Genetic testing can improve newborn screening tests for hearing defects

Researchers have identified several changes that could be made to existing newborn screening tests for hearing defects that could advance the standard of care in detecting deaf infants, according to an article in the New England Journal of Medicine.

Walter E. Nance, M.D., Ph.D., professor of human genetics in Virginia Commonwealth University's School of Medicine, and Cynthia C. Morton, Ph.D., a professor of human genetics at the Harvard Medical School, have summarized four important criteria to be considered for screening programs throughout the country for newborn hearing defects. These include the prompt confirmation of abnormal results from screening tests; adoption of an etiologic focus to determine the cause of the deafness; initiation of molecular genetic testing for all newborns; and better recognition of infants at risk for late-onset hearing loss occurring prior to speech and language development.

Molecular genetic testing of blood spots from all newborn infants for the presence of the CMV virus, connexin deafness, Pendred syndrome and mitochondrial mutations in the 12S rRNA gene would allow the immediate diagnosis of the commonest forms of genetic and environmental deafness that are expressed at birth, according to the article, published in the May 18 issue of the New England Journal of Medicine. In addition, these tests would allow for the identification of infants at risk for the commonest genetic, environmental and preventable causes of delayed onset prelingual deafness.

"If hearing loss is detected at birth and appropriate intervention is promptly initiated the educational outcome for deaf infants can be dramatically improved," said Nance, who is the corresponding author of the article. "Although newborn hearing screening programs have improved the lives of infants throughout the world, our report suggests several specific ways in which these programs can be improved, including the screening of all newborns for a limited number of the major genetic and environmental causes of hearing loss."

According to Nance, who has been studying genetic deafness for more than 30 years, identifying the actual cause of the deafness can be just as important as detecting the hearing loss. He said that data from genetic testing would provide a powerful supplement to audiologic testing that could greatly improve the overall effectiveness of these programs.

In 1964, Marion Downes, a distinguished audiologist, first showed that profound deafness could be recognized in newborn infants by painstaking observations of their response to sounds. Since that time, advances in technology now allow the automated screening of infants by trained technicians. At the same time, dramatic advances have been made in understanding the causes of deafness.

In addition to many environmental causes of deafness, researchers have identified more than 100 genes that are linked to deafness. Nance said that approximately 50 percent to 60 percent of childhood hearing loss in developed countries is due to genetic factors.

Hearing is essential for the normal acquisition of speech. According to Nance, if oral or sign language is not acquired during a critical developmental stage, deaf children may never achieve their full developmental potential. Other studies have indicated that early detection of hearing loss and intervention can improve the educational and social outcomes of these newborns.

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