 Gardner syndrome is caused by mutation in the adenomatous polyposis coli (APC gene), located in chromosome 5q21 (band q21 on chromosome 5).This gene is also mutant in familial adenomatous polyposis (FAP), a more common disease that also predisposes to colon cancer.Nuances in the understanding of genetics have caused some disorders to be split into multiple entities, while others merged into one genetic condition.