Auditory nerve is affected in one of two different point mutations of the neurof

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Clin Neurophysiol. 2007 Nov 16

Auditory nerve is affected in one of two different point mutations

of the neurofilament light gene.

Butinar D, Starr A, Zidar J, Koutsou P, Christodoulou K.

Institute of Clinical Neurophysiology, University of Ljubljana,

Ljubljana, Slovenia.

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.

SIGNIFICANCE: The absence of " deafness " may reflect the ability of

central mechanisms to compensate for the slowly developing auditory

nerve abnormalities.