Assessing the pathogenicity of RYR1 variants in malignant hyperthermia.

BACKGROUND: . Missense variants in the ryanodine receptor 1 gene ( RYR1 ) are associated with malignant hyperthermia but only a minority of these have met the criteria for use in predictive DNA diagnosis. We examined the utility of a simplified method of segregation analysis and a functional assay for determining the pathogenicity of recurrent RYR1 variants associated with malignant hyperthermia. METHODS: . We identified previously uncharacterised RYR1 variants found in four or more malignant hyperthermia families and conducted simplified segregation analyses. An efficient cloning and mutagenesis strategy was used to express ryanodine receptor protein containing one of six RYR1 variants in HEK293 cells. Caffeine-induced calcium release, measured using a fluorescent calcium indicator, was compared in cells expressing each variant to that in cells expressing wild type ryanodine receptor protein. RESULTS.: We identified 43 malignant hyperthermia families carrying one of the six RYR1 variants. There was segregation of genotype with the malignant hyperthermia susceptibility phenotype in families carrying the p.E3104K and p.D3986E variants, but the number of informative meioses limited the statistical significance of the associations. HEK293 functional assays demonstrated an increased sensitivity of RyR1 channels containing the p.R2336H, p.R2355W, p.E3104K, p.G3990V and p.V4849I compared with wild type, but cells expressing p.D3986E had a similar caffeine sensitivity to cells expressing wild type RyR1. CONCLUSIONS: . Segregation analysis is of limited value in assessing pathogenicity of RYR1 variants in malignant hyperthermia. Functional analyses in HEK293 cells provided evidence to support the use of p.R2336H, p.R2355W, p.E3104K, p.G3990V and p.V4849I for diagnostic purposes but not p.D3986E.

Comparison of pathogenicity prediction tools on missense variants in RYR1 and CACNA1S associated with malignant hyperthermia.

BACKGROUND: Malignant hyperthermia (MH) is a pharmacogenetic disorder that has been linked to the skeletal muscle calcium release channel (RYR1) and the α1S subunit of the voltage-dependent L-type calcium channel (CACNA1S). Genomic DNA capture and next generation sequencing are becoming the preferred method to identify mutations in these genes. Bioinformatic pathogenicity prediction of identified variants may help to determine if these variants are in fact disease causing. METHODS: Eight pathogenicity prediction programmes freely available on the web were used to determine their ability to correctly predict the impact of a missense variant on RyR1 or dihydropyridine receptor (DHPR) protein function. We tested MH-causative variants, variants that had been shown to alter calcium release in cells, and common sequence variants in RYR1 and CACNA1S. RESULTS: None of the prediction programmes was able to identify all of the variants tested correctly as either 'damaging' (MH-causative variants, variants that had been shown to alter calcium release in cells) or as 'benign' (common sequence variants). The overall sensitivity of predictions ranged from 84% to 100% depending on the programme used, with specificity from 25% to 83%. CONCLUSIONS: In this study we determined the sensitivity and specificity of bioinformatic pathogenicity prediction tools for RYR1 and CACNA1S. We suggest that the prediction results should be treated with caution, as none of the programmes tested predicted all the variants correctly and should only be used in combination with other available data (functional assays, segregation analysis).

Sequence capture and massively parallel sequencing to detect mutations associated with malignant hyperthermia.

BACKGROUND: Malignant hyperthermia (MH) is a potentially fatal pharmacogenetic disorder in which intracellular calcium homeostasis in the skeletal muscle of susceptible individuals is disrupted upon exposure to halogenated anaesthetics. While MH is linked to the ryanodine receptor (RYR1) on chromosome 19 and the α1S subunit of the voltage-dependent L-type calcium channel (CACNA1S) on chromosome 1, mutations have been found in only 50-70% of patients, and subsequently, there is a need for a more powerful screening tool. METHODS: Genomic DNA capture and next-generation sequencing was used to screen 32 genes involved in excitation-contraction coupling, skeletal muscle calcium homeostasis, or immune response in two MH patients. Lymphoblastoid cell lines were used to functionally characterize candidate RYR1 mutations in one family. RESULTS: Sequence analysis revealed two putative causative mutations in RYR1 in one patient. Segregation analysis and functional analysis support a causative role of the detected variants. The amount of Ca(2+) released after stimulation with 4-chloro-m-cresol from B lymphocytes of the MH-susceptible patients in the family was significantly greater compared with that of Ca(2+) released from cells of an MH-negative family member. In the other patient, no causative mutations were identified in the 32 genes screened. CONCLUSIONS: In this study, we successfully demonstrate the use of genomic DNA capture and next-generation sequencing for identification of putative mutations causing MH. We also suggest that whole exome sequencing may be necessary to identify MH causing mutations in patients where no mutations in RYR1 and CACNA1S have been identified thus far.

Recovery from hemophilia B Leyden: an androgen-responsive element in the factor IX promoter.

One form of the inherited, X-linked, bleeding disorder, hemophilia B, resolves after puberty. Mutations at -20 and -26 in the clotting factor IX promoter impair transcription by disrupting the binding site for the liver-enriched transcription factor LF-A1/HNF4. The -26 but not the -20 mutation also disrupts an androgen-responsive element, which overlaps the LF-A1/HNF4 site. This explains the improvement seen in patients with the -20 mutation and the failure of the -26 patient to recover.

Administration of anaesthetic triggering agents to patients tested malignant hyperthermia normal and their relatives in New Zealand: an update.

Testing for malignant hyperthermia in New Zealand involves two tests-in vitro contracture testing of excised lateral quadriceps muscle and DNA analysis. In vitro contracture testing is regarded as the gold standard in malignant hyperthermia diagnosis but several publications have questioned the reliability of a normal result. Analysis of 479 anaesthetic records in 280 patients or their descendants throughout New Zealand who had tested negative for malignant hyperthermia, demonstrated there was no evidence of malignant hyperthermia episodes in this group who had been administered anaesthetic triggering agents. A wide range of anaesthetics were used over the study period. Analysis of each anaesthetic record was undertaken using the malignant hyperthermia grading scale which determines the likelihood that an anaesthetic event represents a malignant hyperthermia episode. Confirmation of the negative results was further supported by normal DNA analysis of patients in 48% of anaesthetics. There are advantages to using inhalational agents in certain situations and although demonstrating a zero risk of a malignant hyperthermia episode is not statistically possible, evidence in this large series suggests that the risk of an episode in these patients is extremely low and may be negligible. We suggest that anaesthetic triggering agents can be used safely in patients with normal in vitro contracture tests, and in their descendants.

Evidence of malignant hyperthermia in patients administered triggering agents before malignant hyperthermia susceptibility identified: missed opportunities prior to diagnosis.

Malignant hyperthermia (MH) is a hypermetabolic disorder of skeletal muscle triggered almost exclusively by potent inhalational agents and suxamethonium. Signs of an MH reaction are non-specific and may be confused with the presentation of other problems such as sepsis and overheating of a patient. A high index of suspicion is needed to be aware of an early presentation of MH. Nine patients are presented who showed abnormal signs with an earlier anaesthetic where the possible diagnosis of an MH reaction was missed. These patients either presented later with an MH reaction, confirmed by DNA analysis and in some cases in vitro contracture testing, or were diagnosed by the identification of a causative mutation confirming MH susceptibility. The MH clinical grading scale is helpful in determining the likelihood that clinical indicators indicate a possible MH reaction. Masseter muscle rigidity is a known sign of MH, confirmed in this report by positive in vitro contracture testing and DNA analysis. Several uncommon muscle disorders have a high association with MH, and postoperative myalgia unrelated to suxamethonium can be a sign which is associated with MH. These reports emphasise the importance of a thorough family history (as the MH status was known by the family in four patients), a high index of suspicion for MH, and documentation of the possibility of MH susceptibility in the anaesthesia record.

Safe duration of postoperative monitoring for malignant hyperthermia patients administered non-triggering anaesthesia: an update.

The postoperative care of malignant hyperthermia (MH) patients is subject to international variation, with a paucity of data in the literature to guide management. Over a series of three studies, our aim was to evaluate whether MH-susceptible patients (and relatives who had not yet been investigated), who had received a non-triggering anaesthetic, could be managed in the same way as the standard surgical population. Following a retrospective study, 206 anaesthetics were administered in a prospective second study to MH-susceptible/related individuals who were monitored for a minimum of one hour in the post anaesthesia care unit and a further 90 minutes in a step-down facility. No problems relating to MH were encountered. The postoperative monitoring time was subsequently changed and, in a third study, patients were managed no differently from standard surgical patients. One hundred and twenty-five anaesthetics were administered with no evidence of problems. This data shows that standard postoperative monitoring times are safe and appropriate in MH-susceptible patients.

The use of PCR to detect Neospora caninum DNA in the blood of naturally infected cows.

Twelve 2-year old heifers in their fifth month of gestation when pregnancy tested were used in this study. Six heifers aborted at approximately 4 months of gestation and had blood samples drawn less than 6 weeks after the abortions were identified. Blood samples were also drawn from three sero-positive pregnant and three sero-negative pregnant heifers. DNA was isolated from the samples and a 350 bp fragment of the Nc-5 gene was PCR amplified using primer pair Np21+ and Np6+. Also, the Internal Transcribed Spacer 1 (ITS1) was PCR amplified using Tim 3 and Tim 11 primer pair. The Nc-5 gene fragment was cloned, sequenced and the sequence BLAST-tested. Similarly, the ITS1 product was sequenced and BLAST-tested. The BLAST test results revealed that Neospora caninum DNA was present in these blood samples indicating that polymerase chain reaction can be used in the detection of N. caninum DNA in the blood of sero-positive cows.

Lactoferrin cDNA. Expression and in vitro mutagenesis.

The full length copy DNA (cDNA) for human lactoferrin has been synthesised by the polymerase chain reaction (PCR) using sequence specific primers. The template was first strand cDNA, synthesised from human bone marrow RNA using oligo(dT) to prime DNA synthesis by MMLV reverse transcriptase. The full-length human lactoferrin cDNA has been expressed in baby hamster kidney (BHK) cells using the expression vector pNUT. The protein expressed from the cloned cDNA is secreted into the culture medium and yields of up to 40 mg per litre have been obtained. A mutant protein corresponding to the N-lobe of human lactoferrin (LfN) has also been expressed in BHK cells. The cDNA coding for this protein was produced by the introduction of stop codons into the region of the cDNA corresponding to the helix linking the N- and C-lobes of the native protein. LfN is also expressed as a secreted protein and has been obtained in high yield. LfN binds iron and has UV/Vis and ESR spectra which are virtually identical to the native protein. However, the pH at which iron is released from LfN is quite different to the pH of iron release from the native and the full-length recombinant protein. A number of mutations have been introduced into LfN by site-directed mutagenesis and the mutant proteins expressed in BHK cells. These mutations involve the iron binding ligands and have been designed to introduce some of the changes found in the C-lobe of melanotransferrin into LfN. An attempt has been made to express a protein corresponding to the C-lobe of human lactoferrin (LfC) by attaching the sequence for the signal peptide of lactoferrin to the cDNA sequences coding for the C-lobe.

Safety of exposure of malignant hyperthermia non-susceptible patients and their relatives to anaesthetic triggering agents.

As the reliability of malignant hyperthermia normal in vitro contracture test results has been questioned, this study set out to determine the reliability of malignant hyperthermia normal results in New Zealand. Three hundred and twenty-nine anaesthetics were administered to malignant hyperthermia normal patients, identified through the Palmerston North Hospital malignant hyperthermia database. Anaesthetic records were retrieved and scrutinised for a malignant hyperthermia reaction using the Malignant Hyperthermia Clinical Grading Scale. Patients were exposed to one or more of eight triggering agents and multiple anaesthetic agents were administered in 41% of cases. Six variables were analysed, and although a minority of variables were abnormal in a small number of patients, none of the findings supported a malignant hyperthermia reaction. While the analysis was limited by the adequacy of the anaesthesia records, it was supported by negative DNA analysis in 55% of patients. This study supports several previous studies in demonstrating that patients in New Zealand tested non-susceptible to malignant hyperthermia can safely be given triggering agents.

Normal vitamin D receptor function with increased expression of 25-hydroxyvitamin D(3)-24-hydroxylase in Corriedale sheep with inherited rickets.

A likely inherited disease with gross and microscopic features of rickets has been recognised in Corriedale sheep in New Zealand, and a defect in end-organ responsiveness to vitamin D has been proposed as a likely mechanism. The aim of the present study was to characterize the mode of inheritance and determine the disease mechanism. Breeding trials showed that the mode of inheritance was autosomal recessive. Serum chemistry testing using different methodology and studies in cultured skin fibroblasts did not support our previous hypothesis of a defect in end-organ responsiveness. The studies revealed normal serum 1,25-dihydroxyvitamin D concentrations, normal vitamin D receptor function, and the presence of 24-hydroxylase mRNA in cells from affected sheep, even without induction by 1,25-dihydroxyvitamin D(3). In addition, osteocalcin mRNA expression was similar in both affected and control sheep. It was concluded that increased expression of 25-hydroxyvitamin D(3)-24-hydroxylase, the enzyme that breaks down vitamin D, may be involved in the pathogenesis of inherited rickets in Corriedale sheep, but its role requires further clarification.

Neospora caninum: quantification of DNA in the blood of naturally infected aborted and pregnant cows using real-time PCR.

This study quantified Neospora caninum DNA in the blood and brain of pregnant and aborted heifers by monitoring PCR product formation in real-time using SYBR Green I, a double-stranded DNA-binding dye. Primers were designed to amplify a 188 bp product specific to N. caninum from the Nc-5 gene fragment of N. caninum. Similarly, a 71 bp product was amplified from the 28S rRNA gene of bovine genomic DNA that served as a control. Agarose gel electrophoresis and analysis of the melting curve for PCR products showed that both primer pairs were specific to their targets. Standard curves were generated for both bovine and N. caninum genomic DNA, and were used to compute the relative concentration of parasite to bovine DNA in the test samples. The concentration of N. caninum DNA in 1 ng of bovine genomic DNA obtained from blood ranged between 0.097 ng at the 1st week of the observation and 0 ng at the 15th week in aborted cows. In pregnant cows, the values ranged between 0.080 ng at the 1st week and 0.155 ng at the 15th week of observation. There was a sustained decrease of DNA concentration in the aborted group after abortion and an increase in DNA concentration in the pregnant group. Comparison of parasite DNA in blood and brain of infected heifers showed a higher DNA concentration in brain than in blood. This study shows that N. caninum DNA can be quantified to obtain the relative concentration of parasite DNA to host genomic DNA in blood. This technique allows testing of a large number of samples at one time and can be done without the need for slaughter of tested animals.

The effect of acute ethanol treatment on rates of oxygen uptake, ethanol oxidation and gluconeogenesis in isolated rat hepatocytes.

In hepatocytes isolated from fed rats, acute ethanol pretreatment (at a dose of 5.0 g/kg body wt.) did not change rates of O2 uptake. In cells from starved animals, acute ethanol pretreatment increased O2 uptake by 17-29%. The increased O2 uptake in hepatocytes from starved rats was not accompanied by increased rates of ethanol oxidation, but was accompanied by increased rates of gluconeogenesis under some conditions. The provision of ethanol (10 mM) as a substrate to cells from fed or starved rats decreased O2 uptake in the absence of other substrates or in the presence of lactate, and increased it in the presence of pyruvate or lactate and pyruvate. The results of this study show that the acute effects of ethanol on liver O2 uptake are dependent on the physiological state of the liver. Previously reported large (2-fold) increases in O2 uptake after acute ethanol pretreatment may have been an artefact owing to low control uptake rates (approximately 1.8 micromol/min per g wet wt. of cells) in the liver preparation used. The ATP contents (2.4-2.6 micromol/g wet wt. of cells) and rates of O2 uptake (2.5-5.0 micromol/min per g wet wt. of cells) of cells used in the present study were the same as values reported under conditions close to those in vivo. Therefore the increase in O2 uptake in cells from starved rats after acute ethanol pretreatment is likely to be of physiological significance.

Expression of cloned human lactoferrin in baby-hamster kidney cells.

Human lactoferrin was expressed from a cloned cDNA introduced into mammalian cells in tissue culture. Total RNA was extracted from human bone marrow, and lactoferrin cDNA was synthesized by primer-specific polymerase chain reaction after oligo(dT)-primed first-strand synthesis. The cDNA was sequenced to confirm its identity with previously published human lactoferrin sequences and cloned into the eukaryotic expression vector pNUT. Recombinant vector DNA containing the human lactoferrin sequence was introduced into baby-hamster kidney (BHK) cells in culture, and stable transfectants were produced by dominant marker selection. Human lactoferrin was expressed from the metallothionein promoter of pNUT by Zn2+ induction. The protein was secreted into the tissue-culture medium and was subsequently purified to homogeneity in a single step. Initial characterization suggests that the protein expressed by BHK cells is identical with native human lactoferrin.

Studies of the N-terminal half of human lactoferrin produced from the cloned cDNA demonstrate that interlobe interactions modulate iron release.

The factors influencing iron binding and release by lactoferrin have been addressed by comparison of the native full length molecule (Lf) with the N-terminal half of human lactoferrin (LfN) produced from the cloned cDNA expressed in baby hamster kidney (BHK) cells. The coding sequences for LfN were inserted into the expression vector pNUT between the metallothionein promoter and the human growth hormone transcription termination sequences. Transformed BHK cells were grown in roller bottles where concentrations of LfN as high as 35 mg/liter were obtained. The pure protein, produced by the transformed BHK cells, was characterized by sodium dodecyl sulfate-polyacrylamide gel electrophoresis, protein blotting and immunodetection, N-terminal sequence analysis, UV-visible spectroscopy, electron spin resonance spectroscopy, and measurements of metal binding and release. By these criteria LfN was found to be correctly processed, glycosylated, and able to bind iron reversibly. Both UV-visible and electron spin resonance spectra of the half molecule were very similar to those of native lactoferrin and the full length lactoferrin produced in BHK cells, but there were marked differences in the pH at which iron release occurred. Iron release from LfN occurs in the pH range 6.0-4.0, compared with 4.0-2.5 for native lactoferrin and 6.2-4.0 for transferrin. These results suggest that the more facile release of iron from LfN compared with native lactoferrin results from the absence of stabilizing contacts between the N- and C-terminal halves and that the characteristic difference in pH stability between lactoferrins and transferrins is due primarily to differences in these interactions.

The assessment of viability in isolated rat hepatocytes.

Isolated rat hepatocytes are used in many metabolic studies, but the viability of these cell preparations is often not adequately established. The present study shows that ATP content is a more reliable index of metabolic viability than trypan blue exclusion. At some of the low trypan blue exclusion levels quoted in the literature, a high percentage of cell preparations is likely to be nonviable by the criterion of ATP content. We suggest that ATP content measured on initial cell preparations and at the end of all incubation procedures is essential for establishing cell viability for metabolic studies on isolated hepatocytes.

Recognition patterns of Neospora caninum tachyzoite antigens by bovine IgG at different IFAT titres.

This study describes qualitative and quantitative antibody response in cows naturally infected with Neospora caninum. The study was carried out with 269 serum samples obtained from 24 cows over a period of 15 weeks. Prior to sample collection, the cows were tested with ELISA. The 269 samples were screened with IFAT and categorized into seven IFAT titre groups (< 1 : 80, 1 : 80, 1 : 200, 1 : 600, 1 : 1000, 1 : 2000, > 1 : 2000). The samples were finally analysed by Western blotting. Seven immunodominant antigens (approximately 18-, approximately 25-, approximately 33-, approximately 35-36-, approximately 45-46-, approximately 47-, approximately 60-62 kDa) and five minor antigens (approximately 25, approximately 51, approximately 64, approximately 77, approximately 116 kDa) were recognized by cow sera. The recognition of approximately 46 kDa antigen by cow sera was common to samples with IFAT titre 1 : 80 and above. Another common antigen was the approximately 18 kDa antigen, which was recognized by samples with IFAT titre 1 : 200 and above. The most remarkable observation was the presence of the 45-46 kDa, the 77 kDa, and absence of the 18 kDa antigenic bands in samples with IFAT titre 1 : 80. This observation was consistent even in the face of fluctuating antibody titre where serum antibody titres from an animal exceeded then failed to reach 1 : 80. Antibody fluctuation was observed across all cows (pregnant and aborted) with no discernible fluctuation pattern. However, the fluctuation in antibody titre observed appeared to be most remarkable in initially ELISA-negative pregnant cows, and to a lesser extent in ELISA-positive pregnant cows, and ELISA-positive aborted cows. Although there was fluctuation in antibody titre, the banding patterns of N. caninum tachyzoite antigens by cows within the same IFAT titre group remained similar.