Familial Predisposition of Type 1 Diabetes Mellitus in Japan, a Country with Low Incidence

: The study group of the Japan Diabetes Society (JDS) carried out nationwide hospital-based and population-based surveys of childhood type 1 diabetes mellitus (DM) in Japan. According to the nationwide population-based survey, the incidence of childhood type 1 DM in Japan was 1.5 (1.4-1.6)/10(5), which did not differ for the 5 years from 1986-1990. Predisposition for DM and autoimmunity were studied in the first-degree relatives of the patients, including older and later cohorts. The prevalence of type 1 DM was 3.3% (12/369) among siblings and 2.2% (8/369) among parents, while the prevalence of type 2 DM was 0% among siblings and 4.3% (16/369) among parents. The risk of type 1 DM among siblings of the patients was 330 times higher than that among the general population in the Japanese population. The rate of positivity for autoantibodies, including ICA, IAA, GAD and IA-2, was 1.4-2.9% in parents (n=140) and 2.0-3.9% in siblings (n=203). The genetic susceptibility for type 1 DM is far lower in Japanese children than in Caucasian children, but predisposition to the disease and positive autoimmunity are almost the same in Japanese families of patients as in Caucasian families. The quality of life of Japanese parents of children with type 1 DM was less satisfactory that that of the Caucasian parents previously reported, which might be a result of the low incidence of type 1 DM in Japan.