Familial cramp due to potassium-aggravated myotonia

• Published in: Journal of neurology, neurosurgery and psychiatry Vol. 65; no. 4; pp. 569 - 572
• Main Authors: Orrell, Richard W, Jurkat-Rott, Karin, Lehmann-Horn, Frank, Lane, Russell J M
• Format: Journal Article
• Language: English
• Published: London BMJ Publishing Group Ltd 01.10.1998; BMJ; BMJ Publishing Group LTD; BMJ Group
• Subjects: Adult; Biological and medical sciences; Cold; cramp; Diseases of striated muscles. Neuromuscular diseases; DNA Mutational Analysis; Electrodes; Electromyography - methods; Heterozygote; Humans; Kinases; Medical sciences; Muscle Cramp - genetics; Muscle, Skeletal - innervation; Mutation; Myotonia - genetics; Neural Conduction - physiology; Neurology; Pedigree; Phenotype; Point Mutation - genetics; Potassium; Potassium Channels - genetics; potassium-aggravated myotonia; Short Report; Skin; Sodium; sodium channel disease; Human; Neuromuscular diseases; Nervous system diseases; Family study; Myotonia; Ionic channel; Cramp; Case study; Striated muscle disease; Gene; Sodium; Etiology; Mutation; Potassium
• ISSN: 0022-3050; 1468-330X
• DOI: 10.1136/jnnp.65.4.569

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 α-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.