Disease Name: Colon Cancer
Chromosome Number: #2
Locus Designation: 2p16
In the summer of 1993 researchers discovered a gene, known as MSH2, is lacking within colon cells. The MSH2 genes main function is to detect and correct small mutations that occur during cell division. The cause of colon cancer arises when this gene does not provide this protection to colon cells. This lack of protection causes multiple mutations within the colon cells until they become cancerous.
Only about 6% of all colorectal cancer is said to be hereditary. Sporadic, or non hereditary colorectal cancer, makes up the other 94%. Hereditary colorectal cancer is made up of two syndromes- HNPCC (Hereditary Non Polyposis Colorectal Cancer) and FAP (Familial Adenomatous Polyposis). HNPCC is estimated to be 5% of the total hereditary colorectal cancer. HNPCC is a autosomal dominant disease, meaning that children have a 50% chance of inheriting the genetic trait from one of the parents being autosomally dominant. The parents who are autosomal dominant have a defect in their mis- match genes which identify and repair somatic mutations in DNA during cell division. Four genes have been identified as carrying this mutation; hMSH2, hMHL1, hPMS1, and hPMS2. ( h standing for hereditary)
FAP constitutes only about 0.5 % of all hereditary colorectal cancer. It is also an autosomal dominant disease. Patients with FAP have a 100% risk of getting colorectal cancer, but it can be avoided. FAP is caused by a mutation in the APC gene on chromosome 5. The APC gene is able to be detected by a blood test. A study done in 1994 revealed that since the time the APC gene was identified 100 different mutations leading to stop codons have been found. 23% of those mutations were clustered within 300 codons in exon 15 of the APC gene. In codon 1309 there was a 5 base pair deletion found within exon 15. This mutation in codon 1309 leads to development of colonic polyps, thus leading to earlier malignant transformation.
The defective genes job to identify and repair somatic mutations in DNA during cell division was later referred to as microsatellite instability. It was identified in...