Plasma cholinesterase is also known as butyrylcholinesterase, in part because once an individual is given butyrylcholine intravenously, the enzyme converts it to the products butyric acid and choline.
Inherited reductions in butyrylcholinesterase activity occur because of mutations at a single autosomal location on the long arm of chromosome 3.
McGuire et al.[3] compared the entire coding sequences for usual and atypical cholinesterases, and found no other consistent base differences.
Lockridge and La Du[5] measured atypical and usual human serum cholinesterases with the fluorescent probe, N-methyl-(7-dimethylcarbamoxy)quinolinium iodide.
The turnover numbers of usual and atypical cholinesterases were the same: 15,000 μmol of benzoylcholine hydrolyzed/min/μmol of active site; 48,000 min−1 for o-nitrophenylbutyrate; and 0.0025 min−1 for N-methyl-(7-dimethylcarbamoxy)quinolinium iodide.
When given succinylcholine, a commonly used neuromuscular-blocking drug administered for general anesthesia during surgery, the heterozygous and mutant homozygous individual will experience a prolonged duration of action of neuromuscular blockade.
To identify susceptible individuals, the dibucaine number can be determined so as to alert the care team to the risks of use of butyrylcholinesterase substrates.
[2] Pestel et al. conclude that routine measurement of dibucaine number is a cost-effective method of identifying patients at increased risk of prolonged neuromuscular blockade due to atypical cholinesterase.
Today, dibucaine number is typically determined after an episode of prolonged paralysis following administration of succinylcholine in order to explain the cause of the incident.
If activity at the motor endplate is not reestablished, as determined by nerve stimulator testing, an anesthesiologist will grow concerned that the patient may have a mutant form of the plasma cholinesterase enzyme and will withhold subsequent dosing of neuromuscular blocking agents until return of function.