CMT1F is caused by autosomal dominant mutations in the NEFL gene. Symptom onset usually occurs by the time the CMTer is 13 years old. The lower limbs in CMT1E are usually affected more than the upper limbs, and disease severity can be quite variable.
CMT1F is sometimes expressed as 1F/2E. CMT1F is a demyelinating CMT, meaning that the peripheral nerve myelin is primarily affected by the CMT. However, autosomal dominant mutations in the NEFL gene also cause the axonal type CMT2E. Axonal means that the nerve axon is primarily affected by the CMT.