Familial polyposis coli: an unusual family.

Familial polyposis is an autosomal, dominantly inherited disorder. Usually less than 50% of siblings are affected because of incomplete penetrance by the responsible gene. The family described in this paper was unusual in that all seven siblings of one son had the disorder. The chances of this occurring, assuming complete penetrance, is 1 in 128. Moreover, several members of his family had Gardner's syndrome with associated extracolonic manifestations, including a rarely associated papillary carcinoma of the thyroid. There was no evidence of a cosanguineous marriage. Patients with familial polyposis are advised to adopt children, otherwise surveillance of their children must be lifelong, beginning at puberty.