The comprehensive genetic testing offered at one of these labs has dramatically improved the diagnostic rate of hearing loss, said Dr. Smith Recently, he and his colleagues published a study looking at the most current evidence on the use of comprehensive genetic testing for hearing loss in the U.S. All four sites in the U.S. use a technology called massively parallel sequencing (MPS), in which hundreds or thousands of gene
Explore This IssueAugust 2017
regions associated with hearing loss are isolated simultaneously prior to sequencing using a method that relies on targeted genomic enrichment (TGE) (Otolaryngol Head Neck Surg. 2015;153:175-182). Analysis of 20 studies that included 603 patients with unknown causes of hearing loss who underwent genetic testing that used the MPS technology found that this technology provided a better overall diagnostic rate (average 41%) compared with single-gene testing. Overall, the diagnostic rate with this technology ranged from 10% to 83% among the studies.
Given the range of diagnostic rates obtained from the studies, Dr. Smith emphasized that not all comprehensive genetic testing is equal. “Equality can vary at different points along the analysis pipeline,” he said. As such, he said that he and his colleagues “recommend that the testing be comprehensive and that the downstream analysis include an evaluation for copy number variations, with a robust interpretation of the results in the context of the clinical information.” Emphasizing the importance of placing this genetic information in the context of clinical information, he said that he and his colleagues keep an open dialogue with treating clinicians and “always make ourselves available to help.”
The Goals of Genetic Testing
One of the key goals of genetic testing for hearing loss, particularly in children, is to provide a precise diagnosis to guide treatment. This is particularly true in specific situations such as children with the connexin 26 mutation, said Dr. Moody-Antonio. In children with this common cause of nonsyndromic hearing loss, “research predicts that the patient would be very likely to be a successful cochlear implant user,” she said.
A genetic diagnosis of Usher syndrome, another type of hearing loss, may also change how the hearing loss is treated. “In this case, bilateral cochlear implantation and oral language training would be preferred, since the child would eventually lose the ability to communicate with a visual language such as American Sign Language,” she said.
For Rick Friedman, MD, PhD, director of the University of Southern California (USC) Acoustic Neuroma Center and professor of otolaryngology and neurosurgery at USC’s Keck School of Medicine in Los Angeles, one of the key reasons for genetic testing in children is that it is a safer way to determine which children may benefit from a cochlear implant. “Prior to genetic testing, we’d order a CT scan to see if a child would be a good candidate for cochlear implantation or to see if we could find a cochlear anomaly,” he said, adding that it is increasingly recognized that early exposure to radiation by CT scan is probably not good for a child’s brain. “I think genetic testing is helpful because it helps to avoid radiation exposure in some children and gives prognostic information and direction to rehabilitate children.”