The role of genetic factors in the etiology of Wilms' tumor: two pairs of monozygous twins with congenital abnormalities (aniridia; hemihypertrophy) and discordance for Wilms' tumor.

Wilms' tumor was diagnosed in two children each of whom has an identical twin. In one of the pairs of twins the aniridia syndrome with psychomotor retardation was present in both children, but Wilms' tumor was found in only one. In the other twins hemihypertrophy as well as Wilms' tumor were identified in one child, whereas neither of these abnormalities was present in her twin sister. These findings lend support to a hypothesis that the development of Wilms' tumor requires the occurrence of two successive mutational events, one of which may be a germinal mutation. The presence of aniridia, hemihypertrophy, or other associated congenital abnormalities may aid in distinguishing between hereditary and sporadic forms of Wilms' tumor.