Objective: To examine the audiometric patterns of familial hearing impairment due to the A1555G mutation in the mitochondrial DNA.
Patients and methods: We include 55 subjects with the A1555G mutation from 6 unrelated families, affected by nonsyndromic sensorineural hearing loss and residing in Cantabria. The A1555G mutation was found in homoplasmy in all the families, except in one family, in which it was in heteroplasmy. Aside from standard history taking and general otolaryngological examination, pure tone audiometry was carried out in all patients.
Results: Hearing loss was developed by most of the patients. The auditory defect was a slowly progressive bilateral symmetrical sensorineural hearing loss, affecting mainly the high frequencies. In patients in which aminoglycoside ototoxicity could be excluded, hearing loss usually ranged from mild to moderate, with a late onset. In 17 cases there were previous history of treatment with a ototoxic drugs, and most of them developed severe hearing loss. One of them was deaf-mute. No audometric differences between families with the homoplasmic and the heteroplasmic A1555G mutation were observed.
Conclusions: Patients with the A1555G mutation generally present bilateral symmetrical sensorineural hearing loss, ranging from mild to moderate, slowly progressive, which is obvious approximately in the second decade of life and affects specially the high frequencies. Hearing loss severity is increased by treatment with aminoglycosides.