A link has been found between progressive hearing loss and a microRNA (ribonucleic acid) gene - the first time this type of gene has been implicated in any inherited disorder. The findings are the result of convergent research by scientists from the Wellcome Trust Sanger Institute in Hinxton, England, and from Hospital Ramon y Cajal in Madrid, Spain. Companion papers describing the research were published in the journal Nature Genetics.
The Spanish scientists examined people with a family history of deafness, while the British group examined mutant mice called 'diminuendo', which show progressive hearing loss from an early age. Both groups found evidence that implicated mutations in the gene for a microRNA (a small segment of ribonucleic acid that acts to regulate the expression of other genes) as the cause of the hearing loss. The microRNA in these studies is known as miR-96 and is found on chromosome 7 in humans. It is expressed in the hair cells of the inner ear and when mutated may disrupt the function of several other genes.
'We were able quite quickly to show that if the mice carried one copy of the gene variant they suffered progressive hearing loss, if they carried two variants they were profoundly deaf,' said Professor Karen Steel, from the Sanger Institute. Lead author of the mouse paper, Dr Morag Lewis, added: 'The mutation - a change of a single letter of genetic code from A to T - in this tiny stretch of sequence is enough to lead to dramatic loss of hearing in these mice.'
The Spanish researchers found two adjacent mutations in humans that were responsible for the hearing loss but, interestingly, neither were the same as the mutation found in the mice. Family members with one of these mutations had hearing loss while those without the flaw did not. Neither mutation was found in healthy controls.
'The mutation in the second family is just one letter away from the mutation in the first and just one away from the mutation in the mouse gene. All three sit in a vital region of seven letters in the mature sequence of miR96' explained Dr Angeles Mencia from Hospital Ramon y Cajal. Professor Miguel Angel Moreno-Pelayo added 'No one has seen a disease-causing mutation in the mature sequence of a microRNA. This is the first microRNA gene associated with hearing impairment and, remarkably, it is the first to be associated with an inherited disorder.'