CCMB established genetic links to skin colour variations
Further analyses revealed that both the variants together could better explain the variation in skin colour among Indian populations than considering each variant independently.
Skin colour is one of the most distinct phenotypes in humans, which is mainly attributed to the biological pigment 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.
Change of skin color from dark to white is indeed an adaptation of our ancestors and is a reflection of 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 photo protection.
India seems to capture the central stage in the arena when it comes to diversity of skin color. In India, we have populations with 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 color.
A recent study led by Dr Kumarasamy Thangaraj at the CSIR-Centre for Cellular and Molecular Biology (CCMB), Hyderabad, in collaboration with Estonian Biocentre, Estonia and 5 other institutes was published on November 17 in the online edition of The Journal of Investigative Dermatology has explored the genetics of skin colour variations across India.
We have done extensive epidemiological survey of 1167 individuals belonging to 27 populations and quantified melanin content at most exposed and low exposed area of human body at Middle region of Gangatic plains (Uttar Pradesh and Bihar), and selected 374 individuals for the first round of genetic study, said Dr Anshuman Mishra, the first author of the study.
SLC24A5 gene is known to make skin lighter and explains about 25 to 38 per cent of the pigmentation differences between Europeans and West Africans. A variant/modification in the gene has been earlier shown to be associated with skin pigmentation measures in India. In this study, the research team has analysed the entire gene and found another variant ,which contributes to skin pigmentation variation in Indian subcontinent.
Further analyses revealed that both the variants together could better explain the variation in skin colour among Indian populations than considering each variant independently.The difference in skin colour persisted even when the contribution by the previously known SNP was adjusted, suggest that the new SNP has an independent effect on skin colour.
The authors have found that social structure defined by the caste system has a “profound influence on skin pigmentation”. The skin colour was found to vary significantly among ethnic groups and social categories studied. The researchers then compared the skin colour (phenotype) with the genetic variation (genotype) of the individuals. Those with derived (mutant) alleles 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 color contributing to the mosaic of skin tones” says Chandana Basu, one of the authors of the study and researcher at Estonian Biocentre, Tartu, Estonia.
This team has studied 1,825 individuals belonging to 52 diverse populations across India and found that, social category and associated SNPs explain 38.4 per cent of the variation in skin color. Unlike Africans and Europeans, we do not have homogeneous skin colour throughout the country.
This could be due to different waves of human migration into India and recent admixture of all Indian populations, which we predicted in our previous study that it could have happened about two thousand years ago, said Dr Thangaraj.
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 Dr Rakesh Mishra, Director, Centre for Cellular and Molecular Biology. These are steps that point to the era of personalized medicine based on 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, Dr Mishra added.