Mexiletine. A drug used to treat myotonia (delayed muscle relaxation after contraction) in muscle diseases such as myotonic dystrophy and myotonia congenital (brand name is Mexitil).
Modafinil. A drug is used to treat excessive daytime sleepiness (brand name is Provigil).
Motility. The power of spontaneous movement.
Multisystemic disorder. A disease that can affect many different organs and systems in the body.
Mutation. As used on this website, a change in the normal chemistry of a gene.
Myotonia. The inability of contracted muscles to relax on command; or, a special kind of muscle stiffness.
Myopathy. Muscle weakness.