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A disorder caused by atypical or deficiency of pseudocholinesterase (PCE) leading to prolonged paralysis after administration of succinylcholine or mivacurium.

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Pseudocholinesterase Deficiency; Plasma Cholinesterase Deficiency; Butyrylcholinesterase Deficiency; Cholinesterase II Deficiency; Succinylcholine Sensitivity; Suxamethonium Sensitivity.

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For homozygosity, the incidence is approximately 1:2,000-4,000, whereas the incidence for heterozygosity increases to up to 1:500. The gene for the dibucaine-resistant atypical cholinesterase appears to be widely distributed. Among Caucasians, males are affected almost twice as often as females. The frequency for heterozygosity is low among black people, Japanese and non-Japanese Orientals, South Americans, Australian aborigines, and Arctic Inuits (in general). However, there are a few Inuit populations (e.g., Alaskan Inuits) with an unusually high gene frequency for PCE deficiency. A relatively high frequency also was reported among Jews from Iran and Iraq, Caucasians from North America, Great Britain, Portugal, Yugoslavia, and Greece.

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Autosomal recessive. Genes encoding cholinesterase 1 (CHE1) and CHE2 have been mapped to 3q26.1-q26.2. One gene is silent, whereas the other is responsible for the defect in cholinesterase.

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The inherited defect is caused by either the presence of an atypical PCE or complete absence of the enzyme. Cholinesterases are enzymes that facilitate hydrolysis of the esters of choline. Acetylcholine, the most commonly encountered of these esters, is the mediator of the whole cholinergic system. Acetylcholine is immediately inactivated “in situ” by a specific acetylcholinesterase in the ganglions of the autonomic nervous system (preganglionic and postganglionic in the parasympathetic nervous system and almost exclusively preganglionic in the sympathetic nervous system), in the synapses of the central nervous system, and in the neuromuscular junctions. The affinity of PCE is lower for acetylcholine, but higher for other esters of choline, such as butyrylcholine, benzoylcholine, and succinylcholine, and for aromatic esters (e.g., procaine, chloroprocaine, tetracaine). Normal PCE is produced in the liver, has a plasma half-life of 8 to 12 days, and can be found in plasma, erythrocytes, glial tissue, liver, pancreas, and bowel. When succinylcholine is used for anesthesia, its high plasma concentration immediately after intravenous injection decreases rapidly in normal individuals because of the rapid action of plasma PCE. In case of an atypical PCE or complete absence of PCE, the effect of the injected succinylcholine can last for up to 10 hours.

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The disorder is completely asymptomatic prior to the use of succinylcholine. The diagnosis is suspected in any patient with prolonged paralysis (>10 minutes) after succinylcholine administration. A nerve stimulator helps confirm the diagnosis by demonstrating the flaccidity of hand muscles. Laboratory tests use the property of the local anesthetic dibucaine, which can inhibit normal PCE activity in vitro, but has minimal effects on atypical enzymes. Normal PCE activity is reduced by nearly 80%, whereas the activity of atypical enzymes is reduced by only 20%. This defines the “dibucaine number” (DN), which represents the percentage inhibition of PCE by a fixed concentration of dibucaine under standardized conditions using benzoylcholine as the substrate. DN ...

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