Dominant Intermediate CMT-D is caused by autosomal dominant mutations in the MPZ gene. This type of CMT appears to affect only one family.
CMTers in this family experience a symmetric pattern of muscle atrophy, weakness, and sensory loss in the lower limbs, and to a lesser degree, in the upper limbs. Nerve conduction velocities of motor nerves range from 24 meters/sec to 41 meters/sec in the median nerve, and from 33 meters/sec to 48 meters/sec in the ulnar nerve. Nerve biopsy of 2 of the CMTers in the family showed primarily axonal degeneration, but also areas of segmental demyelination and remyelination without onion bulb formation. These findings are characteristic of demyelinating and axonal CMT. However, nerve biopsy is not currently a standard diagnostic tool.
Autosomal dominant mutations in the MPZ gene are associated with several types of CMT – demyelinating, axonal, and intermediate.