INTRODUCTION: Mutations in the butyrylcholinesterase enzyme (BChE) can result in prolonged duration of action of the neuromuscular blocking agents, succinylcholine and mivacurium, as BChE hydrolyses these drugs. Hereditary low BChE activity can cause extensively prolonged apnoea during general anaesthesia when these drugs are used. The aim of this study was to describe novel mutations in the butyrylcholinesterase gene (BCHE) in patients who have experienced prolonged duration of action of mivacurium or succinylcholine. METHODS: The Danish Cholinesterase Research Unit registers patients with prolonged duration of action to succinylcholine and mivacurium. Patients were studied if they had equivocal phenotypes on the basis of BChE activity, biochemical inhibitor reactions and with pedigree if possible. Complete nucleotide sequencing was performed to describe the genotype and pedigree was used to separate the alleles. Multiple sequence alignment of BChE was performed for comparison with other species. RESULTS: Genotyping indicated seven novel mutations in the BCHE (I373T, G467S, W518R, L184S, V421A, M462I and R577H). CONCLUSION: We have found seven new variants of the BCHE, which seem to reduce the activity of BChE in patients undergoing anaesthesia involving succinylcholine or mivacurium.
Title: Two novel mutations in the BCHE gene in patients with prolonged duration of action of mivacurium or succinylcholine during anaesthesia Gatke MR, Bundgaard JR, Viby-Mogensen J Ref: Pharmacogenet Genomics, 17:995, 2007 : PubMed
BACKGROUND: Butyrylcholinesterase (BChE) hydrolyses the neuromuscular blocking agents, succinylcholine and mivacurium used during general anaesthesia. Hereditary low BChE activity may result in an extensively prolonged duration of action of these drugs, especially in patients who are homozygous for the atypical or silent variants. We present three novel mutations in the butyrylcholinesterase gene (BCHE) identified in three families in which a member had experienced severely prolonged duration of action of succinylcholine. METHODS: As the phenotypes of the three probands could not be established with certainty using conventional biochemical tests, DNA samples were collected from two of the probands and four relatives. Genotypes were determined using complete nucleotide sequencing. RESULTS: Three novel mutations were identified: BCHE*FS126, BCHE*I3E4-14C and BCHE*328D. The proband in family 1 was genotyped as BCHE*115D*I3E4-14C/BCHE*FS126, whereas the proband in family 3 was compound heterozygous for BCHE*328D and BCHE*142M. In both patients, BChE activity was below detection limit, and they experienced an extensively prolonged duration of action of succinylcholine. The proband in family 2 was not sequenced, but a relative was heterozygous for BCHE*FS126. BCHE*I3E4-14C was in linkage with a known silent variant. CONCLUSIONS: Two novel variants of BCHE are silencing the enzyme function. BCHE*FS126 results in a truncated protein lacking the active site and is therefore inactive. The second variant is BCHE*328D, also resulting in an inactive protein, as this change in amino acid is radical and furthermore situated in the gorge harbouring the active site. These variants result in extensively prolonged duration of action of succinylcholine.
BACKGROUND: Mivacurium is hydrolyzed by the butyrylcholinesterase enzyme, and patients with hereditary changes of the enzyme often have prolonged duration of action of mivacurium. In this study, the authors investigated the significance of the most commonly occurring variant, the Kalow (K) variant, established using DNA analysis, for the response to mivacurium. METHODS: A total of 58 patients carrying either the wild-type butyrylcholinesterase or different combinations of the atypical (A) variant and the K variant were included. Patients who were homozygous for the A variant were given 0.03 mg/kg mivacurium. All other patients received 0.2 mg/kg mivacurium. The neuromuscular block was measured using train-of-four nerve stimulation and mechanomyography. Genotyping was performed with complete nucleotide sequencing. RESULTS: Heterozygosity of the K variant prolonged the time to train-of-four 0.70 from 26.6 to 34.5 min (30%; not significant) as compared with the wild type. Heterozygosity of the K variant linked to the A variant prolonged the corresponding time from 32 to 42.7 min (33%; P = 0.03) as compared with patients who were heterozygous for solely an A allele. For eight patients who were homozygous for both the A and K variants, the time to 25% recovery was 78-89 min as compared with 44-57 min in patients who were homozygous for the A variant or had only one linked K variant. CONCLUSION: The K variant prolongs the duration of action of mivacurium. The current results indicate that the effect is modest when the K variant occurs heterozygously with the wild type or the A variant but is marked in patients who are homozygous for both the A and K variants.
Title: Rapid simultaneous genotyping of the frequent butyrylcholinesterase variants Asp70Gly and Ala539Thr with fluorescent hybridization probes Gatke MR, Viby-Mogensen J, Bundgaard JR Ref: Scand J Clin Lab Invest, 62:375, 2002 : PubMed
BACKGROUND: The clinically important variants of butyrylcholinesterase (BChE) are the A- (Asp70Gly) and K-variants (Ala539Thr), which are common among Caucasians. These variants are associated with abnormal drug metabolism during anaesthesia, which leads to a prolonged neuromuscular block following administration of the neuromuscular blocking agents, mivacurium and succinylcholine. In addition, the K-variant has been proposed to be associated with Alzheimer's disease together with apolipoprotein E epsilon4. To facilitate diagnostics, we set out to establish a rapid and simple method for simultaneous genotyping of the A- and K-variants. METHODS: Using the LightCycler, a rapid-cycle duplex PCR is combined with generation of allele-specific fluorescent probe melting profiles. This allows simultaneous detection of both of the mutations in the BChE gene. The results were compared with direct sequencing and phenotyping results. RESULTS: Samples from 80 subjects were genotyped. The genotypes determined using the LightCycler were identical to those obtained by direct sequencing of conventional polymerase chain reaction products and was more accurate than phenotyping based on biochemical assays. CONCLUSIONS: A high-speed and easy to perform mutation detection assay has been established for the two most common mutations, Asp70Gly and Ala539Thr, in BChE, using the LightCycler technology and melting curves.
Title: Response to mivacurium in a patient compound heterozygous for a novel and a known silent mutation in the butyrylcholinesterase gene: genotyping by sequencing Gatke MR, Ostergaard D, Bundgaard JR, Varin F, Viby-Mogensen J Ref: Anesthesiology, 95:600, 2001 : PubMed
BACKGROUND Patients who are homozygous for the atypical mutation, compound heterozygous for atypical and silent mutations, or homozygous for silent mutations (SS) respond to mivacurium with extensively prolonged neuromuscular block. Although important, exact phenotyping of these patients is difficult. This article presents the pharmacodynamics and pharmacokinetics of a normal dose of mivacurium in a patient with phenotype SS, including a pedigree analysis and delineation of the molecular genetic method used to identify the genotype.
METHODS:
The neuromuscular block following administration of mivacurium, at a dose of 0.14 mg/kg, was monitored in a 30-yr-old healthy man with use of a mechanosensor and mechanomyography, and times to different levels of recovery were measured. Venous samples for determination of the mivacurium isomers were collected during the interval 134-494 min after administration of mivacurium, and the terminal half-lives were calculated. Butyrylcholinesterase activity, phenotype, and genotype were determined for both the patient and the family. Complete nucleotide sequencing was used to identify the genotype.
RESULTS:
A train-of-four ratio of 0.75 was reached 469 min after the injection of mivacurium. The terminal elimination half-lives of the mivacurium isomers, cis-trans and trans-trans, were 90 min. Complete nucleotide sequencing revealed two point mutations, the known silent variant S7 and a previously undescribed mutation of amino acid residue 170 introducing a stop codon.
CONCLUSIONS:
The patient was compound heterozygous for silent mutations in the butyrylcholinesterase gene. The response to mivacurium was an extensively prolonged duration of action. Identification of the rare silent mutations presupposes access to modern molecular genetic methods such as complete nucleotide sequencing.
