[Future pain treatment]. / Fremtidig smertebehandling.

BACKGROUND: The recent rapid progress in pain research is due in large part to advances in genetics and cell and molecular biology. We now know that chronic pain (hypersensitivity due to inflammation or nerve injury) and acute nociceptive pain are different and must be treated accordingly. We will continue to reveal sophisticated mechanisms underlying different kinds of pain that can be targeted to inhibit nociceptive transmission and produce analgesia. METHODS: This review is based upon literature collected through the authors' own reading and through PubMed searches. New hopes for future pain treatments are discussed. Further, the impact of genetic factors on pain sensitivity and pain modulation are discussed, and conceivable therapeutic approaches based on genetic techniques are mentioned. RESULT: At the level of the peripheral nerve, many novel targets have recently been identified: the tetrodotoxin-resistant sodium channel, the vanilloid receptor and different calcium channels are very interesting. In the spinal cord, different approaches can be used: to either block excitatory input or to increase inhibitory control or to do both at the same time. The mechanisms for hypersensitivity are being identified and offer multiple possible targets for novel analgesics. INTERPRETATION: Many interesting targets for analgetics has emerged during that last few years, lending great hope for new and better (i.e. with less side effects) analgesic drugs in the future.

No pain relief from codeine...? An introduction to pharmacogenomics.

Drug treatment remains a mainstay of medicine. In some situations a drug unexpectedly has no effect, or unforeseen serious side effects occur. For the patient this represents a dangerous and potentially life-threatening situation. It certainly is a distressing experience for the doctor. At the societal level, adverse drug reactions represent a leading cause of disease and death. Genetic variation often underlies these unexpected situations. Pharmacogenetics is the term used about genetically determined variability in the metabolism of drugs. Pharmacogenomics usually refers to drug discovery based on knowledge of genes, but it is a discipline that offers insight into aetiologic mechanisms, and possible prevention and treatment. There is a trend towards a definition of pharmacogenomics that includes both pharmacogenetics and pharmacogenomics as defined above. Our article is an introduction to pharmacogenomics, using the broader definition. Biotechnological methods cannot be understood without a grasp of basic medical genetics, and we provide a brush-up on the fundamentals. We then outline pharmacogenetics, giving examples of genetically based variation in drug metabolising enzymes, drug receptors and drug transporting proteins. Modern biotechnology would be unthinkable without the aid of computers, and we briefly touch upon the field of bioinformatics. Finally, we give an overview of pharmacogenomics in the narrower sense. The rapidly growing field of pharmacogenomics is going to influence our everyday practice of medicine in the immediate future.

Identification of novel mutations in the ryanodine-receptor gene (RYR1) in malignant hyperthermia: genotype-phenotype correlation.

Malignant hyperthermia (MH) is a pharmacogenetic disorder of skeletal muscle that is triggered in genetically predisposed individuals by common anesthetics and muscle relaxants. The ryanodine receptor (RYR1) is mutated in a number of MH pedigrees, some members of which also have central core disease (CCD), an inherited myopathy closely associated with MH. Mutation screening of 6 kb of the RYR1 gene has identified four adjacent novel mutations, C6487T, G6488A, G6502A, and C6617T, which result in the amino acid alterations Arg2163Cys, Arg2163His, Val2168Met, and Thr2206Met, respectively. Collectively, these mutations account for 11% of MH cases and identify the gene segment 6400-6700 as a mutation hot spot. Correlation analysis of the in vitro contracture-test data available for pedigrees bearing these and other RYR1 mutations showed an exceptionally good correlation between caffeine threshold and tension values, whereas no correlation was observed between halothane threshold and tension values. This finding has important ramifications for assignment of the MH-susceptible phenotype, in genotyping studies, and indicates that assessment of recombinant individuals on the basis of caffeine response is justified, whereas assessment on the basis of halothane response may be problematic. Interestingly, the data suggest a link between the caffeine threshold and tension values and the MH/CCD phenotype.

Detection of a novel mutation at amino acid position 614 in the ryanodine receptor in malignant hyperthermia.

Malignant hyperthermia (MH) is a potentially fatal autosomal dominant disorder of skeletal muscle and is triggered in susceptible people by all commonly used inhalation anaesthetics and depolarizing neuromuscular blocking agents. To date, eight mutations in the skeletal muscle ryanodine receptor gene (RYR1) have been identified in malignant hyperthermia susceptible (MHS) and central core disease (CCD) cases. We have screened the RYR1 gene in affected individuals for novel MHS mutations by single stranded conformational polymorphism (SSCP) analysis and have identified a G to T transition mutation which results in the replacement of a conserved arginine (Arg) at position 614 with a leucine (Leu). The Arg614Leu mutation was present in three unrelated MHS individuals of 151 investigated. The mutation was not detected in 148 normal chromosomes and segregated precisely with MHS in family members from one of the probands where DNA was available for analysis. This mutation occurs at the same position as the previously identified Arg to Cys mutation reported in all cases of porcine MH and in approximately 5% of human MH. A comparison of the phenotypes of the Arg614Leu and Arg614Cys probands is presented.

4-Chloro-m-cresol test--a possible supplementary test for diagnosis of malignant hyperthermia susceptibility.

BACKGROUND: In vitro contracture test (IVCT) for diagnosis of MH in our laboratory has a sensitivity of 100% and a specificity of 93%. The results are equivocal in 10-15%, and supplementary tests may thus be required. We have tested the hypothesis that 4-chloro-m-cresol (4-cmc) may be useful for a supplementary test. METHODS: Muscle from 41 consecutive patients from 7 families undergoing diagnostic muscle biopsy with IVCT was exposed in vitro to increasing concentrations of 4-cmc (25, 50, 75, 100, 150, and 200 mumol l-1), and the force development recorded. Diagnosis of MH susceptibility was made with standard halothane and caffeine tests and included as results MHS (MH susceptible), MHN (MH negative), and MHE (equivoval result). RESULTS: At all concentrations of 4-cmc, the increase in baseline force was significantly greater in the MHS group compared to the MHN group (P < 0.05). Muscle from 15 MH-susceptible (MHS) patients responded to 4-cmc with increasing force at a threshold concentration of 75 mumol l-1 or less, whereas muscle from 23 MH-non-susceptible (MHN) patients had thresholds of 100 mumol l-1 or more. The accuracy of the chlorocresol test was thus 100% (95% confidence limits 90.75-100%) at a threshold of 75 mumol l-1. Amplitude of contractures at 2 mmol l-1 caffeine was not different from contractures at 75 mumol l-1 of 4-cmc in either the MHS or the MHN group (P > 0.05). In vivo concentrations of chlorocresol from clinical use of insulin and somatropin are estimated to be 20 times less than the threshold concentration and thus these drugs seem safe in MH patients. CONCLUSION: 4-chloro-m-cresol may be a suitable aid to clarify puzzling results of standard testing of MH susceptibility.

Malignant hyperthermia susceptibility, an autosomal dominant disorder?

A large series of Swedish nuclear families, in which malignant hyperthermia (MH) reactions had occurred during anaesthesia, have been examined with respect to malignant hyperthermia susceptibility. In vitro contracture tests (IVCT) of muscle strips were conducted to diagnose MH status. Included in this series were some families where only one of the parents was tested by IVCT, while in 79 of the families both parents were tested by IVCT. Six known mutations in the gene encoding the calcium release channel of sarcoplasmic reticulum in skeletal muscle (the RYR1 gene), believed to cause MHS in man, were searched for in 41 nuclear families. The present paper focuses on findings in eight families, where both parents were malignant hyperthemia negative (MHN), while at least one child was either malignant hyperthermia susceptible (MHS) or malignant hyperthermia equivocal (MHE). There was no suggestion of non-paternity. The RYR1 mutations investigated were Arg163Cys, Gly341Arg, Ile403Met, Arg614Cys, Gly2433Arg and Arg2434His. No family had any of the six RYR1 mutations searched for.

Discordance between malignant hyperthermia susceptibility and RYR1 mutation C1840T in two Scandinavian MH families exhibiting this mutation.

The ryanodine receptor 1 (RYR1) mutation C1840T has been reported to segregate with malignant hyperthermia (MH) susceptibility in several families. We have investigated several Scandinavian MH families with respect to five different RYR1 mutations reported to cause predisposition to MH, and we here report on two of the families in which the C1840T mutation was detected. In these two families there was recombination between MH susceptibility and this mutation in one and three individuals, respectively. These findings may suggest that it is necessary to reconsider the specificity of the IVCT and the role of C1840T as a cause of MH susceptibility in some families exhibiting this mutation.

Recombination between the postulated CCD/MHE/MHS locus and RYR1 gene markers.

Malignant hyperthermia (MH) susceptibility is considered a subclinical myopathy or a pharmacogenetic trait, and is believed to be closely associated with central core disease (CCD). Data support the notion that MH susceptibility is heterogeneous, with the ryanodine receptor I (RYR1) locus on chromosome 19 being one locus harboring a gene that can cause MH susceptibility. The gene for CCD is believed to reside in the locus on chromosome 19. In the family presented here, a girl has CCD, and several close relatives are MH susceptible (MHS). DNA studies conducted on available family members uncovered recombination between the MH susceptibility locus and RYR1 markers. Consequently, if one postulates that the CCD gene in this family resides in the same locus as the MH susceptibility gene, an additional CCD locus different from the RYR1 locus must also be postulated.

[Analgesic effect of ketamine in a patient with neuropathic pain]. / Analgetisk effekt av ketamin hos en pasient med neuropatiske smerter.

We report the effect of a single daily dose of ketamine in a 54 year old woman with fibromyalgia and severe post-traumatic neuropathic pain. A number of different approaches for pain relief had been tried with little effect. An intramuscular test dose of 0.4 mg/kg ketamine combined with 0.05 mg/kg midazolam lead to analgesia which lasted for almost two days. Long-term analgesia was also obtained by 250 mg/kg ketamine hydrochloride taken orally in the form of capsules every night at bedtime. The patient has now used this dose for nine months. Ketamine is an NMDA receptor antagonist. A single sub-anaesthetic dose of ketamine causes a long-term depression of pain intensity in some, but not in all, patients suffering chronic pain. This effect is distinctly different from the short-lasting (10-30 min) analgesic effect in cases of acute nociceptive pain. The long-term depression of the intensity of chronic pain states may be due to a reversal of NMDA receptor-dependent long-term potentiation of synapses in central pain pathways. By giving ketamine as a single dose at night the mental side-effects are reduced or avoided.

RYR mutation G1021A (Gly341Arg) is not frequent in Danish and Swedish families with malignant hyperthermia susceptibility.

Malignant hyperthermia (MH) is a pharmacogenetic disorder. Susceptibility to MH (MHS) is presumed to be inherited in an autosomal dominant way. MH crises are triggered by halogenated inhalational anaesthetics and suxamethonium, and may be lethal if not treated early and adequately. Until now, eight mutations in the RYR1 gene have been described as causes of MHS phenotype in various MH families. The mutation RYR1 G1021A (Gly341Arg) has been reported to account for approximately 10% of Caucasian MHS cases. However, in our study this mutation was discovered in only 1 out of 89 Scandinavian families, indicating that this mutation may be the cause of MHS in only about 1% of MHS families in those populations. The mutation may have been brought to Scandinavia by an immigrant.

A search for three known RYR1 gene mutations in 41 Swedish families with predisposition to malignant hyperthermia.

Eight mutations in the gene (the RYR1 gene) encoding the calcium release channel of sarcoplasmic reticulum (SR) in skeletal muscle are so far known to be very closely linked to malignant hyperthermia susceptibility in man and are regarded to be causative. We have examined 41 Swedish families where malignant hyperthermia had occurred in at least one member during anaesthesia, with respect to three of the known mutations. The mutations were Arg163Cys; Ile403Met and Arg614Cys (also known as the "pig mutation"). In three (i.e. 7%) of the families we detected the Arg614Cys mutation, and this was the only one of the mutations searched for that was observed. This indicates that other mutations than those searched for in this study must cause malignant hyperthermia susceptibility in most Swedish malignant hyperthermia susceptible families.

A simple method to detect the RYR1 mutation G1021A, a cause of malignant hyperthermia susceptibility.

To search for the mutations RYR1 G1021A in families where malignant hyperthermia (MH) episodes have occurred, we have used an amplification-created restriction sites (ACRS) technique to detect the mutation. The previously described single-stranded conformation polymorphism (SSCP) technique was laborious and time consuming, but necessary to detect the mutation, whereas the method described here discriminates quickly and efficiently between homozygotes with the mutation, heterozygotes and homozygotes without the mutation.

Search for three known mutations in the RYR1 gene in 48 Danish families with malignant hyperthermia.

We have examined 48 Danish families in which malignant hyperthermia reactions have occurred, with respect to three of six published mutations in the gene for the calcium release channel of sarcoplasmic reticulum (the RYR1 gene) believed to cause malignant hyperthermia susceptibility in man. The mutations are Arg614Cys, also known as the "pig mutation"; Arg163Cys; and Ile403Met. The only mutation found was Arg163Cys, which was detected in only one family. The results of this study indicate that other mutations must underlie the disorder in most Danish malignant hyperthermia-susceptible families, and that the "pig mutation" is not a frequent cause of malignant hyperthermia susceptibility in Denmark.

Mutations in the ryanodine receptor gene in central core disease and malignant hyperthermia.

Central core disease (CCD) of muscle is an inherited myopathy which is closely associated with malignant hyperthermia (MH) in humans. CCD has recently been shown to be tightly linked to the ryanodine receptor gene (RYR1) and mutations in this gene are known to be present in MH. Mutation screening of RYR1 has led to the identification of two previously undescribed mutations in different CCD pedigrees. One of these mutations was also detected in an unrelated MH pedigree whose members are asymptomatic of CCD. The data suggest a model to explain how a single mutation may result in two apparently distinct clinical phenotypes.

Genetic recombination between malignant hyperthermia and calcium release channel in skeletal muscle.

Absolute linkage between the gene, on chromosome 19, for the calcium release channel (CRC) of the sarcoplasmic reticulum in skeletal muscle and malignant hyperthermia (MH) has been reported by other workers. In the present study of three Swedish Families informative with respect to this linkage relationship, definite recombinants were found in two families. We conclude that mutations in other genes than the CRC gene can cause the clinical picture of MH. Accordingly, MH appears to be genetically heterogeneous.