Congenital myotonia caused by a mutation in the SCN4A gene
Keywords:
SCN4A gene, myotonia, myotonic phenomenonAbstract
Congenital myotonia caused by a mutation in the SCN4A geneis a specific inherited disorder of muscle membrane hyperexcitability caused by gain-of-function defects in mutant NaV1.4 subunits. This disorder is clinically presented by a myotonic phenomenon – abnormal delay in muscle relaxation following voluntary forceful contraction. Affected individuals describe muscular stiffness upon initiating movement. The stiffness remits with several repetitions of the same movement, giving rise to the so-called warm-up phenomenon.
We present a mother and а daughter with a heterozygous mutation c.1333G> A (NM_000334.4) in the SCN4A gene leading to the replacement of the amino acid valine with methionine at position 445 in the amino acid sequence encoded by the SCN4A gene and causing the atypical myotonia. They described muscular stiffness upon initiating movement, which is present since childhood.
Treatment with Carbamazepine had beneficial effect in these cases.
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