Genotype and phenotype relationships for mutations in the ryanodine receptor in patients referred for diagnosis of malignant hyperthermia.

Anaesthesia-induced malignant hyperthermia (MH) may be caused by specific gene defects in the skeletal muscle ryanodine receptor. We have studied the frequency of occurrence of the C1840T mutation, analogous to the porcine mutation, and three mutations associated both with MH and central core disease (G7301A, C487T and C1209G). We investigated skeletal muscle specimens from up to 137 patients testing negative and 101 patients testing positive for MH susceptibility by the North American MH Group protocol. The presence or absence of the mutations was determined by polymerase chain reaction and restriction enzyme digestion. The frequencies of occurrence of the C1840T and C487T mutations were 2% and 1%, respectively, in MH-positive subjects and were the only two mutations identified. One subject with central core disease did not have any of the three mutations examined associated with this disorder. Therefore, the porcine and central core disease-associated mutations examined in the ryanodine receptor account for a small proportion (approximately 3%) of MH-positive diagnoses. The mutations examined did not occur in any of the MH-negative patients, supporting an association between defects in the ryanodine receptor and a positive diagnosis for MH.(ABSTRACT TRUNCATED AT 250 WORDS)

Masseter muscle rigidity associated with glycine1306-to-alanine mutation in the adult muscle sodium channel alpha-subunit gene.

BACKGROUND: Succinylcholine-induced masseter muscle rigidity (MMR) is a potentially life-threatening complication of anesthesia and is closely correlated with the heterogeneous disorder malignant hyperthermia (MH) susceptibility. MMR also is identified with a variety of neuromuscular disorders, including the myotonias, that are associated with abnormal in vitro contracture test (IVCT) results. Recently, mutations in the adult skeletal muscle sodium channel alpha-subunit gene (SCN4A) have been shown to cause generalized nondystrophic myotonias, some of which are associated with mild nonspecific symptoms. The purpose of the current investigation was to begin to evaluate the molecular genetic relationship between known mutations in the SCN4A gene, MMR, and the results of the IVCT used to diagnose MH-susceptibility. METHODS: A single extended pedigree of 16 individuals was ascertained through a proband who experienced MMR and whole-body rigidity after succinylcholine administration. Subsequently, four individuals were shown to have a mild form of myotonia on clinical and laboratory examination. IVCT was carried out according to standardized protocols. Mutations in the SCN4A gene were sought in exons 22 and 24 using single-strand conformational analyses. Variability in the SCN4A gene sequence was confirmed by direct DNA sequence analyses. RESULTS: Four individuals with myotonia were shown to carry a guanine-to-cytosine mutation at nucleotide position 3917 of the reported SCN4A sequence. This DNA mutation was coinherited with MMR and an abnormal IVCT result in this family. Previous studies have demonstrated that the glycine1306-to-alanine substitution is associated with a mild clinical syndrome referred to as myotonia fluctuans. CONCLUSIONS: The current report provides direct evidence that succinylcholine-induced MMR, whole-body rigidity, and an abnormal IVCT result are associated with a mutation in the SCN4A gene.

Altered [3H]ryanodine binding is not associated with malignant hyperthermia susceptibility in terminal cisternae preparations from swine.

Based on comparisons between Pietrain malignant hyperthermia susceptible swine and Yorkshire control swine, other investigators have reported a 3-fold lower Kd for [3H]ryanodine binding to terminal cisternae in the malignant hyperthermia swine. However, the Kd of [3H]ryanodine binding did not correlate with malignant hyperthermia susceptibility when examined within the same strain (a Yorkshire/Duroc cross) in the present study. The values of Kd for the malignant hyperthermia susceptible and control swine in the present study were similar to those previously reported for the Pietrain strain, suggesting that the control strain chosen, not malignant hyperthermia susceptibility, accounts for what appeared to be a low Kd in Pietrain muscle.

Lipoprotein lipase enhances the cholesteryl ester transfer protein-mediated transfer of cholesteryl esters from high density lipoproteins to very low density lipoproteins.

These studies were undertaken to examine the effects of lipoprotein lipase (LPL) and cholesteryl ester transfer protein (CETP) on the transfer of cholesteryl esters from high density lipoproteins (HDL) to very low density lipoproteins (VLDL). Human or rat VLDL was incubated with human HDL in the presence of either partially purified CETP, bovine milk LPL or CETP plus LPL. CETP stimulated both isotopic and mass transfer of cholesteryl esters from HDL into VLDL. LPL caused only slight stimulation of cholesteryl ester transfer. However, when CETP and LPL were both present, the transfer of cholesteryl esters from HDL into VLDL remnants was enhanced 2- to 8-fold, compared to the effects of CETP alone. The synergistic effects of CETP and LPL on cholesteryl ester transfer were more pronounced at higher VLDL/HDL ratios and increased with increasing amounts of CETP. In time course studies the stimulation of cholesteryl ester transfer activity occurred during active triglyceride hydrolysis. When lipolysis was inhibited by incubating LPL with either 1 M NaCl or 2 mM diethylparanitrophenyl phosphate, the synergism of CETP and LPL was reduced or abolished, and LPL alone did not stimulate cholesteryl ester transfer. These experiments show that LPL enhances the CETP-mediated transfer of cholesteryl esters from HDL to VLDL. This property of LPL is related to lipolysis.