Genetic abnormality of cytochrome-P2C9*3 allele predisposes to epilepsy and phenytoin-induced adverse drug reactions: genotyping findings of cytochrome-alleles in the North Indian population

Background

This research aims to study the association of genetic polymorphism in genes coding for CYP2C9 and CYP2C19 in phenytoin-induced dose-related toxicity and to assess if the presence of allele CYP2C9*3 plays a role in phenytoin-induced idiosyncratic adverse effects. Current observational case control study included 142 patients with phenytoin-induced adverse drug reactions (ADRs) and 100 controls. All these patients underwent genotyping to determine the type of CYP2C9 allele [CYP2C9*1, CYP2C9*2 or CYP2C9*3) and CYP2C19 allele (CYP2C19*1, CYP2C19*2 or CYP2C19*3] by real-time polymerase chain reaction (RT-PCR) using Applied Biosystems (ABI) 7500 Real-Time PCR System (USA).

Results

Presence of homozygous status for allele CYP2C9*3 was associated with significantly higher risk of phenytoin-induced dose-dependent ADRs, dose-independent ADRs, gum hyperplasia, and skin rash. Presence of heterozygous status for allele CYP2C9*3 was associated with significantly higher risk of phyenytoin-induced dose-dependent ADRs and dose-independent ADRs. Presence of either heterozygous or homozygous status for CYP2C9*2 and CYP2C19*2 did not have any bearing on dose-related side effects. None of the patients showed CYP2C19*3 allele.

Conclusion

Variant alleles of CYP2C9*3 are significantly overexpressed among patients with phenytoin-induced ADRs, thereby suggesting the role for CYP2C9 genotype testing to predict risk of phenytoin-related ADRs.