Polydactyly, triphalangism of the thumb, and carpal abnormalities in a family

Many authors have documented the anatomic variability of radial-sided polydactyly and triphalangism of the thumb, but the relationship between these two conditions remains confusing. This study was done to determine if all types of radial-sided polydactyly and triphalangism of the thumb are related. Twenty-five members of a family with these abnormalities were evaluated clinically and radiographically by using radiographs of the hands and feet and, where appropriate, the tibia, in order to ascertain whether all variations of radial-sided polydactyly and triphalangism of the thumb could be found in this family. The hand abnormalities comprised eight types based on the number of digits, the number of phalanges, and whether the digits or phalanges were normal, hypoplastic, or rudimentary. Five distinct carpal anomalies were identified. Essentially all described types of radial-sided polydactyly and triphalangism of the thumb occur in this family. The occurrence of these abnormalities is determined by a single autosomal dominant gene. The manner in which the gene is expressed is determined either by its allele or by a combination of genetic and environmental factors. The findings in the parent cannot be used to predict the findings in the offspring.