A new genetic fault which may account for some cases of inherited deafness has been revealed by Dutch researchers.
It means that parents with the hereditary condition may be able to predict more accurately the chances of passing it on to their children.
The new find, documented in the American Journal of Human Genetics, could even one day contribute to treatments, say the scientists.
One child in 750 is born with severe hearing loss or profound deafness.
The gene in question, labelled PTPRQ, appears to play a role in the development of the inner ear "hair cell" before the birth of the child.
A genetic fault here means that these cells will not form properly or in sufficient numbers, leading to profound deafness or extremely poor hearing.
This can lead to problems throughout childhood, including behavioural and developmental difficulties, and low academic achievement.
The latest gene was tracked down by scientists at Radboud University Nijmegen Medical Centre who looked closely at the DNA of families prone to the condition, looking for shared genetic traits.
There are now more than 60 known locations in our DNA which can contain faulty genes contributing to this form of deafness, although only half the genes in these locations which actually cause the problem are yet to be identified.
Dr Hannie Kremer, who led the research, said: "Our approach is identifying more genes for congenital deafness.
"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 for the deaf and hard of hearing charity 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."
There are hopes that gene therapy will one day be able to correct genetic defects linked to this type of deafness.