French experts report on MUTYH-associated polyposis (MAP)

Recent years have been characterised by an improvement in our knowledge of genetic determinism of adenomatous polyposes and by the description in 2002 of a new entity called “MUTYH-associated polyposis” (MAP), related to biallelic mutations of this gene. Its autosomal recessive mode of inheritance contrasts with the autosomal dominant inheritance of the classical “familial adenomatous polyposis” (FAP), associated with an APC germline mutation. Although some phenotypic features may be of value to distinguish these two conditions, their clinical “spectra” largely overlap and the differential diagnosis may be difficult. The purpose of this expertise conducted under the auspices of the French Institut National du Cancer (INCa) was to assess the current state of knowledge on MUTYH-associated polyposis and to establish some recommendations in the field of molecular analysis (indications of tests and analysis strategies for affected patients and their relatives) and of clinical management based on available data in the literature, on the results from the French molecular genetics laboratories performing MUTYH analysis and on the opinions of biologists and clinicians experts (genetic counsellors and gastroenterologists). The risk of colorectal cancer among relatives carrying a monoallelic MUTYH mutation was also studied.