OPA1 and Friedreich ataxia: For example, patients with Friedreich ataxia (FRDA) have a reduced ABR Wave V/I response amplitude but a normal neural conduction latency, consistent with impaired neural function due to auditory nerve axonal degeneration, but not demyelination.8,27 In patients harbouring the OPA1 mutation, auditory dysfunction is likely caused by degeneration of the unmyelinated portion of the auditory nerve terminal dendrites within the cochlea.