Geneticists at Radboud university medical center have spent more than twenty years looking for the cause of hearing loss in 63 members of twelve families. They have published their results in Journal of Medical Genetics. Now that the cause is known, they estimate that there are about 13,000 Dutch people with the abnormality, 9,000 of whom have actual symptoms.
Family studyHearing loss, which affects about one and a half million people in the Netherlands, can have many different causes, including exposure to loud noise, infection or aging. But it can also be caused by a genetic defect, which means that the hearing loss may not appear until later in life. Researchers at Radboud university medical center, led by Hannie Kremer and Ronald Pennings, theme sensory disorders, tracked down the gene by examining the genetic material (DNA) of entire families, including those with no symptoms. Almost all the family members were also given hearing tests.
Some of these people had been waiting 20 years for an explanation for their hearing loss, and they now have it: a variant of the RIPOR2 gene appears to be responsible for the condition, known as DFNA21. The abnormal gene may cause the cilia (hair cells) to be less firmly embedded in the cochlea, eventually making them less effective at transmitting sound. The study also showed that this form of hearing loss starts around the age of thirty, with some degree of spread between the ages of twenty and fifty. The extent of hearing loss can also vary greatly, even within families.
More carriersWhen the researchers examined a database of almost 23,000 other Dutch people who had been genetically tested, they found that 18 of them also carry this variant of the RIPOR2 gene. They therefore anticipate that about 13,000 Dutch people in total are carriers of the defective gene. Because the hearing damage only appears later in life, they estimate that approximately 9,000 of these people are currently experiencing hearing loss. This makes the abnormal RIPOR2 gene one of the most common hereditary causes of hearing loss in the Netherlands.
A potential treatment is still a long way off, but the Nijmegen researchers have started conducting initial experiments. The affected families are also not sitting idly by and have set up a patients’ association, Stichting DFNA21 Nederland.
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