Prevalence of Gene Mutations in Polyposis Varies by Adenoma Count

Patients with classic familial adenomatous polyposis (FAP) — traditionally defined as ≥100 adenomas in the colorectum but sometimes including cases with <100 — usually have germline mutations in the adenomatous polyposis coli (APC) gene. However, biallelic mutations in the mutY homolog (MUTYH) gene can produce a nearly identical phenotype of multiple colorectal adenomas. To understand the relative contributions of these gene mutations to the adenomatous polyposis phenotypes, investigators examined the prevalence of each mutation and whether it varied by adenoma count and other clinical characteristics in 8676 patients who had undergone genetic testing.

For individuals with ≥1000 adenomas, 80% had a pathogenic APC mutation and 2% had a bialle…