Caffeine-halothane Contracture Test Research Articles

Prolonging viability of swine muscle biopsy specimens in malignant hyperthermia testing.

In North America, the caffeine halothane contracture test (CHCT) is the standard test for the diagnosis of malignant hyperthermia (MH). Current CHCT protocol recommends that the test be completed within 5 h of muscle excision. The purpose of this study was to investigate whether the period of skeletal muscle viability could be extended to 24 h. We tested the gracilis muscle from normal (n = 8) and MH-susceptible swine (n = 8). After baseline (1-2 h after excision) CHCT, the remaining muscles were placed into one of the following four treatment groups. In Groups 1 and 2, the muscles remained under tension and were stored in Krebs buffer (pH 7.4) at 23 degrees C-25 degrees C (clamped-warm) and 4 degrees C (clamped-cold), respectively. In Groups 3 and 4, the muscle strips were dissected, and the ends were tied with silk sutures, cut from the clamp, and placed in Krebs buffer at 23 degrees C-25 degrees C (free-warm) and 4 degrees C (free-cold), respectively. The responses of the treatment groups to halothane (3%) and caffeine (0.5-32 mM) were tested 22-26 h after excision. The clamped-warm storage was the only storage method to correctly diagnose MH susceptibility in all muscle strips tested. This finding was also confirmed in muscle stored under clamped-warm conditions and shipped overnight to another testing center for a parallel CHCT.

Screening of Tissue from Malignant Hyperthermia–susceptible Patients Reveals Novel Genetic Mutations

Screening of Tissue from Malignant Hyperthermia–susceptible Patients Reveals Novel Genetic Mutations. Sambuughin et al. (page 594)More than 20 ryanodine receptor 1 (RyR1) mutations have been identified in families with an inherited susceptibility to malignant hyperthermia (MH). Sambuughin et al. obtained skeletal muscle samples from 73 unrelated people with diagnoses of MH susceptibility by using the caffeine–halothane contracture test of the North American Malignant Hyperthermia Group. The patients had been referred for the test because of either a positive family history of MH or development of signs of MH during anesthesia.The muscle samples were collected during a period of 3 yr and were stored at −70°C. Genomic DNA was extracted from stored muscle tissue or peripheral blood and was amplified using standard polymerase chain reaction–based restriction fragment length polymorphism, single-strand conformation polymorphism, and sequencing analysis. Most of the known RyR1 mutations were analyzed using the restriction fragment length polymorphism method, whereas new mutations were searched by single-strand conformation polymorphism in exons 12, 15, 39, 40, 44, 45, and 46 of the gene. Seven known RyR1 mutations were detected at frequencies ranging from 1.4% to 5.5%. The research team also detected three novel amino acid substitutions, at frequencies of 1.4% each. All 10 mutations were in 16 unrelated individuals and account for 21.9% of the screened North American MH-susceptible population. Statistical correlation between caffeine–halothane contracture test phenotypes and RyR1 was not studied because of the small number of subjects carrying the same mutation and lack of family members for the study. The frequency and distribution of RyR1 gene mutations detected in this North American MH-susceptible population were different from those previously identified in Western Europe. Larger-scale studies are needed, say the authors, to assess the type and frequency of mutations in RyR1 associated with MH in the North American population.

North American malignant hyperthermia population: screening of the ryanodine receptor gene and identification of novel mutations.

Malignant hyperthermia (MH) is a disorder of skeletal muscle manifested as a life-threatening hypermetabolic crisis in susceptible individuals after exposure to inhalational anesthetics and depolarizing muscle relaxants. Mutations in the gene encoding the skeletal muscle ryanodine receptor (RYR1) are considered a common cause of the disorder, and, to date, more than 20 RYR1 mutations have been reported in European and Canadian families. Some studies suggest that differences may exist in the frequencies and distribution of mutations in the RYR1 gene between European and North American MH families the frequency and distribution of mutations in the RYR1 gene. Skeletal muscle samples from 73 unrelated individuals diagnosed as MH susceptible according to the North American MH caffeine-halothane contracture test were studied. Genomic DNA of MH-susceptible patients was investigated by polymerase chain reaction-based restriction fragment length polymorphism, single-strand conformation polymorphism, and sequencing analysis. The majority of known RYR1 mutations were analyzed using the restriction fragment length polymorphism method, whereas new mutations were searched by single-strand conformation polymorphism in exons 12, 15, 39, 40, 44, 45, and 46 of the gene. Seven known RYR1 mutations (Arg163Cys, Gly248Arg, Arg614Cys, Val2168Met, Thr2206Met, Gly2434Arg, and Arg2454His) were detected at frequencies of 2.7, 1.4, 1.4, 1.4, 1.4, 5.5, and 4.1%, respectively. In addition, three novel amino acid substitutions (Val2214Ile, Ala2367Thr, and Asp2431Asn) were detected at frequency of 1.4% each. These 10 mutations account for 21.9% of the North American MH-susceptible population. Three novel candidate mutations in the RYR1 gene were identified in these MH patients. The frequency and distribution of RYR1 mutations observed in this North American MH population was markedly different from that previously identified in Europe. Larger-scale studies are necessary to clarify the type and frequency of mutations in RYR1 associated with MH in North American families.

Malignant hyperthermia: advances in clinical management and diagnosis

Malignant hyperthermia: advances in clinical management and diagnosis

Comparison of the in vitro caffeine-halothane contracture test with the Ca-induced Ca release rate test in patients suspected of having malignant hyperthermia susceptibility.

We compared the results of the in vitro caffeine-halothane contracture test (CHCT) according to the protocols of the North American Malignant Hyperthermia Group (NAMHG) and the European Malignant Hyperthermia Group (EMHG) with the Ca-induced Ca release (CICR) rate test in the same patients with suspected malignant hyperthermia (MH). Five normal controls and 16 patients suspected of having MH susceptibility were studied. Muscle biopsies were usually obtained from the musculus vastus lateralis. Diagnostic cutoff points and procedures for CHCT protocols were as described in the original and renewal versions of NAMHG and EMHGs. The CICR rate test was performed according to the protocol reported by Endo et al. All five normal controls and two patients with abortive MH, two with postoperative hyperthermia, and three with high serum creatine kinase levels were normal in the three tests. Three patients with MH reactions and one patient with a history of masseter spasm were classified as MH positive according to NAMHG criteria and MH susceptible and MH equivocal according to EMHG criteria. There were five cases with discordant results between the CHCT and CICR rate tests. We propose that muscle biopsy for diagnosis of MH susceptibility should combine the CHCT with the CICR rate test, which may identify the defective site of Ca release channels.

The Sensitivity and Specificity of the Caffeine-Halothane Contracture Test

BackgroundThe caffeine-halothane contracture test (CHCT) is the only recognized laboratory test to diagnose malignant hyperthermia (MH). The authors report the results of their analysis of pooled data from the North American Malignant Hyperthermia Registry database to determine the sensitivity and s

Treatment of normal skeletal muscle with FK506 or rapamycin results in halothane-induced muscle contracture.

FKBP12 is a protein that is closely associated with the ryanodine receptor type 1 of skeletal muscle and modulates Ca2+ release by the channel. The immunosuppressants FK506 and rapamycin both bind to FKBP12 and in turn dissociate the protein from the ryanodine receptor. By treating healthy human skeletal muscle strips with FK506 or rapamycin and then subjecting the strips to the caffeine-halothane contracture test, this study determined that FK506 and rapamycin alter the sensitivity of the muscle strip to halothane, caffeine, or both. Skeletal muscle strips from 10 healthy persons were incubated in Krebs medium equilibrated with a 95% oxygen and 5% carbon dioxide mixture, which contained either 12 microM FK506 (n = 8) or 12 microM rapamycin (n = 6), for 15 min at 37 degrees C. The strips were subjected to the caffeine-halothane contracture test for malignant hyperthermia according to the European Malignant Hyperthermia Group protocol. Treatment of normal skeletal muscle strips with FK506 and rapamycin resulted in halothane-induced contractures of 0.44+/-0.16 g and 0.6+/-0.49 g, respectively, at 2% halothane. The results obtained show that pre-exposure of healthy skeletal muscle strips to either FK506 or rapamycin is sufficient to give rise to halothane-induced contractures. This is most likely caused by destabilization of Ca2+ release by the ryanodine receptor as a result of the dissociation of FKBP12. This finding suggests that a mutation in FKBP12 or changes in its capacity to bind to the ryanodine receptor could alter the halothane sensitivity of the skeletal muscle ryanodine receptor and thereby predispose the person to malignant hyperthermia.

The sensitivity and specificity of the caffeine-halothane contracture test: a report from the North American Malignant Hyperthermia Registry. The North American Malignant Hyperthermia Registry of MHAUS.

The caffeine-halothane contracture test (CHCT) is the only recognized laboratory test to diagnose malignant hyperthermia (MH). The authors report the results of their analysis of pooled data from the North American Malignant Hyperthermia Registry database to determine the sensitivity and specificity of the CHCT. The MH Clinical Grading Scale was used to identify 32 case subjects who were "almost certain" to be MH susceptible based on clinical criteria alone. Their CHCT results were compared with those of a group of 120 control subjects considered to be at low risk for MH. Diagnostic thresholds of the CHCT were adjusted, and its component tests were combined to generate receiver operating characteristic curves. The maximal Youden index for each component test was chosen as the diagnostic threshold indicative of MH susceptibility. The highest sensitivity (97%; 95% CI, 84-100%) was achieved with a two-component test with thresholds of > or = 0.5 g contracture for 3% halothane, > or = 0.3 g contracture at 2 mM caffeine, or both, considered positive for MH. The test specificity was 78% (95% CI, 69-85%). The addition of other CHCT component tests did not improve CHCT sensitivity or specificity. The CHCT achieves high sensitivity and acceptable specificity as a clinical laboratory diagnostic test when it is performed according to published standards. However, it cannot be used as a screening test because of the low prevalence of MH in the general population.

Generalized Muscle Rigidity and Hypercarbia with Halothane and Isoflurane

Generalized Muscle Rigidity and Hypercarbia with Halothane and Isoflurane

Caffeine and Halothane Sensitivity of Intracellular Ca2+ Release Is Altered by 15 Calcium Release Channel (Ryanodine Receptor) Mutations Associated with Malignant Hyperthermia and/or Central Core Disease

Malignant hyperthermia (MH) and central core disease (CCD) are autosomal dominant disorders of skeletal muscle in which a potentially fatal hypermetabolic crisis can be triggered by commonly used anesthetic agents. To date, 17 mutations in the human RYR1 gene encoding the Ca2+ release channel of skeletal muscle sarcoplasmic reticulum (the ryanodine receptor) have been associated with MH and/or CCD. Although many of these mutations have been linked to MH and/or CCD, with high lod (log of the odds favoring linkage versus nonlinkage) scores, others have been found in single, small families. Independent biochemical evidence for a causal role for these mutations in MH is available for only two mutants. Mutations corresponding to the human MH mutations were made in a full-length rabbit RYR1 cDNA, and wild type and mutant cDNAs were transfected into HEK-293 cells. After about 48 h, intact cells were loaded with the fluorescent Ca2+ indicator, fura-2, and intracellular Ca2+ release, induced by caffeine or halothane, was measured by photometry. Ca2+ release in cells expressing MH or CCD mutant ryanodine receptors was invariably significantly more sensitive to low concentrations of caffeine and halothane than Ca2+ release in cells expressing wild type receptors or receptors mutated in other regions of the molecule. Linear regression analysis showed that there is a strong correlation (r = 0.95, p < 0.001) between caffeine sensitivity of different RYR1 mutants measured by the cellular Ca2+ photometry assay and by the clinical in vitro caffeine halothane contracture test (IVCT). The correlation was weaker, however, for halothane (r = 0.49, p > 0.05). Abnormal sensitivity in the Ca2+ photometry assay provides supporting evidence for a causal role in MH for each of 15 single amino acid mutations in the ryanodine receptor. The study demonstrates the usefulness of the cellular Ca2+ photometry assay in the assessment of the sensitivity to caffeine and halothane of specific ryanodine receptor mutants.

Identification of heterozygous and homozygous individuals with the novel RYR1 mutation Cys35Arg in a large kindred.

Malignant hyperthermia (MH) is a potentially fatal, often autosomal dominant, disorder of skeletal muscle and is triggered in susceptible people by all commonly used inhalational anesthetics. In this article, the authors describe a malignant hyperthermia susceptible (MHS) kindred in which both parents of the proband are MHS and are first-degree cousins. Haplotype analysis in this kindred with chromosome 19 linked markers revealed that the proband and another sibling were homozygous for the affected RYR1 allele. Eighteen members of this large pedigree were investigated, with a clinical examination for signs of a myopathy, a caffeine halothane contracture test, a histo-enzymologic study on the muscle biopsies, and linkage analysis on genomic DNA isolated from family blood samples. RYR1 cDNA was amplified by polymerase chain reaction and was cloned and sequenced, facilitating mutation detection. Linkage analysis demonstrated linkage between RYR1-linked markers and MH susceptibility in this family. DNA sequencing identified a T to C transition at nucleotide position 103, resulting in the substitution of an arginine for cysteine 35, representing the most N-terminal mutation reported to date in the RYR1 gene. This mutation segregates fully with the MHS trait, generating a lod score of 4.65 in favor of linkage to MHS at a recombination frequency of 0.0. The proband in this kindred is the first reported homozygote to have presented with an MH episode. The homozygotes in this pedigree do not have an overt myopathy. The sensitivity of muscle samples to caffeine clearly distinguished the two homozygotes from other heterozygous-susceptible individuals. No clear differentiation was observed with the halothane contracture results.

Preoperative creatine kinase blood levels and myopathological changes in malignant hyperthermia

In malignant hyperthermia (MH) the fundamental lesion is located in skeletal muscle fibres. The underlying cause of MH is suggested to be an increase in myoplasmic calcium, which is released from the sarcoplasmic reticulum. Although MH is believed to represent myopathy, patients susceptible to MH (MHS) rarely have clinical evidence of muscle diseases [1]. Creatine kinase (CK) as muscle cell enzyme is reported to predict MH disposition when blood levels at rest are raised [2]. The purpose of this study was to determine, whether any clinical prediction could be made of abnormal pre-operative CK blood levels or whether there is a correlation between raised CK values and histological abnormalities. After institutional approval and written informed consent, 196 patients aged 3–71 years with clinical suspicion for MH were enrolled in this prospective study. The patients were first classified as MHS or MHN (MH non susceptible) by the caffeine halothane contracture test (CHCT) according to the European MH protocol [3]. Patients tested equivocal (MHE) were excluded from this study. Additionally, small muscle specimens (approximately 3×3×10 mm) were excised from each patient for histological and morphometric investigation. Preoperative levels of CK in blood were measured and compared both with the CHCT and the histological results. Data are expressed as mean ± SEM or percentages, respectively. Statistical analysis was performed using the Mann-Whitney U-test. P<0.05 was considered significant. 80 from the 196 patients in this study (40.8%) were diagnosed MHS and 116 (59.2%) MHN. In the MHS patients 26 from 80 (32.5%) had elevated CK values compared to 13 from 116 (11.2%) in the MHN group. 52 (65%) of the MHS patients showed myopathological changes (9 specific, 43 unspecific), whereas only 49 (42.2%) of the MHN patients had any myopathological abnormalities (3 specific, 46 unspecific). Preoperative CK blood levels were increased in 39 patients (19.9%) and two thirds of these were classified MHS. While 88 of all patients were female (44.9%) the distribution was a little different in the two diagnostic groups with 26 (32.5%) female MHS and 62 (53.4%) female MHN patients. It was noticed that only 7 of the 39 patients with raised CK were female (17.9%) and all of them showed myopathological abnormalities both in the MHS group (4 female) and in the MHN group (3 female). In contrast only 50% of the male patients with preoperative elevated CK values showed myopathological changes with no differences between MHS and MHN. The results demonstrate that it is not possible to distinguish MHS from MHN individuals by determining the CK blood levels at rest or using histological techniques. At present, the CHCT remains the only reliable test method for the diagnosis of MH susceptibility. There were significantly more male than female patients with elevated CK values. A further significant difference was that 100% of the females but only 50% of the male patients with elevated CK values showed myopathological abnormalities. We recommend that all patients with increased CK levels at rest should have muscle biopsy both for MH diagnostic and histological investigation.

Reduced Mg2+ inhibition of Ca2+ release in muscle fibers of pigs susceptible to malignant hyperthermia.

The inhibitory effect of myoplasmic Mg2+ on Ca2+ release from the sarcoplasmic reticulum (SR) was examined in mechanically skinned skeletal muscle fibers from pigs of different ryanodine-receptor (RyR) genotypes. In fibers from pigs homozygous for the normal RyR allele, the free Mg2+ concentration ([Mg2+]) had to be lowered from the normal resting level of 1 to approximately 0.1 mM to induce Ca2+ release and a force response. Fibers from pigs heterozygous or homozygous for the RyR allele associated with malignant hyperthermia (MH) needed only a smaller reduction in free [Mg2+] to induce Ca2+ release (reduction to 0.1-0.2 and > or = 0.2 mM, respectively). Dantrolene (20 microM) counteracted the effect of this reduced Mg2+ inhibition in MH muscle. The response of muscle fiber bundles to the caffeine-halothane contracture test in the three genotypes correlated well with the responsiveness of single fibers to reduced [Mg2+]. Thus the abnormal responsiveness of MH muscle to various stimuli may largely result from the reduced ability of myoplasmic Mg2+ to inhibit Ca2+ release from the SR.

Effects of the serotonin2 receptor agonist DOI on skeletal muscle specimens from malignant hyperthermia-susceptible patients.

Administration of serotonin2 (5-HT2) receptor agonists in pigs triggers malignant hyperthermia (MH) and psychotic-like behavior. Both can be reduced by 5-HT2 receptor antagonists. Furthermore, an increase in the plasma concentration of 5-HT has been found during onset of halothane-induced MH in pigs. Therefore, in this study, the in vitro effects of the 5-HT2 receptor agonist 1-(2,5-dimethoxy-4-iodophenyl)-2-aminopropane (DOI) were investigated in muscle specimens from MH-susceptible (MHS) and -negative (MHN) patients. After MH classification using the caffeine-halothane contracture test (CHCT), surplus muscle specimens from 23 MHS and 17 MHN patients were used to examine the effects of DOI. In the first study, DOI was added to the bath in a concentration of 0.02 mM. In a second experiment, muscles were preincubated for 60 min with 0.02 mM DOI, and subsequently, halothane was added incrementally to the organ bath (0.11-0.22-0.44 mM) for 15 min according to the CHCT protocol. The in vitro effects of DOI on contracture development and muscle twitch were measured for 120 min in both investigations. Muscle specimens form all patients developed contractures after administration of DOI, characterized by a significantly earlier development of contracture in MHS (16.8 +/- 1.7 min) than in MHN (66.3 +/- 5.8 min) muscles (P < 0.05). There was no overlap between the groups in the range of times. The onset of contracture development after DOI was prolonged by halothane in specimens from MHN patients (89.7 +/- 5.6 min) but not MHS patients. Preincubation with DOI increased the halothane-induced contractures in specimens from MHS patients compared to the results of the CHCT. The contracture development in specimens from MHS patients was larger than from MHN patients. At the end of the experiment, contractures had reached a maximum of 12.9 +/- 1.1 mN in specimens from MHS and 5.3 +/- 0.6 mN in MHN patients (P < 0.05). The additional administration of halothane led to significantly increased contractures in specimens from MHS individuals (15.9 +/- 0.9 mN) at 120 min. However, the contracture development decreased significantly to 3.1 +/- 0.4 mN in MHN muscles. Muscle twitch after DOI administration was reduced significantly in specimens from MHS and MHN patients. A functional or structural altered serotonin system might be involved in the development of MH in humans.

THE NORTH AMERICAN MALIGNANT HYPERTHERMIA REGISTRY

SUMMARY The North American Malignant Hyperthermia Registry acquires, analyzes, and disseminates patient-specific clinical and laboratory information on MH to scientific investigators and health professionals caring for MH susceptible patients. With the help of health care professionals throughout North America, the Registry has enrolled nearly 2200 individuals with a possible history of MH susceptibility. To date, Registry research efforts (1) helped create a MH clinical grading scale that will serve as a clinical case definition for the MH syndrome, (2) determined that a modification of the North American caffeine-halothane contracture test will produce a laboratory test with nearly 100% sensitivity and 78% specificity, and (3) demonstrated that 4% of patients suffering probable MH events died in spite of high dose dantrolene therapy and that 6% of patients treated with dantrolene experienced respiratory failure. The Registry has prepared more than 2000 MH Patient Reports for immediate release to health care professionals caring for patients with a history of possible MH susceptibility. Registry report forms and MH Patient Reports may be obtained by contacting the Registry office during normal working hours. The success of future Registry studies will remain heavily dependent upon the continued cooperation of health care professionals and MH susceptible individuals throughout North America.

The substitution of Arg for Gly2433 in the human skeletal muscle ryanodine receptor is associated with malignant hyperthermia.

Single strand conformational polymorphism analysis was used to screen exons 43 and 44 in the skeletal muscle ryanodine receptor gene from 17 positively diagnosed members of families in which chromosome 19-linked malignant hyperthermia (MH) was segregating. A polymorphism in two unrelated individuals was found to result from the substitution of A for G7297, leading to the substitution of Arg for Gly2433. This mutation is adjacent to a mutation (Arg2434 to His) previously linked to MH and central core disease (Y. Zhang et al., Nature Genet. 1993, 5, 46-50). Subsequent screening showed the presence of the mutation in four of 106 MH families tested and its absence from about 1000 other chromosomes. The mutation was present in all six individuals in four families who had had an MH reaction, in two obligate carriers and in 10 individuals diagnosed as MH susceptible by the caffeine/halothane contracture test (CHCT). The mutation was present in an individual with a normal response to the CHCT and was absent in three individuals with a positive CHCT response. These discrepancies would be consistent with inaccuracies in the CHCT and/or with segregation of a second MH allele within two of the four affected families.

Advances in Understanding Malignant Hyperthermia

SUMMARY Patients with MH susceptibility are usually asymptomatic, otherwise healthy, and of all ages. New anesthetic monitoring techniques that permit the continuous analysis of expired CO2 facilitate the rapid detection and treatment of MH episodes. Because early, appropriate treatment reduces the morbidity and mortality of MH episodes, all patients receiving a general anesthetic should be monitored continuously for expired CO2 and temperature. Acute MH events should be treated immediately with intravenous dantrolene sodium. In virtually all cases, dantrolene rapidly reverses the potentially fatal hypermetabolism and skeletal muscle contracture produced by potent volatile anesthetic agents and/or succinylcholine. Dantrolene sodium should be administered in an initial dose of 2.5 mg/kg and titrated to effect. Dantrolene should be immediately accessible (within 5 minutes) in the office or operating room complex if one ever administers a potent inhalation anesthetic or succinylcholine. Because MH is the subject of active research, once an MH patient has been stabilized with initial treatment, medical personnel should contact the MH hotline consultant for the most up-to-date treatment recommendations. MH-susceptible patients may be safely anesthetized with amide local anesthetics. Potent inhalation anesthetics and succinylcholine must be totally avoided in MH-susceptible patients. Prophylactic dantrolene is generally not indicated unless the patient experiences awake MH episodes. Significant progress has been made in improving the diagnosis of MH susceptibility in patients who have not experienced a fulminant MH episode. A new MH clinical grading scale has been developed by an international MH expert panel. The North American caffeine halothane contracture test has been standardized, and minor modifications yield a test with nearly 100% sensitivity and 80% specificity. A least one molecular genetic defect responsible for MH susceptibility in pigs and humans has been identified. A molecular genetic test that accurately screens individuals preoperatively for MH susceptibility may be available by the end of this decade. The North American Malignant Hyperthermia Registry provides patient-specific clinical information to medical personnel caring for registered MH-susceptible patients. In addition, the Registry accumulates comparative data to support its MH epidemiology studies, including prediction of MH susceptibility and improvement of MH treatment protocols. Dentists, oral surgeons, and nurse-anesthetists should contact the Registry to report acute MH episodes and to obtain information on registering their patients.

Prospects for the diagnosis of malignant hyperthermia susceptibility using molecular genetic approaches.

MHS is a heterogeneous pharmacogenetic disorder in the human that is likely to be caused by one of a variety of genetic defects, in one of a number of genes. Direct molecular methods will provide a rapid, efficient, non-invasive, and low-cost screening test once the causative genetic mutations have been identified. However, until this objective is met, indirect molecular genetic methods can be used to demonstrate the inheritance of an abnormal gene in certain family members at risk. This requires localizing the gene that produces the abnormal phenotype to a subchromosomal segment by linkage analysis and showing the coinheritance of MHS and DNA markers in a number of family members. Indirect molecular genetic methods are likely to be particularly useful in the diagnostic evaluation of children too small to be biopsied in families where others have been biopsied or their phenotypes are known. It appears likely that molecular genetic methods will not eliminate the usefulness of the muscle biopsy and caffeine-halothane contracture test in the near future. Rather, these diagnostic tests will complement one another and significantly improve our understanding of the complexity of this disorder.

Maligne-Hyperthermie-Diagnostik

An eight-year-old boy was scheduled for an orthopaedic operation with a clinically abortive reaction of malignant hyperthermia and a positive platelet test result. Since there has been no validation for this platelet test, we performed a muscle biopsy and the caffeine- halothane-contracture test (CHCT). The young patient was found to be negative (MHN) in CHCT. Furthermore, the valence and the validity of the used platelet test are discussed for diagnostic purposes. With regard to resulting consequences, first of all in respect of possibly false negative results, we suggest to investigate all patients classified by this platelet test with the accepted and established CHCT.

A Comparison of the Caffeine Halothane Muscle Contracture Test with the Molecular Genetic Diagnosis of Malignant Hyperthermia

Malignant hyperthermia (MH) is currently diagnosed by the caffeine-halothane contracture (CHC) test. In a previous study, this test was used to establish linkage between the human gene for MH susceptibility and the ryanodine receptor (RYR) gene. The current study extends the genetic linkage analysis to a large French-Canadian kindred. In this family, genetic linkage between RYR and MH genes was not demonstrable using the currently recommended limits of normal for the CHC test in the identification of MH-susceptible individuals. With CHC test threshold limits below those currently recommended, however, complete linkage between the RYR and MH genes was seen. Comparisons of CHC test results with genetic linkage studies will increase the diagnostic accuracy of both tests as well as generate new insights into the biology of MH.