Invited Reviews
Phenotypic variability in myotonia congenita
Eskild Colding-Jørgensen MD,
Corresponding Author
Eskild Colding-Jørgensen MD
Department of Clinical Neurophysiology 19, Glostrup Hospital, University of Copenhagen DK-2600 Glostrup, Denmark
Department of Clinical Neurophysiology 19, Glostrup Hospital, University of Copenhagen DK-2600 Glostrup, DenmarkSearch for more papers by this authorEskild Colding-Jørgensen MD,
Corresponding Author
Eskild Colding-Jørgensen MD
Department of Clinical Neurophysiology 19, Glostrup Hospital, University of Copenhagen DK-2600 Glostrup, Denmark
Department of Clinical Neurophysiology 19, Glostrup Hospital, University of Copenhagen DK-2600 Glostrup, DenmarkSearch for more papers by this authorAbstract
Myotonia congenita is a hereditary chloride channel disorder characterized by delayed relaxation of skeletal muscle (myotonia). It is caused by mutations in the skeletal muscle chloride channel gene CLCN1 on chromosome 7. The phenotypic spectrum of myotonia congenita ranges from mild myotonia disclosed only by clinical examination to severe and disabling myotonia with transient weakness and myopathy. The most severe phenotypes are seen in patients with two mutated alleles. Heterozygotes are often asymptomatic but for some mutations heterozygosity is sufficient to cause pronounced myotonia, although without weakness and myopathy. Thus, the phenotype depends on the mutation type to some extent, but this does not explain the fact that severity varies greatly between heterozygous family members and may even vary with time in the individual patient. In this review, existing knowledge about phenotypic variability is summarized, and the possible contributing factors are discussed. Muscle Nerve, 2005
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