Hereditary retinoblastoma: lack of maternal effect.

Analysis of two-generation data from published pedigrees with familial cases of retinoblastoma showed that, while the proportion of bilateral cases among affected children varied consistently with expressivity of the parents who transmitted the gene, the proportion did not differ with the sex of the parents. These findings support the view that inherited host resistance to the development of hereditary retinoblastoma is determined by modifying genes, and not influenced by transplacental maternal factors, and that the resistance is mainly directed to the induction (promotion) phase. There was a significant deficit of bilaterally affected mothers relative to bilaterally affected fathers, which could not be accounted for by ascertainment bias or by differential survival or fertility between sexes. It is suggested that female patients who survived bilateral retinoblastoma had much less chance of marriage as compared to male survivors. Examination of pedigrees with multiple cases of retinoblastoma, transmitted via unaffected carriers, revealed no sign of cytoplasmic inheritance associated with a vertically transmitting virus.