Types of Charcot-Marie-Tooth Disease
CMT1, the most common type of the disease, accounting for about two-thirds of cases, is caused by genetic defects that damage the myelin sheath covering the nerves. It is commonly referred to as demyelinating CMT.
CMT2 is caused by genetic defects that disrupt the structure and function of the axons of the peripheral nerves. Commonly referred to as axonal CMT, it is less common than CMT1 and accounts for about one-third of all dominant cases.
CMT3 is a rare, severe, and early-onset type of CMT that disrupts the myelin sheath, resulting in severe muscle atrophy, weakness, and sensory problems that begin in early childhood. It is also known as Dejerine-Sottas disease in its more severe forms, congenital hypomyelination, or Roussy-Levy syndrome.
CMT4 is a rare type of CMT that causes damage to the myelin sheath. It begins in early childhood and causes muscle weakness such that patients lose the ability to walk over time.
CMTX is caused by genetic defects on the X chromosome, which affects the myelin sheath surrounding the nerve fibers of the peripheral nerve cells that connect the brain and spinal cord to muscles and sensory organs. CMTX is the second most common type, accounting or about 10–16% of all cases.
Dominant intermediate Charcot-Marie-Tooth disease, or DI-CMT, is a rare, dominantly inherited type of CMT characterized by intermediate nerve conduction velocity. Nerve biopsies from patients with DI-CMT have shown both axonal degeneration as well as demyelination.