Abstract
Objective: To investigate the clinical features, skeletal muscle imaging, and muscle pathological characteristics of normokalemic periodic paralysis (NormoKPP) caused by mutation of SCN4A gene p.R675Q.Methods: The clinical data, skeletal muscle imaging, pathological data, and gene test results of a family with NormoKPP were collected in detail in October 2018. The previous literature was reviewed and used for comparative analysis.Results: The proband was a 28-year-old male with paroxysmal weakness of both lower limbs for 14 years. Limb weakness was mainly manifested in the proximal extremities of both lower limbs, which occurred two to three times a year. The muscle weakness of each attack lasted for 1–2 weeks and gradually recovered. The blood potassium levels were normal. The abnormal signals of the posterior thigh muscle group and the medial calf muscle group could be seen on the magnetic resonance imaging (MRI) of the skeletal muscle, and the target-fiber could be seen in some muscle fibers in muscle pathology. The father of the proband and his brother had the same symptoms. In the same family, 10 people received genetic testing. The results showed that five had a mutation of SCN4A gene p.R675Q. The mutation gene came from the father of the proband.Conclusion: NormoKPP is a clinically rare form of sodium ion channel disease. The clinical manifestations, skeletal muscle imaging, and pathological changes are different from the common hypokalemic periodic paralysis. SCN4A gene detection is an important means for the diagnosis of NormoKPP.
Highlights
Periodic paralysis (PP) is an ion channel disease characterized by recurrent muscle weakness caused by mutations in the skeletal muscle ion channel gene
After a cold 2 months ago, limb weakness occurred again, mainly in the lower limbs; both upper limbs could be raised above the head, squatting and standing was difficult, and his ability to walk was weakened
The results showed that there was a heterozygous mutation in the patient-related gene SCN4A: c.2024 4 > A, which led to the change of amino acid p.R675Q
Summary
Periodic paralysis (PP) is an ion channel disease characterized by recurrent muscle weakness caused by mutations in the skeletal muscle ion channel gene. According to the level of potassium in the blood, it can be divided into hypokalemic, normokalemic, and hyperkalemic periodic paralysis [1]. Normokalemic periodic paralysis (NormoKPP) is the rarest subtype of PP. NomoKPP is an autosomal dominant hereditary disease. There are more than 20 kinds of sodium channel alpha subunit SCN4A gene mutations reported, including R675G, R675Q, R675H, R675W, R1129Q, T704M, and M1592V. These mutations have been reported to cause
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