Frequencies of pseudocholinesterase variants in Icelanders, Greeks and Pakistanis

Ethnic differences in the frequency of distribution of serum cholinesterase activity in the Iranian population

One thousand Iranians belonging to 5 different Iranian ethnic groups were tested for butyrylcholinesterase (BChE) activity and phenotype. The phenotype was measured as percent inhibition in the presence of dibucaine. It was found that the Iranian population had an extraordinarily high frequency of the atypical variant of butyrylcholinesterase. 70% to 80% of Iranians carried the atypical mutation (Asp70Gly) on one allele. This contrasts with European and American populations where only 4% carry the atypical allele. The atypical variant of butyrylcholinesterase is known to be associated with prolonged apnea after administration of the muscle relaxants succinylcholine and mivacurium, and is also thought to be associated with abnormal sensitivity to cocaine toxicity. This study demonstrates that the ethnic background of a person has an important role in a person's response to drugs.Key words: butyrylcholinesterase, dibucaine number, heterozygous genes, different Iranian ethnics, metabolic polymorphism.

Ethnic differences in the frequency distribution of serum cholinesterase activity

We studied the activity of the enzyme pseudocholinesterase (serum cholinesterase) and its sensitivity to inhibition by dibucaine and fluoride in 400 (200 Iranian and 200 Irish) healthy subjects. The results show Irish subjects have significantly higher serum cholinesterase activity than Iranian subjects (7.82 +/- 0.14 vs 5.22 +/- 0.09 u/ml, mean +/- SEM, p < 0.01). Furthermore, the percent of inhibition of enzyme activity by dibucaine (82.19 +/- 0.68 vs 69.29 +/- 0.68) and fluoride (79.90 +/- 70.13 +/- 0.62) was also significantly higher (p < 0.001) in Irish than in Iranian subjects. One subject (Iranian) with very low pseudocholinesterase activity and a dibucaine number below 20 (atypical) had a history of apnoea following succinylcholine (suxamethonium). These data indicate that the frequency of atypical and heterozygote genes for cholinesterase activity leading to prolonged apnoea is much higher in Iranian than Irish populations. This study emphasises the importance of ethnic pharmacology.

On the geographical distribution of pseudocholinesterase variants

The incidence of pseudocholinesterase (PCHE equals E.C. 3.1.1.8) variants in samples of 8 different population (total of 2218 individuals) is reported. Together with previously mentioned data from the literature, a general survey on the geographical distribution of PCHE isoenzymes is given. Possible reasons for present-day heterogeneity of their distribution are also discussed. Concerning the incidence of the C5 variant, it is pointed out that the validity of applying population genetic models depends upon the accuracy of the genetic basis.