Episodic weakness and axonal sensorimotor neuropathy caused by a mitochondrial MT-ATP6 mutation.

Episodic weakness is typically associated with a group of disorders so called periodic paralyses. Their major causes are mutation of ion channels, and have rarely been linked to mitochondrial disorders. We report a 20-year-old man with episodic weakness and axonal sensorimotor neuropathy since the age of 10 years. Analysis of the next generation sequencing data of the entire mitochondrial genome extracted from the blood revealed a homoplasmic m.9185T > C variant in MT-ATP6. Acetazolamide may be responsive for episodic weakness, and supplements with l-carnitine with coenzyme-Q10 seem to be beneficial as well. To the best of our knowledge, this is the first report in Taiwan which reveals episodic weakness and sensorimotor polyneuropathy as a unique phenotype of MT-ATP6 mutations.

Episodic weakness and Charcot-marie-tooth disease due to a mitochondrial MT-ATP6 mutation.

INTRODUCTION: Episodic muscle weakness is the hallmark of a heterogeneous group of disorders known as periodic paralysis. A majority are due to single nucleotide mutations causing membrane depolarization. METHODS: We report 2 family members with chronic, slowly progressive, distal axonal neuropathy, or Charcot-Marie-Tooth disease type 2 (CMT2) and episodic weakness resembling periodic paralysis. RESULTS: Next generation sequencing (NGS) identified a mitochondrial MT-ATP6 mutation m.9185T>C (p.Leu220Pro) in both patients, consistent with a previous report of an association with this phenotype. The episodic weakness has been responsive to acetazolamide therapy for a few decades. By contrast, the underlying axonal neuropathy is quite progressive despite treatment with acetazolamide. CONCLUSIONS: Mitochondrial DNA mutations should be considered in patients with a history of episodic weakness and axonal inherited neuropathy (CMT2). The episodic weakness is responsive to acetazolamide therapy, and electrophysiological testing for periodic paralysis with a long exercise protocol is negative in these cases. Muscle Nerve 55: 922-927, 2017.

Case report: Dihydropyridine receptor (CACNA1S) congenital myopathy, a novel phenotype with early onset periodic paralysis.

Introduction: CACNA1S related congenital myopathy is an emerging recently described entity. In this report we describe 2 sisters with mutations in the CACNA1S gene and the novel phenotype of congenital myopathy and infantile onset episodic weakness. Clinical description: Both sisters had neonatal onset hypotonia, muscle weakness, and delayed walking. Episodic weakness started in infancy and continued thereafter, provoked mostly by cold exposure. Muscle imaging revealed fat replacement of gluteus maximus muscles. Next generation sequencing found the missense p.Cys944Tyr variant and the novel splicing variant c.3526-2A>G in CACNA1S. Minigene assay revealed the splicing variant caused skipping of exon 28 from the transcript, potentially affecting protein folding and/or voltage dependent activation. Conclusion: This novel phenotype supports the notion that there are age related differences in the clinical expression of CACNA1S gene mutations. This expands our understanding of mutations located in regions of the CACNA1S outside the highly conserved S4 segment, where most mutations thus far have been identified.

Muscle channelopathies.

Muscle channelopathies encompass a wide range of mainly episodic conditions that are characterized by muscle stiffness and weakness. The myotonic conditions, characterized predominantly by stiffness, include myotonia congenita, paramyotonia congenita, and sodium channel myotonia. The periodic paralysis conditions include hypokalemic periodic paralysis, hyperkalemic periodic paralysis, and Andersen-Tawil syndrome. Clinical history is key, and diagnosis is confirmed by next-generation genetic sequencing of a panel of known genes but can also be supplemented by neurophysiology studies and MRI. As genetic testing expands, so have the spectrum of phenotypes seen including pediatric presentations and congenital myopathies. Management of these conditions requires a multidisciplinary approach with extra support needed when patients require anesthetics or when pregnant. Patients with Andersen-Tawil syndrome will also need cardiac input. Diagnosis is important as symptomatic treatment is available for all of these conditions but need to be tailored to the gene and variant of the patient.

A novel ATP1A3 mutation with unique clinical presentation.

Mutations in the ATP1A3 gene are associated with rapid-onset dystonia-parkinsonism (RDP) and alternating hemiplegia of childhood (AHC) as well as RDP/AHC intermediate presentations. Phenotypic diversity is being recognized. In order to identify ATP1A3-related phenotypes not meeting the classical criteria for RDP or AHC we lowered the threshold for mutation analysis in clinical presentations resembling AHC or RDP. A novel heterozygous ATP1A3 missense mutation c.2600G>A (p.Gly867Asp, G867D) was detected in a 15-year-old girl. Her clinical phenotype is partially consistent with an intermediate presentation between alternating hemiplegia of childhood and rapid-onset dystonia-parkinsonism and comprises additional yet unreported features. With onset at 4½ years of age recurrent paroxysmal flaccid hemiplegia alternating in laterality was triggered by watching television or playing computer games. Occlusion of both eyes reliably stopped the plegic attacks with the patient remaining awake. Our observation further widens the phenotypic spectrum associated with ATP1A3 mutations.