Genotype and phenotype relationships for mutations in the ryanodine receptor in patients referred for diagnosis of malignant hyperthermia

Diagnostic evaluation of rhabdomyolysis

Rhabdomyolysis is characterized by severe acute muscle injury resulting in muscle pain, weakness, and/or swelling with release of myofiber contents into the bloodstream. Symptoms develop over hours to days after an inciting factor and may be associated with dark pigmentation of the urine. Serum creatine kinase and urine myoglobin levels are markedly elevated. Clinical examination, history, laboratory studies, muscle biopsy, and genetic testing are useful tools for diagnosis of rhabdomyolysis, and they can help differentiate acquired from inherited causes of rhabdomyolysis. Acquired causes include substance abuse, medication or toxic exposures, electrolyte abnormalities, endocrine disturbances, and autoimmune myopathies. Inherited predisposition to rhabdomyolysis can occur with disorders of glycogen metabolism, fatty acid β-oxidation, and mitochondrial oxidative phosphorylation. Less common inherited causes of rhabdomyolysis include structural myopathies, channelopathies, and sickle-cell disease. This review focuses on the differentiation of acquired and inherited causes of rhabdomyolysis and proposes a practical diagnostic algorithm. Muscle Nerve 51: 793-810, 2015.

Mutations inRYR1in malignant hyperthermia and central core disease

The RYR1 gene encodes the skeletal muscle isoform ryanodine receptor and is fundamental to the process of excitation-contraction coupling and skeletal muscle calcium homeostasis. Mapping to chromosome 19q13.2, the gene comprises 106 exons and encodes a protein of 5,038 amino acids. Mutations in the gene have been found in association with several diseases: the pharmacogenetic disorder, malignant hyperthermia (MH); and three congenital myopathies, including central core disease (CCD), multiminicore disease (MmD), and in an isolated case of a congenital myopathy characterized on histology by cores and rods. The majority of gene mutations reported are missense changes identified in cases of MH and CCD. In vitro analysis has confirmed that alteration of normal calcium homeostasis is a functional consequence of some of these changes. Genotype-phenotype correlation studies performed using data from MH and CCD patients have also suggested that mutations may be associated with a range of disease severity phenotypes. This review aims to summarize the current understanding of RYR1 mutations reported in association with MH and CCD and the present viewpoint on the use of mutation data to aid clinical diagnosis of these conditions.

Identification of the Arg1086His mutation in the alpha subunit of the voltage-dependent calcium channel (CACNA1S) in a North American family with malignant hyperthermia

Individuals from a large North American population were screened for the presence of the mutation in the alpha1 subunit of the voltage-dependent calcium channel (CACNA1S) that has recently been associated with malignant hyperthermia (MH). This Arg1086His mutation was screened for in 154 MH normal (MHN) individuals and 112 MH susceptible (MHS) individuals, who were diagnosed by the North American protocol of the in vitro contracture test. PCR and restriction enzyme analysis was used to test for the mutation. The Arg1086His mutation in the CACNA1S was not found in any of the MHN individuals. In contrast, two related individuals (grandfather and grandson, father and son of the MH proband) among the MHS group exhibited this mutation. However, a third MHS individual in the same family (granddaughter, cousin of the grandson) did not exhibit this mutation. These results indicate that this mutation may be associated with MH in this family. Genetic alterations in the CACNA1S associated with MH are present in approximately 1% of this North American MHS population.

The effects of mutated skeletal ryanodine receptors on calreticulin and calsequestrin expression in the brain and pituitary gland of boars

Mutations in skeletal ryanodine receptors (sRyR) result in malignant hyperthermia in humans and Porcine Stress Syndrome (PSS) in pigs. Whether the sRyR is expressed in neuronal tissue and what impact it has on neuronal function is relatively unexplored. We have hypothesized that the presence of mutated sRyR may be accompanied by compensatory changes in Ca(2+)-binding protein expression. We were interested in whether pigs heterozygous for mutated sRyR would show changes in the expression of Ca(2+)-binding proteins, in specific regions of the brain, and whether changes in this expression would be accompanied by the presence of sRyR within that region. The objectives of the current experiments were to determine (1) whether calreticulin (CR) and calsequestrin (CS) are expressed in the pituitary gland and brain of the pig, (2) if boars heterozygous for mutated sRyR differed from wild-type boars in the expression of CR or CS, and (3) if altered Ca(2+)-binding protein expression would be accompanied by the presence of sRyR mRNA. Boars either heterozygous or wild-type (n=6) for the mutation in sRyR known to cause PSS, were euthanized and the pituitary gland and brains were collected for western blotting for CR and CS. An additional four wild-type boars were sacrificed and brains were collected for in situ hybridization for sRyR mRNA. Immunoreactive CR was expressed in porcine tissues with highest (p<0.0001) expression in the pituitary gland and lower but equivalent expression in the hypothalamus, frontal cortex, and hippocampus. Immunoreactive CS was not detectable in the pituitary gland while low levels were observed in the hypothalamus and frontal cortex. Dramatically higher (p<0.0001) levels of CS were found in the hippocampus. Genotype did not affect CR expression in the pituitary gland or any brain region examined. Immunoreactive CS levels were lower (p<0.002) in the hippocampus of heterozygous compared to wild-type boars. In situ hybridization experiments revealed the presence of sRyR mRNA in the hippocampus equally distributed across all cell subfields. In conclusion, both CR and CS were expressed in the porcine brain with specific patterns of expression across the brain regions examined. Boars heterozygous for mutated sRyR had lower CS in the hippocampus, which was accompanied by the expression of mRNA for sRyR.

Myoglobinuria, malignant hyperthermia, neuroleptic malignant syndrome and serotonin syndrome

This article presents an overview of the causes and manifestations of myoglobinuria and provides criteria for its diagnosis and management. The article also reviews neuroleptic malignant syndrome, malignant hyperthermia, and serotonin syndrome, all of which could cause rhabdomyolysis and myoglobinuria.

In vitro diagnosis of malignant hyperthermia susceptibility with ryanodine-induced contractures in human skeletal muscles

The in vitro contracture test with ryanodine is a new method to distinguish malignant hyperthermia (MH) susceptible (MHS) from normal (MHN) patients. The purpose of our investigation was to determine whether smaller concentrations of ryanodine than those used previously may result in a better differentiation. We performed a ryanodine contracture test (RCT) using concentrations of 1 and 2 microM in muscle specimens of 41 MHS, 58 MHN, and 19 MH-equivocal (MHE) patients. Nine patients were excluded from the study due to neuromuscular diseases. All contracture levels (i.e., start of contractures, contractures of 0.2 g and 1.0 g) were attained significantly earlier in MHS than in MHN muscles at both concentrations of ryanodine. Using a ryanodine concentration of 2 microM, all contracture levels were reached significantly faster than with 1 microM. There was no overlap in the range of times between groups at all contracture levels with ryanodine 1 and 2 microM. The median threshold times for all MHE patients were always between those of MHS and MHN. Defining arbitrarily threshold times for MHS and MHN, an assignment of MHE patients to either MHS or MHN using 1 or 2 microM ryanodine was possible in most cases. Ryanodine administration at a concentration of 1 microM led to a better distinction of MHS from MHN patients than 2 microM. The RCT with ryanodine 1 microM should therefore be added to the current diagnostic methods.