Familial cramp due to potassium-aggravated myotonia.
Clinical, electrophysiological, and molecular genetic features were investigated in two patients from a family a with dominantly inherited myotonic disease, characterised by painful cramps, stiffness without weakness, fluctuation of symptoms, and cold sensitivity. A reduction in amplitude of the compound muscle action potential was demonstrated on cooling and administration of potassium, although no clinical exacerbation was seen. A heterozygote mutation Val1589Met was identified in the alpha-subunit of the skeletal muscle sodium channel gene in both patients, consistent with the diagnosis of potassium-aggravated myotonia. The phenotype in this family is much milder than that previously described in another family with a mutation at this site.
Department of Neuromuscular Diseases, Imperial College School of Medicine, Charing Cross Hospital, London, UK. rfns0010@rfhsm.ac.uk
R W
RW
Orrell
K
K
Jurkat-Rott
F
F
Lehmann-Horn
R J
RJ
Lane
D000328:Adult; D004252:DNA Mutational Analysis; D004576:Electromyography / Q000379:methods; D006579:Heterozygote; D006801:Humans; D009120:Muscle Cramp / Q000235:genetics*; D018482:Muscle, Skeletal / Q000294:innervation; D009222:Myotonia / Q000235:genetics*; D009431:Neural Conduction / Q000502:physiology; D010375:Pedigree; D010641:Phenotype; D017354:Point Mutation / Q000235:genetics; D015221:Potassium Channels / Q000235:genetics*
D015221:Potassium Channels