Lynch 1 Syndrome

**Semantic type:** Disease or Syndrome

**Definition:** A rare genetic neoplastic syndrome with an autosomal dominant pattern of inheritance but incomplete penetrance. It is associated with a greater than 70 % risk of developing colorectal carcinoma. It is caused by a mutation in one of the mismatch repair genes: MSH2, MLH1, MSH6 or PMS2. It usually manifests at age 50 or younger with multiple synchronous or metachronous colorectal carcinomas. Clinical course is rapidly progressive. Prognosis is variable with a high risk for the development of additional colorectal carcinomas. However, survival is significantly better than non-HNPCC carcinomas of equivalent stage.

**Synonyms:** - Familial Non-Polyposis Colon Cancer Type 1 - HNPCC1 - Hereditary Non-Polyposis Colon Cancer Type 1 - Hereditary Nonpolyposis Colorectal Cancer Type 1 - Lynch Syndrome 1 - Lynch Syndrome I