Dominant Intermediate CMT-B is caused by autosomal dominant mutations in the DNM2 gene. CMTDIB is also known as CMT2M.
CMTDIB symptom onset can occur anywhere between early childhood and the CMTers late 40s. Most CMTers who have CMTDIB experience symptom onset in their late teens.
CMTers who have CMTDIB will usually experience the classic CMT symptoms of lower limb weakness and atrophy resulting in gait abnormalities with frequent trips and falls as a result. Nerve conduction studies show motor median nerve conduction velocities ranging from 24 meters/sec to 54 meters/sec. Generally, 38 meters/sec and above is considered axonal CMT, and below 38 meters/sec is considered demyelinating. CMTDIB does not fit within either of those categories.
Additionally, nerve biopsy can show evidence of axonal degeneration, loss of large diameter fibers, rare segmental demyelination, and remyelination with onion bulb formation. These findings are characteristic of demyelinating and axonal CMT. However, nerve biopsy is not currently a standard diagnostic tool.