Scientists establish genetic link to skin colour

What causes your skin colour to be darker or lighter? Scientists say its in your genes and have established a genetic link to skin colour. In keeping with the diversity of its population groups, Indians also exhibit a wide canvas of different skin tones.

According to a scientific study, people in India have skin tones ranging from pinkish, fair, wheatish, brown to dark brown. Hence, it seems to be one of the perfect models to understand the genetic architecture of skin colour. In contrast, Africans and Europeans have homogeneous skin colour.

Kumarasamy Thangaraj at the CSIR-Centre for Cellular and Molecular Biology (CCMB), Hyderabad, in collaboration with the Estonian Biocentre, Estonia, and five other institutes, have published some interesting insights into this phenomenon in the November 17th online edition of The Journal of Investigative Dermatology where they have explored the genetics of skin colour variations across India.

“One of the reasons for this diversity in skin colour in India could be due to different waves of human migration into the country and recent admixture of all Indian populations, which we predicted in our previous study that it could have happened about two thousand years ago,” Thangaraj told BusinessLine .

The scientists also found some influence of the social structure defined by caste system and ethnic groups on skin colour pigmentation. Skin colour was found to vary significantly among ethnic groups and social categories studied. For example a Kashmiri group was extremely fair in colour, while an ethnic group in Kerala exhibited darker colour.

The researchers then compared the skin colour (phenotype) with the genetic variation (genotype) of the individuals. Those with derived (mutant) alleles (gene mixture through marriages) had fairer skin compared to those who had old (wild type) alleles.

“Our study clearly reflects the profound influence of the strict marriage patterns and multi-layered endogamy adding further to the variation in skin colour contributing to the mosaic of skin tones” says Chandana Basu, one of the authors of the study and researcher at Estonian Biocentre, Tartu, Estonia.

Skin colour is one of the most distinct phenotypes in humans and modern science attributes it to the biological pigment called melanin. The global spectrum of skin colour that we see across the world is contributed by several genes acting together to provide a canvas of different skin tones. The change of skin colour from dark to white is indeed an adaptation of our ancestors (read people out of Africa) and is a reflection of the delicate balance between the skin being light enough at low UVR (Ultra Violet Radiation) zones to allow sufficient production of vitamin D and dark enough at high UVR zones for photoprotection.

India seems to capture the central stage in the arena when it comes to diversity of skin colour. “We have done an extensive epidemiological survey of 1,167 individuals belonging to 27 populations and quantified melanin content at the most exposed and least exposed areas of the human body in the middle region of the Gangetic plains (Uttar Pradesh and Bihar), and selected 374 individuals for the first round of genetic study, said Anshuman Mishra, the first author of the study.

The gene SLC24A5 is known to make skin lighter and explains about 25-38 per cent of the pigmentation differences between Europeans and West Africans. A variant/ modification (rs1426654) in the gene was earlier shown to be associated with skin pigmentation measures in India.

In the present study, the research team has analysed the entire gene and found another variant (rs2470102), which contributes to skin pigmentation variation in the Indian subcontinent.

This is yet another effort of CSIR-CCMB in the field of genomics, which helped us in understanding the genetic link to the skin colour, said Rakesh Mishra, Director, CCMB .

On the future implications of such findings, he said they point to the era of personalised medicine based on the link of genomic features with disease susceptibility and drug response. Such studies, at very large scales, will be needed to establish individual specific lifestyle advisory and medical prescriptions as it is clear that “one size does not suit all” is also applicable to the area of human health and disease, Mishra added.

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