Familial adenomatous polyposis (FAP) has been known for over 100 years1; Gardner’s syndrome, the familial association of multiple colonic adenomas and early onset colorectal cancer (CRC) with osteomas and multiple cutaneous fibromas or epidermoid cysts has been known for almost 50 years.2 The discovery of the APC gene3 has changed the diagnosis and clinical management of FAP radically. Firstly, it became clear that FAP and Gardner’s syndrome have the same genetic basis. The expression of osteomas and of the cutaneous signs varies greatly among people with the same mutation. Other phenotypic variations have been found to have a genetic basis. For example, congenital hypertrophy of the retinal pigment epithelium is associated with mutations distal to exon 9,4 whereas susceptibility to desmoid tumours is associated with mutations at codons 1444 and 15785 and a profuse number of colonic adenomas, often more than 5000 (compared with the more typical 1000–2000), is associated with mutations between codons 1250 and 1464.6

A variant called attenuated FAP (AFAP) has been associated with mutations in the 5′ portion of the APC gene.7 AFAP is characterised by the occurrence of often fewer than 100 colonic adenomas (sometimes …