Age and family relationship accentuate the risk of insulin-dependent diabetes mellitus (IDDM) in relatives of patients with IDDM.

The international community of diabetologists is rapidly becoming involved in intervention trials aimed at preventing insulin-dependent diabetes in high risk relatives. Whereas age and relationship to a proband with insulin-dependent diabetes mellitus interacting with detected islet cell autoantibodies (ICA) are risk factors, their independent contribution to that risk remains unclear. In a prospective study of 6851 nondiabetic relatives of 2742 probands conducted between 1979-1993, we found age, but not relationship, to be a dramatic risk variable in ICA-positive persons as estimated by the Cox regression model. The 5-yr risk of insulin-dependent diabetes mellitus was 66% for those found to have ICA detectable before age 10 yr, falling progressively to less than 16% for ICA-positive relatives over age 40 yr. In ICA-negative relatives, age and relationship are independent prognostic variables.