An epidemiological study of childhood diabetes affecting two or more siblings.

The incidence, prevalence, and ages and dates of onset of diabetes, were studied in 184 families with 2 or more affected children. Results suggested that the siblings of children who developed diabetes before the age of 16 years were 26 times more likely to develop diabetes than other children. Of all siblings surveyed it was estimated that 5.6% became diabetic by the age of 16. The distribution of ages at onset in these siblings was similar to that in the general population, and within sibships, age at onset appeared to be independently determined. An interval of less than a year between the dates of onset in siblings occurred with more than twice the expected frequency, and in most the interval was less than 6 months. These results suggest that age at onset is determined by non-genetic factors and that, in at least some cases, aetiological environmental factors may lead to the development of diabetes within a period of a few months.