Evaluation of the functional impact of rare CYP2C19 missense variants identified in understudied Populations: An Integrated in silico and in vitro analysis

Cytochrome P450 enzymes, particularly CYP2D6 and CYP2C19, play a crucial role in metabolizing various prescribed medications. While common CYP2C19 variants, such as *2 and *3 alleles, are well-studied, rare and novel variants remain less understood, especially in understudied populations. This study investigated the functional impact of seven rare or novel CYP2C19 missense variants (p.T55S, p.E92D, p.V113I, p.D262N, p.F267L, p.P337S, and p.I387V) identified in the Emirati population, some of which have also been reported in other populations. In silico prediction programs and molecular modeling have been used to evaluate and predict the expected impacts of these variants. In addition, we employed site-directed mutagenesis to generate these variants in CYP2C19 cDNA, which was cloned into a mammalian expression vector, and evaluated their functional consequences using in vitro enzymatic assays. Our findings revealed that five of the seven variants (p.T55S, p.V113I, p.D262N, p.F267L, and p.P337S) significantly reduced CYP2C19 4'-hydroxylation catalytic activity towards (S)-mephenytoin, suggesting detrimental effects on drug metabolism. These results underscore the clinical importance of considering the impact of rare variants and, consequently, the need for their detailed functional analysis to integrate them into the implementation of pharmacogenomics and personalized medicine. This research contributes to the growing understanding of population-specific genetic variations in CYP2C19 and their potential implications for the response and safety of a significant number of medications metabolized by this enzyme.