Acupuncture was carried out on a patient with rheumatoid arthritis and microangiopathy of the low... more Acupuncture was carried out on a patient with rheumatoid arthritis and microangiopathy of the lower limbs. Photoplethysmographic waves appeared at the right inferior limb where before they had been absent; at the left inferior limb normalization of postural reflexes was achieved, suggesting that acupuncture is effective in vasodilatation of capillaries and preterminal arterioles and in the reactivation of the arterio-venous blood flow.
Agressologie: revue internationale de physio-biologie et de pharmacologie appliquées aux effets de l'agression, 1979
Normal and thymectomised rabbits been have immunized by means of a thymic extract emulsified with... more Normal and thymectomised rabbits been have immunized by means of a thymic extract emulsified with Freund's Complete Adjuvant. The experiment was conducted over a three month period, in order to reproduce an experimental model of chronic myasthenia. During this period immunological, electromyographic and histologic studies were undertaken. Typical findings of partial neuromuscular block were invariably obtained from all the non thymectomized animals, while such signs were constantly absent both in non-treated control rabbits and in the immunized thymectomized ones. This neuromuscular block was intermittent. The compromised neuromuscular conduction was associated to an histological pattern of autoimmune myopathy. Evidence was put on antibodies directed against the thymus, muscular and nervous tissue. The results indicate the important role of the thymus gland both in altering conduction at the neuromuscular junction level and causing histopathologic muscle lesions.
In the present study we investigated the effect of the compound chlorocresol on intracellular Ca2... more In the present study we investigated the effect of the compound chlorocresol on intracellular Ca2+ homeostasis. Three different systems that have been shown to express the ryanodine receptor Ca2+ channel were chosen, i.e., skeletal muscle sarcoplasmic reticulum, cerebellar microsomes, and PC12 cells. In skeletal muscle sarcoplasmic reticulum, 4-chloro-m-cresol was found to be a potent activator of Ca2+ release mediated by a ruthenium red/caffeine-sensitive Ca2+ release channel. In cerebellar microsomes, this compound released Ca2+ from an inositol-1,4,5-trisphosphate-insensitive store, suggesting that there too it was acting at the ryanodine receptor level. When tested on PC12 cells, chlorocresol released Ca2+ from a caffeine- and thapsigargin-sensitive intracellular store. In addition, the compound was capable of releasing Ca2+ after pretreatment of PC12 cells with bradykinin, suggesting that it acts on a channel contained within an intracellular Ca2+ store that is distinct from th...
Calcitonin induces contraction in the vascular and extravascular smooth muscle and facilitates th... more Calcitonin induces contraction in the vascular and extravascular smooth muscle and facilitates the transmission of the excitation in somatic motor nerve endings. These actions are Ca2(+)-dependent. The calcitonin effect on autonomic nerve endings has been studied here by testing influence of calcitonin on the contractile responses of the isolated rat stomach. The organ was submitted to electrical vagal stimulation or, after denervation, to exogenous acetylcholine. Calcitonin invariably increased the muscular tone and reduced the contractile responses to vagal stimulation. Opposite effects were noted after a serotoninergic block with nicergoline. Calcitonin also increased the contractile response evoked by exogenous acetylcholine and the Ca(2)-antagonist nicardipine counteracted the facilitatory effects. We suggest that the inhibitory action of calcitonin is serotonine-dependent while the facilitatory one is Ca2(+)-dependent.
The results of the analgesic block of the lower extremity by means of an anterior (150 patients) ... more The results of the analgesic block of the lower extremity by means of an anterior (150 patients) or a posterior (114 patients) approach to the sciatic nerve, associated to a "3 in 1 block" were compared. The anterior approach technique was associated with a higher incidence of failures, insufficient analgesia and hence a higher demand for intraoperative analgesic and sedative drugs. Also tolerance to a pneumatic tourniquet over the proximal thigh was less than with the posterior approach. However, the sciatic nerve block by anterior approach granted a more prolonged analgesia. This technique was suitable for trauma patients immobilized in the supine position, for patients with skeletal traction on Zupinger frame, both for surgery and for closed reduction of lower extremity fractures.
Malignant hyperthermia (MH) is a rare clinical syndrome, triggered in susceptible subjects by a v... more Malignant hyperthermia (MH) is a rare clinical syndrome, triggered in susceptible subjects by a variety of anaesthetic agents and muscle relaxants, and is the commonest cause of death due to general anaesthesia. Previous studies have reported that inherited mutations in the ryanodine receptor (RYR1) gene co-segregated, in some families, with MH susceptibility; lack of linkage between MH and the RYR1 gene in some other families indicates a heterogenous genetic basis for the syndrome. The in vitro contracture test (IVCT) on muscle biopsy specimens is considered to be the most reliable test for establishing the diagnosis of MH. With the identification of RYR1 point mutations this might in turn result in non-invasive methods for the presymptomatic diagnosis of MH. In the present study we investigated four families suspected to be at risk of MH susceptibility; in all subjects histopathological examination and IVCT were performed on muscle biopsy specimens. We undertook a mutation analysis of RYR1 gene testing for the presence of five point mutations; in one pedigree a C1840-->T point mutation was detected, strictly segregating with in vitro MH susceptibility.
... Manning, BM, Quane, KA, Lynch, PJ, Urwyler, A., Tegazzin, V., Krivosic-Horber, R., Censier, K... more ... Manning, BM, Quane, KA, Lynch, PJ, Urwyler, A., Tegazzin, V., Krivosic-Horber, R., Censier, K.,Comi, G., Adnet, P., Wolz, W., Lunardi, J., Muller, CR and McCarthy, TV (1998), Novel mutations at a CpG dinucleotide in the ryanodine receptor in malignant hyperthermia. ...
The in vitro contracture test with halothane and caffeine is the gold standard for the diagnosis ... more The in vitro contracture test with halothane and caffeine is the gold standard for the diagnosis of susceptibility to malignant hyperthermia (MH). However, the sensitivity of the in vitro contracture test is between 97 and 99% and its specificity is 78-94% with the consequence that false-negative as well as false-positive test results are possible. 4-Chloro-m-cresol is potentially a more specific test drug for the in vitro contracture test than halothane or caffeine. This multicentre study was designed to investigate whether an in vitro contracture test with bolus administration of 4-chloro-m-cresol can improve the accuracy of the diagnosis of susceptibility to MH. Three hundred and fifty-two patients from 11 European MH laboratories participated in the study. The patients were first classified as MH susceptible, MH normal or MH equivocal by the in vitro contracture test according to the European MH protocol. Muscle specimens surplus to diagnostic requirements were used in this study (MH susceptible = 103 viable samples; MH equivocal = 51; MH normal = 204). 4-Chloro-m-cresol was added to achieve a concentration of 75 micromol L(-1) in the tissue bath. The in vitro effects on contracture development and muscle twitch were observed for 60 min. After bolus administration of 4-chloro-m-cresol, 75 micromol L(-1), 99 of 103 MH-susceptible specimens developed marked muscle contractures. In contrast, only two of 204 MH-normal specimens showed an insignificant contracture development following 4-chloro-m-cresol. From these results, a sensitivity rate of 96.1% and a specificity rate of 99.0% can be calculated for the in vitro contracture test with bolus administration of 4-chloro-m-cresol 75 micromol L(-1). Forty-three patients were diagnosed as MH equivocal, but only specimens from 16 patients developed contractures in response to 4-chloro-m-cresol, indicating susceptibility to MH. The in vitro contracture test with halothane and caffeine is well standardized in the European and North American test protocols. However, this conventional test method is associated with the risk of false test results. Therefore, an improvement in the diagnosis of MH is needed. Regarding the results from this multicentre study, the use of 4-chloro-m-cresol could increase the reliability of in vitro contracture testing.
The sarcoplasmic reticulum (SR) controls uptake and release of Ca2+ in muscle. Little information... more The sarcoplasmic reticulum (SR) controls uptake and release of Ca2+ in muscle. Little information is available regarding the effect of volatile anesthetics on Ca2+ release from SR isolated from normal skeletal muscle, even though an abnormality of Ca2+ handling is implicated in malignant hyperthermia. In this study we used a Ca2+ electrode to monitor continuously the release of Ca2+ from SR and the effect of volatile anesthetics on this process. We found that halothane, enflurane, and isoflurane at 0.6, 0.7, and 0.8 vol%, respectively, each increased the velocity of Ca2+ leakage by at least 150% when compared to control. Ruthenium red, a blocker of the SR Ca(2+)-release channel, was shown to have no effect on the velocity of Ca2+ leakage. Halothane and isoflurane both shortened the time at which Ca2+ leakage began (T) in a dose-dependent fashion. Halothane at 4.8 vol% decreased T from 293 +/- 21 s to 149 +/- 20 s. Isoflurane (4.8 vol%) decreased T to 203 +/- 16 s, and enflurane at 5 vol% had little effect, decreasing T to 259 +/- 19 s. We noted a marked stimulation in the ATPase activity of the SR by all three volatile anesthetics. Halothane at 0.63 vol%, isoflurane at 0.42 vol%, and enflurane at 0.62 vol% each increased ATPase activity by at least 300%. We conclude that the stimulation of the velocity of Ca2+ leakage by the volatile anesthetics is related to the more rapid depletion of ATP, but that the shortening of the onset of Ca2+ leakage is a independent phenomenon with a markedly different dose dependence.(ABSTRACT TRUNCATED AT 250 WORDS)
A defect in the ryanodine (Ry1) receptor Ca2+ channel has been implicated as one of the possible ... more A defect in the ryanodine (Ry1) receptor Ca2+ channel has been implicated as one of the possible underlying causes of malignant hyperthermia (MH), a pharmacogenetic disorder characterized by sustained muscle contracture. The disease is triggered by common halogenated anesthetics and skeletal muscle relaxants, such as succinylcholine. This study tested whether the functional properties of the Ry1 receptor Ca2+ channel are affected by chlorocresol, a preservative added to a commercial preparation of succinylcholine (Midarine) and other parenteral compounds. In vitro contracture testing was carried out on muscle biopsies from malignant hyperthermia-susceptible (MHS) and -negative (MHN) individual according to the protocol of the European MH group. Ca2+ flux studies on isolated rabbit sarcoplasmic reticulum fractions were measured spectrophotometrically by following the A710-790 of the Ca2+ indicator antipyrylazo III. Chlorocresol causes muscle contracture in MHS muscles at a concentration of 25-50 microM and potentiates the caffeine contracture response in human MHS muscles. Sub-threshold (20 microM) concentrations of chlorocresol increase both the Kd and the Vmax of caffeine-induced Ca2+ release from isolated rabbit terminal cisternae. These data suggest that, in muscle from MHS individuals, the enhanced Ca2+ released from the sarcoplasmic reticulum may not be due to the effect of succinylcholine alone but rather to the action of the preservative chlorocresol added to the drug.
A novel single-nucleotide deletion in exon 100 of the RYR1 gene, corresponding to deletion of nuc... more A novel single-nucleotide deletion in exon 100 of the RYR1 gene, corresponding to deletion of nucleotide 14,510 in the human RyR1 mRNA (c14510delA), was identified in a man with malignant hyperthermia and in his two daughters who were normal for malignant hyperthermia. This deletion results in a RyR1 protein lacking the last 202 amino acid residues. All three subjects heterozygotic for the mutated allele presented with a prevalence of type 1 fibres with central cores, although none experienced clinical signs of myopathy. Expression of the truncated protein resulted in non-functional RYR1 calcium release channels. Expression of wild-type and RyR1(R4836fsX4838) proteins resulted in heterozygotic release channels with overall functional properties similar to those of wild-type RyR1 channels. Nevertheless, small differences in sensitivity to calcium and caffeine were observed in heterotetrameric channels, which also presented an altered assembly/stability in sucrose-gradient centrifugation analysis. Altogether, these data suggest that altered RYR1 tetramer assembly/stability coupled with subtle chronic changes in Ca2+ homoeostasis over the long term may contribute to the development of core lesions and incomplete malignant hyperthermia susceptibility penetrance in individuals carrying this novel RYR1 mutation.
Malignant hyperthermia (MH) is a condition that manifests in susceptible individuals only on expo... more Malignant hyperthermia (MH) is a condition that manifests in susceptible individuals only on exposure to certain anaesthetic agents. Although genetically heterogeneous, mutations in the RYR1 gene (19q13.1) are associated with the majority of reported MH cases. Guidelines for the genetic diagnosis for MH susceptibility have recently been introduced by the European MH Group (EMHG). These are designed to supplement the muscle biopsy testing procedure, the in vitro contracture test (IVCT), which has been the only means of patient screening for the last 30 years and which remains the method for definitive diagnosis in suspected probands. Discordance observed in some families between IVCT phenotype and susceptibility locus genotype could limit the confidence in genetic diagnosis. We have therefore assessed the prevalence of 15 RYR1 mutations currently used in the genetic diagnosis of MH in a sample of over 500 unrelated European MH susceptible individuals and have recorded the frequency of RYR1 genotype/IVCT phenotype discordance. RYR1 mutations were detected in up to approximately 30% of families investigated. Phenotype/genotype discordance in a single individual was observed in 10 out of 196 mutation-positive families. In five families a mutation-positive/IVCT-negative individual was observed, and in the other five families a mutation-negative/IVCT-positive individual was observed. These data represent the most comprehensive assessment of RYR1 mutation prevalence and genotype/phenotype correlation analysis and highlight the possible limitations of MH screening methods. The implications for genetic diagnosis are discussed.
Acupuncture was carried out on a patient with rheumatoid arthritis and microangiopathy of the low... more Acupuncture was carried out on a patient with rheumatoid arthritis and microangiopathy of the lower limbs. Photoplethysmographic waves appeared at the right inferior limb where before they had been absent; at the left inferior limb normalization of postural reflexes was achieved, suggesting that acupuncture is effective in vasodilatation of capillaries and preterminal arterioles and in the reactivation of the arterio-venous blood flow.
Agressologie: revue internationale de physio-biologie et de pharmacologie appliquées aux effets de l'agression, 1979
Normal and thymectomised rabbits been have immunized by means of a thymic extract emulsified with... more Normal and thymectomised rabbits been have immunized by means of a thymic extract emulsified with Freund's Complete Adjuvant. The experiment was conducted over a three month period, in order to reproduce an experimental model of chronic myasthenia. During this period immunological, electromyographic and histologic studies were undertaken. Typical findings of partial neuromuscular block were invariably obtained from all the non thymectomized animals, while such signs were constantly absent both in non-treated control rabbits and in the immunized thymectomized ones. This neuromuscular block was intermittent. The compromised neuromuscular conduction was associated to an histological pattern of autoimmune myopathy. Evidence was put on antibodies directed against the thymus, muscular and nervous tissue. The results indicate the important role of the thymus gland both in altering conduction at the neuromuscular junction level and causing histopathologic muscle lesions.
In the present study we investigated the effect of the compound chlorocresol on intracellular Ca2... more In the present study we investigated the effect of the compound chlorocresol on intracellular Ca2+ homeostasis. Three different systems that have been shown to express the ryanodine receptor Ca2+ channel were chosen, i.e., skeletal muscle sarcoplasmic reticulum, cerebellar microsomes, and PC12 cells. In skeletal muscle sarcoplasmic reticulum, 4-chloro-m-cresol was found to be a potent activator of Ca2+ release mediated by a ruthenium red/caffeine-sensitive Ca2+ release channel. In cerebellar microsomes, this compound released Ca2+ from an inositol-1,4,5-trisphosphate-insensitive store, suggesting that there too it was acting at the ryanodine receptor level. When tested on PC12 cells, chlorocresol released Ca2+ from a caffeine- and thapsigargin-sensitive intracellular store. In addition, the compound was capable of releasing Ca2+ after pretreatment of PC12 cells with bradykinin, suggesting that it acts on a channel contained within an intracellular Ca2+ store that is distinct from th...
Calcitonin induces contraction in the vascular and extravascular smooth muscle and facilitates th... more Calcitonin induces contraction in the vascular and extravascular smooth muscle and facilitates the transmission of the excitation in somatic motor nerve endings. These actions are Ca2(+)-dependent. The calcitonin effect on autonomic nerve endings has been studied here by testing influence of calcitonin on the contractile responses of the isolated rat stomach. The organ was submitted to electrical vagal stimulation or, after denervation, to exogenous acetylcholine. Calcitonin invariably increased the muscular tone and reduced the contractile responses to vagal stimulation. Opposite effects were noted after a serotoninergic block with nicergoline. Calcitonin also increased the contractile response evoked by exogenous acetylcholine and the Ca(2)-antagonist nicardipine counteracted the facilitatory effects. We suggest that the inhibitory action of calcitonin is serotonine-dependent while the facilitatory one is Ca2(+)-dependent.
The results of the analgesic block of the lower extremity by means of an anterior (150 patients) ... more The results of the analgesic block of the lower extremity by means of an anterior (150 patients) or a posterior (114 patients) approach to the sciatic nerve, associated to a "3 in 1 block" were compared. The anterior approach technique was associated with a higher incidence of failures, insufficient analgesia and hence a higher demand for intraoperative analgesic and sedative drugs. Also tolerance to a pneumatic tourniquet over the proximal thigh was less than with the posterior approach. However, the sciatic nerve block by anterior approach granted a more prolonged analgesia. This technique was suitable for trauma patients immobilized in the supine position, for patients with skeletal traction on Zupinger frame, both for surgery and for closed reduction of lower extremity fractures.
Malignant hyperthermia (MH) is a rare clinical syndrome, triggered in susceptible subjects by a v... more Malignant hyperthermia (MH) is a rare clinical syndrome, triggered in susceptible subjects by a variety of anaesthetic agents and muscle relaxants, and is the commonest cause of death due to general anaesthesia. Previous studies have reported that inherited mutations in the ryanodine receptor (RYR1) gene co-segregated, in some families, with MH susceptibility; lack of linkage between MH and the RYR1 gene in some other families indicates a heterogenous genetic basis for the syndrome. The in vitro contracture test (IVCT) on muscle biopsy specimens is considered to be the most reliable test for establishing the diagnosis of MH. With the identification of RYR1 point mutations this might in turn result in non-invasive methods for the presymptomatic diagnosis of MH. In the present study we investigated four families suspected to be at risk of MH susceptibility; in all subjects histopathological examination and IVCT were performed on muscle biopsy specimens. We undertook a mutation analysis of RYR1 gene testing for the presence of five point mutations; in one pedigree a C1840-->T point mutation was detected, strictly segregating with in vitro MH susceptibility.
... Manning, BM, Quane, KA, Lynch, PJ, Urwyler, A., Tegazzin, V., Krivosic-Horber, R., Censier, K... more ... Manning, BM, Quane, KA, Lynch, PJ, Urwyler, A., Tegazzin, V., Krivosic-Horber, R., Censier, K.,Comi, G., Adnet, P., Wolz, W., Lunardi, J., Muller, CR and McCarthy, TV (1998), Novel mutations at a CpG dinucleotide in the ryanodine receptor in malignant hyperthermia. ...
The in vitro contracture test with halothane and caffeine is the gold standard for the diagnosis ... more The in vitro contracture test with halothane and caffeine is the gold standard for the diagnosis of susceptibility to malignant hyperthermia (MH). However, the sensitivity of the in vitro contracture test is between 97 and 99% and its specificity is 78-94% with the consequence that false-negative as well as false-positive test results are possible. 4-Chloro-m-cresol is potentially a more specific test drug for the in vitro contracture test than halothane or caffeine. This multicentre study was designed to investigate whether an in vitro contracture test with bolus administration of 4-chloro-m-cresol can improve the accuracy of the diagnosis of susceptibility to MH. Three hundred and fifty-two patients from 11 European MH laboratories participated in the study. The patients were first classified as MH susceptible, MH normal or MH equivocal by the in vitro contracture test according to the European MH protocol. Muscle specimens surplus to diagnostic requirements were used in this study (MH susceptible = 103 viable samples; MH equivocal = 51; MH normal = 204). 4-Chloro-m-cresol was added to achieve a concentration of 75 micromol L(-1) in the tissue bath. The in vitro effects on contracture development and muscle twitch were observed for 60 min. After bolus administration of 4-chloro-m-cresol, 75 micromol L(-1), 99 of 103 MH-susceptible specimens developed marked muscle contractures. In contrast, only two of 204 MH-normal specimens showed an insignificant contracture development following 4-chloro-m-cresol. From these results, a sensitivity rate of 96.1% and a specificity rate of 99.0% can be calculated for the in vitro contracture test with bolus administration of 4-chloro-m-cresol 75 micromol L(-1). Forty-three patients were diagnosed as MH equivocal, but only specimens from 16 patients developed contractures in response to 4-chloro-m-cresol, indicating susceptibility to MH. The in vitro contracture test with halothane and caffeine is well standardized in the European and North American test protocols. However, this conventional test method is associated with the risk of false test results. Therefore, an improvement in the diagnosis of MH is needed. Regarding the results from this multicentre study, the use of 4-chloro-m-cresol could increase the reliability of in vitro contracture testing.
The sarcoplasmic reticulum (SR) controls uptake and release of Ca2+ in muscle. Little information... more The sarcoplasmic reticulum (SR) controls uptake and release of Ca2+ in muscle. Little information is available regarding the effect of volatile anesthetics on Ca2+ release from SR isolated from normal skeletal muscle, even though an abnormality of Ca2+ handling is implicated in malignant hyperthermia. In this study we used a Ca2+ electrode to monitor continuously the release of Ca2+ from SR and the effect of volatile anesthetics on this process. We found that halothane, enflurane, and isoflurane at 0.6, 0.7, and 0.8 vol%, respectively, each increased the velocity of Ca2+ leakage by at least 150% when compared to control. Ruthenium red, a blocker of the SR Ca(2+)-release channel, was shown to have no effect on the velocity of Ca2+ leakage. Halothane and isoflurane both shortened the time at which Ca2+ leakage began (T) in a dose-dependent fashion. Halothane at 4.8 vol% decreased T from 293 +/- 21 s to 149 +/- 20 s. Isoflurane (4.8 vol%) decreased T to 203 +/- 16 s, and enflurane at 5 vol% had little effect, decreasing T to 259 +/- 19 s. We noted a marked stimulation in the ATPase activity of the SR by all three volatile anesthetics. Halothane at 0.63 vol%, isoflurane at 0.42 vol%, and enflurane at 0.62 vol% each increased ATPase activity by at least 300%. We conclude that the stimulation of the velocity of Ca2+ leakage by the volatile anesthetics is related to the more rapid depletion of ATP, but that the shortening of the onset of Ca2+ leakage is a independent phenomenon with a markedly different dose dependence.(ABSTRACT TRUNCATED AT 250 WORDS)
A defect in the ryanodine (Ry1) receptor Ca2+ channel has been implicated as one of the possible ... more A defect in the ryanodine (Ry1) receptor Ca2+ channel has been implicated as one of the possible underlying causes of malignant hyperthermia (MH), a pharmacogenetic disorder characterized by sustained muscle contracture. The disease is triggered by common halogenated anesthetics and skeletal muscle relaxants, such as succinylcholine. This study tested whether the functional properties of the Ry1 receptor Ca2+ channel are affected by chlorocresol, a preservative added to a commercial preparation of succinylcholine (Midarine) and other parenteral compounds. In vitro contracture testing was carried out on muscle biopsies from malignant hyperthermia-susceptible (MHS) and -negative (MHN) individual according to the protocol of the European MH group. Ca2+ flux studies on isolated rabbit sarcoplasmic reticulum fractions were measured spectrophotometrically by following the A710-790 of the Ca2+ indicator antipyrylazo III. Chlorocresol causes muscle contracture in MHS muscles at a concentration of 25-50 microM and potentiates the caffeine contracture response in human MHS muscles. Sub-threshold (20 microM) concentrations of chlorocresol increase both the Kd and the Vmax of caffeine-induced Ca2+ release from isolated rabbit terminal cisternae. These data suggest that, in muscle from MHS individuals, the enhanced Ca2+ released from the sarcoplasmic reticulum may not be due to the effect of succinylcholine alone but rather to the action of the preservative chlorocresol added to the drug.
A novel single-nucleotide deletion in exon 100 of the RYR1 gene, corresponding to deletion of nuc... more A novel single-nucleotide deletion in exon 100 of the RYR1 gene, corresponding to deletion of nucleotide 14,510 in the human RyR1 mRNA (c14510delA), was identified in a man with malignant hyperthermia and in his two daughters who were normal for malignant hyperthermia. This deletion results in a RyR1 protein lacking the last 202 amino acid residues. All three subjects heterozygotic for the mutated allele presented with a prevalence of type 1 fibres with central cores, although none experienced clinical signs of myopathy. Expression of the truncated protein resulted in non-functional RYR1 calcium release channels. Expression of wild-type and RyR1(R4836fsX4838) proteins resulted in heterozygotic release channels with overall functional properties similar to those of wild-type RyR1 channels. Nevertheless, small differences in sensitivity to calcium and caffeine were observed in heterotetrameric channels, which also presented an altered assembly/stability in sucrose-gradient centrifugation analysis. Altogether, these data suggest that altered RYR1 tetramer assembly/stability coupled with subtle chronic changes in Ca2+ homoeostasis over the long term may contribute to the development of core lesions and incomplete malignant hyperthermia susceptibility penetrance in individuals carrying this novel RYR1 mutation.
Malignant hyperthermia (MH) is a condition that manifests in susceptible individuals only on expo... more Malignant hyperthermia (MH) is a condition that manifests in susceptible individuals only on exposure to certain anaesthetic agents. Although genetically heterogeneous, mutations in the RYR1 gene (19q13.1) are associated with the majority of reported MH cases. Guidelines for the genetic diagnosis for MH susceptibility have recently been introduced by the European MH Group (EMHG). These are designed to supplement the muscle biopsy testing procedure, the in vitro contracture test (IVCT), which has been the only means of patient screening for the last 30 years and which remains the method for definitive diagnosis in suspected probands. Discordance observed in some families between IVCT phenotype and susceptibility locus genotype could limit the confidence in genetic diagnosis. We have therefore assessed the prevalence of 15 RYR1 mutations currently used in the genetic diagnosis of MH in a sample of over 500 unrelated European MH susceptible individuals and have recorded the frequency of RYR1 genotype/IVCT phenotype discordance. RYR1 mutations were detected in up to approximately 30% of families investigated. Phenotype/genotype discordance in a single individual was observed in 10 out of 196 mutation-positive families. In five families a mutation-positive/IVCT-negative individual was observed, and in the other five families a mutation-negative/IVCT-positive individual was observed. These data represent the most comprehensive assessment of RYR1 mutation prevalence and genotype/phenotype correlation analysis and highlight the possible limitations of MH screening methods. The implications for genetic diagnosis are discussed.
Uploads
Papers by V. Tegazzin