Changes in DNA Sequence of Genes Influence Risk of Colorectal Cancer in African Americans

A new study presented at the Fifth AACR Conference on The Science of Cancer Health Disparities reveals that the risk of colorectal cancer in African Americans can be influenced by how the body produces and destroys vitamin D due to changes in DNA sequence of genes.

"Vitamin D deficiency is associated with a higher risk for colorectal cancer," said Fabio Pibiri, Ph.D., a postdoctoral associate at the University of Illinois at Chicago. "Because increased skin pigment lowers the amount of ultraviolet light that can be used to make vitamin D in the skin, more African-Americans than whites are vitamin D-deficient, putting them at higher risk for colorectal cancer. Our research showed that genetic differences may play an important role as well."

Colorectal Cancer - Types, Causes, Risk Factors, Symptoms, Diagnosis, Treatment, Prognosis & Prevention
Colorectal cancer is a cancer that starts in the colon or the rectum. Colorectal cancer is the third most common cancer in men.

Pibiri and colleagues evaluated 39 single nucleotide polymorphisms (SNPs), DNA sequence variations, in vitamin D-related genes in 1,799 African-Americans - 961 patients with colorectal cancer and 838 controls - who participated in the North Carolina Colorectal Cancer Study and the Chicago Colorectal Cancer Consortium.

They found several SNPs in genes involved in the generation and destruction of vitamin D that were associated with colorectal cancer.

One variation in the gene that tells a cell to make the protein that destroys vitamin D was linked to protection from developing colorectal cancer on the left side of the body. According to Pibiri, this variation is specific to African-Americans and the finding may explain why African-Americans have a lower proportion of left-sided colorectal cancer compared with right-sided colorectal cancer.

Colorectal Cancer Screening
Colorectal screening is done using tests to detect blood in stool, colonoscopy or sigmoidoscopy ordouble contrast barium enema or CT colonography.

"It seems likely that these differences in the DNA sequence alter the function of the vitamin D-related genes," said Pibiri. "For example, we hypothesize that the genetic variation linked to protection decreases levels of the vitamin D-destroying protein. Now all we need to do is show that."

The National Institutes of Health, the American Institute for Cancer Research and the American Cancer Society Illinois Division provided funding for this research.

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Colonoscopy is a widely used endoscopic procedure to screen individuals for colorectal cancer. It is very sensitive in detecting colorectal cancers.

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