Study finds caste-based diseases in South Asia

Hyderabad: Most South Asian linguistic races and caste groups have a high vulnerability for ‘population-specific’ diseases. A CCMB study published in Nature Genetics on Monday found that out of 263 unique South Asian groups studied, around 81 have a large number of recessive diseases.  

A recessive disease is one that can be passed down through families. The interesting study led by CCMB scientist Dr Kumarasamy Thangaraj revealed that the Vaishya community have a 100-fold higher rate of butyrylcholinesterase deficiency, a condition of not being able to assimilate the anaesthetic drug than other groups, Rajus (Andhra Khsatriyas) have high risk of cardiomyopathy and Reddys in specific geographic location in the state suffer arthritis.

Likewise Gujjars of Rajasthan, Baniyas of UP and Pattapu Kapus of AP have got high IBD (Identity-by-descent) score that shows they carry certain gene mutations responsible for diseases to future generations. Scientists say that due to Endogamy and marriage in the same caste groups, for instance for the past 108 generations in Vaishya, and in general in the past 2,000 years due to development of castes the disease causing mutations are carried forward to future generations.

Out of 80 groups identified for having high IBD score around 14 groups have an estimated size of over 10 lakh population.

Founder event higher in case of Vaishyas
CCMB senior principal scientist K. Thangaraj said, “Every person in the world not only in South Asia carriers several mutations that if they occurred in two copies would lead to serious recessive diseases.”

“In South Asia ‘founder events’ (loss of genetic variation where small numbers of ancestors carrying mutations give rise to large number of descendants) combined with endogamy (marriage within groups) cause the mutations to often be carried in two copies. In South Asia as due to these two factors it lead to far higher rate of population specific diseases than elsewhere in the world.”

Dr David Reich of Harvard Medical School and Broad Institute in US along with other collaborative authors devised an algorithm to quantify the measure of the found events in each group based on Identity-By-Descent segments, large stretches of DNA shared from a common founder in the last one hundred generations.

Researchers highlighted the case of Vaishya who are around 30 lakh in population has a founder event that is 1.2 fold stronger than that in Finnish population.

“Vaishya ancestry is a known counter-indication for the use of muscle relaxants such as succinylcholine or mivacurium that are given prior to surgery for anaesthesia purpose. This disease is likely to occur at a higher rate due the lesser genetic variation over generations in the history of Vaishya. The genes that are responsible for production of enzymes which metobolises these anaesthesia drugs are produced low in Vaishya. That is why they are given altered anaesthetic drugs,” he said.

He added, “We haven’t studies in all castes what type of recessive diseases are prevalent but we have analysed the groups that have identity-by-descent factors.”