Clinical and basic scientists have identified a broad spectrum of genetic mutations among Indian populations that cause hearing loss1. The findings may provide answers to about one quarter of the population affected with hereditary nonsyndromic hearing loss in the country.
This answer lies in a gene connexin 26 (Cx26) located on the chromosome 13. Cx26 makes a protein known to be expressed in the inner ear. In a study of 530 families with hereditary hearing loss, four teams from Bangalore, Mumbai, Delhi and Chennai identified a broad spectrum of mutations at Cx26, 18 of them affecting activity of the CX26 protein at multiple levels. "These mutations were mostly recessive implying that both copies of Cx26 should carry mutation to lead to hearing loss," says principal investigator of the study Anuranjan Anand. Individuals who harboured these mutations were hearing impaired since birth or very early childhood and did not manifest any additional medical problem.
The spectrum of mutations observed in India was found to be different from that observed in the European, Ashkenazi, Jewish and Far-Eastern populations. Interestingly, a single mutation accounted for about 75% of all pathological mutations at the gene and was most likely a founder mutation in the Indian population as shown in an earlier study2.
In a country where 4-5 million individuals are estimated to be hearing impaired, this work has important implications for early risk detection for hearing loss especially in families where one child is already affected with hearing impairment.
The authors of this work are from: Jawaharlal Nehru Centre for Advanced Scientific Research, Bangalore; AYJ National Institute for the Hearing Handicapped, Mumbai; Maulana Azad Medical College, New Delhi and Dr. ALM Post Graduate Institute of Basic Medical Sciences, University of Madras, Chennai.
