Autosomal dominant transmission of bilateral "opposable" triphalangeal thumb.

Triphalangeal thumb occurs in two functional types: opposable and non-opposable. The opposable type presents a rudimentary middle phalanx and the thumb is frequently angulated. The non-opposable type presents a finger-like thumb (five-fingered hand). Triphalangeal thumb often occurs in syndromes where other anomalies are present, so its pattern of inheritance has often been described jointly with the syndrome itself, then conflicting patterns of inheritance have been reported in literature. The present study reports upon the character of "bilateral opposable triphalangeal thumb" occurring isolated, without association of other anomalies. Authors studied the phenotype distribution in a family over five generations. They found that this character is transmitted with an autosomal dominant pattern of inheritance, and affected individuals are heterozygotes.