Even though deaths rates from colorectal cancer have been declining in the United States, African-Americans and other minority populations experience a disproportionate share of this cancer burden, Garza says. This disparity exists even after accounting for various environmental and social factors, so it makes sense that genetics could play a contributing role in this cancer disparity, she said.
The researchers focused on the metabolic enzyme 5 10-methelenetetrahydrofolate reductase (MTHFR), whose role is to maintain folate in the blood in order to prevent the buildup of homocysteine,a chemical byproduct that is toxic to cells. The CC version of MTHFR is considered the wild type the version most common in the population as a whole and the CT or TT alleles carry a variant T, a point mutation in which a thymine nucleic acid is substituted for a cytosine in the genes DNA. Compared to CC, enzymatic activity of the CT mutation is reduced to 65 percent; TT has 30 percent the enzymatic activity of CC.
One common variation of the gene, called C677T, has been associated with a lower risk of colorectal cancer in individuals with high levels of folate and low levels of alcohol use, Garza says.
Their finding that the TT version of the gene seems to offer protection against colorectal cancer in Asian, and possibly in other groups except Latinos warrants further examination, Garza says. Normally, if one carries the recessive TT which means reduced enzyme activity, you would expect a higher risk of developing colorectal cancer; however, the opposite is true, she said.
One could speculate that C677T
|Contact: Greg Lester|
American Association for Cancer Research