Gene mutation. Hereditary non-polyposis colon cancer or lynch syndrome is caused by a mutation in a "mismatch repair gene, " or a gene that codes for a protein which recognizes and repairs mistakes during dna replication. It is inherited in an autosomal dominant fashion (so having 1 mutated gene is enough to increase your lifetime cancer risk).
Inherited mutation . HNPCC is caused by an inherited mutation or abnormality in a gene which normally repairs our body's DNA. There are at least five of these genes which are known as mismatch repair genes that are known to be associated with HNPCC. If the genetic damage is not repaired, than cancer can occur.