Mexiletine for Muscle Cramps in Charcot Marie Tooth Disease

Inclusion Criteria: * The subject has known CMT, previously diagnosed by a neurologist with subspeciality expertise in neuromuscular disorders/peripheral neuropathy. The diagnosis of CMT relies on a combination of clinical history (including family history), neurological examination electrophysiological features, and prior genetic testing results. * The subject is at least 18 years old, and has signed the Informed Consent Form. * The subject is ambulatory (cane, walker, orthoses allowed). * The subject has experienced muscle cramps and has known provokable hamstring or calf muscle cramps on MVC. * The subject has a reliable method of birth control (if a female subject of child bearing potential). Reliable birth control is defined as Hormonal contraception Intrauterine contraception/device Any two barrier methods (combination of male or female condom with diaphragm sponge or cervical cap) together with spermicidal foam/gel/film/cream/suppository True abstinence Exclusion Criteria: * The subject has a known neuropathy from another source (e.g., diabetes, drug induced, alcohol, etc.). * The subject has an untreated medical disorder known to predispose to muscle cramps * The subject is pregnant or nursing, has a known mexiletine allergy or has taken mexiletine in the past 12 weeks. * The subject is participating in another therapeutic trial. * The subject has second or 3rd degree heart block, atrial flutter/fibrillation, ventricular arrhythmias, or is receiving treatment of a cardiac arrhythmia. * The subject is currently taking another agent for muscle cramps or a muscle relaxant (e.g., benzodiazepine, baclofen, tizanidine, soma, meprobromate). * The subject is on another sodium channel blocker or medication that precludes administration of mexiletine. * The subject has known diabetes mellitus, liver or kidney disease requiring ongoing treatment, untreated thyroid dysfunction, symptomatic cardiomyopathy, or symptomatic coronary artery disease. * The subject, in the opinion of the investigator, is unsuitable for enrollment for any other reason