Researchers have unearthed a genetic mutation that leaves its victims deaf and blind. The finding should help health providers detect the disease early in certain populations and might furnish clues about how the disease arises.
Usher syndrome type 1 is the most common cause of deaf-blindness, accounting for roughly half of the 16,000 deaf-blind people in the United States. Newborn babies are deaf, and affected children start to have vision problems by about age 10, then lose their sight completely by early adulthood. Only people with mutations in both copies of the same gene develop the incurable disorder. Those with only one mutated copy are healthy, but can pass the disease on to their offspring. Researchers know of six very rare mutations in several genes that can cause Usher syndrome type 1, but they haven't found all the mutations that lead to the syndrome.
Now, geneticist Tamar Ben-Yosef of the National Institute on Deafness and Other Communication Disorders in Bethesda, Maryland, and colleagues have identified a seventh mutation in the Ashkenazi Jewish population, a closely related group of individuals. Although Usher syndrome doesn't occur in Ashkenazi Jews more often than in the general population, this particular mutation, called R245X, does, implicating it as the major cause of the disease in this population. The proportion of Ashkenazi Jews carrying R245X is similar to the proportion of those carrying mutations linked to other diseases--such as Tay-Sachs disease--that are routinely screened for. The team, which reports its results in the 24 April issue of The New England Journal of Medicine, says doctors should regularly screen for R245X in deaf Ashkenazi children to determine whether the children will also eventually go blind. Parents could also potentially screen unborn children for the disease.
"Usher syndrome is a desperate, miserable disease," says human geneticist Paul Sieving of the National Eye Institute in Bethesda, Maryland. "It seems like a modest bit of progress, but it's extremely helpful to provide early detection [to these families] for them to have a sense of what the future brings." Knowing that a deaf child will go blind will help families prepare for the blindness through counseling and perhaps cochlear implants. The new mutation will also help researchers understand what the gene does under normal conditions, says Sieving, eventually leading to treatments.