Turcot syndrome is caused by mutations (changes) in different genes. It's a rare, inherited disorder characterized by the development of polyps in the colon and rectum, along with the formation of brain tumors. Because it's caused by mutations in different genes, it's generally classified into two main types:
Types of Turcot Syndrome and Their Genetic Causes
Understanding the genetic basis of Turcot syndrome is crucial for diagnosis and management. The two main types are distinguished by the genes involved:
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APC-associated Turcot Syndrome: This type arises from mutations in the APC (adenomatous polyposis coli) gene, a gene also associated with familial adenomatous polyposis (FAP).
- Mutations in APC prevent it from producing a protein that helps control cell growth.
- This lack of control leads to the formation of numerous colorectal polyps and an increased risk of medulloblastoma (a type of brain tumor).
- This type is typically inherited in an autosomal dominant pattern, meaning only one copy of the mutated gene is sufficient to cause the condition.
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Mismatch Repair Gene-associated Turcot Syndrome: This type is caused by mutations in mismatch repair (MMR) genes, such as MLH1, MSH2, MSH6, and PMS2. These genes are crucial for correcting errors that occur during DNA replication.
- Mutations in these genes lead to a condition called Lynch syndrome (also known as hereditary nonpolyposis colorectal cancer or HNPCC).
- Individuals with Lynch syndrome have an increased risk of various cancers, including colorectal cancer and, less commonly, glioblastoma (another type of brain tumor).
- Like APC-associated Turcot syndrome, this type also typically follows an autosomal dominant inheritance pattern.
Genetic Testing and Counseling
Genetic testing is available to identify individuals who carry these gene mutations. This is particularly important for families with a history of Turcot syndrome, colorectal cancer, or brain tumors. Genetic counseling can help families understand the risks, inheritance patterns, and available screening options. Early detection and intervention can significantly improve outcomes for those affected by Turcot syndrome.
