Vestibular evoked myogenic potentials in patients with the mitochondrial A1555G mutation.

OBJECTIVES/HYPOTHESIS: To evaluate the vestibular function in patients with the mitochondrial DNA A1555G mutation.

STUDY DESIGN: Data from patients with the mutation at an academic tertiary referral center were prospectively recorded.

METHODS: The histories of five unrelated patients with bilateral moderate to profound sensorineural hearing loss (SNHL) carrying the A1555G (A to G substitution at 1555 nucleotide) mutation were recorded, especially their history of vestibular symptoms. Thereafter, vestibular examinations, including positional, positioning and spontaneous nystagmus testing; caloric response testing; and vestibular evoked myogenic potential (VEMP) testing were performed. In the cases where the VEMP activity presented, the amplitudes of the first positive-negative peak (p13-n23) of the mutation group were compared to a healthy volunteer group and to a sudden SNHL group.

RESULTS: Four of the five patients suffered from repetitive vestibular symptoms. Positioning, positional, and spontaneous nystagmus were not observed except in one patient. Three of the five patients had normal caloric responses, but all the patients had abnormal VEMPs. The interpeak amplitudes in the mutation group were significantly lower at the intensities of 95 and 105 dB normal hearing level (nHL) in comparison to the healthy volunteer group. In addition, the amplitudes in the mutation group were significantly lower at the intensity of 95 dB nHL in comparison to the sudden SNHL groups.

CONCLUSIONS: These results indicated that the A1555G mutation can cause vestibular dysfunction, especially saccular dysfunction and cochlear dysfunction. Further studies are necessary to elucidate the pathophysiological nature of the inner ear dysfunction in patients with the A1555G mutation.