Abstract
Rubinstein et al. (1977) have reported that insulin dependent diabetes mellitus (IDDM) has a recessive genetic character with penetrance of 50%. According to studies made on twins (Barnett et al. 1981, Kikuchi et al. 1982) and an analysis made on family data (Furusho et al. 1983), it is almost an unmistakable fact that IDDM has incomplete penetrance and that penetrance of IDDM is low. Taking into account foregoing, the author has developed a method of estimating 1) the penetrance, 2) the gene frequency of genetic character of incomplete penetrance and 3) the inheritance mode from twin data. In 1), the estimate of penetrance reveals a range of 0.0444 to 0.0888 from family survey data, of 0.3 to 0.5 from IDDM and HLA data, and is 0.5000∿0.7048 from twin data. Consideration has been also made for the high estimate of penetrance from twin data. By using the concordance rate of monozygotic twins (C_1) and of dizygotic (C_2), evaluation of simple dominant inheritance was made when (C_1/C_2)≅2, simple recessive inheritance when (C_1/C_2)≅4, and multifactor inheritance when (C_1/C_2)>4. The possibility of therapy still remains for genetic character of low penetrance, such as IDDM in particular. Since penetrance is extremely important from the standpoint of clinical medicine of IDDM, the author discussed the significance of estimating penetrance with high precision.
