A novel mutation in X-linked Charcot-Marie-Tooth (CMTX1) disease associated with central conduction slowing on brainstem auditory evoked potential (BAEP)

CMTX1, the second most common type of inherited hereditary motor and sensory neuropathy (HMSN), is associated with mutations of the gene for the gap junction protein connexin 32 (Cx32). In this condition, central conduction velocity is known to be delayed, presumably because mutated Cx32 is expressed in oligodendrocytes. A 45-year-old man presented with a 5-year history of progressive gait disturbance due to leg muscle weakness. The family history revealed that the mother had also progressive gait disturbance in her early 40s, and the younger sister could not walk faster than before at the age of 41. On neurological assessment, the patient exhibited pes cavus, distal muscle atrophy and weakness, and absence of the knee and ankle jerks. Touch sensation was impaired in the both feet. Motor and sensory nerve conduction velocities were reduced to 30-36 m/s with mild temporal dispersion. Sural nerve biopsy revealed diffuse loss of large myelinated fibers with the remaining large and intermediate nerve fibers being frequently surrounded by a thin myelin sheath. Onion bulb formation was only occasional and mild in degree. His hearing acuity was normal on pure-tone audiometry, but BAEP test demonstrated prolonged central conduction time (-I wave 1.8 milliseconds, I-V wave 6.4 milliseconds). The BAEP findings prompted us to choose Cx32 gene to analyze first to find a novel mutation of two (A and T) base pairs deletion at codons 277 and 278 (Met93fs). Thus, the present case indicates that Cx32 gene mutation should be targeted first in case of HMSN with abnormal BAEP.