Can Be Homozygous or Can Be Compound Heterozygous
CMT4F is caused by autosomal recessive mutations in the PRX gene. CMT4F was first found in a large Lebanese family in 2000, but there have since been diagnoses beyond the original family.
CMT4F symptom onset usually occurs in early childhood. CMTers who have CMT4F experience significant lower limb weakness by the time they are 10 years old, and then significant hand weakness by the time they are 15 years old.
Sensory and motor responses on nerve conduction study are usually absent. When they are present, conduction velocities are severely slow at only 2-3 meters/sec (normal is considered ~50 meters/sec). However, some CMTers who have CMT4F might have conduction velocities of 10 meters/sec to 20 meters/sec. Researchers believe these differences are linked to the various specific CMT4F causing mutations within the PRX gene.