To compare characteristics at clinical onset of childhood-onset diabetes patients with and without a first-degree relative with childhood-onset insulin-dependent diabetes mellitus (IDDM).
In a nationwide continuous incident diabetes register covering patients from 0 to 14 years of age with a high level of ascertainment, we compared 687 patients who at onset had at least one first-degree relative with insulin-treated diabetes with 5,137 patients without such relatives.
The pattern of change over the 15-year period was similar among familial- and sporadic-case patients. The seasonal pattern, with a lower incidence during the warmer period of the year, was similar in both groups. Age at clinical onset was also similar in both groups in either sex. When the proband had a sibling who already had the disease, the mean age at onset was significantly higher when compared with sporadic-case or other familial-case patients.
This analysis of a very large set of population-based cases of childhood diabetes showed that patients who had one first-degree relative with insulin-treated diabetes at onset shared the onset characteristics of those without such family members, including age at onset, sex ratio, seasonality, and secular trend. The findings may indicate that the complex interactions between genetic and nongenetic risk factors subsequently leading to IDDM are mainly shared by familial- and sporadic-case patients.
