Familial occurrence of Wilms' tumor: nephroblastoma in one of monozygous twins and in another sibling.

We report the occurrence of pathologically documented Wilm's tumor in a 24-month-old male twin and just 9 months later in his 12-month-old male sibling. We considered the twins to be monozygotic because of their phenotypic similarities, the probability computed from analysis of blood groups, and the comparison of their dermatoglphics. There were no other persons in the kindred with either tumor or associated malformations, and the parents were not consanguineous. Because of the frequency of Wilm's tumor, the few instances of demonstrated occurrence in siblings seem insufficient to postulate monogenic determination. Concordance in monozygotic twins has simply not been proven. The monozygotic unaffected twin of our first patient has remained without evidence of tumor to 5 years, and, as long as he remains so, he appears to represent an exception to the hypothesis of the mutagenic origin of this childhood tumor.