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  • Methodology
  • Open Access

Real time PCR detection of common CYP2D6 genetic variants and its application in a Karen population study

Malaria Journal201817:427

https://doi.org/10.1186/s12936-018-2579-8

  • Received: 3 September 2018
  • Accepted: 9 November 2018
  • Published:

Abstract

Background

Plasmodium vivax malaria is characterized by relapses arising from the hypnozoite stages in the liver. The only currently registered drug for radical treatment to prevent relapse is primaquine. Primaquine, a prodrug, requires metabolism through the liver cytochrome CYP2D6 isoenzyme to its active metabolite. Mutations in the CYP2D6 gene may thus affect primaquine efficacy. A SNPs genotyping technique was developed to characterize the CYP2D6 genetic variants and tested this in the patients with Plasmodium vivax infection collected in a Karen population on the Thailand–Myanmar border, where P. vivax malaria is endemic.

Methods

Direct sequencing of PCR-reamplified products (DSP) was used to uncover exonic CYP2D6 sequence variations. Subsequently, an allele-specific oligonucleotide probe real-time SNPs genotyping (ASO) assay was developed for rapid detection of the four clinically relevant CYP2D6 variants occurring in this population. These two in-house developed assays were used to genotype CYP2D6 mutations in blood samples obtained from 70 Karen adults.

Results

Results showed a high degree of concordance between the DSP and ASO methods. Six CYP2D6 point mutations were identified within the Karen population: C100T, C1039T, G1661C, G1846A, C2850T and G4180C, at frequencies of 0.43, 0.43, 0.76, 0.02, 0.32 and 0.76, respectively. The CYP2D6*2, *4, *5, *10 and *36 allelic frequencies were 0.33, 0.02, 0.03, 0.40 and 0.01, respectively. Alleles conferring an intermediate CYP2D6 metabolizer phenotype comprised 46% of the total number of alleles.

Conclusion

The newly developed ASO assay is a reliable and rapid tool for large-scale CYP2D6 genotyping. The high frequency of the CYP2D6*10 allele in the Karen population warrants further assessment of its association with the radical curative efficacy of primaquine.

Keywords

  • Malaria
  • Primaquine
  • CYP2D6
  • Karen

Background

Primaquine (PQ), an 8-aminoquinoline, is currently the only widely available drug for radical treatment of Plasmodium vivax malaria. It is active against the dormant hypnozoite stages of the parasite in the liver responsible for relapse infections [1]. Primaquine itself is biologically inactive and requires biotransformation to active metabolites for its anti-hypnozoite effect. Two metabolic pathways have been identified, involving monoamine oxidase-A (MAO-A) and the cytochrome P450 CYP2D6 isoenzyme. Carboxyprimaquine which is generated via the MAO-A mediated pathway is the most abundant metabolite in plasma, but it is not considered hypnozoitocidal [24]. The active phenolic metabolites resulting from metabolism through CYP2D6 are likely to exert anti-malarial properties mediated by the production of oxidative stress through redox cycling [47]. A number of studies have shown that CYP2D6 plays a crucial role in the metabolic activation of primaquine [4, 811] and that mutations in CYP2D6 can potentially affect primaquine efficacy [12, 13]. Accurate genotyping of the CYP2D6 gene is difficult because of the presence of highly homologous pseudogenes and the highly polymorphic character of the gene. The CYP2D8 and CYP2D7 flanking pseudogenes display over 90% nucleotide sequence homology compared to the active CYP2D6 gene [14, 15], potentially resulting in co-amplification during the gene amplification process [16, 17]. Consequently, multiple homologous PCR templates and mis-primed sequences containing several inactive mutations can easily result in incorrect genotype assignments [14, 18, 19]. In addition, there is wide genetic variability in CYP2D6, including single nucleotide substitutions, insertion/deletion, partial gene conversions [20], CYP2D7/2D6 hybrid tandems [21], copy number variations (CNVs) [16, 22, 23] and complex structural rearrangements [17, 24, 25]. This has resulted in the characterization of over one-hundred CYP2D6 variant alleles, which further complicates genotyping. Furthermore, the prevalence of allelic variants associated with impaired CYP2D6 catalytic activity have been found to vary widely across ethnic populations [2628]. In the present study, a CYP2D6 genotyping protocol was developed to screen for variants with known clinical significance in Southeast Asia and tested the method on P. vivax infection samples collected from a Karen population on the Thailand–Myanmar border.

Methods

Study population and DNA preparation

Seventy anonymized blood samples were collected in the Karen population living in Tak, one of the western provinces in Thailand. All patients were diagnosed by microscopy of thick and thin blood smears, examined by qualified laboratory technicians. Only patients with P. vivax mono-infections were included in the study. Among vivax patients, 39 (56%) were females, the median age was 16 years old (IQR 11–24 years old), the median weight was 40 kg (IQR 18–50 kg), and the median parasitaemia was 4024 parasites/µl (IQR 1592–10,793 parasites/µl). Genomic DNA extraction was by the QIAamp DNA Mini Kit (Qiagen, Germany), according to the manufacturer’s guidelines. The isolated genomic DNA samples were stored at 4 °C until further processing. Allele designation followed the Human Cytochrome P450 (CYP) Allele Nomenclature Database (http://www.imm.ki.se/CYPalleles/) (Table 1). The study was approved by the Ethics Committee of the Faculty of Tropical Medicine, Mahidol University (EC Submission No.: TMEC 15-095).
Table 1

CYP2D6 alleles in the Karen study population and related nucleotide and amino acid substitutions

Alleles

Nucleotide substitutions

Amino acid substitutions

Ref SNP ID

CYP2D6*1

Reference allele

Reference protein

CYP2D6*2

C2850T, G4180C

R296C, S486T

rs16947

CYP2D6*4

C100T, G1846A, G4180C

P34S, splicing defect, S486T

rs3892097

CYP2D6*5

Deletion of CYP2D6 gene

Not applicable

Not applicable

CYP2D6*10

C100T, G4180C

P34S, S486T

rs1065852

CYP2D6*36

C100T, G4180C, gene conversion to CYP2D7 in exon 9

P34S, S486T

The nucleotide and amino acid substitutions in bold letters denote key variations used to assign particular variant alleles, based on Gene bank accession number M33388.1. Unique allele names were assigned as described in the Human Cytochrome P450 (CYP) Allele Nomenclature Database (http://www.imm.ki.se/CYPalleles/)

Primers and probes

Two genomic sequences retrieved from NCBI, CYP2D6 (GeneBank accession number M33388.1) and CYP2D7/8 (GeneBank accession number M33387.1), were used as genomic reference templates. Optimal primer sequences of PCR-reamplified products were selected by Primer3 software version 0.4.0 and were then synthesized by Macrogen Inc. (Korea). Variant-specific primer and probe sets of real-time PCR were designed and supplied directly by Applied Biosystems (Thermal Fisher Scientific, Inc.). Wild-type and mutant CYP2D6 probes were labeled at the 5′ end with VIC and FAM respectively, and both probes included a non-fluorescent quencher. The sequences of primers and probes of all PCRs performed in each step are listed in Table 2. Positive controls are well-characterized samples sequenced across the entire CYP2D6 gene and redetected by real-time PCR assay. A summary of the genotyping method is provided in Fig. 1 and can be summarized in the following four steps.
Table 2

Primer and probe sequences used for detection of CYP2D6 gene mutations

Analysis

Primer and probe names

Sequences (5′–3′)

Length (bp)

GC (%)

Tm (°C)

Amplicon size (bp)

XL-PCR [29]

DPKup

5′-GTTATCCCAGAAGGCTTTGCAGGCTTCA-3′

28

50.0

67.8

5100

DPKlow

5′-GCCGACTGAGCCCTGGGAGGTAGGTA-3′

26

65.4

71.1

2D6dupl-F

5′-CCTGGGAAGGCCCCATGGAAG-3′

21

66.7

65.5

3500

2D6dupl-R

5′-CAGTTACGGCAGTGGTCAGCT-3′

21

57.1

63.2

5′2D6*5

5′-CACCAGGCACCTGTACTCCTC-3′

21

61.9

62.7

3500

3′2D6*5

5′-CAGGCATGAGCTAAGGCACCCAGAC-3′

25

60.0

67.9

Int2

5′2D6Int2

5′-TTTTGCACTGTGGGTCCTC-3′

19

52.6

58.5

1101

3′2D6Int2

5′-CAAGGTGGACACGGAGAAG-3′

19

57.9

58.4

Direct sequencing of PCR-reamplified products, DSP

5′2D6Ex1

5′-GCACAGTCAACACAGCAGGT-3′

20

55.0

61.7

503

3′2D6Ex1

5′-AATGCCCTTCTCCAGGAAGT-3′

20

50.0

59.2

5′2D6Ex2

5′-TTCCTCCATCACAGAAGGTG-3′

20

50.0

57.4

501

3′2D6Ex2

5′-CTCCCTAGTGCAGGTGGTTT-3′

20

55.0

59.9

5′2D6Ex34

5′-GTCTTCCCTGAGTGCAAAGG-3′

20

55.0

59.1

754

3′2D6Ex34

5′-AGTGGGGTCTCCTGGAATG-3′

19

57.9

58.9

5′2D6Ex56

5′-GAGGGACTTGGTGAGGTCAG-3′

20

60.0

60.0

794

3′2D6Ex56

5′-GACACTCCTTCTTGCCTCCT-3′

20

55.0

59.6

5′2D6Ex7

5′-ATGAACTTTGCTGGGACACC-3′

20

50.0

59.0

505

3′2D6Ex7

5′-CCAGCCCTGCCTATACTCTG-3′

20

60.0

59.9

5′2D6Ex89

5′-TCTAGTGGGGAGACAAACCAG-3′

21

52.4

59.3

802

3′2D6Ex89

5′-CTGAGGAGGATGATCCCAAC-3′

20

55.0

57.7

Allele-specific oligonucleotide probes real time SNPs genotyping, ASO

 C100T

5′2D6C100T

5′-CCTGGTGGACCTGATGCA-3′

18

61.1

59.5

73

3′2D6C100T

5′-CCCGGGCAGTGGCA-3′

14

78.6

58.7

2D6C100T_WT

5′-CCTGGTGGGTAGCGTG-3′

16

69.0

51.1

2D6C100T_MT

5′-CCTGGTGAGTAGCGTG-3′

16

63.0

48.5

 G1846A

5′2D6G1846A

5′-GACCCCTTACCCGCATCTC-3′

19

63.2

60.1

73

3′2D6G1846A

5′-GCTCACGGCTTTGTCCAAGA-3′

20

55.0

61.5

2D6G1846A_WT

5′-CCCCCAGGACGCC-3′

13

85.0

48.0

2D6G1846A_MT

5′-CCCCCAAGACGCC-3′

13

77.0

46.0

 C2850T

5′2D6C2850T

5′-CCTGAGAGCAGCTTCAATGATGA-3′

23

47.8

61.3

67

3′2D6 C2850T

5′-CCATCCCGGCAGAGAACAG-3′

19

63.2

60.7

2D6C2850T _WT

5′-ACTATGCGCAGGTTC -3′

15

53.0

41.9

2D6C2850T _MT

5′-CACTATGCACAGGTTC-3′

16

50.0

43.4

 G4180C

5′2D6G4180C

5′-CCACCATGGTGTCTTTGCTTTC-3′

22

50.0

60.9

67

3′2D6G4180C

5′-GCACAGCACAAAGCTCATAGG-3′

21

52.4

60.4

2D6G4180C _WT

5′-CTGGTGAGCCCATCC-3′

15

67.0

47.4

2D6G4180C _MT

5′-CTGGTGACCCCATCC-3′

15

67.0

47.4

Fig. 1
Fig. 1

Summary of the assay development for assessment of common CYP2D6 genetic variants relevant for the Karen study population

Determination of CYP2D6 gene duplications/multiplications and gene deletions by extra-long range polymerase chain reaction (XL-PCR)

In a single tetra-primer XL-PCR mixture, two separate reactions including the CYP2D6 gene duplications/multiplications and deletions, both producing a 3.5 kb long PCR fragment, were determined simultaneously with the amplification of a 5.1 kb fragment encompassing the entire CYP2D6 gene. The generated CYP2D6 fragments were then used as templates for genotyping as described previously [29].

Discrimination of functional CYP2D6 and nonfunctional CYP2D8 and CYP2D7 genes by intron 2 sequencing (INT2)

In each XL-PCR run, the newly produced fragments were randomly sampled to be reamplified and sequenced in the intron 2 region. All nested INT2 reactions were carried out on a Mastercycler pro (Eppendorf, Hamburg, Germany). The XL-PCR products were reamplified in 25 µl reaction volumes containing 19.55 µl of nuclease-free water, 2.5 µl of 1× Master Mix buffer, 0.6 µl of 1.2 mM MgCl2, 1 µl of 0.2 mM dNTPs mix, 1.25 µl of 0.5 µM of both primers, 0.1 µl of 0.5 U Taq DNA Polymerase and 1 µl of CYP2D6 XL-PCR templates. The cycling conditions were as follows: 30 s initial denaturation at 95 °C, then 30 cycles of denaturation at 95 °C for 15 s, annealing 54 °C for 20 s, extension at 68 °C for 72 s, and a final extension step of 5 min at 68 °C. Subsequently, the presence of appropriately sized PCR products was separated on a 1.5% agarose gel electrophoresis and were purified using a FavorgenPrep™ GEL/PCR Purification Kit (Favorgen Biotech Corporation, Taiwan), followed by automated DNA sequencing at Macrogen Inc. (Korea).

Detection of CYP2D6 coding region mutations by direct sequencing of PCR-reamplified products (DSP)

The isolated CYP2D6 gene, which consists of nine exons, was PCR-reamplified by nested DSP primers. The nested DSP reactions were conducted on a Mastercycler-pro (Eppendorf, Hamburg, Germany). All six different PCR mixes were done in a 25 µl reaction mixture containing 19.4 µl of nuclease-free water, 2.5 µl of 1× Master Mix buffer, 0.75 µl of 1.5 mM MgCl2, 1 µl of 0.2 mM dNTPs mix, 1.25 µl of 0.5 µM of each primer pair, 0.1 µl of 0.5 U Taq DNA Polymerase and 1 µl of CYP2D6 XL-PCR template. Since reactions used similar annealing temperatures, identical cycling conditions could be used for all reactions: 30 s initial denaturation at 95 °C, then 30 cycles of denaturation at 95 °C for 15 s, annealing at 53 °C for 20 s, extension at 68 °C for 55 s, and a final extension step of 5 min at 68 °C. Identification of accurately sized PCR products, purification and sequencing were performed as mentioned earlier in the INT2 method. Sequencing was indeed performed bi-directionally, which will decrease the chance of a false-positive result. In addition, the long-range PCR tag polymerase used in the reactions has high fidelity, and a positive control was included in each batch. Finally, mutations identified are known variants, rather than random SNPs. Taken together, the reported mutations are very unlikely explained by sequencing errors.

Rapid identification of four polymorphic loci by allele-specific oligonucleotide probes real-time SNPs genotyping (ASO)

All analyzed samples with known CYP2D6 SNPs were genotyped in duplicate, using diluted XL-PCR fragments derived from both duplications/multiplications and deletions in order to ensure concordant SNPs calls. Genotyping for the key mutations, C100T [rs1065852], G1846A [rs3892097], C2850T [rs16947] and G4180C [rs1135840], were performed on StepOnePlus™ Real-time PCR Systems (Applied Biosystems Inc., Foster City, CA USA). The real-time PCR reactions were carried out in the final volume of 25 µl consisted of: 12.5 µl of 1× Tag Man Genotyping Master Mix (Roche Molecular Systems, Inc.), 1.25 µl of 1× mixed each forward, reverse and variant-specific probes, 10.75 µl of nuclease-free water, and 0.5 µl of XL-PCR template diluted at 3000-fold. Thermocycling conditions were as follows: 60 °C for 30 s followed by 95 °C for 10 min, followed by 40 cycles of 95 °C for 15 s, 60 °C for 1 min, and post-read stage at 60 °C for 30 s. Positive and negative controls were included in each run.

Results

CYP2D6 genotyping assay

Successfully produced entire CYP2D6 fragments (XL-PCR) served as templates in the assay (Fig. 2). Full-length intron 2 sequencing (INT2), which primers anneals internally to the XL-PCR products, distinguished between CYP2D7/8 pseudogenes and the functional CYP2D6 gene. All nucleotide sequences of the intron 2 region showed more than 95% sequence similarity to the CYP2D6 gene, indicating that the desired templates were generated correctly (see Additional file 1). Paired forward-reverse reads of 9 exons in each individual sample demonstrated that the sense CYP2D6-specific strands were perfectly matched base-by-base to their antisense strands, implying that the presence of call variants on the sequences could be identified correctly. Due to the high quality of DNA sequencing, heterozygous (double) peaks could be clearly identified, as shown in Additional file 2. Regarding the ASO genotyping assay, the seventy CYP2D6 specific amplicons were genotyped in duplicate at four selected loci residing within the CYP2D6 target sequence, showing good performance (see Addition file 2). The auto call analytical StepOne Software v2.1 (Applied Biosystems, Inc.) automatically generated allele discrimination plots with well-separated clusters for genotype callings, and the call rate in each assay was above 95%. All replicate assay results of individual samples were 100% identical in the variant call as they clustered in the same region of the scatterplot. Furthermore, in all seventy tested pairs of individual samples the genotyping results generated by the DSP and ASO assays showed perfect concordance for the assayed genotypes, representing the metabolic enzyme variants in the study population (see Additional file 2).
Fig. 2
Fig. 2

Overview of CYP2D locus arrangements and typical recombinant events. a A single CYP2D6 gene is located downstream of the CYP2D locus, with two pseudogenes CYP2D8/2D7 flanking at the 5′ end of the CYP2D6 gene. The position of each forward and reverse pair for amplifying the target fragments are represented by different colored arrows. b In the CYP2D6*5 deletion allele, the entire CYP2D6 is deleted from the CYP2D locus producing the new hybrid (REP DEL) containing 5′ yellow box sequence and 3′ green box sequence. c The general duplication arrangement, the hybrid REP DUP containing 5′ green box sequence and 3′ yellow box sequence were formed at 5′ of the CYP2D6 gene in case of multiple CYP2D6 gene copies occur d the 5.1 kb XL-PCR products encompass the entire CYP2D6 gene consisting of 9 exons with the four known clinically relevant point mutations located at different polymorphic sites. The 3.5 kb long fragment represents either duplications/multiplication or deletion

CYP2D6 variability in the Karen population

CYP2D6-specific XL-PCR products were successfully amplified in all seventy patients, of which 2 (3%) carried multiple active functional CYP2D6 genes and 4 (6%) a whole CYP2D6 gene deletion (Fig. 2). Combining all direct sequencing results of full-length CYP2D6 coding regions, at least one mutation was detected in all exons except in exon 4, 5, 7 and 8. Three non-synonymous substitutions (C100T: Exon1, C2850T: Exon6 and G4180C: Exon9), two synonymous substitutions (C1039T: Exon2 and G1661C: Exon3) and a mutation at the splice junction (G1846A) were detected. Frequencies of each allele and genotype are summarized in Additional file 3. Of the six mutations identified, SNPs at loci G1661C and G4180C were most frequent (0.76), followed by SNPs at loci C100T, C1039T and C2850T (0.43, 0.43 and 0.32, respectively), whereas SNP at loci G1846A was less frequent (0.02). The homozygous mutant genotype 4180C/C was the most common, and was found in 41 individuals (0.59), followed by 100C/T in 38 (0.54), 2850C/T in 32 (0.46), 4180G/C in 22 (0.31), 100T/T in 11 (0.16) and 2850T/T in 6 (0.09). In contrast, genotype frequencies of the splice site defect 1846G/A 3 (0.04) and 1846A/A 0 (0.00) were very low. CYP2D7 exon 9 conversion, assessed through entire exon 9 sequencing and associated with decreased enzymatic activity, was observed in only one individual (see Additional file 4). Data generated from the DSP/ASO genotyping assays, the 6 distinct alleles and 11 genotype frequencies, are summarized in Table 3. Other alleles and genotypes described in the literature were not observed in this Karen study population.
Table 3

Distribution of CYP2D6 genotypes and alleles in the Karen study population

Genotypes

n

Genotype frequencies

*1/*1

3

0.043

*1/*2

8

0.114

*1/*4

3

0.043

*1/*5

2

0.029

*1/*10

10

0.143

*1/*36

1

0.014

*2/*2

7

0.100

*2/*5

1

0.014

*2/*10

23

0.329

*5/*10

1

0.014

*10/*10

11

0.157

Total

70

1

Alleles

n

Allele frequencies

*1

30

0.214

*2

46

0.329

*4

3

0.021

*5

4

0.029

*10

56

0.400

*36

1

0.007

Total

140

1

Comparative analysis of CYP2D6 variants in different populations

The genotyping results was compared to the list of global genetic mutations in CYP2D6 from the 1000 Genome Project (http://www.ensembl.org) (Fig. 3). Although this study was conducted in P. vivax infected patients, the genotypic pattern observed in the Karen study population was similar to other patterns reported from East Asia, including China, Japan and Vietnam. The exception was C2850T, which showed a notably higher frequency in this study population (Table 4). As the geographical distance increased from the study area, including Bangladesh, India, Pakistan and Sri Lanka, the similarity between genotypes decreased. Similarity in the distributions of genotype frequencies was further reduced when comparing populations in Africa, America and Europe (Fig. 3 and Additional file 5).
Fig. 3
Fig. 3

1000 Genomes project phase 3 genotype frequencies. The genotype frequencies differ considerably among the ethnic populations, as demonstrated on selected common allelic variants being present in the Karen, C100T [rs1065852], G1846A [rs3892097], C2850T [rs16947] and G4180C [rs1135840]. The obtained frequencies were from http://www.ensembl.org

Table 4

CYP2D6 allele frequencies in Karen compared with frequencies previously described in other ethnic populations

Population

Year

n

Methods

C100T

P34S

(*10)

C1039T

G1661C

G1846A

Splicing

(*4)

C2850T

R296C

(*2)

G4180C

S486T

Gene conversion

(*36)

Deletion

(*5)

Duplications

Asian

 Karen (current study)

2017

70

DSP/ASO

0.40

0.43

0.76

0.02

0.33

0.76

0.01

0.03

0.01

 Thai [44]

2011

286

M/DHPLC

0.45

ND

ND

0.01

0.10

ND

0.16

0.04

0.004

 Thai [49]

2012

48

AmpliChip

0.44

ND

ND

0.01

0.10

ND

0.01

0.04

ND

 Thai [50]

2013

114

AmpliChip

0.46

ND

ND

0.01

0.10

ND

0.01

0.04

ND

 Thai [51]

2013

233

Amplichip

0.48

ND

ND

0.01

0.09

ND

0.01

0.05

0.004

 Thai [45]

2016

84

Luminex xTag

0.52

ND

ND

0.01

0.06

ND

ND

ND

0.06

 Chinese [52]

2002

223

ASA

0.51

ND

ND

0.002

ND

ND

ND

0.07

0.01

 Chinese [53]

2008

400

Sequencing

0.53

ND

ND

0.001

0.11

ND

ND

0.05

0.02

 Hong Kong Chinese [54]

2000

119

PCR–RFLP

0.65

ND

ND

0.00

0.08

ND

ND

0.05

ND

 Vietnamese [55]

2010

122

mSBE

0.57

ND

ND

ND

0.08

ND

ND

0.06

0.00

 Japanese [56]

1999

98

PCR

0.41

ND

ND

0.02

0.09

ND

ND

0.06

ND

 Japanese [57]

2000

412

PCR–RFLP

0.38

ND

ND

0.002

0.13

ND

ND

0.05

0.01

 Japanese [58]

2003

162

ASA-RFLP

0.38

ND

ND

0.00

0.13

ND

0.01

0.06

ND

 Korean [59]

2006

400

Sequencing

0.45

ND

ND

0.003

0.10

ND

ND

0.06

0.01

 Korean [60]

2009

758

Sequencing

0.46

ND

ND

ND

0.10

ND

ND

0.06

0.01

 Korean [61]

2011

766

SNaPshot

0.43

ND

ND

0.001

0.12

ND

ND

0.06

0.01

 South India [62]

2006

447

PCR–RFLP

0.10

ND

ND

0.07

0.35

ND

ND

0.02

ND

Caucasian

 Germany [63]

1997

589

PCR–RFLP

0.02

ND

ND

0.21

0.32

ND

ND

0.02

0.007

 Mexican-American [64]

2001

349

PCR–RFLP

0.07

ND

ND

0.10

0.23

ND

ND

0.02

0.01

 Spanish [65]

2006

105

RT-PCR

0.02

ND

ND

0.14

0.40

ND

ND

0.03

0.04

African

 African-American [66]

2001

154

PCR–RFLP

0.08

ND

ND

0.08

0.27

ND

ND

0.06

0.02

 African-American [67]

2006

222

AmpliChip

0.04

ND

ND

0.07

0.05

ND

0.005

0.06

0.05

 African-American [68]

2013

75

mPCR

0.03

ND

ND

0.08

0.29

ND

ND

0.09

ND

Allele frequencies of CYP2D6*2, *4, *5, *10 and *36 were calculated based on the presence of C2850T, G1846A, entire CYP2D6 gene deletion, C100T and gene conversion, respectively

n, the number of subjects ND, allele not determined in reference study; DSP/ASO, direct sequencing of PCR-reamplified products and allele-specific oligonucleotide probes real-time SNPs genotyping; ASA, allele-specific amplification assay; mPCR or SBE, multiplex PCR or single-base extension; M/DHPLC, multiplex PCR coupled with semi-quantitative denaturing high-performance liquid chromatography

Discussion

Primaquine is required for preventing P. vivax malaria relapses [1]. The radical curative efficacy of primaquine is thought to be mainly dependent on CYP2D6-mediated metabolism [12]. In addition to primaquine, its long half-life analogue tafenoquine has recently been developed for radical cure of P. vivax malaria. However, there are somewhat conflicting results whether differences in CYP2D6 metabolism confers differences in therapeutic efficacy. A clinical study showed that tafenoquine efficacy in P. vivax-infected patients was not affected by the changes in CYP2D6 activity [30]. In contrast, tafenoquine pharmacokinetic profiles in CYP2D knockout mice were differed significantly from those of wild-type mice, suggesting that tafenoquine could be possibly affected by the CYP2D metabolism [31]. Further studies will be needed to assess the importance of CYP2D6 mutations in tafenoquine biological activity. Since the CYP2D6 gene is highly polymorphic with hundreds of variant alleles described, it potentially affects a large range of clinically used drugs metabolized by the encoded enzyme [32]. Related to this, there is a growing interest for the development of user-friendly CYP2D6 genotyping platforms with sufficiently high throughput to characterize clinically relevant genetic variations in the CYP2D6 gene. Techniques previously described include restriction fragment length polymorphism (PCR–RFLP) [33, 34], single strand conformation polymorphism (SSCP) [35, 36], multiplex allele-specific PCR (Multiplex PCR) [37, 38], and allele-specific oligonucleotide hybridization (PCR-ASO) [39]. However, these techniques are mostly laborious to execute, time-consuming, error-prone and characterize only a limited number of alleles. Real-time PCR-based strategies enable detection of a larger number of mutations and are more rapid, but often deploy in-house developed primers with limited specificity, resulting in unwanted co-amplification of pseudogenes [4042]. More recent techniques including pyrosequencing [43], denaturing high-performance liquid chromatography (DHPLC) [44] and Luminex-xTag [45] perform better with shorter run-times, but all require highly advanced equipment often not available in malaria endemic countries. High-throughput microarray technology, such as GeneChip CYP450, Amplichip CYP450 and the DMET microarray [4648], have excellent performance and allele coverage, but is also technically difficult and costly.

In the current study, several steps were taken to increase performance of the assay: Firstly, the problem of co-amplification of CYP2D with high sequence similarity was overcome by using CYP2D6-specific amplification primers (XL-PCR) and a nested PCR approach (INT2). Secondly, introduction of direct sequencing of PCR-reamplified products (DSP) lowered the chance of missing non-targeted variations within the exonic CYP2D6 sequences. Thirdly, addition of the ASO assay enabled rapid identification of four allelic sites observed in the Karen study population, requiring approximately 90 min for parallel identification. Overall, our customizable ASO assay showed high accuracy with very high SNP call rates for each genotype and absence of contamination errors. Moreover, it yields high-intensity fluorescent signals and clearly separating allelic clusters. Reproducibility of the assay was not formally assessed, since this would involve in the results generated by inter-laboratory tests. However, the DSP and ASO assays were repeatedly genotyped, at least 2 times on different days, to assure the repeatability of the assays, and were analysed simultaneously with known CYP2D6 genotypes. The replications of CYP2D6 genotyping results were in 100% concordance. In order to rule out contamination, negative samples, consisting of nuclease free water, were evaluated in parallel within a single analytical run together with the patients’ samples. To reduce the chance of cross-reactivity in the experiments, 3 approaches were applied (a) all generated CYP2D6 templates were assayed by INT2 to confirm absence of cross-reactivity with the pseudogenes, (b) to minimize unintended binding to the pseudogenes, allele-specific primer and probe sets were designed using the public databases (NCBI and dbSNP), and (c) thermal cycling was optimized to reduce non-specific binding. Particularly, no significant interfering substances have been observed. Comparison of the ASO assay to the reference standard, DSP sequencing, showed full concordance between the two methods. Therefore, the customizable ASO assay is a promising tool for large-scale studies because it is simple, requiring limited processing, reducing the risk for contamination and showing good performance at reasonable costs. Sequencing the purified PCR products with 500–1000 bp coverage of the target site by Macrogen Inc., Korea, costs approximately 3.5 GBP/point mutation. 1 ml of Tag Man Genotyping Master mix, which is approximately 70 GBP, can be used for 70 reactions (12.5 μl/reaction), which translates to around 1 GBP/point mutation. The rough cost comparison of using ASO against a gold standard test revealed that all ASO reagents identified a single point mutation are relatively inexpensive and cost three times cheaper. Compared to the previous published TagMan based CYP2D6 genotyping assays, the here described assay has better performance by lacking cross-reactivity with the two pseudogenes CYP2D7 and CYP2D8. A limitation of the assay is the interpretation of results in heterozygous individuals with gene multiplications; the current method does not assess specific gene allele duplication or quantify the copy number for each allele. However, whereas gene amplification might result in increased production of the active metabolite of primaquine potentially increasing its efficacy, reduced activity of the drug is mainly associated with gene mutations resulting in reduced CYP2D6 activity. The latter was the scope of the study.

Initial use of the assay showed that the CYP2D6 allelic frequencies in this vivax-infected population corresponded well with the observed frequencies in nearby Asian populations, but were different from frequencies in Caucasian and African populations. This similarity suggests absence of selective pressure on the CYP2D6 genotype in this P. vivax infected population. The most abundant allele in the Karen population was the CYP2D6*10 allele, occurred at a frequency of 0.40, suggested that there is a high prevalence of individuals with reduced metabolic capacity for CYP2D6 dependent substrates. Whereas the CYP2D6*4 and *5 defective alleles, occurred at a frequency of 0.02 and 0.03 respectively, represents rare causes of reduced enzyme activity in this population. The CYP2D6*2 allele with a frequency of 0.33 was the most common functional allele in the Karen population, with high frequency of the 2850C/T and 2850T/T alleles. The number of CYP2D7 exon 9 conversion carriers (CYP2D6*36) was very small in the study, and a larger study is warranted to assess the frequency of this clinically important genotype in more detail. Since CYP2D6 allele frequencies vary markedly across ethnic populations, the ASO assay would have to be re-evaluated for other geographical areas. Additional file 1 shows the differences in CYP2D6 allele frequencies present in other areas including Africa, America, Europe and South Asian. The DSP approach providing the sequence the CYP2D6 region of the population of interest could inform which adaptations in a customized ASO assay would be necessary. Further studies are planned on CYP2D6 mutations in the Karen population using the ASO genotyping platform. Results will be compared to the data on the efficacy of primaquine in the study cohort to inform if efficacy proves to be compromised by CYP2D6 mutations associated with decreased CYP2D6 enzyme activity. Indeed, this is not a point of care test, but it is a simple method, which is easy to set up in molecular laboratories in tropical countries. Defining the impact of CYP2D6 mutations on primaquine dosing and efficacy will require a clinical trial, which can make use of the platform described here. The prevalence of mutation associated with defective CYP2D6 phenotypes in the Karen population has prompted our group to initiate such a study. Elimination of P. vivax will require wider deployment of radical cure with primaquine in an effective dose. This effective dose might differ according to the prevalent CYP2D6 mutations in the population. This relationship should be studied more extensively in different populations to ensure proper dosing. The described technique could facilitate this.

Conclusion

The ASO assay is a new CYP2D6 genotyping assay with high-accuracy and high-reproducibility for the detection of common CYP2D6 variant alleles, and is suitable for large-scale surveys. The high prevalence in the P. vivax infected patients in Karen population of the CYP2D6*10 allelic variant associated with reduced CYP2D6 enzyme activity could potentially affect the radical curative efficacy of primaquine and warrants more extensive evaluation.

Declarations

Authors’ contributions

NW, ND, FN, AD and MI contributed to study design. CC and FN collected samples. KP undertook laboratory work. KP, NW, AD, and MI analysed data. KP, NS, MI and AD drafted the manuscript. All authors read and approved the final manuscript.

Acknowledgements

We would like to thank the Shoklo Malaria Research Unit (SMRU), Mae Sot, Thailand for kindly providing the resources and specimens to observe the underlying research. This work is conducted at Mahidol University, Thailand, and received funding from the Wellcome Trust Mahidol University-Oxford Tropical Medicine Research Programme supported by the Wellcome Trust of Great Britain. Kanokpich Puaprasert is supported by the Royal Golden Jubilee Ph.D. Programme, the Thailand Research Fund (PHD/0032/2556).

Competing interests

The authors declare that they have no competing interests.

Consent for publication

Not applicable.

Ethics approval and consent to participate

The protocol of this study was reviewed and approved by the ethical review board of Faculty of Tropical Medicine, Mahidol University, Thailand (MUTM2016-007-01).

Funding

This study was part of the Wellcome Trust Mahidol University-Oxford Tropical Medicine Research Programme supported by the Wellcome Trust of Great Britain. KP is supported by the Royal Golden Jubilee Ph.D. Programme, the Thailand Research Fund (PHD/0032/2556).

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Authors’ Affiliations

(1)
Department of Molecular Tropical Medicine and Genetics, Faculty of Tropical Medicine, Mahidol University, Bangkok, Thailand
(2)
Shoklo Malaria Research Unit, Mahidol-Oxford Tropical Medicine Research Unit, Bangkok, Thailand
(3)
Mahidol Oxford Tropical Medicine Research Unit, Faculty of Tropical Medicine, Mahidol University, Bangkok, Thailand
(4)
Centre for Tropical Medicine and Global Health, Nuffield Department of Medicine, University of Oxford, Oxford, UK

References

  1. Fernando D, Rodrigo C, Rajapakse S. Primaquine in vivax malaria: an update and review on management issues. Malar J. 2011;10:351.View ArticleGoogle Scholar
  2. Mihaly GW, Ward SA, Edwards G, Orme ML, Breckenridge AM. Pharmacokinetics of primaquine in man: identification of the carboxylic acid derivative as a major plasma metabolite. Br J Clin Pharmacol. 1984;17:441–6.View ArticleGoogle Scholar
  3. Constantino L, Paixao P, Moreira R, Portela M, Do Rosario V, Iley J. Metabolism of primaquine by liver homogenate fractions: evidence for monoamine oxidase and cytochrome P450 involvement in the oxidative deamination of primaquine to carboxyprimaquine. Exp Toxicol Pathol. 1999;51:299–303.View ArticleGoogle Scholar
  4. Pybus BS, Sousa JC, Jin X, Ferguson JA, Christian RE, Barnhart R, et al. CYP450 phenotyping and accurate mass identification of metabolites of the 8-aminoquinoline, anti-malarial drug primaquine. Malar J. 2012;11:259.View ArticleGoogle Scholar
  5. Vale N, Moreira R, Gomes P. Primaquine revisited six decades after its discovery. Eur J Med Chem. 2009;44:937–53.View ArticleGoogle Scholar
  6. Vasquez-Vivar J, Augusto O. Hydroxylated metabolites of the antimalarial drug primaquine. Oxidation and redox cycling. J Biol Chem. 1992;267:848–54.Google Scholar
  7. Idowu O, Peggins J, Brewer T, Kelley C. Metabolism of a candidate 8-aminoquinoline antimalarial agent, WR 238605, by rat liver microsomes. Drug Metab Dispos. 1995;23:1–17.PubMedGoogle Scholar
  8. Jin X, Pybus B, Marcsisin S, Logan T, Luong T, Sousa J, et al. An LC–MS based study of the metabolic profile of primaquine, an 8-aminoquinoline antiparasitic drug, with an in vitro primary human hepatocyte culture model. Eur J Drug Metab Pharmacokinet. 2014;39:139–46.View ArticleGoogle Scholar
  9. Pybus BS, Marcsisin SR, Jin X, Deye G, Sousa JC, Li Q, et al. The metabolism of primaquine to its active metabolite is dependent on CYP 2D6. Malar J. 2013;12:212.View ArticleGoogle Scholar
  10. Potter BM, Xie LH, Vuong C, Zhang J, Zhang P, Duan D, et al. Differential CYP 2D6 metabolism alters primaquine pharmacokinetics. Antimicrob Agents Chemother. 2015;59:2380–7.View ArticleGoogle Scholar
  11. Marcsisin SR, Reichard G, Pybus BS. Primaquine pharmacology in the context of CYP 2D6 pharmacogenomics: current state of the art. Pharmacol Ther. 2016;161:1–10.View ArticleGoogle Scholar
  12. Bennett JW, Pybus BS, Yadava A, Tosh D, Sousa JC, McCarthy WF, et al. Primaquine failure and cytochrome P-450 2D6 in Plasmodium vivax malaria. N Engl J Med. 2013;369:1381–2.View ArticleGoogle Scholar
  13. Silvino ACR, Costa GL, de Araujo FCF, Ascher DB, Pires DEV, Fontes CJF, et al. Variation in human cytochrome P-450 drug-metabolism genes: a gateway to the understanding of Plasmodium vivax relapses. PLoS ONE. 2016;11:e0160172.View ArticleGoogle Scholar
  14. Kimura S, Umeno M, Skoda R, Meyer U, Gonzalez F. The human debrisoquine 4-hydroxylase (CYP2D) locus: sequence and identification of the polymorphic CYP2D6 gene, a related gene, and a pseudogene. Am J Hum Genet. 1989;45:889–904.PubMedPubMed CentralGoogle Scholar
  15. Meijerman I, Sanderson LM, Smits PH, Beijnen JH, Schellens JH. Pharmacogenetic screening of the gene deletion and duplications of CYP2D6. Drug Metab Rev. 2007;39:45–60.View ArticleGoogle Scholar
  16. Gaedigk A, Fuhr U, Johnson C, Bérard A, Bradford LD, Leeder JS. CYP2D7–2D6 hybrid tandems: identification of novel CYP2D6 duplication arrangements and implications for phenotype prediction. Pharmacogenomics. 2010;11:43–53.View ArticleGoogle Scholar
  17. Kramer WE, Walker DL, O’Kane DJ, Mrazek DA, Fisher PK, Dukek BA, et al. CYP2D6: novel genomic structures and alleles. Pharmacogenet Genomics. 2009;19:813–22.View ArticleGoogle Scholar
  18. Gonzalez FJ, Skodat RC, Kimura S, Umeno M, Zanger UM, Nebert DW, et al. Characterization of the common genetic defect in humans deficient in debrisoquine metabolism. Nature. 1988;331:442–6.View ArticleGoogle Scholar
  19. Heim MH, Meyer UA. Evolution of a highly polymorphic human cytochrome P450 gene cluster: cYP2D6. Genomics. 1992;14:49–58.View ArticleGoogle Scholar
  20. Gaedigk A, Bradford LD, Alander SW, Leeder JS. CYP2D6* 36 gene arrangements within the cyp2d6 locus: association of CYP2D6* 36 with poor metabolizer status. Drug Metab Dispos. 2006;34:563–9.View ArticleGoogle Scholar
  21. Gaedigk A, Bertino JS Jr, Bérard A, Pratt V, Bradford L, Leeder JS. Identification of novel CYP2D7-2D6 hybrids: non-functional and functional variants. Front Pharmacol. 2010;1:121.View ArticleGoogle Scholar
  22. Hastings P, Lupski JR, Rosenberg SM, Ira G. Mechanisms of change in gene copy number. Nat Rev Genet. 2009;10:551–64.View ArticleGoogle Scholar
  23. Gaedigk A, Ndjountche L, Divakaran K, Dianne Bradford L, Zineh I, Oberlander T, et al. Cytochrome P4502D6 (CYP2D6) gene locus heterogeneity: characterization of gene duplication events. Clin Pharmacol Ther. 2007;81:242–51.View ArticleGoogle Scholar
  24. Steen VM, Molven A, Aarskog NK, Gulbrandsen A-K. Homologous unequal cross-over involving a 2.8 kb direct repeat as a mechanism for the generation of allelic variants of the human cytochrome P450 CYP2D6 gene. Hum Mol Genet. 1995;4:2251–7.View ArticleGoogle Scholar
  25. Gaedigk A. Complexities of CYP2D6 gene analysis and interpretation. Int Rev Psychiatry. 2013;25:534–53.View ArticleGoogle Scholar
  26. Evans WE, Relling MV. Moving towards individualized medicine with pharmacogenomics. Nature. 2004;429:464–8.View ArticleGoogle Scholar
  27. Ma MK, Woo MH, Mcleod HL. Genetic basis of drug metabolism. Am J Health Syst Pharm. 2002;59:2061–9.PubMedGoogle Scholar
  28. Bertilsson L. Geographical/interracial differences in polymorphic drug oxidation. Clin Pharmacokinet. 1995;29:192–209.View ArticleGoogle Scholar
  29. Dorado P, Caceres M, Pozo-Guisado E, Wong ML, Licinio J, Llerena A. Development of a PCR-based strategy for CYP2D6 genotyping including gene multiplication of worldwide potential use. Biotechniques. 2005;39:S571–4.View ArticleGoogle Scholar
  30. St Jean PL, Xue Z, Carter N, Koh GC, Duparc S, Taylor M, et al. Tafenoquine treatment of Plasmodium vivax malaria: suggestive evidence that CYP2D6 reduced metabolism is not associated with relapse in the Phase 2b DETECTIVE trial. Malar J. 2016;15:97.View ArticleGoogle Scholar
  31. Vuong C, Xie LH, Potter BM, Zhang J, Zhang P, Duan D, et al. Differential CYP 2D metabolism alters tafenoquine pharmacokinetics. Antimicrob Agents Chemother. 2015;59:3864–9.View ArticleGoogle Scholar
  32. De Gregori M, Allegri M, De Gregori S, Garbin G, Tinelli C, Regazzi M, et al. How and why to screen for CYP2D6 interindividual variability in patients under pharmacological treatments. Curr Drug Metab. 2010;11:276–82.View ArticleGoogle Scholar
  33. Heim M, Meyer U. Genotyping of poor metabolisers of debrisoquine by allele-specific PCR amplification. Lancet. 1990;336:529–32.View ArticleGoogle Scholar
  34. Gaedigk A, Gotschall RR, Forbes NS, Simon SD, Kearns GL, Leeder JS. Optimization of cytochrome P4502D6 (CYP2D6) phenotype assignment using a genotyping algorithm based on allele frequency data. Pharmacogenet Genomics. 1999;9:669–82.View ArticleGoogle Scholar
  35. Broly F, Marez D, Sabbagh N, Legrand M, Millecamps S, Guidice JL, et al. An efficient strategy for detection of known and new mutations of the CYP2D6 gene using single strand conformation polymorphism analysis. Pharmacogenet Genomics. 1995;5:373–84.View ArticleGoogle Scholar
  36. Marez D, Legrand M, Sabbagh N, Guidice JL, Spire C, Lafitte J, et al. Polymorphism of the cytochrome P450 CYP2D6 gene in a European population: characterization of 48 mutations and 53 alleles, their frequencies and evolution. Pharmacogenet Genomics. 1997;7:193–202.View ArticleGoogle Scholar
  37. Stüven T, Griese E-U, Kroemer HK, Eichelbaum M, Zanger UM. Rapid detection of CYP2D6 null alleles by long distance-and multiplex-polymerase chain reaction. Pharmacogenet Genomics. 1996;6:417–21.View ArticleGoogle Scholar
  38. Hersberger M, Marti-Jaun J, Rentsch K, Hänseler E. Rapid detection of the CYP2D6* 3, CYP2D6* 4, and CYP2D6* 6 alleles by tetra-primer PCR and of the CYP2D6* 5 allele by multiplex long PCR. Clin Chem. 2000;46:1072–7.PubMedGoogle Scholar
  39. Labuda D, Krajinovic M, Richer C, Skoll A, Sinnett H, Yotova V, et al. Rapid detection of CYP1A1, CYP2D6, and NAT variants by multiplex polymerase chain reaction and allele-specific oligonucleotide assay. Anal Biochem. 1999;275:84–92.View ArticleGoogle Scholar
  40. Stamer UM, Bayerer B, Wolf S, Hoeft A, Stüber F. Rapid and reliable method for cytochrome P450 2D6 genotyping. Clin Chem. 2002;48:1412–7.PubMedGoogle Scholar
  41. Müller B, Zöpf K, Bachofer J, Steimer W. Optimized strategy for rapid cytochrome P450 2D6 genotyping by real-time long PCR. Clin Chem. 2003;49:1624–31.View ArticleGoogle Scholar
  42. Arneth B, Shams M, Hiemke C, Härtter S. Rapid and reliable genotyping procedure for detection of alleles with mutations, deletion, or/and duplication of the CYP2D6 gene. Clin Biochem. 2009;42:1282–90.View ArticleGoogle Scholar
  43. Langaee T, Hamadeh I, Chapman AB, Gums JG, Johnson JA. A novel simple method for determining CYP2D6 gene copy number and identifying allele (s) with duplication/multiplication. PLoS ONE. 2015;10:e0113808.View ArticleGoogle Scholar
  44. Suwannasri P, Thongnoppakhun W, Pramyothin P, Assawamakin A, Limwongse C. Combination of multiplex PCR and DHPLC-based strategy for CYP2D6 genotyping scheme in Thais. Clin Biochem. 2011;44:1144–52.View ArticleGoogle Scholar
  45. Vanwong N, Ngamsamut N, Hongkaew Y, Nuntamool N, Puangpetch A, Chamnanphon M, et al. Detection of CYP2D6 polymorphism using Luminex xTAG technology in autism spectrum disorder: CYP2D6 activity score and its association with risperidone levels. Drug Metab Pharmacokinet. 2016;31:156–62.View ArticleGoogle Scholar
  46. Murphy GM, Pollock BG, Kirshner MA, Pascoe N, Cheuk W, Mulsant BH, et al. CYP2D6 genotyping with oligonucleotide microarrays and nortriptyline concentrations in geriatric depression. Neuropsychopharmacology. 2001;25:737–43.View ArticleGoogle Scholar
  47. Leon Jd, Susce MT, Johnson M, Hardin M, Maw L, Shao A, et al. DNA microarray technology in the clinical environment: the AmpliChip CYP450 test for CYP2D6 and CYP2C19 genotyping. CNS Spectr. 2009;14:19–34.View ArticleGoogle Scholar
  48. Burmester JK, Sedova M, Shapero MH, Mansfield E. DMET™ microarray technology for pharmacogenomics-based personalized medicine. Methods Mol Biol. 2010;632:99–124.View ArticleGoogle Scholar
  49. Sukasem C, Sirachainan E, Chamnanphon M, Pechatanan K, Sirisinha T, Ativitavas T, et al. Impact of CYP2D6 polymorphisms on tamoxifen responses of women with breast cancer: a microarray-based study in Thailand. Asian Pac J Cancer Prev. 2012;13:549–53.View ArticleGoogle Scholar
  50. Chamnanphon M, Pechatanan K, Sirachainan E, Trachu N, Chantratita W, Pasomsub E, et al. Association of CYP2D6 and CYP2C19 polymorphisms and disease-free survival of Thai post-menopausal breast cancer patients who received adjuvant tamoxifen. Pharmgenomics Pers Med. 2013;6:37–48.PubMedPubMed CentralGoogle Scholar
  51. Suwannarat P, Chamnanphon M, Ngamsamut AS, Chamkrachchangpada B, Tan-kam T, Puangpetch A, et al. Molecular genetic analysis of CYP2D6and HLA-B* 15: 02 in Thai autistic spectrum disorder children: implication for pharmacogenetics testing and optimization of drug treatments. Thai J Genet. 2013;6:82–7.Google Scholar
  52. Ji L, Pan S, Marti-Jaun J, Hänseler E, Rentsch K, Hersberger M. Single-step assays to analyze CYP2D6 gene polymorphisms in Asians: allele frequencies and a novel* 14B allele in mainland Chinese. Clin Chem. 2002;48:983–8.PubMedGoogle Scholar
  53. Qin S, Shen L, Zhang A, Xie J, Shen W, Chen L, et al. Systematic polymorphism analysis of the CYP2D6 gene in four different geographical Han populations in mainland China. Genomics. 2008;92:152–8.View ArticleGoogle Scholar
  54. Garcia-Barceló M, Chow LY, Chiu HFK, Wing YK, Lee DTS, Lam KL, et al. Genetic analysis of the CYP2D6 locus in a Hong Kong Chinese population. Clin Chem. 2000;46:18–23.PubMedGoogle Scholar
  55. Kim E-Y, Lee S-S, Jung H-J, Jung H-E, Yeo C-W, Shon J-H, et al. Robust CYP2D6 genotype assay including copy number variation using multiplex single-base extension for Asian populations. Clin Chim Acta. 2010;411:2043–8.View ArticleGoogle Scholar
  56. Tateishi T, Chida M, Ariyoshi N, Mizorogi Y, Kamataki T, Kobayashi S. Analysis of the CYP2D6 gene in relation to dextromethorphan O-demethylation capacity in a Japanese population. Clin Pharmacol Ther. 1999;65:570–5.View ArticleGoogle Scholar
  57. Nishida Y, Fukuda T, Yamamoto I, Azuma J. CYP2D6 genotypes in a Japanese population: low frequencies of CYP2D6 gene duplication but high frequency of CYP2D6* 10. Pharmacogenet Genomics. 2000;10:567–70.View ArticleGoogle Scholar
  58. Ishiguro A, Kubota T, Sasaki H, Yamada Y, Iga T. Common mutant alleles of CYP2D6 causing the defect of CYP2D6 enzyme activity in a Japanese population. Br J Clin Pharmacol. 2003;55:414–5.View ArticleGoogle Scholar
  59. Lee S-Y, Sohn KM, Ryu JY, Yoon YR, Shin JG, Kim J-W. Sequence-based CYP2D6 genotyping in the Korean population. Ther Drug Monit. 2006;28:382–7.View ArticleGoogle Scholar
  60. Lee S-J, Lee SS, Jung H-J, Kim H-S, Park S-J, Yeo C-W, et al. Discovery of novel functional variants and extensive evaluation of CYP2D6 genetic polymorphisms in Koreans. Drug Metab Dispos. 2009;37:1464–70.View ArticleGoogle Scholar
  61. Park HS, Choi J-Y, Lee M-J, Park S, Yeo C-W, Lee SS, et al. Association between genetic polymorphisms of CYP2D6 and outcomes in breast cancer patients with tamoxifen treatment. J Korean Med Sci. 2011;26:1007–13.View ArticleGoogle Scholar
  62. Naveen AT, Adithan C, Soya SS, Gerard N, Krishnamoorthy R. CYP2D6 genetic polymorphism in South Indian populations. Biol Pharm Bull. 2006;29:1655–8.View ArticleGoogle Scholar
  63. Sachse C, Brockmöller J, Bauer S, Roots I. Cytochrome P450 2D6 variants in a Caucasian population: allele frequencies and phenotypic consequences. Am J Hum Genet. 1997;60:284–95.PubMedPubMed CentralGoogle Scholar
  64. Mendoza R, Wan YJY, Poland RE, Smith M, Zheng Y, Berman N, et al. CYP2D6 polymorphism in a Mexican American population. Clin Pharmacol Ther. 2001;70:552–60.View ArticleGoogle Scholar
  65. Menoyo A, del Rio E, Baiget M. Characterization of variant alleles of cytochrome CYP2D6 in a Spanish population. Cell Biochem Funct. 2006;24:381–5.View ArticleGoogle Scholar
  66. Wan Y-JY, Poland RE, Han G, Konishi T, Zheng Y-P, Berman N, et al. Analysis of the CYP2D6 gene polymorphism and enzyme activity in African-Americans in southern California. Pharmacogenet Genomics. 2001;11:489–99.View ArticleGoogle Scholar
  67. Cai W, Nikoloff D, Pan R, De Leon J, Fanti P, Fairchild M, et al. CYP2D6 genetic variation in healthy adults and psychiatric African-American subjects: implications for clinical practice and genetic testing. Pharmacogenomics J. 2006;6:343–50.View ArticleGoogle Scholar
  68. Yee MM, Josephson C, Hill CE, Harrington R, Castillejo M-I, Ramjit R, et al. Cytochrome P450 2D6 polymorphisms and predicted opioid metabolism in African-American children with sickle cell disease. J Pediatr Hematol Oncol. 2013;35:e301–5.View ArticleGoogle Scholar

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