I read the fascinating hypothesis by Pandit et al. concerning the high prevalence of pseudocholinesterase (PCHE) deficiency among Inuits and Vysyas with considerable interest.1 The authors dismiss a ‘founder’ effect (due to inbreeding within a culturally and geographically isolated population) in favour of the ‘heterozygote advantage’ conferred by possession of a single abnormal allele. However, I would question this hypothesis, because for PCHE deletion to confer a heterozygote advantage as described, unaffected homozygotes would have to die in significant numbers from their ‘evolutionary disadvantage’ (i.e. PCHE insertion) before reaching reproductive age. Certainly, this is the case with sickle cell disease, in which the incidence of malaria-related deaths is highest among unaffected homozygotes during infancy, but would seem unlikely to be a factor in PCHE deletion/hypolipidaemia because unaffected homozygotes are unlikely to die of ischaemic heart disease/myocardial infarction before they have had a chance to reproduce. Furthermore, any heterozygote advantage might be expected to be balanced by a heterozygote disadvantage resulting from exposure among rural developing populations to organophosphate toxicity,2 which may be of particular relevance to the Vysyas of India.3
A founder effect, therefore, remains a more plausible explanation, further evidence of which is provided by recently observed differences in the relative frequencies of PCHE allele penetrance among three tribes of South American Indians, according to the degree of interbreeding that has taken place with Europeans over time.4
The authors’ hypothesis concerning PCHE deletion might be supported, for example, if evidence was found of high rates of cocaine-related mortality among young, unaffected South Amerindian homozygotes who chew coca leaves to ameliorate symptoms of high altitude, but this would still fail to explain the high prevalence of PCHE deletion among Inuits and Vysyas, excepting a founder effect.
1. Pandit JJ, Gopa S, Arora J. A hypothesis to explain the high prevalence of pseudocholinesterase deficiency in specific population groups. Eur J Anaesthesiol
2. Lockridge O, Masson P. Pesticides and susceptible populations: people with butyrylcholinesterase genetic variants may be at risk. Neurotoxicology
3. Pandit V, Seshadri S, Rao SN, et al. A case of organophosphate poisoning presenting with seizure and unavailable history of parenteral suicide attempt. J Emerg Trauma Shock
4. Acuña M, Eaton L, Ramírez NR, et al. Genetic variants of serum butyrylcholinesterase in Chilean Mapuche Indians. Am J Phys Anthropol