Question

I was talking to a friend about inheritable colon cancer. Most families who inherit an increased risk find that they are encouraged to start getting screened for polyps after age 30 to make sure the pre-cancerous polyps can be removed before they turn into cancer. But, friend was talking about a very different form of inheritable colon cancer that does not cause polyps and is inherited in a dominant fashion. What cancer is he talking about, what gene(s) is mutated, and how is the inheritance dominant? Briefly explain the epidemiology of this cancer and explain the normal function of these gene(s) that are mutated. Then explain why the mutations would cause cancer, and why do they cause predominately colon cancers?

Answer 1

He is talking about Hereditary nonpolyposis colorectal cancer (HNPCC), which is the most common form of hereditary colorectal cancer. This cancer is inherited as an autosomal dominant syndrome. The genes that have been associated with HNPCC are called MLH1, MSH2, MSH6, and PMS2. These genes produce mismatch repair (MMR) proteins.

Mutations in these genes cause defective proteins, that are, unable to repair the mismatches, which further increases mutation that leads to the cancer.