Factors for improved genetic counseling for retinoblastoma based on a survey of 55 families.

Of 55 families in which one or more patients with retinoblastoma were treated, five of these families involved more than one patient. The remaining 50 were sporadic cases. Two of the five familial cases involved collateral inheritance and three involved direct inheritance. Factors important for genetic counseling included the time of onset of first symptoms, the age of the father, the occurrence of a second primary tumor, unilateral vs bilateral involvement, and the cytogenetic analysis of the patient's chromosomes. Additionally, mutational mosaicism was considered as a cause for sporadic cases of retinoblastoma. Use of the risk figures derived from this study should provide more precise genetic counseling for parents, siblings, and patients with retinoblastoma.