Charcot-Marie-Tooth disease type 4J (CMT4J) is a subtype of Charcot-Marie-Tooth disease type 4 characterized by childhood- to adulthood-onset of variably severe, rapidly progressive, axonal and demyelinating sensorimotor neuropathy typically manifesting with delayed motor development, proximal and distal asymmetric muscle weakness and atrophy of the lower and upper extremities, severe motor dysfunction with mildly reduced sensory impairment, and areflexia. Nerve conduction velocities range from very mildly to severely reduced.