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Cochlear Implant Outcomes Linked to Type of Genetic Diagnosis for Childhood Hearing Loss

NEW YORK – In childhood-onset hearing loss that involves a genetic diagnosis, specific genes and variants may provide clues to everything from an individual's symptoms and hearing loss trajectory to their cochlear implant outcomes, new research suggests.

"Using genetic diagnoses provides information about progression of the hearing loss and possible syndromic outcomes, enabling the more optimal timing of treatment," co-corresponding authors Mary-Claire King and Ryan Carlson, both with the University of Washington, and their colleagues wrote in the journal JAMA Otolaryngology-Head and Neck Surgery on Thursday. "Comprehensive genetic testing of children with sensorineural hearing loss is informative, medically necessary, and should be incorporated into standard care whenever possible."

With targeted hybrid capture sequencing focused on 191 genes with known or suspected ties to hearing loss, the researchers tested 449 children from 406 families treated for bilateral sensorineural hearing loss (SNHL) before age 18 at Seattle Children's Hospital and University of Washington clinics, reaching genetic diagnoses for more than half of the families and 67 percent of families with more than one child with SNHL.

The team analyzed the genetic diagnostic data alongside retrospective audiological measurements in the children, along with speech perception data collected over two to 16 years after cochlear implantation.

"Given the genetic heterogeneity of childhood-onset hearing loss, it is possible that variability in [cochlear implant] outcomes is also partially explained by the gene responsible for hearing loss," the authors explained. "We carried out genetic diagnosis of hearing loss for a clinic-based cohort of children with bilateral sensorineural hearing loss to characterize audiological profiles by age and genotype and evaluate the success of [cochlear implants], based on clinical speech perception tests, by age at implant, and genotype."

All but one child with genetic diagnoses carried causal variants in just one gene, the team reported. And while hearing loss-related variants turned up in 43 genes across the genetically diagnosed families, the causal gene or variant involved provided clues to everything from symptom severity to hearing loss progression patterns.

Children with truncating mutations in the GJB2 gene tended to have hearing loss that was more severe than that found in cases marked by missense mutations in the same gene, for example. Hearing loss severity also varied depending on the causal gene involved in some cases, with genes such as SOX10 corresponding to more severe hearing loss and other genes tracking with more mild-to-moderate forms of SNHL or with hearing loss that involved specific sound frequencies.

Likewise, the researchers found that cochlear implants improved speech perception in all of the children who received them, though the extent of the improvement was linked to the causal hearing loss variants identified. In particular, they saw pronounced speech perception improvements in children with hearing loss linked to MITF or TMPRSS3 mutations.

"Speech perception testing from the time of implant during the next two to 16 years indicated that implant was successful for all of [the patients with TMPRSS3-related hearing loss], with among the highest post-implant speech perception scores for patients of any genotype," the authors reported. "These findings suggest that best clinical practice should include genetic testing to identify patients whose genotype suggests that they may be good candidates for [cochlear implant] perhaps earlier than their standard audiometric testing would suggest."

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