Fundus lesions of adenomatous polyposis.

Congenital hypertrophy of the retinal pigment epithelium (CHRPE) is the most frequent extraintestinal manifestation of familial adenomatous polyposis. Present in 70% of families with familial adenomatous polyposis, CHRPE is a highly reliable and early marker of the disease. Studies over the past 5 years have addressed the histologic characteristics of the pigmented fundus lesions, the definition of universal positive fundus criteria, and mostly the genotype-phenotype correlation. Indeed, the position of the mutation site of the APC (adenomatous polyposis coli) gene on chromosome 5 influences the retinal expressivity because CHRPE is present only if the mutation is located between exons 9 and 15. In CHRPE-positive families, fundus examination is simple, noninvasive, reproducible, inexpensive, and allows early detection of the mutant gene carriers. Knowing the CHRPE status of patients in a family with familial adenomatous polyposis helps to identify constitutional APC mutations. The combination of genetic analysis and fundus examination offers a 100% diagnostic predictability.