c.1227_1228dupGG (p.Glu410Glyfs), a frequent variant in Tunisian patients with MUTYH associated polyposis.

Introduction: Familial adenomatous polyposis (FAP) is an autosomal dominant-inherited disease caused by germline variants in the APC gene. It is characterized by the development of hundreds to thousands of adenomatous polyps in colon and rectum. Recently, biallelic germline variants in the base excision repair (BER) gene: MUTYH have been identified in patients with attenuated FAP and/or negative APC result. It can be responsible for an autosomal recessive inherited colorectal cancer syndrome (MAP syndrome: MUTYH-associated polyposis).

Objective: The aim of this study was to evaluate germline variants of MUTYH gene in Tunisian patients with attenuated FAP.

Methods: thirteen unrelated patients from Tunisia with attenuated FAP were screened for MUTYH germline variants. Direct sequencing was performed to identify point variants in this gene.

Results: A Biallelic MUTYH germline variant were found in all patients and showed an attenuated polyposis phenotype almost of them without extra-colic manifestations: The known pathogenic frameshift variant c.1227_1228dupGG (p. Glu410Glyfs) was found, in homozygous state, in 13 index patients.

Conclusion: Patients with attenuated familial adenomatous polyposis (<=100) and no obvious vertical transmission of the disease should be considered for MUTYH gene testing.