Unilateral enlarged vestibular aqueduct syndrome: clinical profiles, SLC26A4 mutations, and the diagnostic utility of the ASNR waveform.

Background: Unilateral enlarged vestibular aqueduct syndrome (EVAS) is a clinically insidious condition, and its aetiology and relationship to the common bilateral phenotype remain insufficiently characterised. Objectives: Explore the clinical and molecular genetic characteristics of unilateral EVAS to improve diagnostic accuracy and hearing loss prevention strategies. Methods: We retrospectively reviewed clinical, audiological, imaging, and genetic data from two paediatric patients with unilateral EVAS, and compiled genetic profiles from 10 studies. Results: Case 1, a 10-year-old boy with sudden hearing loss of the right ear, harboured compound heterozygous SLC26A4 variants (c.919-2A > G; c.1003T > C). Case 2, an 8-year-old boy with incidental hearing loss of the right ear, exhibited an acoustically evoked short-latency negative response (ASNR) on auditory brainstem response (ABR) testing. Both cases showed unilateral enlargement of the endolymphatic duct and sac in the affected ear. Reported frequencies varied considerably across studies: compound heterozygous variants from 4% to 10%, and single heterozygous variants ranged from 8% to 62.5%. Conclusions: Unilateral EVAS presents with heterogeneous audiological profiles and genetic backgrounds. In patients who pass the hearing screening but harbor SLC26A4 mutations, particularly those with single heterozygous variants-a frequent observation in clinical practice-clinicians should remain vigilant to the possibility of unilateral EVAS.