Adenomatous Polyposis of the Colon

Clinical Characteristics
Ocular Features: 

The ocular hallmark of this disease is the presence of congenital hypertrophy or hyperplasia of the retinal pigment epithelium (CHRPE).  Singular lesions have little diagnostic significance and are not pathognomonic of FAP but the presence of 4 or more lesions is highly specific for the diagnosis of familial polyposis of the colon.  Lesions are often teardrop-shaped and average between 4 and 5 mm in size.  They are usually located in the midperiphery of the fundus and exhibit autofluorescence.  Malignant changes in the form of adenocarcinomas have been reported but are rare.

CHRPE has been reported in the absence of colonic polyposis but has been reported in up to 90% of patients with some variant of FAP and is a highly sensitive marker.

Systemic Features: 

The signature non-ocular feature of this syndrome is the occurrence of numerous, sometimes thousands, of gastrointestinal polyps located mainly in the colon.  Precancerous colonic polyps generally develop by the age of 16 years.  Many of these eventually show malignant changes with colorectal cancer developing in nearly all patients by the sixth decade of life but the mean age of colon cancer diagnosis is at 39 years.  Extracolonic lesions such as desmoid tumors, sebaceous cysts, osteomas, fibrosarcomas, and other tumors are frequently seen.  Patients are also at higher risk of thyroid, adrenal, and liver cancer.

Dental anomalies, soft tissue tumors, and jaw osteomas are prominent features found in a variant of FPC known as Gardner syndrome.

Genetics

This is an autosomal dominant disorder resulting from mutations in the APC gene (5q22.2).  This gene is a gatekeeper tumor suppressor gene which controls proliferation of colon epithelial cells.   Loss or inactivation of APC is considered to be the basis of several cancer syndromes such as hereditary desmoid disease (135290), somatic gastric cancer (613659), and hepatocellular carcinoma (114550).

Treatment
Treatment Options: 

Colectomy remains the mainstay of treatment and can be lifesaving if done before the polyps become malignant.  NSAIDs such as sulindac and the use of celecoxib, a COX2 inhibitor, can reduce the number of colorectal polyps but these agents are unlikely to replace colectomy as the primary treatment.  Evaluation and surveillance for at-risk relatives are mandatory.

The fundus lesions do not cause symptoms and do not require treatment.  The remote risk of malignant change in CHRPE lesions, however, suggests that they should be kept under observation.

References
Article Title: 

Familial adenomatous polyposis

Half E, Bercovich D, Rozen P. Familial adenomatous polyposis. Orphanet J Rare Dis. 2009 Oct 12;4:22. Review.

PubMed ID: 
19822006

References

Shields JA, Eagle RC Jr, Shields CL, Brown GC, Lally SE. Malignant transformation of congenital hypertrophy of the retinal pigment epithelium. Ophthalmology. 2009 Nov;116(11):2213-6.

PubMedID: 19744732

Half E, Bercovich D, Rozen P. Familial adenomatous polyposis. Orphanet J Rare Dis. 2009 Oct 12;4:22. Review.

PubMedID: 19822006

Shields CL, Pirondini C, Bianciotto C, Harmon SA, Shields JA. Autofluorescence of congenital hypertrophy of the retinal pigment epithelium. Retina. 2007 Oct;27(8):1097-100.

PubMedID: 18040252