However, ocular findings in Gardner Syndrome are often incidental so family history is the most important assessment of a patient's risk. The earliest and most common extra-colonic finding in Gardner syndrome is CHRPE and is found in nearly 90% of patients. Mutations of TP53 on chromosome 17, a deletion of the colon cancer gene (DCC) on chromosome 18, and loss of DNA methylation on chromosome 12 which causes a mutation of the RAS gene have all been linked as possible causes of Gardner syndrome. While Gardner syndrome is commonly recognized with mutations within the APC gene, there are other mutations that have been linked as possible causes of Gardner syndrome. APC gene is located on chromosome 5, within band 5q21, and encodes for a tumor suppressor gene. Gardner syndrome is an autosomal dominant disorder caused by germline mutations in the adenomatous polyposis coli (APC) gene. While the penetrance of the gene is nearly 100% in those affected with Gardner syndrome, there is variation in the expression both between and within affected families. In the United States, the prevalence of Gardner syndrome is 1 in 1,000,000 and has an incidence of 1 in 8,000. However, the absence of CHRPE cannot be considered a negative predictive indicator of Gardner syndrome. The presence of multiple and bilateral CHRPE is considered a clinical disease marker and is useful for early detection in individuals that are at risk. Gardner syndrome can also present with ocular manifestations that include the presence of multiple patches of congenital hypertrophy of the retinal pigment epithelium (CHRPE). However, Gardner syndrome has characteristic polyps in the colon and osteomas that help distinguish the disease from FAP. Both Gardner syndrome and FAP are characterized by the numerous adenomatous polyps lining the intestinal mucosal surface. Gardner syndrome is a rare phenotypic variant of familial adenomatous polyposis (FAP). 7.2.2 Characteristics of Gardner Syndrome related CHRPE.
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