Paramyotonia congenita is an inherited myopathy, a disease that causes problems with the tone and contraction of skeletal muscles. (Some researchers regard paramyotonia congenita as a form of periodic paralysis.)
Paramyotonia congenita causes episodes of muscle stiffness and weakness — mostly in the face, neck and upper extremities — that can last from minutes to hours. The stiffness is sensitive to exercise and cold. During brief exercise, overexcitation of muscles can cause stiffness, and with prolonged exercise, the overexcitation can occasionally lead to a fatigue-like weakness or even complete paralysis.
Cold exposure can have similar effects, but some people experience muscle stiffness, weakness, or sometimes, temporary paralysis even when they’re warm. For more, see Signs and Symptoms.
Sodium channels normally open to cause muscle excitation, and then close to end the excitation. In paramyotonia congenita, mutations in the muscle sodium channel gene prolong the channel’s opening, causing higher-than-normal muscle excitation. It is inherited in an autosomal dominant pattern, meaning it is produced by a defective gene contributed by one parent. See Causes/Inheritance for more.
Episodes of prolonged muscle contraction (inability to relax muscles at will) begin in infancy. Episodes of weakness generally begin in adolescence, if they occur at all. The disease is not progressive.
MDA supports ongoing research into the molecular bases of inherited myopathies and to find effective treatments. For more, see Research.