Non-dystrophic
myotonias are
rare diseases caused by mutations in skeletal muscle
chloride and
sodium ion channels with considerable phenotypic overlap between diseases. Common symptoms include muscle stiffness, transitory weakness,
fatigue, and
pain. Although seldom life-shortening, these
myotonias cause life-time disability and affected individuals cannot perform many daily activities. A notable feature of the recessive form of
chloride channelopathies is the presence of transient weakness. While there has been considerable progress in skeletal muscle
channelopathies with regards to identifying biophysical abnormalities, the mechanism of transient weakness remains unclear. A recent study published in Experimental Neurology (Desaphy et al., 2013) explored this question further by comparing the biophysical properties of 3
chloride channel mutations associated with recessive
myotonia congenita, with varying susceptibility to transient weakness. The authors identified a variety of functional defects in channel behavior among the 3 mutations, suggesting that this variability contributes to the differing phenotypes among
chloride channelopathies. This commentary discusses nondystrophic
myotonias, the results of Desaphy et al., and the treatment challenges in this
rare disease.