title: Phosphorylase ratio and susceptibility to malignant hyperthermia.
abstract: The ratio of muscle phosphorylase a to total phosphorylase, expressed as a percent, was determined in vastus lateralis muscle of 26 patients to examine the efficacy of this parameter as a method for screening for susceptibility to malignant hyperthermia (MH). As standard screening, all patients also had muscle contracture responses determined to 2% halothane and 0.25-32 mM caffeine at 37 degrees C. Each drug was given separately and not combined. Nine patients were susceptible to MH, based upon caffeine threshold of 2 mM or less (seven patients) or a rapidly developing contracture tension to halothane of more than 400 mg (seven patients, including five with positive caffeine responses). Mean phosphorylase ratio in these nine patients was 14.5 +/- 2.0% (mean, SEM). In the 17 nonsusceptible patients mean phosphorylase ratio (12.4 +/- 1.9%) was not significantly different. The range of phosphorylase ratios in susceptible patients was 6.5-26% while 13 nonsusceptible patients had ratios greater than 6% and up to 29%. The unacceptably high number of false-positive responses in nonsusceptible patients precludes the use of phosphorylase ratio as a definitive diagnostic test.
mesh_terms: D000293:Adolescent; D000328:Adult; D002110:Caffeine / Q000494:pharmacology; D004796:Clinical Enzyme Tests; D005260:Female; D006801:Humans; D066298:In Vitro Techniques; D008297:Male; D008305:Malignant Hyperthermia / Q000175:diagnosis* / Q000209:etiology; D009119:Muscle Contraction / Q000187:drug effects; D009132:Muscles / Q000201:enzymology*; D010762:Phosphorylase a / Q000378:metabolism*; D006005:Phosphorylases / Q000378:metabolism*; D010766:Phosphorylation; D010770:Phosphotransferases / Q000378:metabolism*; D012306:Risk
chemical_list: D002110:Caffeine; D010762:Phosphorylase a; D006005:Phosphorylases; D010770:Phosphotransferases