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Neurology
2019 Mar 26;9213:e1405-e1415. doi: 10.1212/WNL.0000000000007185.
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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
.
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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.
Figure 1. Sodium channel mutations(A) Segregation of clinical phenotype and genotype among 7 carriers of p.R1460Q in family 1 from Finland. (B) Location of p.R1460 in the pore-forming subunit (NaV1.4) along with established sites for sodium channelopathies of skeletal muscle. CMS = congenital myasthenic syndrome; HyperPP = hyperkalemic periodic paralysis; HypoPP = hypokalemic periodic paralysis; PAM = paramyotonia congenita; SCM = sodium channel myotonia.
Figure 2. Sodium current density was reduced for cells transfected with R1460 mutant constructs, but the voltage dependence of activation was not altered(A) Traces show sodium currents elicited by depolarization from â120 mV to test potentials between â75 and +60 mV. Note the higher gain for the scale bars in the mutant channel traces. (B) Peak current density is shown as a function of test potential and displays a marked reduction in current amplitude for both mutants. (C) The voltage dependence of channel activation, as shown by relative conductance, was indistinguishable between the wild-type (WT) and mutant channels. Black squares, blue triangles, and red circles correspond to WT (n = 16), R1460Q (n = 12), and R1460W (n = 16), respectively.
Figure 3. Fast inactivation of R1460 mutant channels had both gain-of-function and loss-of-function defects(A) The steady-state voltage dependence of fast inactivation was shifted leftward (hyperpolarized) for both R1460 mutant channels relative to wild-type (WT). Inset shows the voltage protocol used to measure inactivation produced by a 300 ms conditioning pulse at various potentials. (B) The rate of inactivation was slower for R1460 mutant channels at depolarized potentials, as shown by the superposition of amplitude normalized currents elicited at 10 mV. (C) Recovery from fast inactivation was faster for both R1460Q and R1460W, compared to WT channels (tau recovery of 4.7 ± 0.6 ms, p < 0.0001 [n = 5]; 6.4 ± 0.6 ms, p < 0.0001 [n = 7]; 16.8 ± 0.4 ms [n = 4], respectively). Data show the time course for the recovery of peak current amplitude at a holding potential of â80 mV, after channels were inactivated with a conditioning pulse of 30 ms at â10 mV (inset). (D) Plot summarizing the voltage-dependent kinetics for entry to or recovery from fast inactivation. Three separate protocols were used to measure inactivation kinetics, over the entire voltage range (see text, Results). Overall, the changes in steady-state fast inactivation (A) are loss of function, whereas the slower entry and more rapid recovery from fast inactivation are gain-of-function changes.
Figure 4. The use-dependent reduction in sodium current peak amplitude was less pronounced in R1460 mutants than in wild-type (WT) channelsData show relative peak sodium current elicited by 2 ms depolarizing pulses to 10 mV applied at 60 Hz (A) or 100 Hz (B), from a holding potential of â80 mV.
Figure 5. Slow inactivation was not altered by either R1460W or R1460Q(A) Onset of slow inactivation showed identical kinetics between wild-type (WT) and mutant channels. Inset shows the voltage protocol to characterize the onset of slow inactivation by stepping to â10 mV for a variable duration (entry time), and then measuring the decline in relative loss current that fails to recover within 20 ms at â120 mV. (B) The rate of recovery from slow inactivation was comparable between WT and R1460 mutant channels. Channels were slow inactivated by a 30-second step to â10 mV (inset), and the data show recovery as the relative increase in current after repolarizing to â80 mV for a variable duration (recovery time). (C) The voltage dependence of steady-state slow inactivation was indistinguishable between WT and R1460 mutant channels. Thirty-second conditioning pulses to various conditioning potentials (inset) were used to determine the voltage dependence of inactivation. Smooth curves show best fits to the data with V1/2 of â59.1 ± 1.9 mV for WT, â60.9 ± 2.8 mV for R1460Q, and â63.4 ± 2.6 mV for R1460W. The number of cells for the mean values shown in the data was 5â8 for WT and both R1460 mutant channels.
Figure 6. The R1460 mutations did not cause a gating pore leakage currentThe steady-state current (without subtraction of the nonspecific leak) recorded from oocytes expressing high levels of wild-type (WT) or R1460 mutant channels is plotted as a function of the membrane potential. Tetrodotoxin was added to block sodium currents through the main pore. The IâV relation was identical for WT and R1460 mutant channels, while the positive control for the p.R1132Q mutation in hypokalemic periodic paralysis showed a gating pore leakage current (large negative current for membrane potentials more negative than â80 mV). Data are from 6 to 8 oocytes per construct.
Arnold,
Defective fast inactivation recovery of Nav 1.4 in congenital myasthenic syndrome.
2015, Pubmed
Arnold,
Defective fast inactivation recovery of Nav 1.4 in congenital myasthenic syndrome.
2015,
Pubmed
Cannon,
Sodium Channelopathies of Skeletal Muscle.
2018,
Pubmed
Cannon,
Voltage-sensor mutations in channelopathies of skeletal muscle.
2010,
Pubmed
Capes,
Domain IV voltage-sensor movement is both sufficient and rate limiting for fast inactivation in sodium channels.
2013,
Pubmed
,
Xenbase
Evilä,
Targeted Next-Generation Sequencing Reveals Novel TTN Mutations Causing Recessive Distal Titinopathy.
2017,
Pubmed
Fournier,
Cold extends electromyography distinction between ion channel mutations causing myotonia.
2006,
Pubmed
Fournier,
Electromyography guides toward subgroups of mutations in muscle channelopathies.
2004,
Pubmed
Francis,
Leaky sodium channels from voltage sensor mutations in periodic paralysis, but not paramyotonia.
2011,
Pubmed
Gamal El-Din,
Structural and Functional Analysis of Sodium Channels Viewed from an Evolutionary Perspective.
2018,
Pubmed
Gosselin-Badaroudine,
Gating pore currents and the resting state of Nav1.4 voltage sensor domains.
2012,
Pubmed
,
Xenbase
Habbout,
A recessive Nav1.4 mutation underlies congenital myasthenic syndrome with periodic paralysis.
2016,
Pubmed
Hayward,
Inactivation defects caused by myotonia-associated mutations in the sodium channel III-IV linker.
1996,
Pubmed
Hayward,
Slow inactivation differs among mutant Na channels associated with myotonia and periodic paralysis.
1997,
Pubmed
Kato,
A case of non-dystrophic myotonia with concomitant mutations in the SCN4A and CLCN1 genes.
2016,
Pubmed
Li,
Fast and accurate short read alignment with Burrows-Wheeler transform.
2009,
Pubmed
Luo,
Hypokalaemic periodic paralysis and myotonia in a patient with homozygous mutation p.R1451L in NaV1.4.
2018,
Pubmed
Matthews,
Voltage sensor charge loss accounts for most cases of hypokalemic periodic paralysis.
2009,
Pubmed
McKenna,
The Genome Analysis Toolkit: a MapReduce framework for analyzing next-generation DNA sequencing data.
2010,
Pubmed
Poulin,
Substitutions of the S4DIV R2 residue (R1451) in NaV1.4 lead to complex forms of paramyotonia congenita and periodic paralyses.
2018,
Pubmed
Skov,
Extracellular magnesium and calcium reduce myotonia in ClC-1 inhibited rat muscle.
2013,
Pubmed
Tsujino,
Myasthenic syndrome caused by mutation of the SCN4A sodium channel.
2003,
Pubmed
Wu,
Mice with an NaV1.4 sodium channel null allele have latent myasthenia, without susceptibility to periodic paralysis.
2016,
Pubmed
Zaharieva,
Loss-of-function mutations in SCN4A cause severe foetal hypokinesia or 'classical' congenital myopathy.
2016,
Pubmed
,
Xenbase
