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Neurology January 1, 2019; 92 (13): e1405-e1415.

Myasthenic congenital myopathy from recessive mutations at a single residue in NaV1.4.

Elia N , Palmio J , Castañeda MS , Shieh PB , Quinonez M , Suominen T , Hanna MG , Männikkö R , Udd B , Cannon SC .

OBJECTIVE: To identify the genetic and physiologic basis for recessive myasthenic congenital myopathy in 2 families, suggestive of a channelopathy involving the sodium channel gene, SCN4A. METHODS: A combination of whole exome sequencing and targeted mutation analysis, followed by voltage-clamp studies of mutant sodium channels expressed in fibroblasts (HEK cells) and Xenopus oocytes. RESULTS: Missense mutations of the same residue in the skeletal muscle sodium channel, R1460 of NaV1.4, were identified in a family and a single patient of Finnish origin (p.R1460Q) and a proband in the United States (p.R1460W). Congenital hypotonia, breathing difficulties, bulbar weakness, and fatigability had recessive inheritance (homozygous p.R1460W or compound heterozygous p.R1460Q and p.R1059X), whereas carriers were either asymptomatic (p.R1460W) or had myotonia (p.R1460Q). Sodium currents conducted by mutant channels showed unusual mixed defects with both loss-of-function (reduced amplitude, hyperpolarized shift of inactivation) and gain-of-function (slower entry and faster recovery from inactivation) changes. CONCLUSIONS: Novel mutations in families with myasthenic congenital myopathy have been identified at p.R1460 of the sodium channel. Recessive inheritance, with experimentally established loss-of-function, is a consistent feature of sodium channel based myasthenia, whereas the mixed gain of function for p.R1460 may also cause susceptibility to myotonia.

PubMed ID: 30824560
PMC ID: PMC6453767
Article link: Neurology
Grant support: [+]

Species referenced: Xenopus laevis
Genes referenced: nav1 scn4a
GO keywords: sodium channel activity

Disease Ontology terms: myopathy

Article Images: [+] show captions
References [+] :
Arnold, Defective fast inactivation recovery of Nav 1.4 in congenital myasthenic syndrome. 2015, Pubmed