Disease-linked genes in 14 Indian groups – Calcutta Telegraph

Posted By on July 20, 2017

New Delhi, July 19: Millions of people in each of at least 14 population groups across the Indian subcontinent may possess disease-linked genes, inherited from roots in founding populations and passed down generations through within-community marriages.

A genetic study of 260 distinct South Asian population groups has identified 14 groups, each with census counts of more than one million and each displaying genetic evidence for what scientists call "founder events", or descent from small founding populations.

Scientists have long known that similar founder events for certain populations such as the Ashkenazi Jews or the Finns have contributed to high rates of so-called recessive disease-linked genes in these populations.

The South Asian study, published yesterday in the research journal Nature Genetics, has now detected a stronger founder-effect in the 14 populations than what had been observed in the Ashkenazi Jews or the Finns.

The 14 groups sampled in the study were Arunthathiyars from Tamil Nadu, Baniyas from Uttar Pradesh, Manipur Brahmins, Nepal Brahmins, Gujjars from Jammu and Kashmir, Kumhars from Uttar Pradesh, Yadavs from Puducherry, and Reddys and Vysyas from Telangana, among others.

"Fragments of DNA present in the founders of each of these populations have been handed down for at least 100 generations and persist today," said Kumarasamy Thangaraj, a senior scientist at the Centre for Cellular and Molecular Biology (CCMB), Hyderabad, who led the study.

Thangaraj and his colleagues from Harvard University analysed sections of the genomic make-up of 2,800 individuals from 260 distinct South Asian population groups and assigned an "identity-by-descent" (IBD) score, a measure of common ancestry.

Each of the 14 population groups had higher IBD scores than Ashkenazi Jews and Finns, who have higher rates of certain congenital disorders such as cystic fibrosis (in the Jews), or congenital newborn kidney disease (in the Finns) than in general populations.

India's Vyasa community in the southern states, for instance, with a census count of about 3 million, has a founder effect 1.2-fold stronger than in the Finnish population. Earlier studies have shown that members of the Vyasa community on average have unusually high rates of a specific enzyme deficiency that makes them particularly sensitive to certain drugs, including muscle relaxants, given prior to surgery.

The study underscores the potential to look for such recessive gene-linked diseases in such populations with strong founder events and within-community marriages. "Groups with strong founder events are expected to have a high recurrence rate of the same rare diseases that arise from mutations carried in the founders," David Reich, principal investigator at Harvard University, told The Telegraph.

Mapping such mutations could help develop strategies for diagnosis, counselling, or managing such disorders. The scientists say a knowledge of these mutations could also guide match-making.

They cite an example of this strategy in a community genetic testing programme among Orthodox Ashkenazi Jews which screens students for common recessive disease-causing mutations and enters those results in a confidential database. Matchmakers can query this database to determine the risk of a couple passing a recessive gene to children. The risk is highest when both the boy and girl carry the same recessive gene.

"This strategy has reduced the rate of many recessive diseases to near-zero among Orthodox Ashkenazi Jews who use the service," said Reich. "A similar strategy may (also) be effective in South Asians."

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Disease-linked genes in 14 Indian groups - Calcutta Telegraph

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