Detection of atypical cholinesterase by an automated pH stat method. Report of a family with both atypical and silent gene alleles.

Plasma pseudocholinesterase has no known physiological role but is essential for the rapid degradation of succinyicholine, a muscle relaxant used in surgical procedures. Depression of effective enzyme concentrations as a result of hepatocellular disease or exposure to anticholinesterase agents will increase the patient’s sensitivity to succinyicholine and prolong postoperative apnea. Synthesis of this enzyme is controlled by an autosomal gene with multiple variant alleles; individuals phenotypically homozygotic for one of these variants will have either qualitatively “atypical” pseudocholinesterase with decreased activity or no enzyme at all, and will thus be more sensitive to succinylcholine. The automated pH stat system described here detects atypical cholinesterase by measuring the degree of inhibition of butyrylcholine hydrolysis by dibucaine. The sensitivity and reproducibility of this technique equals that of standard spectrophotometric methods and its speed is comparable to that of the most rapid screening tests. A family pedigree is also presented, exemplifying a rare genotype in which two siblings are double heterozygotes for “atypical” and “silent” alleles.