Autosomal recessive generalized myotonia (Becker's disease) (GM) and autosomal dominant myotonia congenita (Thomsen's disease) (MC) are characterized by skeletal muscle stiffness that is a result of muscle membrane hyperexcitability. For both diseases, alterations in muscle chloride or sodium currents or both have been observed. A complementary DNA for a human skeletal muscle chloride channel (...

We report a patient with paramyotonia congenita/hyperkalemic periodic paralysis due to Nav1.4 I693T mutation who had worsening of myotonia and muscle weakness in the setting of hypomagnesemia and hypocalcemia with marked recovery after magnesium administration. Computer simulations of the effects of the I693T mutation were introduced in the muscle fiber model by both hyperpolarizing shifts in t...

Autosomal dominant myotonia congenita (Thomsen's disease) is caused by mutations in the muscle chloride channel CIC-1. Several point mutations found in affected families (I29OM, R317Q, P480L, and Q552R) dramatically shift gating to positive voltages in mutant/WT heterooligomeric channels, and when measurable, even more so in mutant homooligomers. These channels can no longer contribute to the r...

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Missense mutations in the skeletal muscle Na+ channel alpha subunit occur in several heritable forms of myotonia and periodic paralysis. Distinct phenotypes arise from mutations at two sites within the III-IV cytoplasmic loop: myotonia without weakness due to substitutions at glycine 1306, and myotonia plus weakness caused by a mutation at threonine 1313. Heterologous expression in HEK cells sh...

INTRODUCTION Two previously reported Norwegian patients with painful muscle cramps and giant myotonic discharges were genotyped and compared with those of members of 21 families harboring the same mutation. METHODS Using primers specific for SCN4A and CLCN1, the DNA of the Norwegian family members was amplified and bidirectionally sequenced. Clinical and neurophysiological features of other f...

Electromyographic (EMG) and histological studies were carried out with the new mouse mutant myotonia (mto, autosomal recessive). Affected animals exhibited behavioral myotonia which was apparent at 2 weeks of age. EMG studies revealed myotonic discharges (prolonged repetitive discharges with recurrent variation in amplitude and frequency) in all skeletal muscles tested. These discharges were no...

A 48-year-old man presented with episodic paraplegia and stiffness of hands, face, and tongue, along with eyelid myotonia when exposed to cold temperature, which he had since childhood. Eyelid myotonia was evoked either by exposure to cold weather (video on the Neurology® Web site at www.neurology.org and figure 1) or by forceful eye closure. Myotonia was elicited with percussion of the tongue ...