Nov. 29, 2000 -- When researchers found seven members of a large Pakistani family, who should be deaf but weren't, they were alerted to the existence of a powerful gene that appears to block hearing loss. The finding may make it possible to design new therapies for deafness, suggest researchers in the December issue of the journal Nature Genetics.
Although their relatives who inherited both copies of a deafness-causing gene have profound hearing loss, seven family members who inherited the same gene but also inherited a second, unidentified "anti-deafness" gene escaped the seemingly inevitable fate of hearing loss, report Edward R. Wilcox, PhD, and colleagues at the National Institute on Deafness and Other Communication Disorders, or NIDCD, in Bethesda, MD, and Punjab University in Lahore, Pakistan.
"About one in 2000 children are born profoundly deaf due to genetic causes, but little is known about how such genes cause hearing loss or what to do about it," says Xue-Zhong Liu, MD, PhD, who reviewed the study for WebMD. He explains that scientists from NIDCD have found a gene that is able to influence and modify other genes for genetic deafness.
"The finding may help researchers figure out on a molecular level what goes wrong in deafness and eventually design a therapy, although any such possibility is far in the future," says Liu, an assistant professor of human genetics and otolaryngology at the Medical College of Virginia in Richmond.
More than half of all cases of childhood deafness are inherited. Some occur in connection with other genetic disorders such as profound mental retardation, but the large majority of hereditary hearing loss cases occur as isolated genetic defects.
Wilcox and his colleagues looked at a large Pakistani family with a history of deafness. The investigators first performed a genome scan, looking at the entire library of genetic information that occurs on the chromosomes within the cells of the family members. They were looking for specific markers that act as signposts pointing to the likely whereabouts of a specific gene.
They found a marker for a deafness gene in eight deaf family members. But to their surprise, they also identified seven family members who had the same gene but had normal hearing, indicating that the researchers were either looking at the wrong gene or had found evidence of an unknown gene -- one that could counteract or neutralize the effects of the deafness gene.
To see whether this type of gene could indeed be at work, Wilcox and colleagues performed another genome scan. The hearing individuals were all found to carry markers for the "anti-deafness" gene, whereas none of the deaf family members carried the gene.
Although neither the deafness-promoting nor the deafness-preventing genes have been precisely identified, the finding that a certain gene can have such a profound influence on a critical bodily function such as hearing is unusual to say the least, Wilcox says.
Whether the discovery can be translated into a practical therapy is another matter, he adds. "Complexities of hearing are pretty high ... If you interrupt any part of the [hearing] pathway, the outcome is deafness." He explains that there are so many factors at work that finding a remedy is very difficult.
Liu, however, sees promise in the discovery. "The identification of these types of genes for deafness opens a new avenue to pinpoint the molecular mechanisms of [hearing] function and facilitate the rational design of therapies for hearing impairment," he comments.