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HEREDITARY MONOGENIC DISEASES

           

Familial adenomatous polyposis

Familial adenomatous polyposis (FAP) is characterized by the appearance in the second decade of life, hundreds or thousands of adenomas in the rectum and colon.

The PAF has a birth incidence of 1/8,300, affects both sexes equally, and represents less than 1% of cases of colorectal cancer (CRC).
The prevalence in the EU is estimated at 1 / 11,300 to 37,600.

Classic FAP is inherited in an autosomal dominant manner and is the result of a mutation in the germline in the APC gene (5q21-q22). Most patients (70%) have a family history of colorectal polyps and cancer. In a subset of individuals, one MUTYH (1p34.1) causes a recessive mutation polyposis, familial adenomatous polyposis linked to MUTYH, characterized by a slightly increased risk of developing CRC and the presence of polyps / adenomas in the upper and lower gastrointestinal tract.

Most patients are asymptomatic for years until adenomas are large and numerous, and even cause rectal bleeding or anemia. Cancer usually begins to develop a decade after the onset of polyps. Non-specific symptoms include constipation or diarrhea, abdominal pain, palpable abdominal mass and weight loss. PAF may have some intestinal manifestations: osteomas, dental abnormalities, congenital hypertrophy of the retinal pigment epithelium (CHRPE), desmoid tumors and cancers extracolonic.

There is a less aggressive variant of the PAF, attenuated PAF, characterized by fewer polyps (usually between 10 and 100), the appearance of adenomas at a later age, and reduced risk of cancer. Some lesions (skull and jaw osteomas, dental abnormalities, and fibromas on the scalp, shoulders, arms and back) are indicative of Gardner syndrome, while the association of PAF and medulloblastoma is known as Turcot syndrome.

Diagnosis is based on family history, clinical findings, and endoscopy of the large intestine or a complete colonoscopy. Whenever possible, the clinical diagnosis must be confirmed by genetic testing. If a patient is identified mutation in the APC gene, a genetic test to all blood relatives of the first degree must perform. Are possible presymptomatic and prenatal genetic tests, and even preimplantation test.

The main objectives of management are cancer prevention and a good quality of life; all patients should have a systematic and regular monitoring. FAP patients have a 100% risk of CRC, although this risk is reduced significantly when they enter a screening program and are treated.

GENE OR REGION STUDIED


  • MUTYH
  • APC