Managing pregnancy and anaesthetics in patients with skeletal muscle channelopathies.

The skeletal muscle channelopathies are a group of rare diseases and include non-dystrophic myotonia and periodic paralysis. Given their rarity, little has been published on the management of anaesthesia and pregnancy in this cohort despite being important aspects of care. We have conducted a large study of over 70 patients who underwent anaesthesia and 87 pregnancies to investigate the problems encountered following anaesthesia or during pregnancy.

Atypical periodic paralysis and myalgia: A novel phenotype.

Objective: To characterize the phenotype of patients with symptoms of periodic paralysis (PP) and ryanodine receptor () gene mutations.

Methods: Cases with a possible diagnosis of PP but additional clinicopathologic findings previously associated with related disorders were referred for a tertiary neuromuscular clinical assessment in which they underwent detailed clinical evaluation, including neurophysiologic assessment, muscle biopsy, and muscle MRI. Genetic analysis with next-generation sequencing and/or targeted Sanger sequencing was performed.

Novel mutations in human and mouse SCN4A implicate AMPK in myotonia and periodic paralysis.

Mutations in the skeletal muscle channel (SCN4A), encoding the Nav1.4 voltage-gated sodium channel, are causative of a variety of muscle channelopathies, including non-dystrophic myotonias and periodic paralysis. The effects of many of these mutations on channel function have been characterized both in vitro and in vivo.

Chloride channels in myotonia congenita assessed by velocity recovery cycles.

Introduction: Myotonia congenita (MC) is caused by congenital defects in the muscle chloride channel CLC-1. This study used muscle velocity recovery cycles (MVRCs) to investigate how membrane function is affected.

Methods: MVRCs and responses to repetitive stimulation were compared between 18 patients with genetically confirmed MC (13 recessive, 7 dominant) and 30 age-matched, normal controls.

Muscle MRI reveals distinct abnormalities in genetically proven non-dystrophic myotonias.

We assessed the presence, frequency and pattern of MRI abnormalities in non-dystrophic myotonia patients. We reviewed T1-weighted and STIR (short-tau-inversion-recovery) 3T MRI sequences of lower limb muscles at thigh and calf level in 21 patients with genetically confirmed non-dystrophic myotonia: 11 with CLCN1 mutations and 10 with SCN4A mutations, and 19 healthy volunteers. The MRI examinations of all patients showed hyperintensity within muscles on either T1-weighted or STIR images.

Prevalence study of genetically defined skeletal muscle channelopathies in England.

Objectives: To obtain minimum point prevalence rates for the skeletal muscle channelopathies and to evaluate the frequency distribution of mutations associated with these disorders.

Methods: Analysis of demographic, clinical, electrophysiologic, and genetic data of all patients assessed at our national specialist channelopathy service. Only patients living in the United Kingdom with a genetically defined diagnosis of nondystrophic myotonia or periodic paralysis were eligible for the study.

Double trouble in a patient with myotonia.

Non-dystrophic myotonias (NDM) are characterised by muscle stiffness during voluntary movement owing to delayed skeletal muscle relaxation caused by mutations in the chloride (CLCN1) and sodium (SCN4A) skeletal muscle channel genes. Late onset acid maltase deficiency (AMD) is characterised by progressive respiratory and proximal muscle weakness; electrical but not clinical myotonia can be observed. Case report of a unique patient with concurrent NDM and AMD.

Mexiletine for symptoms and signs of myotonia in nondystrophic myotonia: a randomized controlled trial.

Context: Nondystrophic myotonias (NDMs) are rare diseases caused by mutations in skeletal muscle ion channels. Patients experience delayed muscle relaxation causing functionally limiting stiffness and pain. Mexiletine-induced sodium channel blockade reduced myotonia in small studies; however, as is common in rare diseases, larger studies of safety and efficacy have not previously been considered feasible.

A quantitative measure of handgrip myotonia in non-dystrophic myotonia.

Introduction: Non-dystrophic myotonia (NDM) is characterized by myotonia without muscle wasting. A standardized quantitative myotonia assessment (QMA) is important for clinical trials.

Methods: Myotonia was assessed in 91 individuals enrolled in a natural history study using a commercially available computerized handgrip myometer and automated software.

Skeletal muscle channelopathies: nondystrophic myotonias and periodic paralysis.

Purpose Of Review: The aim is to review the recent findings in relation to the genetics, pathophysiology, clinical phenotypes, investigation and treatment of the nondystrophic myotonias (NDMs) and periodic paralyses.

Recent Findings: The number of pathogenic mutations causing NDMs and periodic paralyses in known genes continues to expand. In addition, a mutation has been identified in the ryanodine receptor gene manifesting as an atypical periodic paralysis phenotype.