Familial adenomatous polyposis

An endoscopic image showing abundant polyps, as seen in 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.

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.