ON DISTRIBUTION AND INHERITANCE OF ATYPICAL FORMS OF HUMAN SERUM CHOLINESTERASE, AS INDICATED BY DIBUCAINE NUMBERS

Abstract

Type and activity of serum cholinesterase (pseudocholinesterase) have been studied in nearly 1700 human sera. The type was determined by an inhibition test with dibucaine; per cent inhibition achieved under specified conditions was termed dibucaine number (DN). The DNs can be classified into the three groups—usual, intermediate, and atypical. This triple division is consistent with the assumption that there exist two different types of enzyme which occur either in pure form or in a mixture; the proportion of the two enzymes in the mixture varies considerably from person to person but there are equal proportions on the average. Most observations on the inheritance of DN can be explained by the presence of two autosomal allelic genes without dominance, each gene causing the formation of one of the two types of enzyme. Some observations pointed to additional factors which may be variants of the normal gene, or modifying genes which influence the expressivity of the normal gene. There was an excess of male offspring in the investigated families but a connection with DN not established. In a healthy population, the frequency of the atypical gene was calculated to be 0.0140 ± 0.0036. Thus roughly one out of 30 persons has an intermediate DN but only one out of 3000 to 10,000 is expected to have an atypical DN.