Archives of Dermatological Research

, Volume 305, Issue 6, pp 477–482

Association of IL-12B gene rs6887695 polymorphism with hereditary susceptibility and clinical characterization of psoriasis vulgaris in the Chinese Han population

Authors

  • Yumei Wu
    • Department of Dermatology, Luwan BranchRuijin Hospital, Shanghai JiaoTong University School of Medicine
  • Zhiyong Lu
    • Department of DermatologyXinhua Hospital, Shanghai JiaoTong University School of Medicine
  • Yingwei Chen
    • Department of Dermatology, Luwan BranchRuijin Hospital, Shanghai JiaoTong University School of Medicine
  • Feng Xue
    • Department of DermatologyRuijin Hospital, Shanghai JiaoTong University School of Medicine
  • Xiaoying Chen
    • Department of DermatologyRuijin Hospital, Shanghai JiaoTong University School of Medicine
  • Meng Pan
    • Department of DermatologyRuijin Hospital, Shanghai JiaoTong University School of Medicine
    • Department of DermatologyRuijin Hospital, Shanghai JiaoTong University School of Medicine
Original Paper

DOI: 10.1007/s00403-013-1342-9

Cite this article as:
Wu, Y., Lu, Z., Chen, Y. et al. Arch Dermatol Res (2013) 305: 477. doi:10.1007/s00403-013-1342-9

Abstract

We aimed to investigate the role of IL-12B gene polymorphism (rs6887695) in the disease susceptibility and clinical phenotypes of psoriasis vulgaris patients in the Chinese Han population. The genotype data of the IL-12B gene polymorphism (rs6887695) in 575 psoriasis patients and 1,403 normal controls were investigated using TaqMan technology. The Chi-square test was used to compare the genotype and allele frequency distribution among the groups. The genotypic and allelic frequencies of rs6887695 in the IL-12B gene between the cases and controls, as well as between the guttate and plaque psoriasis cases, were statistically significant (Pgenotype <0.01, Pallele <0.01). However, the differences between the pediatric and adult onset psoriasis patients, between familial and sporadic cases, and between female and male cases were not statistically significant (P > 0.05). The genetic polymorphism of the IL-12B gene (rs6887695) may be associated with the psoriasis susceptibility in the Chinese Han population, especially for the plaque cases, but not associated with the age at onset, family history, or sex.

Keywords

PsoriasisPhenotypePolymorphismSusceptibilityIL-12B rs6887695

Introduction

Psoriasis is a common hereditary and chronic inflammatory skin disorder characterized by the infiltration of inflammatory elements, keratinocyte hyperproliferation, and altered differentiation [3]. Psoriasis affects approximately 2–5 % of the Caucasian population, the incidence of this dermatosis in the Chinese Han population is lower but estimated at 0.123 % [7]. The disease appears to be both genetically and clinically heterogeneous, and its clinical characterizations (onset, gender, and clinical phenotypes) have been described.

Recently, several genome-wide association (GWAs) and replicated studies [5, 7, 17, 19, 24] have identified the psoriasis susceptibility loci within the beta subunit of interleukin 12 (IL-12B) gene, which encodes the p40 subunit common to both IL-12 and IL-23. IL-12B single-nucleotide polymorphisms (SNPs), rs6887695 [7, 19] and rs3212227 [5] are demonstrated to be associated with psoriasis in the Caucasian population, whereas rs3213094 and rs7709212 are identified to be associated with psoriasis in the Chinese population [23] (the LD information among these four SNPs is shown in Fig. 1). Given the genetic heterogeneity of psoriasis within different ethnic groups, the investigation on the association of IL-12B gene (rs6887695) polymorphism with psoriasis in the Chinese Han population is also replicated in our previous study [22]. Our findings indicate that rs6887695 of IL-2B positive in Caucasian population is also significantly associated with psoriasis in the Chinese Han population. In this study, we aimed to further investigate the correlation between the genotype and allele gene frequencies of IL-12B gene polymorphism site rs6887695 and different clinical features of psoriasis (including initial onset age, gender, clinical phenotype, and family history) in 575 Han Chinese psoriasis patients and 1,403 normal controls. To our knowledge, this is the first study to associate IL-12B rs6887695 polymorphism with clinical features of psoriasis.
https://static-content.springer.com/image/art%3A10.1007%2Fs00403-013-1342-9/MediaObjects/403_2013_1342_Fig1_HTML.gif
Fig. 1

The association evidence and LD pattern within the IL12B gene. The number in each box stands for the pairwise LD as assessed by D’; where there is no number D’ = 1

Materials and methods

Patients and controls

A total of 575 Chinese patients with psoriasis vulgaris (234 females and 341 males; age, 30.98 ± 12.31 years) from the Department of Dermatology, Ruijin Hospital were enrolled between 2004 and 2008, as well as 1,403 healthy controls (613 females and 790 males; age, 35.10 ± 13.20 years) from the health care center of Ruijin Hospital. The patients were diagnosed by two dermatologists based on clinical and pathological evidence using standard clinical criteria. The controls were healthy subjects without any clinical evidence or family history of psoriasis or any other autoimmune diseases such as diabetes, rheumatoid arthritis, or lupus. The patients and the control subjects were recruited after giving their fully informed written consent. The normal controls were matched with the psoriasis patients according to age, gender, and ethnicity from the same areas. This study was approved by the Jiao Tong University School of Medicine Ethics Committee.

Clinical investigation

Clinical information was obtained through a structured questionnaire, which included age, gender, age at onset, clinical phenotype, and family history. Family history was defined as positive if the patient had an affected relative at or within three meioses.

Positive and negative psoriasis patients—an analysis

The patients were divided into two groups, namely, pediatric and adult, according to the age of onset. The pediatric onset psoriasis patients were defined as those with an onset at or before the age of 16, whereas the adult onset psoriasis patients were defined as those whose psoriasis appeared after the age of 16 [21]. Meanwhile, the clinical types of psoriasis vulgaris were divided into two types, namely, the chronic plaque and acute guttate psoriasis [10]. The clinical assessment was conducted and recorded by two dermatologists prior to IL-12B allele typing.

Genotyping

High-molecular-weight genomic DNA was extracted from venous blood using the QuickGene 610L Automatic DNA/RNA Extraction System (Fijifilm, Tokyo, Japan). The rs6887695 allele was genotyped using TaqMan technology on an ABI 7900 system (Applied Biosystems, Foster City, California, USA). The probe and primer were designed by the Assays-by-Design or Assays-on-Demand service of Applied Biosystems, Inc., Foster City, California. Standard 5-μl polymerase chain reactions (PCR) were performed using TaqMan Universal PCR Master Mix (USA) reagent kits according to the guidelines provided. The mean cell rate across all samples was above 95 %, and the concordance was above 99 %.

Statistical analysis

Data were analyzed using SPSS 14.0 (SPSS Inc., Chicago, IL, USA) for Windows. The allele and genotype frequencies were estimated via direct gene counting. Allele and genotype frequencies were compared using the Pearson’s χ2 test (with Yates’ correction) and by calculation of odds ratios (OR) between the psoriasis and control subjects assuming Hardy–Weinberg equilibrium based on SHEsis, a robust user-friendly online software platform (http://analysis.bio-x.cn/). The Fisher’s exact test was used to compare the frequencies of the variables when the expected count was less than 5. The level of statistical significance was set at 5 % (P < 0.05). Associations between age at disease onset, age, family history, psoriasis type, and genotype were determined by the χ2 test.

Results

A comparison of allele and genotype frequencies between patients with psoriasis and controls revealed a statistically significant increase in allele (P = 0.000287) and genotype frequency [P = 4.77e−005, OR = 1.34 (95 % CI 1.17–1.55)] for IL-12B rs6887695 in psoriasis patients group (Table 1). To further examine the association of IL-12B rs6887695 with psoriasis, the patients were stratified according to the different clinical characterizations, including the age of onset, family history, clinical phenotype, and gender.
Table 1

Genotype frequency and allele gene frequency distribution of the IL-12B gene polymorphism in each group

Groups

n

Genotype frequency (%)

Allele gene frequency (%)

GG

GC

CC

χ2

P value

G

C

χ2

P value

OR (95 % CI)

Cases

575

245 (42.61)

261 (45.39)

69 (12.0)

16.31

0.000287

751 (65.30)

399 (34.70)

16.54

4.77e−005

1.34 (1.17–1.55)

Male

341

139 (40.77)

167 (48.97)

35 (10.26)

8.04

0.0180

445 (65.25)

237 (34.75)

6.51

0.0108

0.78 (0.65–0.95)

Female

234

97 (41.45)

113 (48.29)

24 (10.26)

11.89

0.00262

307 (65.60)

161 (34.40)

10.93

0.000946

0.69 (0.55–0.86)

Family historya

102

38 (37.25)

56 (54.90)

8 (7.85)

6.69

0.0357

132 (64.71)

72 (35.29)

3.18

0.0745

1.31 (0.97–1.36)

No family historya

440

183 (41.59)

210 (47.73)

47 (10.68)

15.17

0.000508

576 (65.45)

304 (34.55)

14.13

0.000170

1.35 (1.16–1.59)

Adolescent

35

15 (42.86)

16 (45.71)

4 (11.43)

1.51

0.471

46 (65.71)

24 (34.29)

1.53

0.216

1.37 (0.83–2.26)

Adults

540

221 (40.93)

264 (48.89)

55 (10.18)

18.89

7.90e−005

706 (65.37)

374 (34.63)

16.10

5.99e−005

1.35 (1.17–1.56)

Plaque psoriasis

543

229 (42.17)

266 (48.99)

48 (8.84)

26.89

1.45e−006

724 (66.67)

362 (33.33)

22.75

1.84e−006

1.43 (1.23–1.65)

Guttate psoriasis

32

7 (21.88)

15 (46.87)

10 (31.25)

4.61

0.100

29 (45.31)

35 (54.69)

4.36

0.0368

0.59 (0.36–0.97)

Control

1403

483 (34.42)

671 (47.83)

249 (17.75)

  

1,637 (58.34)

1,169 (41.66)

   

Male

790

281 (35.57)

379 (47.97)

130 (16.46)

  

941 (59.56)

639 (40.44)

6.51

  

Female

613

202 (32.95)

292 (47.63)

119 (19.41)

  

696 (56.77)

530 (43.23)

10.93

  

aA total of 33 cases of un-interpretable family history were found in 575 patients

Age of onset

Of the 575 cases, 35 were adolescent and 540 were adult patients. No significant differences were observed for allele and total genotype frequency between the adolescent patients and the controls (Table 1), between the adolescent and adult patients (Table 2), but there was significant statistical difference between the adult patients and the controls.
Table 2

Comparison of the IL-12B gene polymorphism site rs6887695 genotype and allele gene frequencies between different clinical types

 

Adolescents vs. adults

Family history vs. without family history

Plaque psoriasis vs. guttate psoriasis

Male vs. female

P value

OR (95 % CI)

P value

OR (95 % CI)

P value

OR (95 % CI)

P value

OR (95 % CI)

Genotype

χ2 = 0.147

 

χ2 = 1.91

 

χ2 = 18.1

 

χ2 = 0.0294

 

Total difference

P = 0.929

 

P = 0.385

 

P = 0.000117

 

P = 0.985

 

GG

0.822

1.08 (0.54–2.16)

0.422

0.83 (0.54–1.30)

0.023

2.61 (1.11–6.13)

0.869

0.97 (0.69–1.36)

GC

0.716

0.88 (0.44–1.75)

0.192

1.33 (0.87–2.06)

0.816

1.09 (0.53–2.22)

0.872

1.03 (0.74–1.43)

CC

0.814

1.14 (0.39–3.34)

0.392

0.71 (0.33–1.56)

4.30e−005

0.21 (0.10–0.48)

0.435

1.19 (0.73–1.95)

Allele gene

 G

0.953

1.02 (0.61–1.69)

0.840

0.97 (0.70–1.33)

0.000480

2.41 (1.45–4.01)

0.903

0.99 (0.77–1.26)

 C

0.953

0.99 (0.59–1.64)

0.840

1.03 (0.75–1.42)

0.000480

0.41 (0.25–0.69)

0.903

1.02 (0.79–1.30)

Family history

Among the 575 cases, 542 had a detailed family history, which included 102 positive cases and 440 negative cases. Among the patients with a positive family history, the difference in allele frequency was not statistically significant between the cases and the controls, whereas in analysis of total genotype distribution, comparing cases and controls produced a significant change (Table 1). No significant difference between the allele and total genotype frequencies of the positive and negative family history groups was observed (Table 2).

Clinical types

Of the 575 cases, 543 were of plaque psoriasis and 32 were of the guttate psoriasis type. The differences for the allele and total genotype frequencies were statistically significant between the plaque psoriasis cases and controls. The difference for the total genotype frequency was not statistically significant between the guttate psoriasis cases and the controls, whereas significant difference was present between them for the allele frequency (Table 1). Significantly statistical differences in the allele and total genotype frequencies were observed between the plaque and guttate psoriasis cases, whereas no significant difference in the GC genotype frequency was detected between the two clinical types (Table 2).

Gender

Of the 575 patients, 341 were males and 234 were females. There were significant differences in the allele and total genotype frequencies between the male patients and the male controls, and between the female patients and the female controls (Table 1). By contrast, the difference between the male and female patients in terms of the allele and total genotype frequencies was not significant (Table 2).

Discussion

Psoriasis vulgaris is a chronic, recurrent inflammatory dermatopathy that causes excessive proliferation of the epidermis. Its pathogenic mechanism remains unknown. Psoriasis vulgaris has been widely accepted as a polygenic disease caused by immunologic dissonance after stimulation from multiple environmental factors.

Both IL-23 and IL-12 belong to the molecular family of IL-12, which are cytokines that mediate the immunoinflammatory responses. IL-23 and IL-12 play an important role in the pathogenic mechanism of immunologic diseases such as psoriasis vulgaris and Crohn’s disease [13, 20, 23]. Studies have shown that the IL-12 level in the serum samples of psoriasis vulgaris patients is significantly higher than that of people who do not have the disease. This high level of IL-12 is in turn associated with a high psoriasis area and severity index score in psoriasis vulgaris patients [2]. Psoriasis vulgaris patients have increased expression of skin lesion RNA and proteins than normal individuals [9, 15, 16]. Multiple studies have shown that both IL-23 and IL-12 are vital in the pathogenesis of psoriasis and are associated with the disease in terms of immunology and acology. Genetic studies have also suggested that the gene coding IL-12B, which is the common p40 subunit of IL-12 and IL-23, is the gene susceptible to psoriasis vulgaris [3, 5, 7, 17, 19, 24]. The current study combined the genomic association studies on the psoriasis vulgaris susceptible gene in northern Americans and Caucasians and applied a TaqMan probe fluorescent PCR technique to reveal the association between the IL-12B (rs6887695) gene polymorphism and psoriasis vulgaris susceptibility in the Chinese Han population. Through the analysis of the frequency distribution of the three genotypes (GG, CG, and CC) of the psoriasis vulgaris IL-12B gene polymorphism site rs6887695, our results found that the frequencies of the IL-12B (rs6887695) allele gene G and the genotype GG in the case groups were significantly higher than those of the control group. The findings also suggested that the allele gene G was the risk allele gene (OR = 1.34) for the psoriasis vulgaris susceptibility in the Chinese Han population, whereas the genotype GG was the most vital genotype in the pathogenesis of psoriasis vulgaris, which are in agreement with previous reports [7, 19, 22].

Furthermore, the association between the IL-12B (rs6887695) gene polymorphism and various clinical features of psoriasis was also investigated. Although psoriasis affects people of all ages, a strong tendency for disease onset in adulthood has been described for patients who develop psoriasis due to genetic transmission. Two main peaks of age of onset have been described: the largest is between 20 and 30 years, and a smaller peak occurs at 50–60 years [11]. As expected, there was significant difference in the allele and total genotype frequencies of the adult psoriasis patients with an onset after the age of 16 [21] when compared with the normal control. However, there was no significant difference for allele and total genotype frequency between the adolescent and adult patients. We consider it may be attributable to small samples. In addition, more frequent split method of psoriasis needs to be applied based on age at onset below (type 1) or above (type 2) 40 years [12]. Psoriasis does not exhibit sexual dimorphism as many other autoimmune diseases. In autoimmune-like illnesses caused by recognized environmental agents, sex discrepancy is usually explained by differences in exposure. Krämer et al. [14] suggest that in the case of psoriasis, either the influence of the environment compensates the male-specific genetic effect, that is, men are more resistant to such effects, or women are affected more strongly by environmental factors. As a result, the frequency of the disease is not gender-biased. Similarly, there was no significant association with gender in psoriasis patients [8]. The patient group was also stratified based on family history of psoriasis; however, no association with IL-12B (rs6887695) was observed in those with and without a family history of psoriasis. This suggests separation on the basis of family history of psoriasis is not an effective means of screening out individuals from the region overlapping with the normal distribution of psoriasis [1]. Psoriasis is a heterogeneous disease and various clinical subtypes have been defined including chronic plaque psoriasis (characterized by plaques of psoriasis on extensor surfaces), and guttate psoriasis (characterized by the eruption of small red scaly lesions) [18]. The cause of its subtypes is still unknown, but several studies point to a strong genetic predisposition, which leads to proteins differentially expressed [6]. In this study, there were significantly statistical differences in the allele and total genotype frequencies between the plaque and guttate psoriasis cases. In addition, we also have confirmed the strong association between IL-12B (rs6887695) and plaque or guttate psoriasis which is consistent with previous study that shows that the frequency of the APOE e4 allele (+3937C/+4075C) is found higher in patients with chronic plaque and guttate psoriasis than in controls [4]. However, only 32 patients with guttate psoriasis were included between 2004 and 2008 in this study, which led to large differences in allele frequencies such that the G allele confers susceptibility to plaque but protection from guttate. Further studies with larger samples are necessary.

In conclusion, the SNP rs6887695 is associated with psoriasis vulgaris susceptibility in the Chinese Han population, particularly with plaque psoriasis. However, the SNP rs6887695 is not associated with the age of onset, family history, and gender. The current study further reveals that IL-12B gene polymorphism is associated with psoriasis vulgaris and provides a basis for further investigation on the pathogenesis of the disease.

Copyright information

© Springer-Verlag Berlin Heidelberg 2013