CMT4H is caused by autosomal recessive mutations in the FGD4 gene. CMT4H tends to be a severe type of CMT, but with slow progression.
CMT4H symptom onset usually occurs in early childhood, or even in infancy. Some CMTers who have CMT4H might not have symptom onset until well into adulthood. Most CMTers who have CMT4H will experience severe lower limb weakness and sensory loss. Most CMTers who have CMT4H will experience significant scoliosis. Nerve conduction velocities are usually severely slowed to less than 13 meters/sec in CMT4H (normal is ~50 meters/sec), and sensory responses on nerve conduction study are usually absent.