The McKusick-Kaufman syndrome: phenotypic variation observed in familial cases as a clue for the evaluation of sporadic cases.

The characteristic clinical picture of the McKusick-Kaufman syndrome was observed in a girl of Belorussian background. A supernumerary nipple was the only finding not previously described in reported familial cases of this syndrome. In general, the range of phenotypic variability should be the same in both familial and sporadic cases. For this reason we feel that some sporadic cases reported as patients with unusual variants of the McKusick-Kaufman syndrome have more likely "new" genetic syndromes or non-genetic conditions, which only resemble the syndrome. The comparison of the phenotypes of alleged sporadic cases with familial cases of single gene syndromes should be helpful in syndrome delineation, if the number of familial observations is sufficient.