The prevalence of IDDM in the first degree relatives of children newly diagnosed with IDDM in Austria - a population-based study

Insulin dependent diabetes mellitus shows a strong familial predisposition and an unexplained geographical variation in incidence. It is not known whe ther the risk of IDDM in first degree relatives depends on the risk in the background population. The aim of the study was to assess the prevalence of IDDM in parents and si blings of newly diagnosed children with IDDM in Austria, a known area of lo w risk for IDDM. The family history data of all diabetic children (<15 years) diagnosed betw een 1988-1994 in Austria were analysed. The cumulative incidence of IDDM in siblings of newly diagnosed diabetic ch ildren was 0.0026772 cases/year, this means 29.7 times increased risk compa red to the background population. Of the diabetic children 5.8% had at leas t one parent with IDDM and the prevalence of IDDM in fathers (3.9%) was hig her (p = 0.015) compared to mothers (1.9%). The risk of IDDM tended to be h igher for offsprings of diabetic fathers (OR 3.8, p < 0.003) in families wi th 2 or more children than in single child families, where the prevalence w as 4.2% both in fathers and mothers. In conclusion the prevalence of IDDM in parents of diabetic children in Aus tria was lower than reported in populations with high IDDM incidence. This may reflect a lesser degree of genetic predisposition of the Austrian popul ation. The prevalence of IDDM in siblings was similar to that in high risk populations. We saw an interaction of gender of the diabetic parent and dia betic offspring and the family size.