The disease affects the myelin sheath, which is the fatty substance that insulates the nerves. Myelin is needed to transmit impulses along nerve cells. In CMT, genetic mutations cause the peripheral nerves to become damaged or the myelin to become dysfunctional, which makes the nerves vulnerable to damage.
The disorder typically causes muscle weakness and sometimes numbness in the arms, legs, hands, and feet. Symptoms usually develop during adolescence or early adulthood, but they may occur at any time from early childhood into middle age.
CMT is the most common hereditary form of neuropathy, affecting about one in 2,500 people worldwide. It is estimated that 150,000 people in the United States have CMT.
There are five main variations of CMT. Each type is caused by different genetic mutations, or abnormal changes in a person's biological makeup. Each is inherited, or passed down among families, in a different pattern. In addition, the age of onset, symptoms, severity, and progression of the disease varies, depending on the specific variation of CMT a person has.
The most common form of CMT is called CMT1. People with CMT1 are born with abnormal genes that are involved in the development and function of the myelin sheath. These defective genes cause the breakdown of myelin called demyelination. When the protective myelin deteriorates, the peripheral nerves are exposed and are vulnerable to damage. Other, less common, forms include CMT2 (which is predominantly axonal), and also, CMT3, CMT4, and CMTX.
Although this condition is not considered life-threatening, symptoms worsen over time. There is currently no cure for CMT, but treatments are available to help manage the symptoms of the disease. Physical and occupational therapy or surgery can help people with CMT to lead active, productive lives.
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