Serum pseudocholinesterase

deficiency (butyrylcholinesterase)
About 1 in 200 individuals reacts to muscle relaxants,
such as suxamethonium (succinylcholine),
with prolonged muscle relaxation and
respiratory arrest. In such persons, serum pseudocholinesterase
activity is decreased. Persons
at risk cannot be identified by determining their
pseudocholinesterase activity alone (1), but by
determining dibucaine inhibition of their
enzyme activity. Whereas homozygous normal
persons show 80% enzyme activity after dibucaine
administration, persons at risk show only
20%. Individuals with intermediate values of
60% are regarded as heterozygotes (2). A number
of different alleles can lead to different
degrees of reduced enzyme activity. (Figure
after Harris, 1975.) This enzyme is now referred
to as butyrylcholinesterase because it hydrolyzes
butyrylcholine more readily than acetylcholine.