X-Linked Hearing Loss: Two Gene Mutation Examples Provide Generalizable Implications for Clinical Care
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To describe the inheritance patterns and auditory phenotype features of 3 Canadian families with mutations in 2 X-linked “deafness” genes (DFNX). Audiological, medical, and family histories were collected and family members interviewed to compare hearing thresholds and case histories between cases with mutations in SMPX versus POU3F4. The family pedigrees reveal characteristic X-linked inheritance patterns. Phenotypic features associated with the SMPX (DFNX4) mutation include early onset in males with rapid progression from mild and flat to sloping sensorineural loss, with highly variable onset and hearing loss severity in females. In contrast, phenotypic features associated with the POU3F4 (DFNX2) mutation are characterized by an early onset, mixed hearing loss with fluctuation in males, and a normal hearing phenotype reported for females. The study shows how this unique inheritance pattern and both gender and mutation-specific phenotype variations can alert audiologists to the presence of X-linked genetic etiologies in their clinical practice. By incorporating this knowledge into clinical decision making, audiologists can facilitate the early identification of X-linked hearing loss and contribute to the effective team management of affected families.