Auditory nerve is affected in one of two different point mutations of the neurofilament light gene.
OBJECTIVE
To define auditory nerve and cochlear functions in two families with autosomal dominant axonal Charcot-Marie-Tooth (CMT).


METHODS
Affected members in two families with different point mutations of NF-L gene were screened with auditory brainstem responses (ABRs). Those with abnormal ABRs were further investigated with clinical, neurophysiological and audiological procedures. The point mutations of NF-L gene involved were Glu397Lys in 8 affected members of the family with AN, and Pro22Ser in 9 affected members of the family without AN.


RESULTS
ABRs and stapedial muscle reflexes were absent or abnormal in affected members of only one family consistent with auditory neuropathy (AN). In them, audiograms, otoacoustic emissions, and speech comprehension were normal. Absent or abnormal ABRs were consistent with slowing of conduction along auditory nerve and/or brainstem auditory pathway. Wave I when present was of normal latency.


CONCLUSIONS
Auditory nerve involvement in the presence of normal cochlear outer hair cell activity is asymptomatic in one of two families with CMT disorder with different point mutations of the NF-L gene. The nerve disorder is consistent with altered synchrony and slowed conduction.


CONCLUSIONS
The absence of "deafness" may reflect the ability of central mechanisms to compensate for the slowly developing auditory nerve abnormalities.
Butinar
Dusan
D
Institute of Clinical Neurophysiology, University of Ljubljana, Ljubljana, Slovenia.
Starr
Arnold
A
Zidar
Janez
J
Koutsou
Pantelitsa
P
Christodoulou
Kyproula
K
D000161:Acoustic Stimulation / Q000379:methods; D000293:Adolescent; D000328:Adult; D000368:Aged; D002607:Charcot-Marie-Tooth Disease / Q000235:genetics* / Q000503:physiopathology; D016057:Evoked Potentials, Auditory, Brain Stem / Q000502:physiology; D005192:Family Health; D005260:Female; D007839:Functional Laterality; D018698:Glutamic Acid / Q000235:genetics; D006801:Humans; D008239:Lysine / Q000235:genetics; D008297:Male; D008875:Middle Aged; D016900:Neurofilament Proteins / Q000235:genetics*; D017354:Point Mutation / Q000235:genetics*; D011392:Proline / Q000235:genetics; D011930:Reaction Time / Q000502:physiology; D012694:Serine / Q000235:genetics; D000159:Vestibulocochlear Nerve / Q000503:physiopathology*
D016900:Neurofilament Proteins; C044882:neurofilament protein L; D018698:Glutamic Acid; D012694:Serine; D011392:Proline; D008239:Lysine