| Abstract: | Data of 1313 microphthalmos probands and 5325 sibs in 1290 families based on a nation-wide genetic survey of the visually handicapped in 1959 and 1964 in Japan, were analyzed. The probability of ascertainment and prevalence of microphthalmos in the Japanese population was estimated at 0.34 and 3.9×10?5, respectively. The consanguinity among the normal parents of probands was higher in families with more affected sibs (inbreeding coefficient (F)=0.0192, first cousin marriages=27%) than in isolated cases where only the proband was affected (F=0.0057, first cousin marriages=8%).The rate of recessive inheritance was estimated at 12% by an inbreeding analysis The incidence of the affected sibs of probands was empirically determined: 2.2% (two normal parents), 13.6% (one parent affected) and 18.8% (both parents affected).By means of segregation analysis the proportion of monogenic modes of simple recessive, dominant inheritance and unknown etiology was 14.7, 21.7 and 63.6%, respectively. It was shown that cases with unknown etiology may be caused by a polygenic heredity and some environmental factors, among which birth order and maternal age were significant in isolated cases, despite of the fact that these factors were not significant in multiple cases. |
