2.4 .DNA methylation assay
Genomic DNA was extracted from peripheral blood leukocytes according to standard procedures using a commercially available kit (E.Z.N.A.TM SQ Blood DAN Kit) following the manufacturer’s instructions. Genomic DNA is treated with bisulfite using EZ DNA Methylation-Gold™ Kit. Multiplex PCR reaction was performed on the DNA after methylation. Primer information was shown in supplementary Table 2. Products were purified using AMPure XP beads. The Qubit 3.0 was used to determine the concentration of the library; Agilent 2100 Bioanalyzer system was used to determine the length of library fragments. Qualified libraries would be sequenced on an Illumina platform. Thirty-nine CpG loci on CYP2C19 gene were detected, and the GRCh38.p14 location information of each loci was summarized as shown in supplementary Table 3. The level of methylation (%methylation) is expressed as the beta value, which = methylated cytosine/(methylated cytosine+unmethylated cytosine).