Gene Chip for Congenital Deafness Offers Hope
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| With advances in genetic testing and high-resolution imaging, it is now possible to explain the cause of a child's hearing loss more than 60 percent of the time. |
Hearing loss is the most common neurological birth defect in the United States. It's reported, in the New England Journal of Medicine in 2006, that there is a hereditary or genetic basis in more than 50 percent of infants diagnosed with congenital hearing loss.
As the number of infants identified with hearing loss increases through universal hearing screening, so has the opportunity for clinicians to more accurately diagnose the etiology of their hearing loss.
Through their research, Daniel Choo, MD, and John Greinwald, MD, otolaryngologists and clinician scientists in the Ear and Hearing Center at Cincinnati Children's, have reported that advances in genetic testing are opening new opportunities for diagnosing and managing congenital deafness. The Ear and Hearing Center was the first to show that some genetic testing results can be very predictive of the level of hearing loss.
Before the availability of DNA testing, it was challenging to determine the cause of deafness 50 to 60 percent of the time, says Dr. Greinwald. But with advances in genetic testing and high-resolution imaging, it is now possible to explain the cause of a child's hearing loss more than 60 percent of the time, and the most common genetic causes have been identified.
As a result, genetic testing is becoming an important tool at Cincinnati Children's to help specialists implement early and appropriate intervention. For example, if genetic testing may assist in the decision of whether an infant may be a future cochlear implant candidate, families can begin to explore options at diagnosis.
Information about the genetics of hearing loss is now incorporated into the counseling that patients receive at Cincinnati Children's as part of their interdisciplinary Ear and Hearing Clinic evaluation.
Not only is genetic testing cost effective, it provides the family with a more accurate prediction of whether other children are at risk of having hearing loss.
It also can enhance audiometric testing in the very young infant, and it can diagnose other conditions, such as Usher and Pendred syndrome, that are associated with mutations that cause deafness in about 15 percent of cases. This information allows specialists to better tailor language therapy and monitor for other medical problems.
Gene Chip Technology and Genetic Testing at Cincinnati Children's
Previously, physicians at Cincinnati Children's ordered a series of tests and consultations to evaluate every possible cause of congenital hearing loss. This shotgun approach included blood tests for anemias, leukemias, syphilis, kidney disorders and abnormal thyroid gland function, as well as CT scans, ophthalmology consultations, human genetics consultations and electrocardiograms. Diagnostic tests could cost as much as $2,000 to $3,000, yet provided a frustratingly low yield in terms of identifying the exact cause of hearing loss.
In a study that began in 2004 and was funded by Ohio's Third Frontier initiative, the research team at Cincinnati Children's developed a custom gene chip to detect genetic causes of deafness from a single blood sample. The chip screens 10 to 15 genes simultaneously, offering unparalleled sensitivity, speed and cost effectiveness. This technology is now ready for wider clinical application.
Beginning in April 2007 the Molecular Genetics Laboratory at Cincinnati Children's will perform a mini-panel of three new genetic tests using high throughput techniques based on chip technology. The full version of the deafness chip is expected to be available later in 2007.
