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- Hypokalemic periodic paralysis
- normokalemic periodic paralysis
- skeletal muscle sodium channel α subunit (SCN4A) gene
Periodic paralysis (PP) is one type of skeletal muscle channelopathies characterised by episodic attacks of weakness. It is usually classified into hyperkalaemic periodic paralysis (HyperPP) and hypokalaemic periodic paralysis (HypoPP). Autosomal dominant inherited PP is commonly linked to the calcium-channel α-1 subunit (CACNA1S) gene and skeletal-muscle sodium-channel α subunit (SCN4A) gene.1 Defects in CACNA1S usually result in HypoPP, whereas mutations in SCN4A can give rise to HyperPP or HypoPP. Since SCN4A mutations in T704M or M1592V are sometimes linked with HyperPP accompanied by normokaleamia during attack, normokalaemic periodic paralysis (NormPP) is considered as a variant of HyperPP.2 Here we describe a novel SCN4A mutation in the voltage sensor domain, resulting in NormPP and HypoPP in different individuals in a single family.
The proband 30-year-old experienced a severe quadriplegic attack at age 8. The attack lasted for half an hour and resolved spontaneously. Since then, weakness attacks were usually provoked by fasting or cold once a month, occasionally with postcritic myalgia. The episodic attacks became more frequent and lasted for several hours to several days in his 20s. The serum potassium level was always within normal limits during attacks. The episodic weakness was non-responsive to potassium (5 g daily) or acetazolamide (750 mg daily) administration, but seemed to be improved by intravenous infusion of saline. At the …