Genetic fault linked to hereditary deafness

Scientists have discovered a gene mutation that can cause children to be born deaf.

A team from the Radboud University Nijmegen medical centre (RUN MC), Netherlands, studied the DNA of a nonconsanguineous Dutch family and a consanguinous Moroccan family who had a recessive hearing impairment. Consanguineous marriage - a union between close relations, commonly first cousins - can be associated with a higher risk of recessive genetic disorders.

They identified mutations on the PTPRQ gene, which is necessary for normal development of inner ear 'hair cells'. The Dutch family has a 'missense' mutation that caused moderate to severe hearing loss. The Moroccan family had the severest hearing loss - their PTPRQ gene contained a 'nonsense' mutation, which made the gene produce a malformed and truncated protein.

Interestingly, while PTPRQ is expressed in many tissues of the body, the only symptom other than deafness observed in the patients was a dysfunction in the vestibular system. This system is responsible for spatial awareness and balance and is also located in the inner ear.

Approximately one in 750 children are born with profound deafness or hearing loss, which equates to about 840 babies per year in the UK. In half of these cases the deafness is inherited.

Some 60 different locations in our DNA are now known to contain genes that can contribute to this form of inherited deafness if they are faulty. But only half the genes at these key 'problem' locations have been identified.

'Our approach is identifying more genes for congenital deafness', said Dr Hannie Kremer, who led the research at RUN MC, adding: 'This knowledge will help improve treatments for patients, genetic counselling, molecular diagnosis and the development of advanced therapeutic strategies'.

Dr Sohaila Rastan, chief scientific officer at the Royal National Institute for Deaf People (RNID), said: 'Knowledge of genes causing deafness tells us more about how our hearing works. This research will help develop medicines that are desperately needed to prevent deafness and restore hearing'.

The Dutch scientists, who were funded by the RNID, published their work in the American Journal of Human Genetics.