High inbreeding, disease risks in south Indian communities: Genetics study

A study that analysed genes of South Indian populations suggests a high inbreeding rate of nearly 60 per cent.

The historic practice of inbreeding or endogamy in which one marries within a small community, increases chances of passing down disease-causing gene variants -- changes to one's DNA -- to children, thereby raising the risk of genetic disorders.

Lead author Kumarasamy Thangaraj, senior scientist at the Council of Scientific and Industrial Research (CSIR)-Centre for Cellular and Molecular Biology, Hyderabad, said endogamy is the primary cause for population-specific diseases in India.

The study, published in the Journal of Genetics and Genomics, also reported a high prevalence of ankylosing spondylitis, a common form of inflammatory arthritis, in the Reddy population of Andhra Pradesh.

The researchers attributed this result to the presence of the 'HLA-B27:04' -- a genetic variant known to increase risk of the condition -- and a "strong founder effect".

A founder event is when a new population is formed by a small group of people. The endogamy practice, deeply rooted in the caste system, is significant to the South Indian society.

However, despite a large number of endogamous population in India, comprehensive studies on resulting disease risks remain limited, the team said.

Using the '1000 Genomes' dataset, the researchers looked at blood samples of 281 individuals, belonging to four such populations -- Yadav of Puducherry, Kalinga and Reddy of Andhra Pradesh, and Kallar of Tamil Nadu.

Whole exome sequencing, a genetic test for analysing sample of an individual with a family history of a disease was used for analysis.

The results revealed "a high inbreeding rate of 59 per cent across the populations".

"We found a high incidence of ankylosing spondylitis disease in the Reddy community, who dwell in a specific geographical region of Andhra Pradesh," said author Dr Sarath Chandra Mouli Veeravalli, a rheumatologist at Krishna Institute of Medical Sciences, Hyderabad.

The authors also identified variants responsible for diseases and drug responses unique to a specific population. Results related to drug responses have implications for personalised medicine.

Thangaraj said, "Our study forecasts the impact of endogamy in causing population specific genetic diseases and drug responses."  The lead author stressed on "appropriate genetic screening, counselling and clinical care for the communities that are vulnerable to various health conditions".

The 1000 Genomes Project ran between 2008 and 2015, creating a catalogue of common gene variations in around 1,000 individuals from Europe, Asia and Africa.