Turcot syndrome: A genetic disease characterized by polyps in the colon (large intestine) in addition to tumors in the brain. The polyps in the colon tend to become malignant. The brain tumors are also malignant. Skin abnormalities can also occur. Turcot syndrome is inherited in an autosomal recessive manner and can result from mutations in either the adenomatous polyposis coli (APC) gene or the mismatch repair genes underlying the syndrome of hereditary nonpolyposis colon cancer (HNPCC).