Study on genetic polymorphisms and phenotypic frequency distribution of CYP2C9, CYP2C19 and CYP2D6 in Han Chinese population

Purpose Genetic mutations and phenotypic changes of CYP2C9, CYP2C19 and CYP2D6 are vital for individual variations in clinical drug responses. Elucidating the mutating frequencies and phenotypic distributions of these genes shall facilitate the implementation of preemptive pharmacogenetic testing. We analyzed the gene polymorphisms and phenotypic frequencies of CYP2C9, CYP2C19 and CYP2D6 in Han Chinese population. Methods Tests of CYP2C9, CYP2C19 and CYP2D6 were performed in over 3200 (3276-3293) samples in Han Chinese population; furthermore, systematic review was employed for analyzing the mutation frequency and phenotypic distribution of CYP2C9 and CYP2C19 in Han Chinese population. Results Among 9062 samples, the mutation frequency of CYP2C9 was 11.49% and the frequency of phenotypic changes 7.1%; in 8222 samples, the mutation frequency of CYP2C19 was 66.07% and the frequency of phenotypic changes 63.75%; among 3931 samples, the mutation frequency of CYP2D6 was 88.04% and the frequency of phenotypic changes 3.87%. Among 2690 samples, gene mutations and phenotypic distributions of CYP2C9, CYP2C19 and CYP2D6 were simultaneously examined and it was found that 96.36% samples became mutated and the frequency of phenotypic changes was 66.51%. Conclusions In Han Chinese population, the gene mutations and phenotypic changes of CYP2C9, CYP2C19 and CYP2D6 are all relatively frequent. Prior to dosing, preemptive pharmacogenetic testing of CYP2C9, CYP2C19 and CYP2D6 is recommended.

have been most thoroughly examined so far in P450 metabolic enzymes [3]. However, there is still an ongoing debate on guiding drug dosing by detecting these main PGx genes [4]. Even the guideline of CPIC only discussed the issue of transforming PGx genotype into clinical phenotype [5]. There was no recommendation of whether or not conducting preemptive pharmacogenetic testing. Existing confusion of PGx genotype testing was mainly due to a lack of convincing evidences for large-scaled clinical trials for con rming the clinical values of PGx [6]. Recently more and more such trials of PGx are performed.
For example, CHANCE study has con rmed that, in patients with mild ischemic stroke or transient ischemic attack (TIA), as compared with aspirin dosing alone, a combined use of aspirin and clopidogrel could only lower the occurring rate of new stroke among patients not carrying CYP2C19 loss-of-function allele [7]. As demonstrated by Genetic Informatics Trial (GIFT), among patients undergoing elective hip/knee joint replacement and receiving warfarin therapy during perioperative period, as compared with routine clinical drug dosing, genotype-guided dosing of warfarin could lower the risks of major hemorrhage, venous thrombus/embolism and death [8]. As con rmed by a randomized clinical trial of Syn NL et al, the dosing scheme based upon a formula of pharmacogenetic might reduce the dose of warfarin and better predict its maintenance dose in Asian populations. With the elapsing of time, a growing body of convincing evidences from clinical trials shall reiterate the needs of conducting preemptive pharmacogenetic testing [9]. And many current controversies of pharmacogenetic testing may be settled.
However, in addition to the strong clinical research evidence of preemptive pharmacogenetic testing, we should not ignore the in uence of genetic polymorphisms and phenotype frequency distribution on preemptive pharmacogenetic testing. If the frequency of genetic polymorphism is low and a small variation exists in phenotypic frequency, then the cost effectiveness of pharmacogenetic test shall be minimal. Thus implementing pharmacogenetic test is to restrain clinically. Other than providing study evidences, we should also pay attention to the frequencies of these VIP PGx genes and their phenotypes. Thus it is possible to evaluate objectively the value of preemptive pharmacogenetic testing. For such wellestablished P450 enzymes as CYP2C9, CYP2C19 and CYP2D6, examining their polymorphisms and phenotypes may provide more comprehensive rationales of guiding clinical drug dosing with preemptive pharmacogenetic testing in Han Chinese population.

Allele frequency Data
Collaborating with Pharmacogenomics database (PGxC, www.chnpgxc.com), Third Xiangya Hospital of Central South University utilized an Illumina HI SEQ X-10 sequencer for detecting multiple VIP PGx genes, including CYP2C9, CYP2C19 and CYP2D6 polymorphisms, in Han Chinese population of 3200 (3276-3293) subjects. The study was approved by the ethics committee of the Third Xiangya Hospital of Central South University. Furthermore, the PubMed database was searched for the literature reports of CYP2C9 and CYP2C19 polymorphism frequency in healthy Han Chinese population having a sample size of over 100. Ultimately systematic reviews were conducted for analyzing the distributions of CYP2C9 and CYP2C19. Wildtype frequency = (1 -overall mutant frequency) ×100%. Due to the complexity of CYP2D6 polymorphism involving variation in copy number, only samples supplied by PGxC were detected for CYP2D6 and no systematic review was performed.

Allele nomenclature and de nitions
Based upon the Human CYP Allele Nomenclature Database (https://www.pharmvar.org/) and PharmGKB database (https://www.pharmgkb.org/), star (*) allele was adopted for naming and functional notes. CYP allelic genotypic functions included the increased function, normal function, decreased function and no function. Based upon standardized pharmacogenetic terms from the CPIC, the phenotypes of CYP enzymes were classi ed as ultrarapid, rapid, normal, intermediate and poor metabolizers [10].

Discussion
Systemic studies were performed for the genotypic and phenotypic distributions of CYP2C9, CYP2C19 and CYP2D6 in Han Chinese population. Furthermore, we also examined the co-existing patterns of genotypes and phenotypic changes for CYP2C9, CYP2C19 and CYP2D6.
In the mean time, we also analyzed the genotypes and phenotypes of CYP2C9, CYP2C19 and CYP2D6.
The overall mutation rate was as high as 96.36%; and the ultimate mutating frequency of inducing altered enzymatic activity was up to 66.51%. It hinted that adjusting drug doses was essential for at least half of Chinese populations using common substrate drugs of CYP2C9, CYP2C19 and CYP2D6.
In Han Chinese population, the genetic mutations and phenotypic changes of CYP2C9, CYP2C19 and CYP2D6 are all relatively frequent. It is worth noting that the mutations and phenotypic changes of CYP2C19 have surpassed 60%; there is a higher prevalence of triple-gene mutations and phenotypic changes. This study shall facilitate the implementation of preemptive pharmacogenetic testing in Chinese population.

Declarations
Authors' contributions All authors including LH, SC, JL, XX, LH, YK, YZ, HT, QP, GY and CG have made substantial, direct and intellectual contribution to the work and approved it for publication. Con ict of interest The authors declare that they have no con ict of interest.

Gene
Sample size Other* as clustering of non-common genotypes Table 2 Distribution frequencies of CYP2C9, CYP2C19 and CYP2D6 phenotypes