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Genetic Study of Skin Pigmentation in African Americans Uncovers Links to Vitamin D Deficiency

NEW YORK – A team from the US, Brazil, and the UK has expanded the repertoire of genetic factors influencing skin pigmentation in African Americans, in hopes of better understanding vitamin D deficiency and conditions suspected of stemming from it such as bone disorders, autoimmune diseases, or cancer.

"Skin color has strong social and biological significance — social because of race and racism and biological because over 70 [percent] of African Americans are vitamin D deficient, resulting in increased risk for cancer and cardiovascular disease," senior and corresponding author Rick Kittles, director of the division of health equities at the Beckman Research Institute of City of Hope, said in a statement.

Kittles argued that "[w]e should not shy from this new study looking at the genetics of skin color and its effects on vitamin D deficiency because being 'colorblind' is what has led to the widespread health disparities that we as a society are now trying to address."

As they reported in PLOS Genetics on Thursday, he and his colleagues conducted a genome-wide association study for skin pigmentation that included nearly 400 individuals who self-identified as African American. They used SNP genotyping data and reflectometer-based melanin measurements at skin sites that are typically protected from the sun to identify pigmentation-related variants that were subsequently validated in another 681 African American individuals.

The strongest ties to pigmentation turned up near the SLC24A5 gene, followed by loci containing the SLC45A2 and OCA2 genes, the team reported. By bringing in available genetic data for hundreds of individuals from European, West African, and Native American populations for a related admixture analysis, the team saw signs that West African ancestry tended to correspond with the presence of variants influencing skin pigment variation.

"A genetic score calculated using the top [GWAS] variants … and West African genomic ancestry together account for a large proportion of skin pigmentation variation," the authors reported, noting that the "pattern of association between the genetic score and skin pigmentation was different between men and women suggesting an interaction between sex and genetic variation."

In a follow-up analysis that included nearly 600 African American participants, the investigators saw signs that some of the same loci implicated in skin pigmentation in the GWAS — particularly a genetic score centered on the pigment-associated SLC24A5, SLC45A2, and OCA2 sites — also appeared to coincide with vitamin D deficiency, based on 25-hydroxyvitamin D measurements in blood.

From these and other findings, the authors speculated that it may ultimately be possible to better target treatments or possible preventative measures such as vitamin D supplementation by taking individuals' pigmentation and related genotypic information into account.

"With more research, in the future doctors could offer patients of color with an inexpensive way to reduce their risk of vitamin deficiency," Kittles suggested, "which ultimately could help protect against certain cancers."

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