Non-dystrophic myotonias

The non-dystrophic myotonias (NDMs) are characterised by the presence of stiffness. This is caused by hyperexcitability of the muscle membrane which results in spontaneous electrical discharges called myotonia. NDM can be split into myotonia congenita and paramyotonia congenita.

Myotonia congenita can be split into recessive myotonia congenita or dominant myotonia congenita. Which type of myotonia congenita a patient has depends on the type of mutation they have and how it affects the channel function. We can help give advice about which type of myotonia congenita a patient has or do further more detailed testing in the lab to work this out.

Recessive Myotonia congenita

In recessive myotonia congenita (MC) patients have mutations in both of their chloride channel genes (CLCN1). This causes stiffness that warms up with exercise and usually affects the legs more than the arms.

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Dominant Myotonia congenita

In dominant myotonia congenita, patients have a single dominant mutation in their chloride channel gene. They will usually have stiffness in their arms which gets better with repeated movements.

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Paramyotonia congenita

Paramyotonia congenita is caused by mutations in the sodium channel gene SCN4A. It characteristically causes stiffness that worsens with exertion and is much worse in the cold.

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Non-dystrophic myotonias