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Gene Identified for a Disorder that Causes Deafness and Blindness
Scientists have identified a gene that causes Usher syndrome (US) type IIa, the most common condition that involves disorders of both hearing and vision. This finding is reported in the June 12, 1998, issue of the journal Science, by Dr. William J. Kimberling, an investigator supported by the National Institute on Deafness and Other Communication Disorders (NIDCD), and a team of scientists from around the world.
The scientists described three different mutations in a gene called USIIa. This gene was previously mapped to a location on chromosome 1 and is associated with the syndrome. The three mutations were found in families from three distinct geographic areas.
"In addition to potential treatment strategies, discovery of this gene may provide insight into links between the auditory and visual developmental pathways," stated Dr. James F. Battey, Jr., Director, NIDCD.
There are three types of Usher syndrome: Usher syndrome type I (USI); Usher syndrome type II (USII); and, Usher syndrome type III (USIII). USI and USII are the most common types of Usher syndrome. Together, they account for approximately ten percent of all cases of children who are born deaf. So far, at least nine different genetic locations have been identified as causing all types of Usher syndrome.
People with USI are profoundly deaf from birth and have severe balance problems. Many of these individuals obtain little or no benefit from hearing aids. All individuals born with USII have moderate to severe hearing impairment and normal balance. Not all families with USII, however, have the same gene for Usher syndrome. USIIb refers to USII families who do not have this gene for Usher syndrome, but are born with moderate to severe hearing impairment and normal balance. Although the severity of hearing impairment varies, most children with USIIb perform well in traditional classrooms and can benefit from hearing aids. Some children use speech to communicate and depend, at least to some degree, on lip reading. Others use sign language to communicate.
The vision problem associated with US, retinitis pigmentosa, is a degeneration of the retina, the part of the eye that receives images. This disorder is characterized by blind spots that begin to appear shortly after the teenage years and progresses to blindness. This loss increases the disability for individuals who depend heavily upon vision for communication.
The current emphasis in Usher syndrome research is to locate all of the genes that cause the syndrome and identify the function of those genes. Locating US genes and discovering the role they play will ultimately permit early diagnosis, allow for genetic counseling to occur and may, eventually, provide treatment options.
As the nation's focal point for research in human communication, the NIDCD conducts and supports biomedical and behavioral research and research training on normal mechanisms as well as diseases and disorders of hearing, balance, smell, taste, voice, speech and language that affect 46 million Americans.