Implications of correlations between skin color and genetic ancestry for biomedical research

Abstract

Skin pigmentation is a central element of most discussions on 'race' and genetics. Research on the genetic basis of population variation in this phenotype, which is important in mediating both social experiences and environmental exposures, is sparse. We studied the relationship between pigmentation and ancestry in five populations of mixed ancestry with a wide range of pigmentation and ancestral proportions (African Americans from Washington, DC; African Caribbeans living in England; Puerto Ricans from New York; Mexicans from Guerrero; and Hispanics from San Luis Valley). The strength of the relationship between skin color and ancestry was quite variable, with the correlations ranging in intensity from moderately strong (Puerto Rico, ρ = 0.633) to weak (Mexico, ρ = 0.212). These results demonstrate the utility of ancestry-informative genetic markers and admixture methods and emphasize the need to be cautious when using pigmentation as a proxy of ancestry or when extrapolating the results from one admixed population to another. Importance of pigmentationThe prevalence of several common diseases differs among populations. Although such health disparities may largely be the result of differential access to health care and differences in socioeconomic factors and environmental exposures, there may also be risk alleles that differ in frequency among populations. Therefore, tests of correlations between genetic ancestry and phenotype can be a good starting point for research on the causes of health disparities 1 . Even if the ultimate cause for the difference is primarily environmental, individual genetic ancestry analysis can provide a biological reference point against which to study cultural and environmental factors. This line of investigation is in the very early stages of development and has benefited tremendously from studies of skin pigmentation.Skin pigmentation is one of the most variable phenotypes in humans, but very little is known about the genetic basis and evolutionary history of this polygenic trait. Understanding the genetics of human pigmentation and the distribution of pigmentation alleles within and among populations is important. To a large extent in the US, skin pigmentation is a proxy for 'race' , on the basis of which racism has been manifested. Skin color can affect the level of discrimination a person experiences or the quality of medical care he or she receives. Differences in skin color among populations are commonly (and incorrectly) understood as an indication of deeper biological differences among populations. Pigmentation genes are unlike the bulk of the genetic variation among populations and can, and should, be used to help educate the general public about the distribution of genetic variation across the populations of the world and the lack of meaning of 'race' as a system of biological classification. Skin pigmentation is also of interest from the biological point of view. Melanin has a key physiological role, mediating the amount of ultraviolet (UV) radiation reaching the dermal ...

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