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Distinct effects on Ca2+ handling caused by malignant hyperthermia and central core disease mutations in RyR1.

ABSTRACT: Malignant hyperthermia (MH) and central core disease (CCD) are disorders of skeletal muscle Ca2+ homeostasis that are linked to mutations in the type 1 ryanodine receptor (RyR1). Certain RyR1 mutations result in an MH-selective phenotype (MH-only), whereas others result in a mixed phenotype (MH + CCD). We characterized effects on Ca2+ handling and excitation-contraction (EC) coupling of MH-only and MH + CCD mutations in RyR1 after expression in skeletal myotubes derived from RyR1-null (dyspedic) mice. Compared to wild-type RyR1-expressing myotubes, MH + CCD- and MH-only-expressing myotubes exhibited voltage-gated Ca2+ release (VGCR) that activated at more negative potentials and displayed a significantly higher incidence of spontaneous Ca2+ oscillations. However, maximal VGCR was reduced only for MH + CCD mutants (Y4795C, R2435L, and R2163H) in which spontaneous Ca2+ oscillations occurred with significantly longer duration (Y4795C and R2435L) or higher frequency (R2163H). Notably, myotubes expressing these MH + CCD mutations in RyR1 exhibited both increased [Ca2+]i and reduced sarcoplasmic reticulum (SR) Ca2+ content. We conclude that MH-only mutations modestly increase basal release-channel activity in a manner insufficient to alter net SR Ca2+ content ("compensated leak"), whereas the mixed MH + CCD phenotype arises from mutations that enhance basal activity to a level sufficient to promote SR Ca2+ depletion, elevate [Ca2+]i, and reduce maximal VGCR ("decompensated leak").

SUBMITTER: Dirksen RT

PROVIDER: S-EPMC1304789 | biostudies-literature | 2004 Nov

REPOSITORIES: biostudies-literature

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Distinct effects on Ca2+ handling caused by malignant hyperthermia and central core disease mutations in RyR1.

Dirksen Robert T RT Avila Guillermo G

Biophysical journal 20040903 5

Malignant hyperthermia (MH) and central core disease (CCD) are disorders of skeletal muscle Ca2+ homeostasis that are linked to mutations in the type 1 ryanodine receptor (RyR1). Certain RyR1 mutations result in an MH-selective phenotype (MH-only), whereas others result in a mixed phenotype (MH + CCD). We characterized effects on Ca2+ handling and excitation-contraction (EC) coupling of MH-only and MH + CCD mutations in RyR1 after expression in skeletal myotubes derived from RyR1-null (dyspedic) ...[more]

PMID: 15347586

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Project description:ImportanceTotal ophthalmoplegia can result from ryanodine receptor 1 (RYR1) mutations without overt associated skeletal myopathy. Patients carrying RYR1 mutations are at high risk of developing malignant hyperthermia. Ophthalmologists should be familiar with these important clinical associations.ObjectiveTo determine the genetic cause of congenital ptosis, ophthalmoplegia, facial paralysis, and mild hypotonia segregating in 2 pedigrees diagnosed with atypical Moebius syndrome or congenital fibrosis of the extraocular muscles.Design, setting, and participantsClinical data including medical and family histories were collected at research laboratories at Boston Children's Hospital and Jules Stein Eye Institute (Engle and Demer labs) for affected and unaffected family members from 2 pedigrees in which patients presented with total ophthalmoplegia, facial weakness, and myopathy.InterventionHomozygosity mapping and whole-exome sequencing were conducted to identify causative mutations in affected family members. Histories, physical examinations, and clinical data were reviewed.Main outcome and measureMutations in RYR1.ResultsMissense mutations resulting in 2 homozygous RYR1 amino acid substitutions (E989G and R3772W) and 2 compound heterozygous RYR1 substitutions (H283R and R3772W) were identified in a consanguineous and a nonconsanguineous pedigree, respectively. Orbital magnetic resonance imaging revealed marked hypoplasia of extraocular muscles and intraorbital cranial nerves. Skeletal muscle biopsy specimens revealed nonspecific myopathic changes. Clinically, the patients' ophthalmoplegia and facial weakness were far more significant than their hypotonia and limb weakness and were accompanied by an unrecognized susceptibility to malignant hyperthermia.Conclusions and relevanceAffected children presenting with severe congenital ophthalmoplegia and facial weakness in the setting of only mild skeletal myopathy harbored recessive mutations in RYR1, encoding the ryanodine receptor 1, and were susceptible to malignant hyperthermia. While ophthalmoplegia occurs rarely in RYR1-related myopathies, these children were atypical because they lacked significant weakness, respiratory insufficiency, or scoliosis. RYR1-associated myopathies should be included in the differential diagnosis of congenital ophthalmoplegia and facial weakness, even without clinical skeletal myopathy. These patients should also be considered susceptible to malignant hyperthermia, a life-threatening anesthetic complication avoidable if anticipated presurgically.

Project description:BackgroundVariants in RYR1, the gene encoding the ryanodine receptor-1, can give rise to a wide spectrum of neuromuscular conditions. Muscle imaging abnormalities have been demonstrated in isolated cases of patients with a history of RYR1-related malignant hyperthermia (MH) susceptibility.ObjectiveTo provide insights into the type and prevalence of muscle ultrasound abnormalities and muscle hypertrophy in patients carrying gain-of-function RYR1 variants associated with MH susceptibility and to contribute to delineating the wider phenotype, optimizing the diagnostic work-up and care for MH susceptible patients.MethodsWe performed a prospective cross-sectional observational muscle ultrasound study in patients with a history of RYR1-related MH susceptibility (n = 40). Study procedures included a standardized history of neuromuscular symptoms and a muscle ultrasound assessment. Muscle ultrasound images were analyzed using a quantitative and qualitative approach and compared to reference values and subsequently subjected to a screening protocol for neuromuscular disorders.ResultsA total of 15 (38%) patients had an abnormal muscle ultrasound result, 4 (10%) had a borderline muscle ultrasound screening result, and 21 (53%) had a normal muscle ultrasound screening result. The proportion of symptomatic patients with an abnormal result (11 of 24; 46%) was not significantly higher compared to the proportion of asymptomatic patients with an abnormal ultrasound result (4 of 16; 25%) (P = 0.182). The mean z-scores of the biceps brachii (z = 1.45; P < 0.001), biceps femoris (z = 0.43; P = 0.002), deltoid (z = 0.31; P = 0.009), trapezius (z = 0.38; P = 0.010) and the sum of all muscles (z = 0.40; P < 0.001) were significantly higher compared to 0, indicating hypertrophy.ConclusionsPatients with RYR1 variants resulting in MH susceptibility often have muscle ultrasound abnormalities. Frequently observed muscle ultrasound abnormalities include muscle hypertrophy and increased echogenicity.

Project description:Abstract Malignant hyperthermia and exertional rhabdomyolysis have conventionally been considered episodic phenotypes that occur in otherwise healthy individuals in response to an external trigger. However, recent studies have demonstrated a clinical and histopathological continuum between patients with a history of malignant hyperthermia susceptibility and/or exertional rhabdomyolysis and RYR1-related congenital myopathies. We hypothesize that patients with a history of RYR1-related exertional rhabdomyolysis or malignant hyperthermia susceptibility do have permanent neuromuscular symptoms between malignant hyperthermia or exertional rhabdomyolysis episodes. We performed a prospective cross-sectional observational clinical study of neuromuscular features in patients with a history of RYR1-related exertional rhabdomyolysis and/or malignant hyperthermia susceptibility (n = 40) compared with healthy controls (n = 80). Patients with an RYR1-related congenital myopathy, manifesting as muscle weakness preceding other symptoms as well as other (neuromuscular) diseases resulting in muscle weakness were excluded. Study procedures included a standardized history of neuromuscular symptoms, a review of all relevant ancillary diagnostic tests performed up to the point of inclusion and a comprehensive, standardized neuromuscular assessment. Results of the standardized neuromuscular history were compared with healthy controls. Results of the neuromuscular assessment were compared with validated reference values. The proportion of patients suffering from cramps (P < 0.001), myalgia (P < 0.001) and exertional myalgia (P < 0.001) was higher compared with healthy controls. Healthcare professionals were consulted because of apparent neuromuscular symptoms by 17/40 (42.5%) patients and 7/80 (8.8%) healthy controls (P < 0.001). Apart from elevated creatine kinase levels in 19/40 (47.5%) patients and mild abnormalities on muscle biopsies identified in 13/16 (81.3%), ancillary investigations were normal in most patients. The Medical Research Council sum score, spirometry and results of functional measurements were also mostly normal. Three of 40 patients (7.5%) suffered from late-onset muscle weakness, most prominent in the proximal lower extremity muscles. Patients with RYR1 variants resulting in malignant hyperthermia susceptibility and/or exertional rhabdomyolysis frequently report additional neuromuscular symptoms such as myalgia and muscle cramps compared with healthy controls. These symptoms result in frequent consultation of healthcare professionals and sometimes in unnecessary invasive diagnostic procedures. Most patients do have normal strength at a younger age but may develop muscle weakness later in life. Van den Bersselaar et al. report that patients with RYR1-related malignant hyperthermia susceptibility and/or exertional rhabdomyolysis frequently report neuromuscular symptoms such as myalgia and muscle cramps. This results in consultation of healthcare professionals and sometimes in unnecessary invasive diagnostic procedures. Graphical Abstract Graphical abstract

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Distinct effects on Ca2+ handling caused by malignant hyperthermia and central core disease mutations in RyR1.

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Distinct effects on Ca2+ handling caused by malignant hyperthermia and central core disease mutations in RyR1.

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