Elsevier

Molecular Genetics and Metabolism

Volume 104, Issues 1–2, September–October 2011, Pages 167-173
Molecular Genetics and Metabolism

Genetic risk for malignant hyperthermia in non-anesthesia-induced myopathies

https://doi.org/10.1016/j.ymgme.2011.07.001Get rights and content

Abstract

Malignant hyperthermia (MH) is a pharmacogenetic, autosomal dominantly inherited disorder of skeletal muscle triggered by volatile anesthetics and infrequently by extreme exertion and heat exposure. MH has variable penetrance with an incidence ranging from 1 in 5000 to 1 in 50,000–100,000 anesthesias. Mutations in the ryanodine receptor gene, RYR1, are found in 50–70% of cases. We hypothesized that a portion of patients with drug-induced muscle diseases, unrelated to anesthesia, such as severe statin myopathy, have underlying genetic liability that may include RYR1 gene mutations. DNA samples were collected from 885 patients in 4 groups: severe statin myopathy (n = 197), mild statin myopathy (n = 163), statin-tolerant controls (n = 133), and non-drug-induced myopathies of unknown etiology characterized by exercise-induced muscle pain and weakness (n = 392). Samples were screened for 105 mutations and variants in 26 genes associated with 7 categories of muscle disease including 34 mutations and variants in the RYR1 gene. Disease-causing mutations or variants in RYR1 were present in 3 severe statin myopathy cases, 1 mild statin myopathy case, 8 patients with non-drug-induced myopathy, and none in controls. These results suggest that disease-causing mutations and certain variants in the RYR1 gene may contribute to underlying genetic risk for non-anesthesia-induced myopathies and should be included in genetic susceptibility screening in patients with severe statin myopathy and in patients with non-statin-induced myopathies of unknown etiology.

Introduction

Malignant hyperthermia (MH; MIM #145600) is a pharmacogenetic disorder of skeletal muscle that is triggered by volatile anesthetics, such as succinylcholine, and, in rare cases, by vigorous exercise and heat exposure. The disorder is caused by a disturbance in calcium homeostasis. Diagnostic features include an unexplained elevation in end-tidal carbon dioxide (ETCO2) concentration, muscle rigidity, tachycardia, acidosis, hyperthermia, and hyperkalemia [1]. MH is inherited as an autosomal dominant trait with variable penetrance. The incidence has been reported to range from 1 in 5000 to 1 in 50,000–100,000 anesthesias, however, the prevalence of causative genetic abnormalities may be as high as 1 in 2000 to 1 in 3000 [1], [2].

Ryanodine receptor proteins (RyR) are homotetrameric intracellular calcium release channels that are located in the endoplasmic and sarcoplasmic reticulum membranes [3]. The primary RyR protein of skeletal muscle, RyR1, is encoded by a gene (RYR1; MIM #180901), on chromosome 19q13.1 [3].The gene spans 158 kb, contains 106 exons, and transcribes to an RNA molecule that is 15 kb long. The CACNA1S gene (MIM #114208), encoding the calcium channel, voltage-dependent, L type, α1 subunit of the voltage-gated dihydropyridine receptor (DHPR), is located on chromosome 1q32 [4], [5]. A number of studies have reported that mutations in the RYR1 gene are found in or associated with 50–70% of MH cases and mutations in the CACNA1S gene (MIM#601887) are found in 1% of cases [4], [6], [7]. Four additional loci are believed to be causally associated with MHS cases when RYR1 and CACNA1S gene mutations are not found. These include the SCN4A gene (MIM#154275) on chromosome 17q.2–q24 encoding the sodium channel voltage-gated, type IV alpha subunit; the CACNL2A gene (MIM#154276) on chromosome 7q21–q22; on chromosome 3q13.1 (MIM#600467); and on chromosome 5p (MIM#601888) [5], [8], [9], [10]. In addition, the calsequestrin-1 (CASQ1) gene (MIM#114250) on chromosome 1q21 is a moderate affinity, high-capacity calcium-binding protein in the sarcoplasmic reticulum terminal cisternae of skeletal muscle. It functions not only as a calcium-binding protein but also as a luminal regulator of ryanodine receptor-mediated calcium release [11] and has recently been identified as a candidate gene for MH [12]. There is clinical evidence for a synergistic effect between genetic variants in the genes encoding proteins vital to skeletal muscle calcium regulation (CASQ1, RYR1, and CACNA1S) in a case that began with exercise-induced rhabdomyolysis, followed by a clinical episode of MH with exposure to anesthesia, and then a positive CHCT [13]. In spite of good progress in uncovering mutations causative for MH, there remain a sizeable number of cases in which the genetic etiology is unknown.

The caffeine halothane contracture test (CHCT), requiring an open muscle biopsy, is the most sensitive means of confirming a clinical MH episode. The test measures skeletal muscle contracture response following exposure to halothane or caffeine in a temperature-controlled bathing solution to which caffeine or halothane is added in a dose-controlled manner. Interpretation of the test results vary. The European MH Group assigns MH susceptibility phenotypes as MH sensitive (MHS) when an abnormal response occurs with both halothane and caffeine and MH equivocal (MHE) when there is an abnormal response to only one of the stimulants. The CHCT may have reduced specificity, sensitivity and predictive value in patients with coexisting neuromuscular diseases and enzymopathies. An evidence-based approach was used to score disorders that may be associated with MH [11]. Beyond the well-known association of MHS with central core disease, minicore disease, and King–Denborough syndrome, weak evidence has been presented for susceptibility to MH-like episodes with the following disorders: osteogenesis imperfecta, arthrogryposis, carnitine palmitoyltransferase (CPT) II deficiency, myophosphorylase deficiency (McArdle disease), myoadenylate deaminase deficiency and hyperCKemia [14]. Recently, patients with chronic unexplained hyperCKemia who were MHS or MHE were found to have a number of known and novel mutations and variants in RYR1 [15].

The suspicion that MH susceptibility could be unmasked by an adverse reaction to statin therapy was proposed by Guis et al. [16] who demonstrated positive CHCT results in a number of patients with statin myopathy. These abnormal findings clearly indicated an alteration of calcium homeostasis during statin therapy. Molecular studies for mutations in the RYR1 or CACNA1S gene or any other genes involved in muscle disease were not included in their studies. In another study, the effect of statins was examined on the expression of genes implicated in the regulation of calcium and membrane repair, lipid homeostasis, remodeling of myocytes and mitochondrial function [17]. Statins were found to impact genes involved in the regulation of calcium and membrane repair but not those involved in myocyte remodeling or mitochondrial function. Most recently, a study was performed to determine if statins modified the contracture response in isolated muscle bundles in MHS versus MH-normal (MHN) pigs [18]. Both atorvastatin and simvastatin induced significant muscle contractures in muscle bundles from MHS pigs but not in bundles from MHN pigs. It was inferred that a preexisting impairment of calcium homeostasis must be necessary for this outcome and that there was a greater vulnerability of muscle cells toward statins in MHS patients.

In the present study, we hypothesized that a portion of patients with statin-induced myopathy and idiopathic myopathies have underlying genetic abnormalities that may include RYR1 gene mutations. To test this hypothesis, a study was undertaken to broadly evaluate disease-causing mutations and variants in genes associated with muscle disease by testing several high risk groups. The need for a more comprehensive analysis of disease gene mutations in these patient groups will be determined from the outcome of this study.

Section snippets

Subjects

A total of 885 subjects were evaluated through analysis of genomic DNA derived from peripheral blood or skeletal muscle specimens. Subjects were derived from multiple collaborating centers across the U.S. and Canada. Subjects provided informed consent approved by the NYS Department of Health and the University at Buffalo Health Sciences Institutional Review Board.

DNA isolation

Genomic DNA was isolated from whole blood collected in EDTA or from frozen skeletal muscle tissue using Puregene DNA isolation kits (Qiagen, Germantown, MD).

SNP and mutation genotyping assay

Genotyping was performed using GoldenGate Genotyping with VeraCode technology (Illumina, Inc., San Diego, CA). A complete description of the methodology is described at http://www.uthscsa.edu/csb/CSBPDFfiles/genomics-GoldenGateGenotypingOverview.pdf. Briefly, a total of 384 variants were multiplexed in a single well of a standard microplate

Patient 1

A 47-year old Caucasian female with severe statin myopathy and symptoms of severe pain, stiffness, cramps, rhabdomyolysis with myoglobinuria and elevated plasma CK. The patient also had persistent pain and weakness post-statin therapy. A blood sample originally had been sent to the laboratory for the EIP; the results of the profile were negative. With microarray analysis, she was found to have a proven causative mutation for MH in the RYR1 gene (R614C; Table 2). She was the only one of 197

Acknowledgments

This work was supported by grants from the NHLBI (1R41HL093956-01 and RO1HL085800; GDV) and an Interdisciplinary Research and Creative Activities Award from the UB Office of the Vice President for Research (GDV). We are especially grateful to Dr. Nyamkhishig Sambuughin for her assistance in the interpretation of RYR1 gene variant data. We thank Dr. Henry Rosenberg for his helpful comments during the preparation of this manuscript. We thank Ms. Shanping Huang for technical assistance with

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