Increased risk of insulin-dependent diabetes for siblings of diabetic children with the DR 3 haplotype of the mother

Among 285 caucasoid families genotyped for HLA-A, B, C, DR including at least one insulin-dependent diabetic child, we have studied the effect of the DR3 and DR4 antigens inherited from the father or the mother (DR3p, DR3m, DR4p and DR4m, respectively) on the recurrence of the disease among siblings; families with affected parents being excluded, a total of 37 affected and 200 non affected siblings have been taken into consideration. Among the DR3, DR4 positive siblings, the DR4p/DR3m genotype was observed at a greater frequency than the DR3p/DR4m genotype among affected, but not among unaffected siblings. Comparing the respective frequencies between affected and unaffected siblings, the relative risk was 8.1 (p less than 10(-6) among DR4p/DR3m positive siblings, but is was not significantly increased among DR3p/DR4m positive siblings. The excess of maternal DR3 among affected siblings of diabetic children could be due to a gestational event associated with HLA-DR3, e.g. education of the fetal immune repertoire or the transmission of a viral infection by the mother to the fetus during pregnancy, after reactivation of the latent viral disease.