The following rare syndromes also increase the risk for colorectal cancer:
- Turcot syndrome – a rare disorder that includes colorectal polyposis, colon cancer and brain tumors. Mutations in different genes have been found in individuals with this syndrome, including mutations in the APC, MLH1 and MSH2 genes. For this reason, Turcot syndrome is said to be genetically heterogeneous.
- Peutz-Jeghers syndrome– an autosomal dominant disorder that is associated with the following characteristics:
- Melanocytic macules (dark blue or brown moles) – can be located around and/or in the mouth including the lips, and around the eyes, nostrils and anus. Dark moles also may appear on the fingers. The lesions may fade by adulthood.
- Multiple polyps in the gastrointestinal tract.
- Increased risk of benign (noncancerous) tumors of the ovaries and testes.
- Increased risk of cancers of the stomach, esophagus, breast, colon and pancreas.
Peutz-Jeghers syndrome is caused by mutations in a gene on chromosome #19 known as STK11, which functions as a tumor suppressor gene.
- Familial colorectal cancer – up to 15 percent of colorectal cancer patients have family members with colorectal cancer, but do not have a known colorectal cancer syndrome such as familial adenomatous polyposis or hereditary nonpolyposis colon cancer. Colon cancer in these families may appear to follow an autosomal dominant pattern of inheritance. As genetic research continues, genes may be identified to explain these family histories.
- Juvenile polyposis coli – this rare, childhood-onset disease is an autosomal dominant disorder that results from mutations in various cancer susceptibility genes, including the SMAD4/DPC4 and BMPR1A genes. The condition is associated with the development of hamartomatous polyps (few to numerous) that can be present throughout the gastrointestinal tract. Other symptoms can include diarrhea, hemorrhage and protein-losing enteropathy. Juvenile polyposis is associated with an increased chance for gastrointestinal and pancreatic cancers. Most patients appear to be sporadic cases (i.e., happening for the first time in a family). However, it may actually be the result of decreased penetrance (i.e., the causative gene mutation is present in one of the parents but the symptoms did not develop).