Digital PCR for determination of cytochrome P450 2D6 and sulfotransferase 1A1 gene copy number variations

CYP2D6 and SULT1A1 occasionally show copy number variations (CNVs), with a larger number generally indicating greater enzymic activity. However, those variations are difficult to calculate using standard methods. With digital PCR, a recently introduced method for CNV analysis, DNA molecules are subjected to limited dilution and separated into nano-scale droplets prior to a PCR assay. Absolute quantitation of copy number can then be performed with high accuracy and sensitivity by determining the number of droplets showing an amplified signal for the target gene. This is the first report of analyses of CYP2D6 and SULT1A1 CNVs using a digital PCR method with blood sample from Japanese subject. Primers and probes were synthesized for the target and reference genes, and copy number calculation was performed using a QX200 Droplet Digital PCR System. Our results showed that the copy numbers in CYP2D6*5 hetero, non-CNV, and CYP2D6xN subjects were 1, 2, and 3 to 4, respectively. In addition, in non-CNV and multiplication subjects, the number of copies for SULT1A1 was 2 and 3 to 6, respectively. We found that the present digital PCR method was useful as well as accurate. In the future, a combined genotyping, allele distinction, and copy number calculation technique will be helpful for analysis of enzymic activity.