Complete Pseudocholinesterase Deficiency: Genetic and Immunologic Characterization*

The plasma enzyme pseudocholinesterase (acyl-choline acyl hydrolase) is composed of a series of related glycoproteins that comprise no more than 0.017o of the total plasma proteins (1). Its biological function in normal metabolism is not fully understood (2). Pseudocholinesterase is essential for the rapid breakdown of the muscle relaxant suxamethonium (succinylcholine), which is frequently used in surgery and electroshock therapy. Thus, if pseudocholinesterase activity is defective or markedly decreased, prolonged muscle relaxation and apnea may follow the ad-ministration of the drug (3, 4). Pseudocholinesterase activity is markedly in-hibited by a number of compounds. There are, however, two variant forms of the enzyme, which are characterized by decreased susceptibility to inhibition by the local anesthetic dibucaine (5, 6), on the one hand, and by fluoride (7) on the other. The formation of these enzymes is pre-sumably controlled by allelic mutants of the nor-mal gene, E1u, which determines the usual esterase (8, 9). The dibucaine-resistant enzyme is pro-duced by the gene called Ela, for which 3 to 4%o of the population are heterozygous (10). The other gene E1l, associated with fluoride-resistant esterase production, has a much lower frequency. Individuals who are either homozygous for these genes (i.e., E1a/Ela and E1l/El') or who possess * Submitted for publication September 15, 1964; ac-