Functional Characterization of Endogenously Expressed Human RYR1 Variants

More than 700 variants in the RYR1 gene have been identified in patients with different neuromuscular disorders including malignant hyperthermia ...

Basel University Hospital

Malignant hyperthermia (MH) is a potentially lethal pharmacogenetic disease, triggered by inhalative anesthetics or depolarizing muscle relaxants in genetically predisposed individuals. Linkage analysis have revealed MH to be a heterogenetic disease with about 50% of MH families linked to the locus of the ryanodine receptor calcium channel (RYR1). We investigated the frequency of the 23 published MH linked RYR1 gene mutations in the Swiss MH population and compared our findings to the results of the in vitro contracture test (IVCT). IVCT was performed following the protocol of the European MH Group and mutation screening was done by PCR amplification of genomic DNA followed by restriction enzyme digestion or SSCP. We identified RYR1 gene mutations in 40% of unrelated MH families (19/48) with a high incidence of the mutation V2168M (27%). IVCT results revealed a significantly stronger functional effect of mutations R614C and V2168M as compared to mutations G2434R and R2458C. This is the first time that such a high incidence of RYR1 gene mutations in an MH population has been found, supporting the use of molecular genetic testing for the diagnosis of MH susceptibility in suitable families. In addition our data show that different RYR1 gene mutations are associated with different IVCT phenotypes.

Genotype-phenotype comparison of the Swiss malignant hyperthermia population.

A 55-year-old man presented for coronary artery bypass graft (CABG) surgery. Malignant hyperthermia (MH) was suspected in his family. This case report describes a diagnostic approach to obtain a definite MH diagnosis by performing an in vitro contracture test at the time of CABG surgery in combination with molecular genetic investigations.

Diagnosis of malignant hyperthermia susceptibility during CABG surgery.

The use of computers in scientific and educational presentations is rapidly increasing. As a digital presentation is ideal for showing moving images, the use of multimedia files, e.g., echocardiographic loops within these presentations, is common. Even though recent echocardiography machines store acquired data in a digital format, these data are often not readily accessible to be transferred to a personal computer. We present an easy and cost-efficient method for transferring frames and loops from any echocardiography machine into a personal computer using a digital video camera equipped with a standard analog input and flash memory. Still images and movies are stored in the camera to be subsequently transferred to a personal computer. In the computer, still images and movies are post-processed with graphical and video editing software. Finally, the still images and movies can be projected from the video camera or presented with specialized software such as PowerPoint. The images can also be used for Web-based publications and production of educational material or books on electronic media such as CD-ROM. The described method can also be used to transfer images from other proprietary devices and programs, as long as the devices are equipped with an analog video outlet.

From the echocardiography machine to the lecture room: a simple method for transferring echocardiographic frames and loops to a personal computer.

For more than 30 yr, the in vitro contracture test (IVCT) was the only appropriate diagnostic tool for malignant hyperthermia (MH). After the introduction of molecular genetics into MH research, guidelines for molecular genetic diagnosis of MH susceptibility were published. The aim of this study was to establish applicability of the guidelines, sensitivity, and specificity of genetic testing in MH and advantages for studied patients.

Molecular genetic testing for malignant hyperthermia susceptibility.

Dosing of midazolam in neonates.

Ropivacaine might be superior to bupivcaine for epidural labour analgesia because it appears to induce less lower extremity motor blockade. The clinical relevance of this difference is not yet clear.

Ropivacaine versus bupivacaine 0.125% with fentanyl 1 microg/ml for epidural labour analgesia: is daily practice more important than pharmaceutical choice?

A 37-yr-old patient scheduled for elective bursectomy developed fulminant malignant hyperthermia (MH) under sevoflurane anesthesia. The first sign was a dramatic increase in end-tidal CO(2). Symptomatic and specific therapy was rapidly instituted. Postoperative rhabdomyolysis was treated with veno-venous hemofiltration. The patient rejected open muscle biopsy for in vitro contracture testing. Therefore, molecular testing was performed. An infrequent MH causative mutation was identified on the ryanodine receptor gene. This case report confirms the causative nature of this mutation. It also shows that molecular genetic investigation may be as appropriate as in vitro contracture testing to confirm the diagnosis after a clinical episode of MH.

A fulminant malignant hyperthermia episode in a patient with ryanodine receptor gene mutation p.Tyr522Ser.

Prolonged depolarization of skeletal muscle cells induces entry of extracellular calcium into muscle cells, an event referred to as excitation-coupled calcium entry. Skeletal muscle excitation-coupled calcium entry relies on the interaction between the 1,4-dihydropyridine receptor on the sarcolemma and the ryanodine receptor on the sarcoplasmic reticulum membrane. In this study, we directly measured excitation-coupled calcium entry by total internal reflection fluorescence microscopy in human skeletal muscle myotubes harbouring mutations in the RYR1 gene linked to malignant hyperthermia (MH) and central core disease (CCD). We found that excitation-coupled calcium entry is strongly enhanced in cells from patients with CCD compared with individuals with MH and controls. Furthermore, excitation-coupled calcium entry induces generation of reactive nitrogen species and enhances nuclear localization of NFATc1, which in turn may be responsible for the increased IL-6 released by myotubes from patients with CCD.

Enhanced excitation-coupled Ca(2+) entry induces nuclear translocation of NFAT and contributes to IL-6 release from myotubes from patients with central core disease.

JP-45 (also JP45; encoded by JSRP1) is an integral protein constituent of the skeletal muscle sarcoplasmic reticulum junctional face membrane interacting with Ca(v) 1.1 (the α.1 subunit of the voltage-sensing dihydropyridine receptor, DHPR) and the luminal calcium-binding protein calsequestrin. Two JSRP1 variants have been found in the human population: c.323C>T (p.P108L) in exon 5 and c.449G>C (p.G150A) in exon 6, but nothing is known concerning the incidence of these polymorphisms in the general population or in patients with neuromuscular diseases nor the impact of the polymorphisms on excitation-contraction (EC) coupling. In the present report, we investigated the frequencies of these two JSRP1 polymorphisms in the Swiss malignant hyperthermia population and studied the functional impact of the variants on EC coupling. Our results show that the polymorphisms are equally distributed among malignant hyperthermia negative, malignant hyperthermia equivocal, and malignant hyperthermia susceptible individuals. Interestingly, however, the presence of either one of these JP-45 variants decreased the sensitivity of the DHPR to activation. The presence of a JSRP1 variant may explain the variable phenotype seen in patients with malignant hyperthermia carrying the same mutation and, more importantly, may counteract the hypersensitivity of EC coupling caused by mutations in the RYR1 gene.

JP-45/JSRP1 variants affect skeletal muscle excitation-contraction coupling by decreasing the sensitivity of the dihydropyridine receptor.

The risk profile of patients in obstetric anesthesia has substantially changed. Even more so than other disciplines, obstetric anesthesia is therefore in the true sense of the word dependent on the close coordination of all concerned and a good interdisciplinary cooperation.

[New aspects of obstetric anesthesia].

Parenteral opioids have been used in labour analgesia for many years, but the ideal opioid in this setting is yet to be found. We review the properties of currently used opioids, their analgesic properties and side effects to mother and foetus. Parenteral opioids can be administered as intermittent boluses or through a patient-controlled intravenous administration system. A wide range of opioid drugs are currently used and provide a variable degree of analgesia. All opioids can cause unwanted maternal side effects such as nausea, vomiting, sedation and respiratory depression. They cross the placenta and have the potential to cause neonatal respiratory depression. Remifentanil patient-controlled intravenous analgesia is becoming increasingly available and popular on some delivery suites. It can provide adequate analgesia and is useful when epidural analgesia is contraindicated. Remifentanil patient-controlled analgesia requires close monitoring in an environment familiar with the technique to avoid maternal hypoxia due to respiratory depression.

Thierry Girard

Department of Anesthesia

Basel University Hospital

Functional Characterization of Endogenously Expressed Human RYR1 Variants

Thierry Girard

.css-o250i3{font-size:18px;font-family:Open Sans,sans-serif;line-height:21.6px;}Department of Anesthesia

Basel University Hospital

Functional Characterization of Endogenously Expressed Human RYR1 Variants

Department of Anesthesia