Understanding India’s uniqueness in its genetic diversity

Understanding India’s uniqueness in its genetic diversity

By Sam Santhosh

Ever since the pandemic started, we have been seeing the hurdles faced by India on account of its huge population. Let us take a moment to recognise the uniqueness of our population which can give us valuable insights into identifying and treating genetic disorders. Amongst all the lessons learnt through this challenging period, there is one thing it has made us all realise again – the uniqueness of our biological responses to the external environment, be it the way the virus affects us or the response our body generates to fight it. For India, the impact has yet again highlighted our geographical and biological diversity.

Interestingly our geography and culture drive this biological diversity. Modern humans are considered to have emerged about 200,000 years ago in East Africa, and then dispersed throughout Africa, and then Eurasia and Oceania. During the migration from Africa, our ancestors also interbred with other archaic cousins like the Neanderthals and Denisovans. In fact, we now carry around 2 to 5 percent of Neanderthal genes and about 3 to 7 percent of Denisovan genes! Selective pressures of climate and availability of resources created concentrated groups of populations. Around 55,000 years ago, India acted as a major corridor for early human migration. The migrations happened in clusters and thus even today most of us have descended from a small group of founding individuals who have been isolated from the others. The boundaries further remained closed with social stratifications, such as religion, castes, and tribes.

The caste system in India is a hierarchical structure divided into several endogamous groups which govern all social, religious, and economic activities of the people. The social boundaries through endogamy and founder effects have given birth to diverse, population-specific traditions and genetic variations among the populations. This has resulted in disease-causing mutations to spread to a greater number of people. When parents have the same common ancestry, there is a greater risk that they will both carry the same mutation, and the off-springs are at a greater risk of inheriting the disease-causing mutation. Further other social practices like consanguineous marriages have increased these effects in some population groups.

On the other hand, this ‘inbreeding’ also results in extremities such as gene knockouts which can provide good insights into the biology of modern humans. Since we do not understand the function of many genes even now, these insights can help in drug development and disease treatment. India has over a billion people and nearly 4500 population groups.

India is thus a genetic goldmine in comparison with countries such as Iceland, Finland which had the advantage of having started from a small number of colonizing individuals resulting in the number of disease-associated genetic variants to be relatively small for each individual disease. Similarly, Indian population data provides the ideal conditions for genetic research and makes it easier to identify common gene variants and the associated diseases. Discovering these disease-inducing genetic variants and adopting prenatal screening to determine carriers will play a major role in identifying and preventing these rare diseases.

Numerous such evidence-based community genetics studies in the past have helped in eradication of genetic diseases from specific populations. One such example is the successful elimination of Tay-Sachs, a rare inherited disorder eliminated by the Ashkenazi Jews, a fairly closed community with mainly central and eastern European ancestry. Tay–Sachs is caused by recessive genes, parents who carry the gene have no indication until they have a baby with the disease, or they get a genetic test done. There is no treatment, and most children with the disease die by the age of five. In 1980’s, five families in Brooklyn affected by this disease decided to work collectively towards eliminating this disease and enrolled people in the anonymous screening program and counselled them about the risks of having babies with the disease. Thirty years later Tay-Sachs incidence in the community has been slashed by more than 95 percent.

Genetic knowledge about Ashkenazi Jews is not only a reflection of their genetic value or uniqueness as a population, but also their active participation as research subjects with physicians, and scientists generating and shaping this knowledge. If recessive disease mutations are catalogued, they could potentially be used for prenatal or premarital screening programs. Studies of such groups will lead to the rapid discovery of genes that cause devastating diseases and will help in the clinical care of individuals and their families who are at risk.

Many companies in India now offer clinical genetic diagnostic tests to detect genetic disorders at an early stage making the management of the disease easier with the right targeted therapy. Becoming aware of the need to identify these diseases at the right time and preventing them from passing on to the next generations is the need of the hour.

With India’s population being unique and valuable in understanding rare diseases, it is time we explore India’s unity in genetic diversity!

By Sam Santhosh, Founder and Chairman of MedGenome.

News source- Economic Times

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