Hearing Health Summer 2012 Page 12

12 | HEARING HEALTH | A PUBLICATION OF HEARING HEALTH FOUNDATION Pediatrics HEARING HEALTH By Elizabeth Stump C ongenital hearing loss means hearing loss is present in an infant at birth. More than half of congenital hearing loss cases are due to genetic factors, according to the Centers for Disease Control and Prevention. To date, more than 50 deafness genes have been genetically sequenced, and there are likely to be hundreds more identified, according to Joseph L. Hegarty, M. D., a hearing specialist who practices in Colorado Springs, Colo. Genetic causes of hearing loss can come from recessive or dominant genes. “ Recessive versus dominant causes refer to the two major patterns of inheritance,” says William J. Kimberling, Ph. D., a senior scientist at the Boys Town National Research Hospital in Omaha, Neb., and a professor of ophthalmology at the University of Iowa Carver School of Medicine. Kimberling studies Usher syndrome, which includes hearing loss as a symptom. The difference is primarily in the way the gene is expressed. Generally speaking, a recessive condition requires two copies of an inactivated gene in order for the disorder to manifest. Carriers of just one gene do not have any symptoms. Most family histories are negative for the condition, or show only an affected sibling. Multiple generations with the condition are seldom seen. About 90 percent of children with hearing loss have parents with typical hearing, according to Anna Frangulov, a research coordinator involved with genetic studies at Children’s Hospital Boston. If both parents have a recessive mutation, each of their children has a 25 percent chance of having hearing loss. A Genetics Crash Course Understanding the root cause of a hearing loss can help you find the right treatment. A Genetics Crash Course PHOTO CREDIT: © ISTOCKPHOTO. COM/ GMUTLU