Embryonic testicular regression syndrome: variable phenotypic expression in siblings.

Two 46,XY agonadal siblings with variable degrees of sexual ambiguity are described. The eldest child is a phenotypic male with micropenis. The younger patient, a phenotypic female with slight fusion of the genital folds and absent müllerian ducts, conforms to the criteria usually accepted for the diagnosis of true agonadism. Coexistence of anorchia and true agonadism in the same sibship supports the hypothesis, suggested by others, that both disorders are related and are due to the regression of the embryonic testes.