th percentiles in 354 finnish , nondiabetic children and adolescents , and were 2.80 relative units ( ru ) for iaa , 5.36 ru for gada , and 0.77 ru for ia-2a . according to the 2005 diabetes autoantibody standardization program , the disease sensitivities of these assays were 44 , 82 , and 72% and specificities were 98 , 97 , and 100% , respectively . when calculating the median antibody titers , we included only samples at or above the cutoff for antibody positivity . hla typing of major dr - dq haplotypes was performed with a pcr - based , lanthanide - labeled hybridization method using time - resolved fluorometry for detection ( 26 ) . blood ph , plasma glucose , and -hydroxybutyrate levels of the index children were analyzed in local laboratories at the time of diagnosis . hemoglobin a1c was not recorded because the methods used locally were not standardized and , accordingly , varied considerably between laboratories , hampering any nationwide comparison . spss 17.0 and 19.0 statistical software packages ( spss , inc . , chicago , il ) were used for statistical analyses . cross tabulation ,  statistics , and fisher exact test were applied for comparing frequencies of different variables . differences in levels of variables were analyzed with student t test or one - way anova for parametric and mann - whitney u test / wilcoxon rank sum test or kruskal - wallis test with dunn post hoc test for nonparametric variables . a two - tailed p value of 0.05 or less was considered statistically significant , and bonferroni correction for multiple comparisons was not applied due to its overly conservative nature . since june 2002 , the finnish pediatric diabetes register and biobank has invited all pediatric patients diagnosed with diabetes in finland to participate in the register and the biobank . compared with the information provided by all the pediatric units in finland , the coverage of the register is 92% ( 25 ) . around 70% of the families participating in the register also provide blood samples for the biobank from the index case and/or the first - degree relatives as soon as possible after the diagnosis of the index case . the samples are analyzed for diabetes - related autoantibodies ( ica , iaa , gada , and antibodies to the islet antigen 2 molecule [ ia-2a ] ) and hla - dr - dqa1-dqb1 haplotypes ( 26 ) . families participating in the register receive a structured questionnaire ( supplementary data ) at the time of diagnosis of the index child . a diabetes nurse or doctor answers the questions regarding clinical status and degree of metabolic decompensation at diagnosis and assists the family with questions on the family history of diabetes . the total number of first - degree relatives ( parents and siblings ) is asked , but the number of second - degree relatives other than grandparents ( i.e. , siblings of parents ) is unknown . for parents , siblings , and grandparents , the diabetes status ( no , yes , or unknown ) and the diabetes type ( type 1 , type 2 , gestational , or other diabetes ) are asked separately , and families are asked to list any other relatives with type 1 diabetes . if the family is unsure of the diabetes type of a relative , the diabetes doctor or nurse classifies the disease according to the information provided by the family . for our analysis , however , parents with type 2 diabetes marked in the questionnaire were considered to have type 1 diabetes if autoantibodies other than iaa were detectable in their serum ( 8 of 2,916 , 0.3% ) . the legal guardians of the children and their siblings 18 years of age or older give informed written consent . the protocol has been approved by the ethics committee of the hospital district of helsinki and uusimaa . by october 2006 , the median age was 8.23 years ( range 016.98 ) , and 56.2% were male . we excluded children with age at diagnosis > 15 years , no information on their relatives in the register , or incomplete diabetes - associated autoantibody analyses by april 2007 . one child with an affected father and two affected brothers was excluded because a novel insulin gene mutation was recognized . we planned to exclude any autoantibody - negative children with diabetes occurring in three successive generations as suspected mody ( maturity - onset diabetes of the young ) cases . only the first child from any family to be diagnosed with diabetes and registered was included as an index case . the demographic characteristics of the children included in or excluded from the study did not differ . for most of the children ( 92.2% ) , the sample was drawn within 14 days . those with the serum sample taken > 30 days after the diagnosis ( 103 of 1,488 , 6.9% ) were excluded from the autoantibody analysis . we have shown that insulin antibody levels 1 month after the diagnosis correlate more strongly with the iaa titers at diagnosis than with insulin antibody levels 3 months later ( unpublished data ) , indicating that even insulin antibodies detected 30 days after the diagnosis reflect an autoimmune response rather than a response to exogenous insulin . 1 displays the grouping of the case subjects . for the analyses , the following categories were used . second , we used a classification into familial cases with affected first - degree relatives , familial with affected second - degree relatives , and familial with type 1 diabetes in both first- and second - degree relatives , as well as sporadic cases . third , a closer analysis of familial cases was performed according to who in the immediate family ( parent or sibling ) or extended family ( paternal or maternal second - degree relative ) had diabetes . grouping of the index case subjects according to who in the extended family was affected by type 1 diabetes . the dashed lines refer to the case subjects with affected relatives from more than one category of relatives . these case subjects are also included in the total number of each category of relatives . icas were analyzed with indirect immunofluorescense on human group 0 donor pancreas with 2.5 jdfu as the detection limit ( 27 ) . iaas , gadas , and ia-2as were quantified with specific radiobinding as - says ( 2830 ) . the cutoff limits for antibody positivity were determined as the 99th percentiles in 354 finnish , nondiabetic children and adolescents , and were 2.80 relative units ( ru ) for iaa , 5.36 ru for gada , and 0.77 ru for ia-2a . according to the 2005 diabetes autoantibody standardization program , the disease sensitivities of these assays were 44 , 82 , and 72% and specificities were 98 , 97 , and 100% , respectively . when calculating the median antibody titers , we included only samples at or above the cutoff for antibody positivity . hla typing of major dr - dq haplotypes was performed with a pcr - based , lanthanide - labeled hybridization method using time - resolved fluorometry for detection ( 26 ) . blood ph , plasma glucose , and -hydroxybutyrate levels of the index children were analyzed in local laboratories at the time of diagnosis . hemoglobin a1c was not recorded because the methods used locally were not standardized and , accordingly , varied considerably between laboratories , hampering any nationwide comparison . statistics , and fisher exact test were applied for comparing frequencies of different variables . differences in levels of variables were analyzed with student t test or one - way anova for parametric and mann - whitney u test / wilcoxon rank sum test or kruskal - wallis test with dunn post hoc test for nonparametric variables . a two - tailed p value of 0.05 or less was considered statistically significant , and bonferroni correction for multiple comparisons was not applied due to its overly conservative nature . at diagnosis , the index cases were between 0.28 and 14.99 years of age ( median 8.23 ) . a majority of the subjects were male ( 846 of 1,488 , 56.9% ) , and 80.6% ( 1,200 of 1488 ) had at least one biological sibling . the proportion of children with a first - degree relative affected by type 1 diabetes was 12.2% ( fig . twelve children had two first - degree relatives with type 1 diabetes ( 0.8% ) and one had four ( 0.1% ) . ninety children ( 6.2% ) had a father with type 1 diabetes , and 47 ( 3.2% ) had an affected mother . fifty seven subjects ( 3.9% out of a total of 1,488 children or 4.8% out of 1,200 children with at least one sibling ) had a sibling with type 1 diabetes . of the 1,488 children , 177 ( 11.9% ) had a second - degree relative affected by type 1 diabetes ( fig . 1 ) . the number of these relatives per child varied between one and five . thirty eight ( 2.8% ) had a paternal grandparent and 40 ( 2.8% ) a maternal grandparent affected by type 1 diabetes , whereas 54 ( 3.7% ) had an affected paternal sibling and 63 ( 4.2% ) an affected maternal sibling . taken together , 88 ( 6.0% ) index children had an affected second - degree relative from the paternal side and 97 ( 6.5% ) from the maternal side of the family . the proportions of children with affected grandfathers and grandmothers were similar , with 41 ( 2.9% ) children having an affected grandfather and 37 ( 2.6% ) an affected grandmother . among the 5,580 grandparents with information on their diabetes status , 79 ( 1.4% ) had type 1 diabetes . in summary , 324 children ( 21.8% ) had a first- and/or second - degree relative with type 1 diabetes , and 35 ( 2.4% ) had both an affected first- and second - degree relative . the age of the index cases at diagnosis did not differ between any categories of comparisons . both sexes equally often had a first - degree ( 12.2% of the boys and 12.3% of the girls , p = 1.00 ) or second - degree relative ( 12.4% of boys and 11.2% of girls , p = 0.53 ) with type 1 diabetes . similarly , both sexes equally often had a father with type 1 diabetes ( 6.4% of the boys and 6.0% of the girls , p = 0.82 ) , a mother with type 1 diabetes ( 3.3% of boys and 3.0% of the girls , p = 0.83 ) , or a sibling with type 1 diabetes ( 3.7% of boys and 4.1% of girls , p = 0.79 ) . however , the proportion of children with an affected paternal second - degree relative was 4.9% among boys and 7.5% among girls ( p = 0.06 ) . the respective proportion for affected maternal second - degree relatives was 7.8% for boys and 4.8% for girls ( p = 0.03 ) . a conspicuous majority of children with an affected maternal second - degree relative were boys ( 71.9% ) , when compared with those with an affected paternal relative ( 46.6% ) or sporadic cases ( 56.6% , p = 0.002 ) . at the time of diagnosis , the clinical condition was significantly poorer in sporadic than familial cases ( table 1 ) . accordingly , the sporadic cases had ketoacidosis ( p < 0.001 ) and impaired level of consciousness ( p = 0.02 ) more often than the familial cases . moreover , their weight loss was greater ( p < 0.001 ) , -hydroxybutyrate ( p < 0.001 ) and plasma glucose concentrations ( p < 0.001 ) were higher , and blood ph was lower ( p < 0.001 ) ( table 1 ) . when comparing four groups ( table 2 ) , it became evident that the less severe clinical condition at diagnosis was also true for children with an affected second - degree relative . demographic , metabolic , immunological , and genetic markers in index children with familial type 1 diabetes and sporadic cases demographic , metabolic , immunological , and genetic markers in index children with affected first - degree ( group i ) , second - degree ( group ii ) , or both first- and second - degree relatives ( group iii ) and sporadic cases ( group iv ) no significant differences in the frequencies or titers of various autoantibodies were observed when familial children were compared with sporadic cases ( table 1 ) , or when comparing four groups ( table 2 ) . however , the children with both affected first- and second - degree relatives tended to have a lower number of positive antibody responses ( table 2 ) . there were no major differences in the levels or frequencies of autoantibodies between the index children with affected parents or siblings . the children with familial type 1 diabetes carried the drb1 * 0401/2/4/5-dqa1 * 0301-dqb1 * 0302 ( dr4-dq8 ) haplotype more often than sporadic children ( 74.0 vs. 67.0% , p = 0.02 ) ( table 1 ) . comparison between the four groups ( presented in table 2 ) revealed that the only significant difference was in the frequency of the dr4-dq8 haplotype between sporadic cases and those with an affected second - degree relative ( 67.0 vs. 78.4% , p < 0.04 ) . when comparing the sporadic cases with those with an affected maternal or paternal second - degree relative , the index cases with affected maternal relatives more often carried the dr4-dq8 haplotype than the sporadic cases ( 80.7 vs. 67.0% , p = 0.01 ) . this finding differed significantly between the sexes , in that boys with affected maternal relatives more often carried the dr4-dq8 haplotype compared with boys with affected paternal relatives ( 81.0 vs. 58.5% , p = 0.03 ) or sporadic cases ( 81.0 vs. 66.5% , p = 0.03 ) ( supplementary table 1 ) . in contrast , girls with affected paternal relatives had dr4-dq8 ( 84.1 vs.67.7% , p = 0.04 ) and girls with affected maternal relatives had the dr4/non - dr3 genotype ( 68.0 vs. 45.1% , p = 0.04 ) more frequently when compared with the sporadic group ( supplementary table 1 ) . there were no differences in the hla genetics of the index children with affected parents or siblings . at the time of diagnosis , the clinical condition was significantly poorer in sporadic than familial cases ( table 1 ) . accordingly , the sporadic cases had ketoacidosis ( p < 0.001 ) and impaired level of consciousness ( p = 0.02 ) more often than the familial cases . moreover , their weight loss was greater ( p < 0.001 ) , -hydroxybutyrate ( p < 0.001 ) and plasma glucose concentrations ( p < 0.001 ) were higher , and blood ph was lower ( p < 0.001 ) ( table 1 ) . when comparing four groups ( table 2 ) , it became evident that the less severe clinical condition at diagnosis was also true for children with an affected second - degree relative . demographic , metabolic , immunological , and genetic markers in index children with familial type 1 diabetes and sporadic cases demographic , metabolic , immunological , and genetic markers in index children with affected first - degree ( group i ) , second - degree ( group ii ) , or both first- and second - degree relatives ( group iii ) and sporadic cases ( group iv ) no significant differences in the frequencies or titers of various autoantibodies were observed when familial children were compared with sporadic cases ( table 1 ) , or when comparing four groups ( table 2 ) . however , the children with both affected first- and second - degree relatives tended to have a lower number of positive antibody responses ( table 2 ) . there were no major differences in the levels or frequencies of autoantibodies between the index children with affected parents or siblings . the children with familial type 1 diabetes carried the drb1 * 0401/2/4/5-dqa1 * 0301-dqb1 * 0302 ( dr4-dq8 ) haplotype more often than sporadic children ( 74.0 vs. 67.0% , p = 0.02 ) ( table 1 ) . comparison between the four groups ( presented in table 2 ) revealed that the only significant difference was in the frequency of the dr4-dq8 haplotype between sporadic cases and those with an affected second - degree relative ( 67.0 vs. 78.4% , p < 0.04 ) . when comparing the sporadic cases with those with an affected maternal or paternal second - degree relative , the index cases with affected maternal relatives more often carried the dr4-dq8 haplotype than the sporadic cases ( 80.7 vs. 67.0% , p = 0.01 ) . this finding differed significantly between the sexes , in that boys with affected maternal relatives more often carried the dr4-dq8 haplotype compared with boys with affected paternal relatives ( 81.0 vs. 58.5% , p = 0.03 ) or sporadic cases ( 81.0 vs. 66.5% , p = 0.03 ) ( supplementary table 1 ) . in contrast , girls with affected paternal relatives had dr4-dq8 ( 84.1 vs.67.7% , p = 0.04 ) and girls with affected maternal relatives had the dr4/non - dr3 genotype ( 68.0 vs. 45.1% , p = 0.04 ) more frequently when compared with the sporadic group ( supplementary table 1 ) . there were no differences in the hla genetics of the index children with affected parents or siblings . this study had an optimal setting to characterize familial and sporadic type 1 diabetes in that the study subjects were derived from a nationwide register with a high level of ascertainment in the country with the highest incidence of type 1 diabetes globally . in keeping with earlier findings , we observed that 12.2% of the children with newly diagnosed type 1 diabetes had at least one affected first - degree relative ( 811 ) . in previous studies , the proportion of type 1 diabetes patients with affected second - degree relatives has varied from 4.8 to 16.7% ( 1,5,11,1719 ) , with a proportion of 16% reported for newly diagnosed pediatric patients ( 5,11 ) . in some studies , third - degree relatives ( 5,17,19 ) or only grandparents ( 18 ) have been included in the analyses , which hampers any subsequent comparison . in addition , misclassification of type 1 diabetes as type 2 diabetes in older individuals might affect the results , as type 1 diabetes in such individuals might be milder at diagnosis and not requiring immediate insulin treatment ( 18,31 ) . in our study , 11.9% of the children had type 1 diabetes in their second - degree relatives , a proportion similar to that of children with affected first - degree relatives . taken together , 21.8% had an affected relative among first- and/or second - degree relatives , making the true proportion of children with newly diagnosed sporadic type 1 diabetes < 80% . in accordance with earlier reports ( 812,15,17 ) , a higher proportion of fathers with type 1 diabetes than affected mothers reports on reduced risk of type 1 diabetes in the same - sex offspring of an affected parent , i.e. , fathers transmitting preferentially to daughters and mothers to sons , are controversial ( 3,4,9,12,16 ) . based on the data at hand our results suggest , however , a similar phenomenon at the level of second - degree relatives ; affected boys more often had maternal than paternal second - degree relatives with type 1 diabetes . although the statistical power of the analysis is limited , hla genetics support this finding ; boys with affected maternal relatives and girls with affected paternal relatives had higher frequencies of the high - risk hla haplotype dr4-dq8 . in general , the case subjects having affected grandfathers ( 2.9% ) and grandmothers ( 2.6% ) were equally distributed , and the proportions of type 1 diabetes from maternal ( 6.5% ) and paternal ( 6.0% ) second - degree relatives were equal . as our case subjects were ascertained through offspring rather than affected parents , differential transmission from fathers and mothers as well as reduced risk in the same - sex offspring could theoretically result from the male preponderance among type 1 diabetes cases ( 32 ) . sex differences in fecundity of affected fathers and mothers might cause a similar bias , but this could be excluded because affected fathers had an average of 2.18 children , compared with 2.02 among diabetic mothers ( p = 0.53 ) . as expected , those with prior experiences of type 1 diabetes in the immediate family had a milder metabolic decompensation at diagnosis than sporadic cases ( 8,13,21 ) . this can be readily explained by the better awareness of the parents in terms of early symptoms of type 1 diabetes facilitating a swift diagnosis and initiation of treatment . recognition of hyperglycemia with blood glucose self - measurement equipment readily available in these families could be part of the explanation . importantly , our results indicate that the metabolic status at diagnosis is ameliorated also if the relative with type 1 diabetes is a grandparent or parental sibling . in these families , the small group of children with type 1 diabetes in both first- and second - degree relatives demonstrated a tendency to have even less metabolic decompensation at diagnosis than those with only one affected patient in the family , emphasizing the accumulated knowledge of the disease in such families . as reported previously from finland ( 8) , the frequencies or levels of disease - associated autoantibodies in sporadic and familial cases of type 1 diabetes were alike . we were unable to reproduce the recent findings from israel where higher frequencies of iaa as well as a higher number of positive antibody responses were observed among familial cases ( 13 ) . as hypothesized , the index cases with affected relatives in the extended family , especially among second - degree relatives , carried the dr4-dq8 haplotype more often than the sporadic cases . ( 8) have reported in familial type 1 diabetes a higher frequency of dr3/dr4 heterozygosity and lower frequency of protective alleles ( dqb1 * 0602 , 0603 , or 0301 ) . similar differences have been observed in other studies ( 20,22,23 ) , but not in all ( 24 ) . our observations suggest that the diabetes status of second - degree relatives affects the frequency of the dr4-dq8 haplotype in the index case more than that of the first - degree relatives . this finding is difficult to explain , although affected grandparents have been shown to transmit their hla haplotypes to affected grandchildren more often than expected ( 18 ) . our findings of genetic differences between familial and sporadic cases implicate a weak contributing effect of differential hla dr - dq haplotype frequencies to the familial clustering of type 1 diabetes . the data should be interpreted with caution , however , since these haplotypes are relatively frequent in the general population , and the differences are of borderline statistical significance and only seen in terms of one haplotype . a limitation of our study is the lack of knowledge of the total number of second - degree relatives except grandparents , which prevents us from reporting the actual prevalence of diabetes in parental siblings . in addition , a questionnaire - based study design is prone to recall bias either by over- or underreporting family members with type 1 diabetes . in this survey , information on second - degree relatives was insufficient for completion of all the fields in the questionnaire in 122 families ( 8.2% ) . given that these cases were counted as nonfamilial cases in the analysis , our results are likely to be conservative and somewhat underestimate the prevalence of familial diabetes . our study setting lacked a control group of nondiabetic finnish children , and we are thus not able to directly compare the prevalence of type 1 diabetes in families of diabetic and nondiabetic children . however , the prevalence of 2.9% of type 1 diabetes in siblings observed here can be compared with 0.5% in the general population < 20 years of age in finland in 2006 . according to these estimates , the siblings of affected children have , compared with the general population , a sixfold risk of type 1 diabetes . our register - based data on the time of diagnosis is a point estimation , and thus the life - time risk of type 1 diabetes in relatives , especially among siblings , is underestimated . our study shows that , considering the extended family history , the proportion of true sporadic cases of type 1 diabetes at diagnosis may be < 80% . the proportion of case subjects with type 1 diabetes in first- and second - degree relatives was similar . the case subjects had equally affected paternal and maternal relatives , but an interesting difference in the distribution of sexes was observed between these groups . a novel observation is that the metabolic status at diagnosis is ameliorated in familial type 1 diabetes also when the affected person is a second - degree relative . children with familial type 1 diabetes had an autoantibody profile very similar to that of sporadic cases , implying similar pathogenetic disease mechanisms . familial cases carried the dr4-dq8 haplotype more often than sporadic cases , implying that the enrichment of hla class ii