Lynch syndrome in a 15-year-old boy.

Hereditary nonpolyposis colorectal cancer (HNPCC), or Lynch syndrome, dominantly inherited, is characterized by the development of a variety of cancers due to germline mutations in DNA mismatch repair genes (MMR). This syndrome was diagnosed in a 15-year-old boy because his father and grandmother were also found to have the same kind of cancer. Microsatellite instability prompted a search for germline mutations in the MLH1, MSH2, MSH6, and PMS2 genes. Use of immunohistochemical staining for MMR proteins, genomic sequencing, and deletion studies, evidenced MSH2 axonal deletion. Neoplastic lesions of colon are most often encountered in the adult population but can, on rare occasions, be found in younger patients. We would like to emphasize the importance of suspecting Lynch syndrome and performing genetic studies, even in young patients, when there is a family history of colorectal cancer.