Does a polymorphism in the methylenetetrahydrofolate reductase gene predispose to colorectal cancers with microsatellite instability?
The TT genotype of MTHFR is associated with an increased risk of CRC in older populations, possibly due to age related disturbances in folate metabolism. The TT genotype appears to predispose to CRC that is MSI+. This may reflect the involvement of aberrant DNA methylation frequently associated with MSI+. The 844ins68 CBS polymorphism may protect against proximal tumours.
The presence of atypia on initial   biopsy is a strong predictor of malignancy in   subsequent biopsy specimens.