Hereditary retinoblastoma: Penetrance,expressivity and age of onset

Summary Analyses of family data published in Japan concerning 29 kindreds with 2 or more cases of retinoblastoma revealed that, in the children who received the gene from a carrier parent, both penetrance and expressivity increase with increasing degree of expressivity in the parent. The estimate for the average degree of penetrance varies from 0.7 to 0.9, depending upon the method employed. The value will be increased with increasing number of survivors of hereditary retinoblastoma. Data were presented to indicate that the hereditary form of retinoblastoma onset tends to be later in unilateral than in bilateral affection, though in the non-hereditary form onset will be further delayed. No effect of birth order was detected. It was suggested that suppressor genes at other loci play a significant role in manifestation of the major dominant gene for retinoblastoma. Implications of these findings were discussed.This work, contribution number 1093 from the National Institute of Genetics, was supported by grants-in-aid from the Ministry of Education and the Ministry of Health and Welfare.