Charcot-Marie-Tooth disease (CMT), named for the three physicians who first identified it, is an umbrella term for a series of genetic disorders that affect peripheral nerves, the motor and sensory pathways that carry signals from the spinal cord and brain to the entire body. Type 1 CMT affects the protective covering that insulates nerves, called the myelin sheath, while type 2 CMT actually affects the fibers of the nerves, or the axons. Type 3 CMT is the most severe form of Charcot-Marie-Tooth disease and is more commonly referred to as Dejerine-Sottas disease.
Frequency
According to the National Institute of Health, CMT is one of the most common inherited diseases, affecting 1 in 2,500 people. In the U.S. alone, there are more than 100,000 people affected with some form of the disorder.
Chromosomes
Researchers at the Muscular Dystrophy Association have identified three specific genes that result in Charcot-Marie-Tooth disease when they are abnormal. Two of the genes are found on the first and seventeenth chromosomes, while the third is found on the X chromosome. Females have two X chromosomes and males have both X and Y chromosomes, meaning that females, with a second X chromosome as back-up, often experience less severe symptoms than males.
Onset of Symptoms
CMT most commonly affects the lower legs and feet, but over time may begin to affect the hands as well. The onset of symptoms of Charcot-Marie-Tooth disease is very gradual, with presentation of symptoms often appearing in early adulthood. In fact, many people may have a mild form of the disease, yet never know. Generally, type 1 CMT, which affects the myelin, is noticed earlier than type 2 or 3, and may even become apparent during childhood. Fortunately, except in rare cases, people with CMT are not expected to have a shortened life expectancy.
Weakness
As the sensory and motor nerves become degraded with progression of the disease, patients may begin to experience slowed reaction times, weakness in the muscles of the lower legs and feet, and eventually atrophy of underused muscles. Over time, this weakness can lead to dropping of the feet and exaggerated gait while walking, as well as an increased risk of falling and tripping.
Deformities
Deformities begin when weakness and muscle atrophy increase and there is a decrease in mobility. According to the Mayo Clinic, hammertoes, turning in of the feet, toes that curl or flex upward, heightened arches and deformation of muscle mass due to diminished bulk are all symptoms of Charcot-Marie-Tooth.
Pain and Numbness
As CMT progresses and muscle weakness and atrophy become more severe, some patients may begin to experience pain, and even numbness. The most common pain complaint is from muscle cramping, particularly in the feet and ankles. The severity of pain and degree of numbness is usually worse for those who have more extreme forms of the condition; some patients may experience no pain at all.
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