Familial adenomatous polyposis

Familial adenomatous polyposis, abbreviated FAP and also known as familial polyposis coli and adenomatous polyposis coli‎, is a genetic condition that predisposes to adenomatous polyps and thus invariably results in colorectal cancer.

An endoscopic image showing abundant polyps, as seen in familial adenomatous polyposis.

Gardner syndrome is a subset of FAP. Both FAP and Gardner syndrome have a mutation in the FAP gene.

General

• Life expectancy 40-50 years.

Leading causes of death in FAP (according to The American Society of Colon and Rectal Surgeons):

1. Colorectal carcinoma.
2. Desmoid tumour.
3. Ampullary adenocarcinoma (a type of duodenal adenocarcinoma).

Inheritance

• Autosomal dominant.

Gene

• APC gene mutation.

Variants

FAP comes in two main flavours:

1. FAP (not otherwise specified - the plain vanilla flavour).
   • Many polyps - typically > 100.
2. Attenuated FAP, abbreviated AFAP.
   • Less polyps - typically 10 to 100.
     • As one may think... they tend to get cancer later than (the plain vanilla) FAP.
     • In a cohort of 190 individuals, median number of polyps = 25.

Gardner syndrome

FAP with prominent extraintestinal manifestations - including:

• Osteomas.
• Desmoid tumours.
• Congenital hypertrophy of the retinal pigment epithelium.
• Fibromas.
• Epidermal inclusion cysts.
  • Considered useless for screening as they are so common otherwise. Multiple lipomas are statistically more common; however, they are also useless.
• Osteosclerotic jaw lesions.

Mneumonic DO STOP (modified):

• Desmoid-type fibromatosis.
• Osteoma.
• Skin lesions - multiple lipomas. ‡
• Thyroid carinoma - papillary thyroid carcinoma cribriform morular variant.
• Osteosclerotic jaw lesions.
• Polyps, adenomatous.

Note:

• Osteochondroma does not appear to be part of the syndrome, as suggested by pathologyexpert.com.
• ‡ Sebaceous cysts are considered the classic lesion; however, they are not considered a useful predictor of FAP.

Turcot syndrome

The term is somewhat ambiguous and probably ought to be avoided:

• Half et al. says Turcot syndrome is FAP associated with a medulloblastoma... while OMIM says Turcot syndrome is tied to Lynch syndrome and autosomal recessive.
  • The discussions by Half et al. and in OMIM are informative.

FAP associations

Benign things:

• Fundic gland polyps.

Malignant tumours:

• Hepatoblastoma.
• Medulloblastoma.
• Colorectal carcinoma.
• Gastric adenocarcinoma.
• Papillary thyroid carcinoma cribriform-morular variant.

Benign tumours:

• Osteomas.
• Desmoid tumour.

Prevalence

1/11,300-37,600 in Europe.

See also

• Colorectal carcinoma.
• Adenomatous polyps.
• MUTYH polyposis syndrome - an autosomal recessive polyposis syndrome.