Penetrance and expressivity of the gene responsible for the Gardner syndrome

The Gardner syndrome is an autosomal dominant condition characterized by multiple polyposis of the colon, associated with various soft- and hard-tissue tumors. Our original kindred, first reported in the early 1950's has been updated and serves as the basis for a discussion of the penetrance and expressivity of the gene responsible for the syndrome. The family consists of 188 members spread over six generations, with 28 individuals clearly documented as having the syndrome. Using two different methods of calculating penetrance, the responsible gene was found to be fully penetrant. This observation was confirmed by an analysis of 160 additional sibships from the literature. This estimation of penetrance is considerably higher than has been previously reported. The expressivity of the gene, however, is quite variable, and this is illustrated using examples from both our kindred and the literature.