Familial Williams syndrome.

Characteristic features of the Williams syndrome were observed in a mother and her presumably dizygotic twin daughters, suggesting either an X-linked dominant, autosomal dominant or multifactorial inheritance in this pedigree. The Williams syndrome generally has been thought to have a sporadic occurrence. The rare familial occurrence, however, suggests a possible heterogeneity in its etiology and also points out the importance of careful examination of the other family members for proper genetic counseling.