Background: Familial adenomatous polyposis (FAP) has been divided into two entities: classical (CFAP) and attenuated (AFAP). With the discovery of MYH associated polyposis (MAP) syndrome, the clinical differences have become unclear. The aim of our study was to investigate patients with polyposis treated in our institution for a correlation between genotype and phenotype.
Methods: Between 1978 and 2007, 515 patients were followed. Four groups were identified: AFAP, CFAP, MAP, and no-mutation patients. Clinical, surgical, histological, and genetic data of patients were collected and compared. Two ranges of mutations responsible for AFAP were used.
Results: Patient breakdown was CFAP patients (n = 322/294), AFAP patients (n = 13/41), MYH patients (n = 17) and no-mut patients (n = 32). Patients not tested for APC mutation (n = 131) were excluded. Genotype/phenotype evaluation showed no difference in the number or location of polyps, age at colectomy, presence of cancer, or duodenal polyps. Major differences were found for MYH patients: later age at diagnosis, more cancers, fewer polyps, and more located in the right part of the colon. For phenotype/genotype correlation, patients aged more than 35 years at the time of colectomy and with fewer than 100 polyps had significantly more mutation found on MYH.
Conclusions: This two-way analysis did not show any correlation that might help to identify a subgroup of patients with APC mutation that may be considered attenuated. It is more likely that the MAP syndrome is the real AFAP.