About 15% of the colorectal tumors are hereditary. There are two main groups: the familiar adenomatous polyposis (FAP) and the non-polyposis colorectal cancer (HNPCC), both autosomal dominant diseases. Patients with FAP present hundreds to thousands of adenomas in colorectum. usually after puberty. The cause of FAP is mutation of the adenomatous polyposis coli (APC) gene, located on long arm of chromosome 5 (5q). Patients who have not undergone to colectomy, the only treatment avaiable, will develop colorectal cancer and die at the age of 45 years. Extracolonic manifestations can occur: gastric and small bowel adenomas, soft tissue tumors, retinal pigmentation. osteomas. Patients with HNPCC do not present hundreds of benign polyps, but already a solitary colorectal cancer: This disease is caused by mutations in one of the several mismatch repair genes (hMSH2, hMLHI, hPMSI, hPMS2, hPMS6/GTBP). The average age of the diagnosis is 45 years and usually the disease produces cancer in the right colon. Other carcinomas can occur: endometrial, stomach, pancreas and others. Prophylactic surgery in asymptomatic gene carriers are controversial. Nowadays it is possible to identify asymptomatic genes carriers of FAP and HNPCC by genetic testing. The analysis can be done by direct gene sequencing or by in vitro synthesized protein assay (IVSP), which finds defective truncate proteins. Genetic testing for hereditary forms of colorectal cancer requires not only an appropriate laboratory, but genetic counseling with an ethical multidisciplinary approach considering the psychological and social consequences.
Familial adenomatous polyposis; FAP; Adenoma; Hereditary non-polyposis colorectal cancer; HNPCC; Genetic tests