Charcot-Marie-Tooth Disease (CMT)
What is Charcot-Marie-Tooth disease type 1 (CMT1)?
CMT Type 1 is the most common subtype of CMT, accounting for roughly two-thirds of all cases. CMT1 is inherited in an autosomal dominant pattern.
What are the symptoms of CMT1?
CMT1 is characterized by muscle weakness and atrophy, and changes in sensation, mostly in the periphery of the body — particularly in the feet, lower legs, hands and forearms.
What causes Charcot-Marie-Tooth disease type 1 (CMT1)?
CMT1 is caused by damage to the myelin sheath covering nerves. CMT1 is commonly referred to as “demyelinating” CMT.
CMT1A: A subtype of CMT1, called CMT1A (caused by a duplication in the PMP22 gene on chromosome 17) accounts for around 60 percent of CMT1 cases, making it the most common subtype of CMT1. The PMP22 gene encodes for peripheral myelin protein, and disruption of this gene leads to a dysfunctional myelin sheath on nerves. CMT1A patients usually present with typical CMT onset within adolescence, but remain ambulatory with no reduced life expectancy.
CMT1B: CMT1B is the second most common subtype of CMT1. CMT1B is caused by a defect within the MPZgene, which lies on chromosome 1. The MPZ gene produces myelin protein zero, and disruption of this gene also causes deficits within the myelin sheath. CMT1B patients have onset and symptoms similar to those of CMT1A patients, although there is a wide range of variability within CMT1B.
Other more rare forms of CMT1 and their gene defects include:
CMT1C is caused by defects in the LITAF gene.
CMT1D is caused by defects in the ERG2 gene.
CMT1E is caused by defects in the PMP22 gene, which is also associated with CMT1A. Instead of having a duplication of the normal PMP22 gene, CMT1E patients harbor different genetic abnormalities called point mutations within the PMP22 gene.
CMT1F is caused by defects in the NEFL gene.