Key result
A 14-year-old boy with an atypical overlapping phenotype of skeletal muscle sodium channelopathy was found to have a heterozygous pathogenic mutation (p.Thr704Met) in the SCN4A gene.
Case Report (n=1)
No
Atypical phenotypes of skeletal muscle sodium channelopathies can pose diagnostic dilemmas, highlighting the importance of focused genetic testing in unusual clinical presentations.
May aid diagnosis in atypical sodium channelopathy cases; hypothesis-generating for SCN4A phenotypic expansion and requires validation.
Skeletal muscle sodium channelopathies (SMSCs) including hyperkalemic periodic paralysis (HyperPP), paramyotonia congenita (PC), and sodium channel myotonia are caused by sodium channel gene (SCN4A) mutations, with altered sarcolemal excitability, and can present as episodes of skeletal muscle weakness, paralysis, and myotonia. We report a teenage boy, who presented with features of HyperPP, PC, myotonia congenita, and sodium channel myotonia. His electromyography (EMG) revealed myopathic changes, myotonia, and Fournier EMG pattern I, and posed a diagnostic challenge. Genetic analysis showed Thr704Met mutation in SCN4A gene. While with typical clinical phenotypes, the electromyographic patterns can be used to direct genetic testing, atypical phenotypes may pose diagnostic dilemmas. Clinicians dealing with neuromuscular disorders in children need to be aware of the unusual clinical presentations of SMSC, so that focused genetic testing can be carried out.
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Saleem et al. (2013) conducted a case report in Skeletal muscle sodium channelopathy (n=1). SCN4A gene mutation (Thr704Met) was evaluated on Clinical and genetic diagnosis. A 14-year-old boy with an atypical overlapping phenotype of skeletal muscle sodium channelopathy was found to have a heterozygous pathogenic mutation (p.Thr704Met) in the SCN4A gene.
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