Expression of three naturally occurring genetic variants (G75R, E90D, I99M) of the BCHE gene of human butyrylcholinesterase.

The present paper examined the effects of three non synonymous BCHE mutations (G75R, E90D and /99M) on enzyme kinetic parameters obtained after the expression of the respective recombinant BChEs. The respective nucleotide substitution that characterizes each of the three variants was introduced into BCHE cDNA by site directed mutagenesis and transfected into human embryonic kidney 293 T cells and Chinese hamster ovary cells (for E90D). BChE catalysed hydrolysis of butyrylthiocoline (BTC) was measured by Ellman method. The expression results showed that: (1) the activity of the G75R enzyme represents approximately 45% of the wild-type activity, whereas that of the I99M enzyme does not differ from the wild-type; (2) the E90D enzyme presents a silent phenotype; disruption of the salt bridge between E90 and R42 may cause the enzyme to be rapidly degraded inside the cells. In homozygous form the E90D enzyme may confer increased susceptibility to succinylcholine, but may delay cognitive impairment in aged individuals. BChE genotyping may become important for estimating prognosis, and the knowledge of the genetic variants of BChE in a particular population may be useful for carrying out the genotyping assays.