title: Abnormal Cochlear Potentials in Friedreich's Ataxia Point to Disordered Synchrony of Auditory Nerve Fiber Activity.
abstract: BACKGROUND
  Friedreich's ataxia (FRDA) is a degenerative disorder caused by mutations of the FXN gene. Sensorineural hearing loss is one of the clinical features of FRDA, and the majority of hearing-impaired patients have shown evidence of auditory neuropathy.
  
  
  OBJECTIVE
  This study characterizes the cochlear receptor and auditory nerve potentials in a patient with FRDA who had the clinical profile of auditory neuropathy. The aim was to investigate the site of the lesion and the pathophysiological mechanisms behind the hearing dysfunction.
  
  
  METHODS
  Using transtympanic electrocochleography, both receptor (cochlear microphonic, CM, and summating potential, SP) and auditory nerve potentials were recorded in response to trains of clicks with stimulation intensities from 60 to 120 dB SPL. The results were compared with recordings obtained from two groups of subjects, i.e. 20 normally hearing controls and 19 subjects with cochlear hearing loss.
  
  
  RESULTS
  The results showed that the synchronized neural response seen in both normally hearing and hearing-impaired subjects was lacking in our patient, replaced by a prolonged, low-amplitude negative potential that decreased in both amplitude and duration for rapid stimulation rates, consistent with adaptation of neural sources. CMs were recorded with a normal amplitude, consistent with preserved outer hair cell function. SP peak latency was within normal limits, whereas SP amplitude was comparable with that of subjects with cochlear hearing loss, consistent with inner hair cell loss.
  
  
  CONCLUSIONS
  These findings suggest that underlying auditory neuropathy in FRDA is a disordered synchrony in auditory nerve fiber discharge, possibly resulting from auditory nerve fiber degeneration and inner hair cell loss.
authors: Department of Neurosciences, University of Padova, Padova,Italy.
authors: Rosamaria
authors: R
authors: Santarelli
authors: Elona
authors: E
authors: Cama
authors: Elena
authors: E
authors: Pegoraro
authors: Pietro
authors: P
authors: Scimemi
mesh_terms: D000161:Acoustic Stimulation; D000328:Adult; D001300:Audiometry, Evoked Response; D003056:Cochlear Nerve / Q000503:physiopathology*; D016057:Evoked Potentials, Auditory, Brain Stem / Q000502:physiology*; D005621:Friedreich Ataxia / Q000473:pathology*; D007839:Functional Laterality; D006801:Humans; D008297:Male; D011571:Psychoacoustics; D013067:Speech Perception / Q000502:physiology