In one of the first direct results of the Human Genome Project, scientists have found the gene for a disease that causes congenital deafness. Researchers report in the December issue of Nature Genetics that the gene--which was discovered after just 13 months of investigation--points to an unexpected role for sulfate in the fetal development of proper hearing.
The newly-discovered PDS gene manufactures a protein called pendrin that seems to transport sulfate across cell membranes throughout the body. When PDS is defective, however, it leads to Pendred syndrome, a rare disease that produces deafness at birth due to improper fetal development of the inner ear and accounts for 7% to 10% of all congenital deafness. Later in life, Pendred syndrome patients frequently develop goiters, abnormal swellings in the neck caused by an enlarged thyroid.
The identification of PDS is the result of a collaboration of researchers at the National Human Genome Research Institute (NHGRI) in Bethesda, Maryland, the University of Iowa in Iowa City, and Hadassah University Hospital in Jerusalem. Hadassah researchers had been collecting DNA samples from several large Arabic families with a high incidence of Pendred syndrome. Once they and the Iowa researchers had narrowed the suspect gene's location to a specific region on human chromosome 7, they enlisted NHGRI scientists, who have been mapping that chromosome. Each time a gene was found in that region, it was immediately tested for a link with Pendred syndrome. After only 13 months, much quicker than the normal 10 years, the team found its quarry: a gene heavily expressed in the thyroid and altered in Pendred syndrome patients.
PDS's role as a sulfate transporter makes it unique among genes linked to deafness, says NHGRI team leader Eric Green. However, researchers still don't understand the link to Pendred syndrome and the resulting malformation of the inner ear, which occurs early in fetal development. So Green and his colleagues are developing "knockout mice," with their PDS genes inactivated, so the developmental effects of the mutation can be observed directly.
The discovery of PDS is extremely important for the study of deafness, says James Battey, Jr. of the National Institute on Deafness and Other Communication Disorders. "We never would have guessed that sulfate transport was involved in hearing impairment," he says. Battey believes that pegging the gene is a first step toward developing therapies that might treat such congenital deafness.