Congenital hypertrophy of the retinal pigment epithelium (CHRPE) in familial colorectal cancer

Abstract

Congenital hypertrophy of the retinal pigment epithelium (CHRPE) is a pigmented fundus lesion associated with familial adenomatous polyposis (FAP). CHRPE prevalence has been reported to be increased in subjects with familial or sporadic non-polyposis colorectal cancer (CRC), suggesting that some individuals with non-polyposis CRC have an attenuated form of FAP. Other studies have not confirmed these clinical observations and have failed to identify mutations in the gene responsible for FAP, but the reason for the discrepancy in relation to CHRPE prevalence has not been resolved. We determined the prevalence of CHRPE in subjects without CRC (negative control cohort), subjects with FAP (positive control cohort), and subjects with familial non-polyposis CRC (test cohort). A cohort study consisting of 37 negative control subjects, 9 positive control subjects with documented APC gene mutations, and 36 test subjects with familial non-polyposis CRC but no identified pathogenic APC gene mutation. The diagnosis of hereditary non-polyposis colon cancer was excluded in the test cohort by testing for microsatellite instability in tumour tissue. None of the 37 people in the negative control group had CHRPE. Five of nine (56%) patients with FAP had multiple CHRPE lesions. None of the 36 subjects in the test cohort had CHRPE lesions. Ophthalmoscopy may contribute to risk assessment in families with FAP but not in familial non-polyposis CRC. Care must be exercised when interpreting pigmented fundus lesions because 8-13% of subjects in each of the cohorts had pigmented retinal lesions that were not CHRPE. Bilateral lesions and lesions with a depigmented halo were the hallmarks of CHRPE associated with FAP.