Familial cramp due to potassium-aggravated myotonia
- aDepartment of Neuromuscular Diseases, Division of Neuroscience and Psychological Medicine, Imperial College School of Medicine, Charing Cross Hospital, London, UK, bDepartment of Applied Physiology, University of Ulm, Germany
- Dr Richard W Orrell, Department of Clinical Neurosciences, Royal Free and University College Medical School of University College London, Rowland Hill Street, London NW3 2PF, UK. Telephone 0044 171 0500; fax 0044 171 431 1577; email rfns0010{at}rfhsm.ac.uk
- Received 8 December 1997
- Revised 25 February 1998
- Accepted 6 April 1998
Abstract
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.
