Severe upper gastrointestinal polyposis associated with sparse colonic polyposis in a familial adenomatous polyposis family with an APC mutation at codon 1520

Background—Familial adenomatouspolyposis usually results in colonic polyposis with hundredsto thousands of polyps, congenital hypertrophy of the retinal pigmentepithelium (CHRPE), and variable extracolonic features. Recent reportsindicate that patients with distal mutations between codons 1445 and1578 do not express CHRPE and have a high incidence of desmoid tumours.
Patients—The family studied has an unusualphenotype of sparse colonic polyposis but profuse uppergastrointestinal polyposis. Affected subjects do not have CHRPE.
Methods—The protein truncation testfollowed by sequencing identified a 2 base pair deletion at codon 1520 in the APC gene. This results in a frameshift creating a stop codon 13 codons downstream.
Results—This family demonstrates that sparsecolonic polyposis but severe upper tract polyposis may be associatedwith mutations between codons 1445 and 1578.
Conclusions—Study of duodenal and colonic polypsin further cases with mutations in this region is warranted. Suchmutations may preferentially cause duodenal adenomas and desmoidtumours as somatic mutations in these tumours also occur in thisregion, unlike colorectal tumours where somatic mutations occur moreproximally. This study emphasises the importance of screening the uppergastrointestinal tract even when the colonic disease is mild.

Keywords:familial adenomatous polyposis; duodenal polyps; APCmutations; colorectal polyps