Aim: Biallelic MUTYH germline mutations predispose to recessively inherited adenomatous polyposis, designated MUTYH-associated polyposis (MAP), and colorectal cancer (CRC). The hotspot mutations p.Y179C and p.G396D account for the majority of pathogenic variants in Caucasians. Our aim was to evaluate the prevalence of MUTYH mutations in clinical routine patients with different colorectal diseases.
Method: The hotspot mutations p.Y179C and p.G396D were genotyped in 352 consecutive patients undergoing colonoscopy at our tertiary referral centre. Exons 2-14 were sequenced in hotspot mutation carriers to exclude additional variants.
Results: Overall we identified five heterozygous p.Y179C mutations and three heterozygous p.G396D mutations in seven hotspot mutation carriers (risk allele frequencies 0.7% and 0.4%). Two of these hotspot mutation carriers harboured a heterozygous p.Q338H variant, which is of uncertain clinical significance, on the other allele. Overall, three individuals were biallelic MUTYH variant carriers (p.Y179C/p.G382D: typical MAP; p.Y179C/p.Q338H: atypical MAP with late onset and lower polyp burden; p.G382D/p.Q338H: inflammatory bowel disease), and four subjects were monoallelic mutation carriers.
Conclusions:MUTYH-associated disease, and hence genetic counselling and MUTYH genetic testing, should be considered in the clinical routine of an endoscopy unit, but the wide range of phenotypes represents a challenge for patient identification. The clinical significance of p.Q338H should be evaluated in future case-control studies, since compound heterozygotes for pathogenic mutations and p.Q338H may be at increased risk for mild polyposis or CRC. In addition MUTYH should be assessed as a potential susceptibility gene for the development of colitis-associated CRC in future.