Insulin dependent diabetes mellitus epidemiology: HLA genotype study in 12 north eastern Italian families with two siblings affected by type I diabetes.

The purpose of our study was to evaluate the relationship between the histocompatibility antigens and type I diabetes mellitus in families living in the north-eastern part of Italy. In each family two siblings were affected by diabetes. HLA-antigens were determined with the lymphocytotoxicity test, utilizing antisera of the series A-B-C-DR. The phenotypic frequencies were compared with those observed in controls. We showed that diabetes has a strong association with HLA DR 3 and/or DR 4 antigens. In particular we registered high frequency of compound heterozygous DR 3 - DR 4 subjects, and this fact supports the hypothesis of the existence of two different genes for diabetes associated with these HLA antigens. Moreover we observed a particular haplotype segregation with a very high percentage of HLA identity between patients belonging to the same family, confirming the association between HLA and genetic susceptibility to insulin dependent diabetes. These results confirm data in the literature and, completed by other data from other patients' families living in our area, will be useful in providing reliable genetic counselling.