What is Charcot-Marie-Tooth disease type 4 (CMT4)?
CMT4 is a rare subtype of CMT, a genetic, neurological disorder that causes damage to the peripheral nerves — tracts of nerve cell fibers that connect the brain and spinal cord to muscles and sensory organs. CMT4 is a subtype of CMT that is inherited in an autosomal recessive pattern.
What are the symptoms of CMT4?
CMT4 causes weakness, usually mostly distal (far from the center of the body) but sometimes involving proximal (near the center of the body) muscles. Impairment or changes in sensations (such as the sense of touch or ability to perceive temperature changes) also can occur. When CMT4 begins in infancy, it’s characterized by low muscle tone. CMT4 patients may also develop other symptoms such as cataracts or deafness. Generally, cases of CMT4 present with more severe symptoms compared to CMT1 or CMT2. Since some of the symptoms are severe and the onset can be early, some subtypes of CMT4 may also be called Severe, Early-Onset CMT. See Signs and Symptoms for more.
What causes CMT4?
In general, CMT4 is caused by defects in the myelin sheath which insulates the axon.
CMT4A is caused by defects in the GDAP1 gene.
CMT4B is caused by defects in the genes MTMR2 (CMT4B1), or MTMR13 (CMT4B2).
CMT4C is caused by defects in the SH3TC2 gene.
CMT4D is caused by defects in the NDRG1 gene.
CMT4E is caused by defects in the EGR2 gene.
CMT4F is caused by defects in the PRX gene.
CMT4H is caused by defects in the FDG4 gene.
CMT4J is caused by defects in the FIG4 gene.