Myotonia congenita is an inherited myopathy, a disease that causes problems with the tone and contraction of skeletal muscles. It doesn’t cause muscle atrophy (shrinkage); instead, it sometimes can cause muscle enlargement and increased muscle strength.
There are two types of myotonia congenita: Becker-type myotonia is the most common form, while Thomsen disease is a very rare, relatively mild form.
The main problems faced by people with this disease are delayed muscle relaxation and muscle stiffness, typically provoked by sudden movements after rest. See Signs and Symptoms .
This disease is caused by mutations in the gene for a chloride channel that’s necessary for shutting off the electrical excitation that causes muscle contraction.
The Becker type is inherited in an autosomal recessive pattern, meaning it is produced by defective genes contributed by both parents.
The Thomsen type is autosomal dominant, meaning it is produced by a defective gene contributed by one parent. For more, see Causes/Inheritance .
Myotonia congenita has its onset in early to late childhood and does not progress. Someone who has myotonia congenita can lead a long, productive life, and can even excel at sports where strength is more important than agility.
For an article about a professional boxer with myotonia congenita, see Despite Muscle Disease, 'Toy Tiger' Was an Awesome Fighting Machine .
MDA supports ongoing research into the molecular bases of inherited myopathies and to find effective treatments. For more, see Research .