More kids in Tamil Nadu born deaf, doctors look at family marriage

04.03.2017

CHENNAI: Congenital deafness is one of the most common birth defects in Tamil Nadu and doctors at a city-based ENT research centre say the cause may lie in the gene.

A team of doctors from Madras ENT Research Foundation(MERF) is looking into genes of more than 300 people from 60 families with deaf children to see if the birth defect has been passed on by a rouge gene from parents. In 2013, studies showed that six out of every 1,000 children born in the state have profound hearing loss -three times the national average. Doctors found that parents of at least two-thirds of the 50,000 deaf children surveyed had consanguineous mar riage. Yet, not all children born to such couples had the birth defects.

Now, MERF scientists led by Dr Sudha Maheshwari hope the study, when completed, will indicate primary causes for inherited deafness. "As of now we don't know why just some of the children are affected. We are looking at nearly three generations in every family. The study will help us prove our hypothesis that consanguinity is one of the primary causes for birth defects.The next step will be to isolate the gene and determine precisely how it causes hearing loss. When we learn about the genes we can also look therapies at the molecular level," she said.

Earlier studies had shown that certain gene mutations have the ability to block the protein that aids cochlear function. Gene therapy helps doctors modify the rouge gene so a person can hear. It is not reality yet, but trials on mice and zebra fish are beginning to show positive results, say doctors. While some gene association studies of newborns have been conducted in the past in a small number of people, no large study has been done in India. Genome-wide association studies search the entire DNA for common mutations to see if any of those are linked to a trait.

The study of 300 people may generate adequate scientific data, but it will show the need for multi-centric clinical trials, said ENT specialist Dr Mohan Kameshwaran. "In fact, on several occasions we find that children with deafness have other complications such as congenital hypothyroidism that can stunt their growth," he said.

Doctors at another research centre, Fetal Research Foundation, which screens newborns for metabolic disorders like congenital hypothyroidism and congenital adrenal hyperplasia, say these are also above the national average."As of now we just know the numbers.We don't know the reason why these happen," said fetal medicine expert Dr S Suresh, who heads Mediscan.

More than 55% of patients with these metabolic disorders are born to parents who have married near blood relatives. "We have to establish this genetically. We also think other environmental factors such as iodine levels in salt and malnutrition of pregnant women have a large role to play ," said paediatrician Dr Sudha Rathinaprabu, who also planning a detailed study.

3,000 got cochlear implants in 3 years

At least 3,000 children born with deafness were given cochlear implants under the state health insurance scheme in the past three years. The only option for children born deaf is to undergo cochlear implant, preferably before they are six. "Each of these devices cost Rs `8 lakh. It one of the advanced machines that is given to patients who come to private hospitals," said ENT specialist Dr Mohan Kameshwaran. "It is a complicated surgery. Surgeons will have to operate a small crowded area in the base of the skull to implant the device." After implant these children go to state-run habitation centres or private hospitals to get trained in hearing and speech.