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European studies shed light on progressive hearing loss

European researchers have carried out two parallel studies indicating that a new kind of gene is linked to progressive hearing loss. The gene 'miR-96' is a small fragment of RNA affecting the generation of other molecules within the inner ear's sensory hair cells. The research...

European researchers have carried out two parallel studies indicating that a new kind of gene is linked to progressive hearing loss. The gene 'miR-96' is a small fragment of RNA affecting the generation of other molecules within the inner ear's sensory hair cells. The research is part of the SIROCCO and EuroHear projects (supported by the EU with EUR 11.78 million and EUR 12.5 million in funding). Published in the journal Nature Genetics, the findings provide greater insight into a condition that affects millions of people worldwide. Researchers from the Spain-based Hospital Ramón y Cajal led the first team which followed families showing hearing loss; the other team, led by Wellcome Trust Sanger Institute researchers in the UK, investigated diminuendo, a new mouse model for understanding progressive hearing loss. The researchers shared the emerging data of both groups. '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, lead investigator of the Sanger Institute team. 'The important questions were could we determine what the variant is and how does it exert its effect on hearing?' Based on the results of the first group, the Spanish-led team suggested that the gene responsible lay on chromosome 7, which has already been implicated in various human diseases and malformations. Both teams attempted to sequence every gene in the 'equivalent genomic regions in human and mouse identified as implicated in hearing loss'. The sequencing demonstrated that the majority of the region's genes could not be responsible for loss of hearing. But both teams discovered a mutation in a microRNA gene; the miR-96 gene is linked to hearing loss. 'We know of a number of genes involved in deafness in humans and mice but, to our great surprise, this was one of a new class of genes called microRNAs,' remarked senior author Professor Miguel Angel Moreno-Pelayo, a researcher from Hospital Ramón y Cajal. Experts recognise that microRNAs, which are able to control the activity of many genes, can bind to the messengers active in cell protein generation, effectively interrupting the process. 'No one has seen a disease-causing mutation in the mature sequence of a microRNA,' Professor Moreno-Pelayo said. 'This is the first microRNA gene associated with hearing impairment and, remarkably, it is the first to be associated with an inherited disorder.' The researchers found that the role of the mutation can be investigated in the mouse. The sensory hair cells in the mutant mice were seemingly disrupted by the miR-96 gene, they said. While the mice with two copies of the mutant gene had malformed hair cells from birth and the cells degenerated from an early age, the researchers found that the effects were less severe in mice with one copy of the mutant gene. They noted, however, that the effects worsened as the mice got older. '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,' Sanger Institute's Dr Morag Lewis, who found this mutation, pointed out. Concerning the human studies, the researchers found that two families showed mutations in miR-96. However, each carried the mutation at different locations in the miR-96 gene, they said. While neither mutation in humans is the same letter as in the mouse, all three are close to one another in the miR-96 sequence. 'All three sit in a vital region of seven letters in the mature sequence of miR-96,' explained Dr Angeles Mencía from Hospital Ramón y Cajal. The findings will help scientists develop treatments to mitigate the effects of progressive deafness, the researchers said. Other participants of the studies included the GSF National Research Center for Environment and Health (Germany) and the University of East Anglia (UK).

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