CMT can be diagnosed through three different forms of tests: measurement of the speed of nerve impulses (nerve conduction studies), a biopsy of the nerve, and DNA testing. DNA testing can give a definitive diagnosis, but not all the genetic<unk> rs for CMT are known. CMT is first most noticed when someone develops lower leg weakness, such as foot drop, or foot deformities, including hammertoes and high arches, but signs alone do not lead to diagnosis. Patients must be referred to a physician specialising in neurology or rehabilitation medicine. To see signs of muscle weakness, the neurologist may ask patients to walk on their heels or to move part of their leg against an opposing force. To identify sensory loss, the neurologist tests for deep-tendon reflexes, such as the knee jerk, which are reduced or absent in CMT. The doctor may also ask the patient's family history since CMT is hereditary. The lack of family history does not rule out CMT, but is helpful to rule out other causes of neuropathy, such as diabetes or exposure to certain chemicals or drugs. In 2010, CMT was one of the first<unk> s where the genetic cause of a particular patient's<unk>  was precisely determined by sequencing the whole genome of an affected individual. This was done by the scientists employed by the<unk><unk><unk>  Association (CMTA). Two mutations were identified in a gene, SH3TC2, known to cause CMT. Researchers then compared the affected patient's genome<unk> e genomes of the patient's mother, father, and seven siblings with and without the<unk> . The mother and father each had one normal and one mutant copy of this gene, and had mild or no symptoms. The offspring who inherited two mutant genes presented fully with the<unk> . Histology Denervation atrophy of type II muscle fibers The constant cycle of demyelination and remyelination, which occurs in CMT, can lead<unk> e formation of layers of myelin around some nerves, termed an "onion bulb". These are also seen in chronic inflammatory demyelinating polyneuropathy. Muscles show fiber type grouping, a similarly nonspecific finding that indicates a cycle of denervation/reinnervation. Normally, type I and type II muscle fibers show a checkerboard-like random distribution. However, when reinnervation occurs, the group of fibers associated with one nerve are of the same type. The standard for indicating fiber type is histoenzymatic adenosine triphosphatase (ATPase at pH 9.4).
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