Diagnosis of susceptibility to malignant hyperthermia with flanking DNA markers.

OBJECTIVE--To define the region on human chromosome 19 carrying the gene for malignant hyperthermia susceptibility and to evaluate the use of flanking DNA markers in diagnosing susceptibility. DESIGN--Prospective molecular genetic linkage studies in a large malignant hyperthermia pedigree. SETTING--Irish malignant hyperthermia testing centre. SUBJECTS--A large Irish malignant hyperthermia pedigree. MAIN OUTCOME MEASURES--Routine diagnosis of susceptibility to malignant hyperthermia with in vitro contracture test on muscle biopsy specimens and genetic linkage between susceptibility and polymorphic DNA markers in a malignant hyperthermia family. RESULTS--Genetic typing of polymorphic DNA markers in a large Irish malignant hyperthermia pedigree generated a lod score of greater than 3 for the marker D19S9 and showed that the gene for susceptibility is flanked by the markers D19S9 and D19S16. These tightly linked flanking markers allowed non-invasive presymptomatic diagnosis of susceptibility in five untested subjects in the large pedigree with an accuracy of greater than 99.7%. CONCLUSIONS--DNA markers flanking the gene for susceptibility to malignant hyperthermia can be used with high accuracy to diagnose susceptibility in subjects in large known malignant hyperthermia pedigrees and may replace the previous in vitro contracture test for diagnosing this inherited disorder in large families with malignant hyperthermia.     

Abnormal ryanodine receptor channels in malignant hyperthermia.

Previous studies have demonstrated a defect associated with the calcium release mechanism of sarcoplasmic reticulum (SR) from individuals susceptible to malignant hyperthermia (MH). To examine whether SR calcium release channels were indeed altered in MH, SR vesicles were purified from normal and MH susceptible (MHS) porcine muscle. The Ca2+ dependence of calcium efflux rates from 45Ca2(+)-filled SR vesicles was then compared with the Ca2+ dependence of single-channel recordings of SR vesicles incorporated into planar lipid bilayers. The rate constants of 45Ca2+ efflux from MHS SR were two to threefold larger than from normal SR over a wide range of myoplasmic Ca2+. Normal and MHS single channels were progressively activated in a similar fashion by cis Ca2+ from pCa 7 to 4. However, below pCa 4, normal channels were inactivated by cis Ca2+, whereas MHS channels remained open for significantly longer times. The altered Ca2+ dependence of channel inactivation in MHS SR was also evident when Ca2+ was increased on the trans side while cis Ca2+ was held constant. We propose that a defect in a low-affinity Ca2+ binding site is responsible for the altered gating of MHS SR channels. Such a defect could logically result from a mutation in the gene encoding the calcium release channel, providing a testable hypothesis for the molecular basis of this inherited disorder.     

Adenylate kinase deficiency and malignant hyperthermia

Summary In a report of two patients who died of malignant hyperthermia, muscle adenylate kinase deficiency was identified in the father and brother of the deceased. To determine if this enzyme deficiency was a biochemical marker for susceptibility to malignant hyperthermia, we measured adenylate kinase in muscle of three survivors of malignant hyperthermia (MH) and five relatives of survivors of MH attacks with positive caffeine contracture tests. Neither the activity nor the electrophoretic mobility of adenylate kinase differed from four control values. The results show that muscle adenylate kinase deficiency is not a biochemical abnormality shared by all individuals susceptible to malignant hyperthermia.This work has been supported by grants from Muscular Dystrophy Association of America, NIH (NS 11766)Dr. Cerri is recipient of a postdoctoral fellowship from Muscular Dystrophy association and Dr. Willner is recipient of a Teacher Investigator Award from NINCDS     

SR Function in malignant hyperthermia

Malignant hyperthermia (MH) is a genetic disease in man and other animal species that predisposes to a catastrophic hypermetabolic syndrome that is triggered by certain anesthetic agents. A working hypothesis is that a defect in regulation of muscle cell calcium is the primary mechanism that initiates the MH syndrome. This paper reviews the evidence for a defect in muscle cell calcium as regulated by the sarcoplasmic reticulum membrane system. Skeletal muscle biopsied from MH man, pigs and dogs has abnormal in vitro contracture response to halothane and caffeine and these responses can be altered by lowering calcium content of the bathing solution and/or the muscle. Measurements of MH muscle cell Ca2+ by Ca2+-specific microelectrodes in vivo and fura-2 in vitro have demonstrated abnormal Ca2+ levels in resting and in caffeine-stimulated states. The SR membrane system is the primary calcium regulating organelle in skeletal muscle and a likely site for the defect in MH muscle. Two Ca2+ regulating functions of the SR have been explored in SR isolated from MH muscle. An abnormality of the 100K Ca2+-ATPase protein that functions to transport Ca2+ from myoplasm to inside the SR does not appear to be responsible for MH. The most probable defective site in the SR appears to be Ca2+ release channels and a Ca2+-induced Ca2+ release pathway has been shown to be abnormal in SR from MH human and pig muscle.     

Evidence for genetic heterogeneity in malignant hyperthermia susceptibility.

Malignant hyperthermia susceptibility (MHS) is a clinically heterogeneous pharmacogenetic disorder characterized by accelerated metabolism, hyperthermia, and frequently muscle rigidity. MHS is elicited by all commonly used potent inhalation anesthetics and depolarizing neuromuscular blockers and remains an important cause of death due to anesthesia. Recent linkage studies suggest a single genetic locus for this disorder on chromosome 19q13.1. The results of our linkage analyses exclude several loci on 19q13.1 as a site for the gene(s) that produces the MHS phenotype in three unrelated families and clearly establish genetic heterogeneity in this disorder. These results are consistent with the hypothesis that the genetic defect that alters thermoregulation may vary in MHS and that clinical variability in the expression of MHS may be explained by genetic heterogeneity.     

Voltage-dependent calcium release in human malignant hyperthermia muscle fibers.

Malignant hyperthermia (MH) results from a defect of calcium release control in skeletal muscle that is often caused by point mutations in the ryanodine receptor gene (RYR1). In malignant hyperthermia-susceptible (MHS) muscle, calcium release responds more sensitively to drugs such as halothane and caffeine. In addition, experiments on the porcine homolog of malignant hyperthermia (mutation Arg615Cys in RYR1) indicated a higher sensitivity to membrane depolarization. Here, we investigated depolarization-dependent calcium release under voltage clamp conditions in human MHS muscle. Segments of muscle fibers dissected from biopsies of the vastus lateralis muscle of MHN (malignant hyperthermia negative) and MHS subjects were voltage-clamped in a double vaseline gap system. Free calcium was determined with the fluorescent indicator fura-2 and converted to an estimate of the rate of SR calcium release. Both MHN and MHS fibers showed an initial peak of the release rate, a subsequent decline, and rapid turn-off after repolarization. Neither the kinetics nor the voltage dependence of calcium release showed significant deviations from controls, but the average maximal peak rate of release was about threefold larger in MHS fibers.     

100 telephone conversations about malignant hyperthermia

Background

Paraplegia associated with epidural anesthesia or caused by intramedullary spinal tuberculoma is rare but catastrophic. We present a case of paraplegia following epidural anesthesia in a patient with an undiagnosed intramedullary spinal tuberculoma.

Case presentation

A 42-year-old man developed paraplegia after an open cholecystectomy under epidural anesthesia. Spinal cord infarction, acute transverse myelitis, and intramedullary neoplasms were ruled out by histopathologic examination, and intramedullary spinal tuberculoma at the T₆–T₇ level was identified. Despite surgical treatment and subsequent antituberculous therapy, the patient retained some disability attributable to the delay in diagnosis.

Conclusion

Physicians should be aware of coexisting disease as a cause of paraplegia following procedures using epidural anesthesia. Magnetic resonance imaging is the most sensitive diagnostic test, although it is still difficult to differentiate spinal cord infarction, myelitis, intramedullary spinal tuberculoma, and neoplasms from imaging features alone.

     

Transverse tubule calcium regulation in malignant hyperthermia

Transverse tubule (TT) calcium transport and permeability were examined in the inherited skeletal muscle disorder malignant hyperthermia (MH). ATP-dependent calcium uptake by TT vesicles isolated from normal and MH-susceptible (MHS) pig muscle had a similar dependence on ionized Ca2+ concentration (K1/2 for Ca2+ of 0.21 +/- 0.04 and 0.25 +/- 0.05 microM for MHS and normal TT, respectively), as well as a similar Vmax (20.9 +/- 2.0 and 23.7 +/- 4.5 nmol Ca/mg protein/min for MHS and normal TT, respectively). Furthermore, the stimulation of calcium uptake by either calmodulin or cAMP-dependent protein kinase was similar in normal and MHS TT. Halothane concentrations greater than 2 mM inhibited calcium uptake by either normal or MHS TT to a similar extent (IC50 = 8 mM). Dantrolene (10 microM), nitrendipine (1 microM), and Bay K 8644 (1 microM) had no significant effect on either the initial rates of calcium uptake or maximal calcium accumulation of either MHS or normal TT vesicles. However, in the absence of any added agents, maximum calcium accumulation by MHS TT was significantly less than by normal TT (90 +/- 10 versus 130 +/- 9 nmol Ca/mg protein after 15 min of uptake). This difference was not due to an increased permeability of MHS TT to calcium, nor was it due to a difference in the sarcoplasmic reticulum contamination (less than 5%) of the MHS and normal preparations. Although our results indicate there is no significant defect in MHS TT calcium regulation, the diminished maximum calcium accumulation by MHS TT may contribute to the abnormal sarcoplasmic calcium homeostasis in skeletal muscle during an MH crisis.