De novo amplification within a "silent" human cholinesterase gene in a family subjected to prolonged exposure to organophosphorous insecticides

Abstract

A 100-fold DNA amplification in the CHE gene, coding for serum butyrylcholinesterase (BtChoEase), was found in a farmer expressing the "silent" CHE phenotype. Individuals homozygous for this gene display a defective serum BtChoEase and are particularly vulnerable to poisoning by agricultural organophosphorous insecticides, to which all members of this family had long been exposed. DNA blot hybridization with regional BtChoEase cDNA probes suggested that the amplification was most intense in regions encoding central sequences within BtChoEase cDNA, whereas distal sequences were amplified to a much lower extent. This is in agreement with the "onion skin" model, based on amplification of genes in cultured cells and primary tumors. The amplification was absent in the grandparents but present at the same extent in one of their sons and in a grandson, with similar DNA blot hybridization patterns. In situ hybridization experiments localized the amplified sequences to the long arm of chromosome 3, close to the site where we previously mapped the CHE gene. Altogether, these observations suggest that the initial amplification event occurred early in embryogenesis, spermatogenesis, or oogenesis, where the CHE gene is intensely active and where cholinergic functioning was indicated to be physiologically necessary. Our findings demonstrate a de novo amplification in apparently healthy individuals within an autosomal gene producing a target protein to an inhibitor. Its occurrence in two generations from a family under prolonged exposure to parathion indicates that organophosphorous poisons may be implicated in previously unforeseen long-term ecological effects.