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BMC Genetics

Open Access

Genetic polymorphisms of VIP variants in the Tajik ethnic group of northwest China

  • Jiayi Zhang1, 2,
  • Tianbo Jin1, 2,
  • Zulfiya Yunus1, 2, 3,
  • Xiaolan Li1, 2,
  • Tingting Geng2,
  • Hong Wang2,
  • Yali Cui1, 2 and
  • Chao Chen1, 2Email author
BMC Genetics201415:102

https://doi.org/10.1186/s12863-014-0102-y

Received: 31 May 2013

Accepted: 18 September 2014

Published: 30 September 2014

Abstract

Background

Individual response to medications varies significantly among different populations, and great progress in understanding the molecular basis of drug action has been made in the past 50 years. The field of pharmacogenomics seeks to elucidate inherited differences in drug disposition and effects. While we know that different populations and ethnic groups are genetically heterogeneous, we have not found any pharmacogenomics information regarding minority groups, such as the Tajik ethnic group in northwest China.

Results

We genotyped 85 Very Important Pharmacogene (VIP) variants selected from PharmGKB in 100 unrelated, healthy Tajiks from the Xinjiang Uygur Autonomous Region and compared our data with HapMap data from four major populations around the world: Han Chinese (CHB), Japanese in Tokyo (JPT), Utah Residents with Northern and Western European Ancestry (CEU), and Yorubia in Ibadan, Nigeria (YRI). We found that Tajiks differed from CHB, JPT and YRI in 30, 32, and 32 of the selected VIP genotypes respectively (p < 0.005), while differences between Tajiks and CEU were found in only 6 of the genotypes (p < 0.005). Haplotype analysis also demonstrated differences between the Tajiks and the other four populations.

Conclusion

Our results contribute to the pharmacogenomics database of the Tajik ethnic group and provide a theoretical basis for safer drug administration that may be useful for diagnosing and treating disease in this population.

Keywords

PharmacogenomicsGenetic polymorphismHaplotypeTajikEthnic difference

Background

To date, pharmacogenomic studies have focused on candidate genes involved in drug pharmacokinetics or pharmacodynamics. Many of these genes contain functional polymorphisms that are obvious pharmacological choices for investigation in appropriate clinical populations [1],[2]. For some drugs, genetic information is important to avoid drug toxicity and to optimize response [2],[3]. Pharmacogenomic studies are rapidly elucidating the inherited nature of differences in drug disposition and effects, thereby enhancing drug discovery and providing a stronger scientific basis for optimizing drug therapy on an individual basis [4].

Tajiks are an ethnic group with a worldwide population of 15 to 20 million; they live mostly in Tajikistan, Afghanistan, Uzbekistan, and the Xinjiang Uygur Autonomous Region [4]. According to the 2010 census, approximately 51,000 Tajiks live in China, mostly in the Tashkurgan Tajik Autonomous County, which is located in the eastern part of the Pamir Plateau.

The Pharmacogenetics and Pharmacogenomics Knowledge Base (PharmGKB: http://www.pharmgkb.org) is devoted to disseminating primary data and knowledge in pharmacogenetics and pharmacogenomics and has annotated genes that are important for drug response. This information is presented in the form of Very Important Pharmacogene (VIP) summaries, pathway diagrams, and curated literature [5]. It currently contains information for more than 3000 drugs, 3000 diseases, and 26,000 genes with genotyped variants [4].

We systematically genotyped 85 VIP variants selected from PharmGKB VIP in 100 Tajiks from Xinjiang [6]. We compared genotype frequencies and haplotype construction with those in Han Chinese (CHB), Japanese in Tokyo (JPT), Utah Residents with Northern and Western European Ancestry (CEU), and Yorubia in Ibadan, Nigeria (YRI). Our goals were to identify differences and determine their extent and provide a theoretical basis for safer drug administration and better therapeutic treatment in the Tajik population.

Methods

Ethics statement

All participants recruited and genotyped in the present study had at least three generations of paternal ancestry in their ethnic group, and each subject provided written informed consent. The Ethics Committees of Xinjiang University and Northwest University approved the use of human samples in this study.

Study participants

We recruited a random sample of 100 healthy, unrelated Tajiks (50 males and 50 females) from Tashkurgan Tajik Autonomous County between July and October 2010 using detailed recruitment and exclusion criteria. All of the chosen subjects were Tajik Chinese living in the Xinjiang Uygur Autonomous Region.

Polymerase chain reaction (PCR) and DNA sequencing

We successfully genotyped 85 VIP variants in 37 pharmacogenomic genes in 100 participants. Genomic DNA from whole blood was isolated using the GoldMag® nanoparticles method according to the manufacturer’s protocol, and DNA concentration was measured by spectrometry (DU530 UV/VIS spectrophotometer, Beckman Instruments, Fullerton, CA, USA). We designed primers for amplification and extension reactions using Sequenom MassARRAY Assay Design 3.0 Software [6] and used a Sequenom MassARRAY RS1000 to genotype the single nucleotide polymorphisms (SNPs) using the protocol recommended by the manufacturer. Sequenom Typer 4.0 Software was used for data management and analysis [6],[7].

Data analysis

Statistical analyses were performed using Microsoft Excel (Redmond, WA, USA) and SPSS 16.0 statistical package (SPSS, Chicago, IL, USA). All p values in this study were two-sided, and p ≤ 0.005 after Bonferroni correction was considered the statistical significance threshold [8]. We calculated and compared the genotype frequencies of Tajiks and four other populations (CHB, JPT, CEU, and YRI) using chi-squared tests [9]. We used the Haploview software package (version 4.2) for analysis of linkage disequilibrium (LD), haplotype construction, and genetic associations at polymorphic loci [10]-[12]. Our method excluded SNPs with minor allele frequency < 0.001 for SNPs with lower frequencies that have little power to detect LD. We also ignored SNPs with Hardy-Weinberg equilibrium (HWE) p values < 0.001 for their small probability that their deviation from HWE could be explained by chance. The D’ values on the square is a measure of the LD extent for each pair of SNPs, squares in red without D’ values indicate the two sites are in complete LD (D’ = 1). We constructed haplotypes using the common sites of the selected SNPs and sites downloaded from HapMap for the VDR gene and derived the haplotype frequencies in all five populations.

Results

We successfully sequenced 85 VIP pharmacogenomic variant genotypes from 100 Tajiks. The PCR primers used for the selected variants are listed in Additional file 1. Table 1 lists the basic characteristics of the selected variants, including gene name, chromosome number and position, and their allele frequencies in Tajiks.
Table 1

Basic characteristics of the selected variants

SNP ID

Genes

Chromosome

Position

Allele

Allele frequencies

A

B

A(%)

B(%)

rs1801131

MTHFR

1

11854476

C

A

35.0

65.0

rs1801133

MTHFR

1

11856378

T

C

19.2

80.8

rs890293

CYP2J2

1

60392494

G

T

48.5

51.5

rs3918290

DPYD

1

97915614

G

/

100

0

rs6025

F5

1

169519049

C

A

100

0

rs20417

PTGS2

1

186650320

G

C

97.0

3.0

rs689466

PTGS2

1

186650750

A

G

85.4

14.7

rs4124874

UGT1A10

2

234665659

C

A

42.8

57.2

rs10929302

UGT1A10

2

234665782

G

A

73.5

26.5

rs4148323

UGT1A10

2

234669144

A

G

3.5

96.5

rs7626962

SCN5A

3

38620907

G

/

100

0

rs1805124

SCN5A

3

38645420

G

A

29.0

71.0

rs6791924

SCN5A

3

38674699

G

/

100

0

rs3814055

NR1I2

3

119500034

C

T

58.0

42.0

rs2046934

P2RY12

3

151057642

T

C

90.0

10.0

rs1065776

P2RY1

3

152553628

T

C

6.1

93.9

rs701265

P2RY1

3

152554357

G

A

20.0

80.0

rs975833

ADH1A

4

100201739

G

C

74.2

25.8

rs2066702

ADH1B

4

100229017

C

T

97.5

2.5

rs1229984

ADH1B

4

100239319

G

A

70.5

29.5

rs698

ADH1C

4

100260789

A

G

67.0

33.0

rs17244841

HMGCR

5

74607099

A

/

100

0

rs3846662

HMGCR

5

74615328

T

C

48.5

51.5

rs17238540

HMGCR

5

74619742

T

/

100

0

rs1042713

ADRB2

5

148206440

G

A

60.5

39.5

rs1042714

ADRB2

5

148206473

G

C

34.0

66.0

rs1800888

ADRB2

5

148206885

C

T

98.0

2.0

rs1142345

TPMT

6

18130918

G

A

0

100

rs1800460

TPMT

6

18139228

A

G

0

100

rs2066853

AHR

7

17379110

G

A

82.5

17.5

rs1045642

ABCB1

7

87138645

T

C

57.1

42.9

rs2032582

ABCB1

7

87160617

G

T

42.7

57.3

rs2032582

ABCB1

7

87160617

G

A

86.4

13.6

rs2032582

ABCB1

7

87160617

T

A

92.7

7.4

rs1128503

ABCB1

7

87179601

T

C

58.1

41.9

rs10264272

CYP3A5

7

99262835

C

/

100

0

rs776746

CYP3A5

7

99270539

G

A

89.5

10.5

rs4986913

CYP3A4

7

99358459

C

T

99.0

1.0

rs4986910

CYP3A4

7

99358524

T

/

100

0

rs4986909

CYP3A4

7

99359670

C

/

100

0

rs12721634

CYP3A4

7

99381661

T

/

100

0

rs2740574

CYP3A4

7

99382096

A

G

98.5

1.5

rs3815459

KCNH2

7

150644394

A

G

40.5

59.5

rs36210421

KCNH2

7

150644428

G

T

99.0

1.0

rs12720441

KCNH2

7

150647304

C

/

100

0

rs3807375

KCNH2

7

150667210

A

G

43.0

57.0

rs4986893

CYP2C19

10

96540410

G

/

100

0

rs4244285

CYP2C19

10

96541616

G

A

92.5

7.5

rs1799853

CYP2C9

10

96702047

C

T

100

0

rs1801252

ADRB1

10

115804036

G

A

20.2

79.8

rs1801253

ADRB1

10

115805055

C

G

79.8

20.2

rs5219

KCNJ11

11

17409572

C

T

56.1

43.9

rs1695

GSTP1

11

67352689

A

G

77.0

23.0

rs1138272

GSTP1

11

67353579

T

C

9.0

91.0

rs1800497

DRD2

11

113270828

T

C

17.9

82.1

rs6277

DRD2

11

113283459

G

A

61.5

38.5

rs4149056

SLCO1B1

12

21331549

T

C

90.5

9.5

rs7975232

VDR

12

48238837

C

A

49.0

51.0

rs1544410

VDR

12

48239835

G

A

66.0

34.0

rs2239185

VDR

12

48244559

T

C

51.0

49.0

rs1540339

VDR

12

48257326

G

A

67.2

32.8

rs2239179

VDR

12

48257766

A

G

56.5

43.5

rs3782905

VDR

12

48266167

C

G

70.0

30.0

rs2228570

VDR

12

48272895

T

C

34.5

65.5

rs10735810

VDR

12

48272895

C

T

66.5

33.5

rs11568820

VDR

12

48302545

G

A

77.3

22.7

rs1801030

SULT1A2

16

28617485

A

/

100

0

rs3760091

SULT1A1

16

28620800

C

G

54.1

45.9

rs7294

VKORC1

16

31102321

C

T

67.0

33.0

rs9934438

VKORC1

16

31104878

G

A

50.5

49.5

rs28399454

CYP2A6

19

41351267

G

/

100

0

rs28399444

CYP2A6

19

41354190

A

/

100

0

rs1801272

CYP2A6

19

41354533

T

/

100

0

rs28399433

CYP2A6

19

41356379

G

T

10.5

89.5

rs3745274

CYP2B6

19

41512841

G

T

64.0

36.0

rs28399499

CYP2B6

19

41518221

T

/

100

0

rs3211371

CYP2B6

19

41522715

C

T

50.0

50.0

rs12659

SLC19A1

21

46951555

C

T

56.6

43.4

rs1051266

SLC19A1

21

46957794

G

A

55.7

44.3

rs1131596

SLC19A1

21

46957915

T

C

60.6

39.4

rs4680

COMT

22

19951271

A

G

53.5

46.5

rs59421388

CYP2D6

22

42523610

C

/

100

0

rs28371725

CYP2D6

22

42523805

G

A

90.0

10.0

rs16947

CYP2D6

22

42523943

G

A

74.1

25.9

rs5030656

CYP2D6

22

42524175

AAG

delAAG

99.5

0.5

rs61736512

CYP2D6

22

42525134

C

/

100

0

rs28371706

CYP2D6

22

42525772

C

T

99.0

1.0

Table 2 lists the genotype frequencies in Tajiks and identifies significant variants in Tajiks compared with the other four populations (p < 0.005), all variant data are shown in Additional file 2. We also categorized the genes into different families and phases related to pharmacogenomics, the statistically significant values are shown in red (p < 0.05). We found that Tajiks differed from CHB, JPT, and YRI in 30, 32, and 32 selected VIP genotypes, respectively. These genes encode phase I drug metabolic enzymes (VCORC1, MTHFR, and CYP3A5), a phase II drug metabolic enzymes (COMT), and transporters, channel proteins, and receptors (e.g., ADRB1, KCNH2, and VDR, respectively). However, the difference between Tajiks and CEU was much smaller; just six SNP genotypes were different, and these were randomly distributed on genes such as CYP2C9, which encodes a phase I enzyme. For genes such as ADH1B and PTGS2, we observed differences between Tajiks and the other four populations.
Table 2

Genotype frequencies in Tajiks compared with four other populations

SNP ID

Gene

Category

Allele

Tajik genotype frequencies

pvalues against four populations (after Bonferroni correction)

Family

Phase

A

B

AA(%)

AB(%)

BB(%)

CHB

JPT

CEU

YRI

rs1045642

ABCB1

ABC transporters

others

T

C

34.3

45.5

20.2

8.49E-03

3.42E-02

3.10E-01

2.17E-18

rs1128503

ABCB1

ABC transporters

others

T

C

32.3

51.5

16.2

3.09E-02

8.73E-01

1.69E-02

3.03E-19

rs2032582

ABCB1

ABC transporters

others

G

T

18

49.4

32.6

9.02E-01

6.07E-01

8.24E-02

-

rs975833

ADH1A

alcohol dehydrogenase

phase I

G

C

55.6

37.4

7.1

4.86E-16

3.45E-14

6.46E-01

5.79E-01

rs1229984

ADH1B

alcohol dehydrogenase

phase I

G

A

48

45

7

3.76E-12

7.23E-11

9.18E-11

1.26E-10

rs2066702

ADH1B

alcohol dehydrogenase

phase I

C

T

95

5.1

0

2.97E-01

2.97E-01

1.94E-01

1.61E-11

rs698

ADH1C

alcohol dehydrogenase

phase I

A

G

44.3

45.4

10.3

1.21E-09

3.22E-09

1.24E-02

7.40E-11

rs1801252

ADRB1

adrenergic receptors

others

G

A

3

34.3

62.6

1.22E-05

1.52E-05

-

2.53E-06

rs1801253

ADRB1

adrenergic receptors

others

C

G

63.6

32.3

4

6.12E-01

3.88E-01

5.87E-02

4.12E-04

rs1042713

ADRB2

adrenergic receptors

others

G

A

36

49

15

4.49E-03

5.67E-01

7.34E-01

6.05E-02

rs1042714

ADRB2

adrenergic receptors

others

G

C

14

40

46

1.26E-03

3.39E-05

2.70E-02

9.85E-03

rs2066853

AHR

AHR

others

G

A

69

27

4

1.18E-05

7.65E-08

6.87E-02

9.06E-08

rs4680

COMT

COMT

phase II

A

G

31

45

24

9.95E-05

1.56E-05

5.25E-01

3.15E-05

rs28399454

CYP2A6

cytochrome P450

phase I

G

/

100

0

0

-

-

1.00E + 00

7.81E-07

rs3745274

CYP2B6

cytochrome P450

phase I

G

T

46

36

18

1.07E-03

2.03E-03

5.17E-02

1.50E-01

rs28399499

CYP2B6

cytochrome P450

phase I

T

/

100

0

0

-

-

-

2.04E-06

rs4244285

CYP2C19

cytochrome P450

phase I

G

A

85

15

0

1.00E-03

1.56E-05

4.07E-02

8.50E-02

rs1799853

CYP2C9

cytochrome P450

phase I

C

T

100

0

0

-

-

6.25E-05

-

rs776746

CYP3A5

cytochrome P450

phase I

G

A

81

17

2

2.78E-05

8.74E-05

2.58E-02

1.23E-34

rs10264272

CYP3A5

cytochrome P450

phase I

C

/

100

0

0

1.00E + 00

1.00E + 00

-

8.95E-09

rs6277

DRD2

G-protein-coupled receptor

others

G

A

38

47

15

7.41E-08

1.01E-07

1.98E-02

6.51E-11

rs1800497

DRD2

G-protein-coupled receptor

others

T

C

3.1

29.6

67.4

8.59E-06

1.43E-05

7.19E-01

2.25E-06

rs1695

GSTP1

glutathione S-transferase

phase II

A

G

59

36

5

5.70E-01

1.96E-03

2.32E-04

1.50E-03

rs1138272

GSTP1

glutathione S-transferase

phase II

T

C

0

18

82

3.00E-03

2.00E-03

9.22E-01

2.28E-03

rs3846662

HMGCR

HMGCR

phase I

T

C

18

61

21

2.49E-01

7.26E-01

2.12E-02

2.79E-24

rs3807375

KCNH2

eag

others

A

G

19

48

33

6.73E-07

8.34E-12

4.02E-01

1.13E-11

rs3815459

KCNH2

eag

others

A

G

16

49

35

6.04E-06

2.69E-09

-

6.88E-01

rs1801131

MTHFR

methylenetetrahydrofolate reductase

phase I

C

A

7

56

37

9.07E-03

5.46E-04

2.32E-01

7.36E-09

rs1801133

MTHFR

methylenetetrahydrofolate reductase

phase I

T

C

4

30.3

65.7

3.13E-07

1.21E-03

1.92E-02

9.34E-03

rs3814055

NR1I2

nuclear receptor

others

C

T

30

56

14

8.60E-03

2.15E-03

1.00E-01

1.32E-03

rs701265

P2RY1

G-protein coupled receptor

others

G

A

4

32

64

7.61E-02

3.04E-01

9.33E-01

2.96E-25

rs2046934

P2RY12

G-protein coupled receptor

others

T

C

82

16

2

5.69E-02

4.97E-02

4.49E-03

6.23E-03

rs20417

PTGS2

nuclear receptor

others

G

C

97

0

3

5.43E-04

1.57E-03

3.65E-07

4.82E-17

rs689466

PTGS2

nuclear receptor

others

A

G

73.7

23.2

3

3.68E-11

4.34E-07

7.13E-01

1.12E-01

rs1805124

SCN5A

sodium channel gene

others

G

A

9

40

51

1.23E-04

7.59E-04

7.80E-03

4.96E-01

rs6791924

SCN5A

sodium channel gene

others

G

/

100

0

0

-

-

-

2.00E-03

rs7626962

SCN5A

sodium channel gene

others

G

/

100

0

0

-

-

-

1.24E-03

rs1051266

SLC19A1

solute carrier

others

G

A

29.9

51.6

18.6

3.65E-01

8.28E-02

8.36E-01

2.83E-06

rs4149056

SLCO1B1

solute carrier

others

T

C

82

17

1

2.30E-01

7.68E-01

1.47E-01

2.66E-04

rs4124874

UGT1A10

UDP-glucuronosyltransferase

phase II

C

A

14.4

56.7

28.9

1.64E-02

6.88E-02

3.31E-01

2.73E-23

rs4148323

UGT1A10

UDP-glucuronosyltransferase

phase II

A

G

0

7

93

7.23E-08

3.22E-03

9.00E-02

9.00E-02

rs10929302

UGT1A10

UDP-glucuronosyltransferase

phase II

G

A

53

41

6

2.58E-03

3.31E-03

9.38E-01

4.91E-02

rs1540339

VDR

nuclear receptor

others

G

A

47.5

39.4

13.1

1.60E-10

1.42E-11

7.78E-01

1.80E-02

rs1544410

VDR

nuclear receptor

others

G

A

40

52

8

3.05E-12

2.03E-06

1.75E-02

2.50E-01

rs2239179

VDR

nuclear receptor

others

A

G

31

51

18

4.01E-04

6.14E-05

3.63E-02

8.58E-03

rs2239185

VDR

nuclear receptor

others

T

C

22

58

20

2.86E-04

1.55E-01

-

4.37E-01

rs3782905

VDR

nuclear receptor

others

C

G

46

48

6

1.20E-01

6.72E-04

3.92E-01

7.74E-02

rs7975232

VDR

nuclear receptor

others

C

A

20

58

22

9.30E-05

2.13E-03

1.92E-02

2.44E-02

rs10735810

VDR

nuclear receptor

others

C

T

48.4

36.3

15.4

8.17E-02

8.74E-01

2.72E-01

4.64E-03

rs11568820

VDR

nuclear receptor

others

G

A

60.6

33.3

6.1

1.12E-04

4.25E-05

6.86E-01

8.35E-38

rs7294

VKORC1

VKORC1

phase I

C

T

44

46

10

8.00E-10

1.09E-06

7.69E-01

1.59E-04

rs9934438

VKORC1

VKORC1

phase I

G

A

26

49

25

1.29E-17

4.64E-14

1.01E-01

9.39E-25

We counted the variants in each family, excluding those that belonged to none of the families or were not significantly different between Tajiks and the other four populations. The remaining 71 sites belonged to 26 genes in 12 families (Table 3). We found that the difference between Tajiks and CEU existed in only one site in the nuclear receptor family and 0 site in adrenergic receptors family respectively. However, in the nuclear receptor family, Tajiks differed from CHB, JPT, and YRI in 66.7%, 75%, and 33.3% of selected sites, respectively. In the adrenergic receptor family, Tajiks differed from CHB, JPT, and YRI in 60%, 40%, and 40% of selected sites, respectively. For genes in ATP-binding cassette (ABC) transporters, Tajiks differed from YRI in 66.7% of the selected sites, but there was no difference between Tajiks and CHB, JPT, CEU.
Table 3

Numbers and frequencies of significant variants

Family

Variants (n)

Significant variants, n (%)

CHB

JPT

CEU

YRI

Adrenergic receptors

5

3 (60.0)

2 (40.0)

0 (0)

2 (40.0)

Alcohol dehydrogenase

4

3 (75.0)

3 (75.0)

1 (25.0)

3 (75.0)

ATP-binding cassette (ABC) transporters

3

0 (0)

0 (0)

0 (0)

2 (66.7)

Cytochrome P450

24

3 (24.9)

3 (24.9)

1 (8.3)

4 (16.7)

Eag

4

2 (50.0)

2 (50.0)

0 (0)

1 (25.0)

Glutathione S-transferase

2

1 (50.0)

2 (100)

1 (50.0)

2 (100)

G-protein coupled receptor

5

2 (40.0)

2 (40.0)

1 (20.0)

3 (60.0)

Methylenetetrahydrofolate reductase

2

1 (50.0)

2 (100.0)

0 (0)

1 (50.0)

Nuclear receptor

12

8 (66.7)

9 (75.0)

1 (8.3)

0)

4 (33.3)

Sodium channel gene

3

1 (33.3)

1 (33.3)

0 (0)

2 (66.7)

Solute carrier

4

0 (0)

0 (0)

0 (0)

2 (50.0)

UDP-glucuronosyltransferase

3

2 (33.7)

2 (66.7)

0 (0)

1 (33.3)

We performed LD analysis using Haploview to define blocks and haplotypes. Using the common sites of our study and those from HapMap in the VDR gene, we identified two LD blocks in Tajiks, JPT, and CEU and one LD block in CHB and YRI (Figure 1). The block identified in all five populations spans 0.4 kb and consists of two complete LD markers (rs1540339 and rs2239179) with a D’ value equal to 1. The block identified in Tajiks, JPT, and CEU spans 0.9 kb and also consists of two complete LD markers (rs7975232 and rs1544410) with a D’ value equal to 1.
Figure 1

Linkage disequilibrium (LD) analysis of VDR in five populations. LD is displayed by standard color schemes, with bright red for very strong LD (LOD > 2, D’ = 1), light red (LOD > 2, D’ < 1) and blue (LOD < 2, D’ = 1) for intermediate LD, and white (LOD < 2, D’ < 1) for no LD. A. Tajiks, B. CHB, C. JPT, D. CEU, E. YRI.

Haplotype analysis results are shown in Figure 2. For the common block comprised of rs1540339 and rs2239179, three kinds of haplotypes were identified in all five populations, but they differed in frequency. Three colors of bars indicate the three kinds of haplotypes. The highest and lowest frequencies of haplotype “AA” were found in JPT (73.8%) and YRI (20.0%). The highest and lowest frequencies of haplotype “GG” were observed in CEU (47.0%) and JPT (22.1%). The highest and lowest frequencies of haplotype “GA” were found in YRI (50.4%) and JPT (4.1%). The haplotype constitutions and frequencies show that there are relatively minimal differences between Tajik and CEU, CHB, and JPT, whereas the differences between YRI and the other four populations seem obvious. These findings are in accordance with the results shown in Table 3.
Figure 2

Haplotype analysis results of rs1540339 and rs2239179 in VDR .

Discussion

With the rapid development of pharmacogenetics, serious attention has been given to interethnic and interracial differences in drug responses [13]. Here, we genotyped 85 variants related to pharmacogenomics in the Tajik ethnic group for the first time and compared the results with other ethnic populations around the world. We found that 30, 32, 32, and 6 VIP variants differed from CHB, JPT, YRI, and CEU respectively (p < 0.005). These findings corroborate the current opinion that polymorphisms with varying frequencies occur among different populations.

Vitamin D receptor (VDR) is a gene whose function has been widely reported. Epithelial cells convert the primary circulating form of vitamin D to its active form, which binds VDR to regulate a variety of genes that keep cellular proliferation and differentiation within normal ranges to prevent malignant transformation [14]. That is to say, the active form of vitamin D can induce apoptosis and prevent angiogenesis by binding VDR, which reduces the survival potential of malignant cells. Studies have demonstrated that rs10735810 and rs1544410 SNPs in VDR might modulate the risk of breast, skin, and prostate cancers, as well as other forms [15],[16]. An Italian study reported that GA and AA rs1544410 genotypes were associated with decreased cutaneous malignant melanoma (CMM) risk (odds ratio = 0.78 and 0.75, respectively) compared with the GG genotype [16]. A study in Japan found that head and neck squamous cell carcinoma patients with the TT rs10735810 genotype was associated with poor progression-free survival compared with CC or CT genotype patients (log-rank test, p = 0.0004; adjusted hazard ratio, 3.03; 95% confidence interval, 1.62 to 5.67; p = 0.001), and the A-T-G (rs11568820-rs10735810-rs7976091) haplotype showed a significant association with a higher progression rate (p = 0.02). [14] We found that the GA and AA genotype frequencies of rs1544410 in Tajiks were as much as 52% and 8% respectively, which is different from those in CHB and JPT (data not shown), suggesting that Tajiks may have decreased susceptibility to CMM.

The gene alcohol dehydrogenase 1B (ADH1B) produces a key protein for alcohol metabolism that determines blood acetaldehyde concentrations after drinking [17]. This member of the alcohol dehydrogenase family also metabolizes a wide variety of substrates besides ethanol, including retinol, other aliphatic alcohols, hydroxysteroids, and lipid peroxidation products. The minor allele “A” of rs1229984 encodes a super-active allozyme that is reportedly associated with lower rates of alcohol dependence in numerous association studies, and its frequency varies widely across different populations. It is 69% (19-91%) in normal Asian normal populations, 5.5% (1-43%) in normal European populations, and just 3% (2-7%) in normal Mexican populations [18]. Other studies have shown that rs1229984 may influence alcohol consumption behavior and is associated with upper aerodigestive (UADT) cancers [19]-[24]. A genome-wide association study found that the “A” allele of rs1229984 was associated with decreased UADT risk (p = 7 × 10-9) [19]. The data in our study is in accordance with previous findings; we found that the “A” allele frequency of rs1544410 in Tajiks was 29.5%, which was significantly different (p < 0.05) from 76.67%, 73.86%, 0%, and 0% in CHB, JPT, CEU, and YRI respectively, suggesting that Tajiks have an intermediate susceptibility to UADT cancer.

The catechol-o-methyltransferase gene (COMT) is responsible for eliminating dopamine from the synaptic cleft in the prefrontal cortex (PFC) [25]. Variations in the COMT gene exert complex effects on susceptibility to depression through various intermediate phenotypes, such as impulsivity and executive function [26]. The common functional COMT polymorphism rs4680 has been shown to affect enzyme activity and, consequently, intrasynaptic dopamine content. The “G” allele is associated with 40% higher enzymatic activity in the human brain compared to the “A” allele, leading to more efficient elimination of dopamine from the synaptic cleft; therefore, the GG genotype is associated with reduced synaptic dopamine in the PFC, and in turn, more active striatal dopamine neurotransmission [25],[27]-[29]. A study in northern Italy reported an association between the GG genotype and the risks of Alzheimer’s disease (AD) and its precursor, mild cognitive impairment (MCI) [30]. The GG genotype frequency in our study was just 24% in Tajiks, compared with 51.2%, 50%, and 46% in CHB, JPT, and YRI respectively (p < 0.05). This suggests that Tajiks may be less vulnerable to diseases related to dopamine content, including AD and MCI.

Our study also found significant differences in genotype frequencies between Tajiks and other populations in genes such as DRD2 and F5. Polymorphisms in these genes have been shown to be associated with dyskinesia induced by levodopa therapy in Parkinson’s disease patients and coronary artery disease, respectively [31],[32].

The Tajiks speak a western Indo-Iranian language and their presence in China dates to the 10th-century Muslim invasion, suggesting they are descendants of eastern Indo-Iranian speakers [33]. This may explain the smaller differences between Tajiks and CEU compared to other three populations we investigated.

However, intrinsic limitations still exist in our study. Our sample size is relatively not big enough, thus further investigation related to pharmacogenomics gene polymorphisms in a larger Tajik population is necessary to ascertain the results obtained in the current study.

Conclusions

These results provide the first pharmacogenomics information in Tajiks and illustrate the difference of selected genes between Tajiks and four other populations. Present-day China is a nation with 56 distinct ethnic groups. Our study provides a theoretical basis for safer drug administration and better therapeutic treatments in this unique population, and may also be applied in the diagnosis and prognosis of specific diseases in Tajiks.

Authors’ information

Jiayi Zhang and Tianbo Jin joint first authors.

Additional files

Declarations

Acknowledgments

This work was supported by the National 863 High-Technology Research and Development Program (No. 2012AA02A519).

Authors’ Affiliations

(1)
School of Life Sciences, Northwest University
(2)
National Engineering Research Center for Miniaturized Detection Systems
(3)
College of Life Sciences and Technology, Xinjiang University

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This article is published under license to BioMed Central Ltd. This is an Open Access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/2.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly credited. The Creative Commons Public Domain Dedication waiver (http://creativecommons.org/publicdomain/zero/1.0/) applies to the data made available in this article, unless otherwise stated.

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