Lung DOI 10.1007/s00408-014-9648-8
Association of Vitamin D Receptor Gene Polymorphisms with Asthma Risk: Systematic Review and Updated Meta-analysis of Case–Control Studies Kalthoum Tizaoui • Anissa Berraies • Besma Hamdi • Wajih Kaabachi • Kamel Hamzaoui Agne`s Hamzaoui
•
Received: 9 May 2014 / Accepted: 22 September 2014 Ó Springer Science+Business Media New York 2014
Abstract Background The association between vitamin D receptor (VDR) polymorphisms and asthma risk has been inconsistently investigated, but published studies demonstrated conflicting results. The aim of the current study was to investigate the impact of TaqI, BsmI, ApaI, and FokI VDR polymorphisms on asthma disease by using a meta-analysis approach. Methods Following the preferred reporting items for systematic reviews and meta-analyses guidelines, a systematic search and meta-analysis of the literature were conducted. Subgroup analyses were performed to detect potential sources of heterogeneity from selected study characteristics. Results A total of 2,097 cases and 1,968 controls in eight case–control studies were included in meta-analyses. A significant association was found between TaqI polymorphisms and asthma risk [OR 1.488 (95 % CI 1.019–2.174); P = 0.040] in a codominant model. In the same way, BsmI was significantly associated with asthma risk [OR 2.017 (95 % CI 1.236–3.851); P = 0.017] in the codominant model. The homozygote BB BsmI genotype was found to confer significant asthma risk. FokI polymorphism was
K. Tizaoui (&) A. Berraies B. Hamdi W. Kaabachi K. Hamzaoui A. Hamzaoui Department of Basic Sciences, Medicine Faculty of Tunis, Tunis El Manar University, 15 Rue Djebel Lakdar, 1007 Tunis, Tunisia e-mail:
[email protected] A. Berraies B. Hamdi A. Hamzaoui Division of Pulmonology, Department of Respiratory Diseases, Unit Research: (UR/12SP15), Ministry of Health, Abderrahman Mami Hospital, Ariana, Tunisia
marginally associated with asthma risk [OR 1.187 (95 % CI 0.975–1.446); P = 0.088] in the codominant model. In contrast, no significant association was found between ApaI polymorphism and asthma risk. Subgroup analyses revealed that gender and age modified significantly the association between FokI polymorphisms and asthma risk (P = 0.035 and 0.013, respectively). Publication year and serum 25(OH) D level tended, marginally, to moderate the association between FokI polymorphism and asthma risk. Conclusion TaqI, BsmI, and FokI VDR polymorphisms contribute to asthma susceptibility. The association between FokI polymorphism and asthma risk is influenced by study characteristics. Keywords BsmI ApaI TaqI FokI VDR polymorphism Asthma Meta-analysis
Introduction Asthma is a chronic respiratory disease characterized by airway inflammation, airway hyper-responsiveness, and airflow obstruction in response to specific triggers [1, 2]. It has also an immunological component [3]. In the last years, vitamin D and its nuclear receptor VDR have emerged as new factors contributing to asthma disease. A growing body of evidence showed that Vitamin D deficiency is associated with markers of allergy and asthma severity and exacerbation [4, 5]. Vitamin D supplementation decreases asthma exacerbations frequency in vitamin D deficient patients [6–8] probably by influencing airway remodeling [9], steroid sensitivity, and risk of respiratory infections via its genomic and non-genomic effects [10]. Vitamin D may play an important role in pulmonary health by inhibiting inflammation, in part through maintaining
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and asthma in different ethnic groups but results were inconsistent [27–36].
regulatory T cells, and direct induction of innate antimicrobial mechanisms [7, 8]. Vitamin D and its analogs exert their actions through the nuclear VDR ligand-dependent transcription factor [11]. Linking of vitamin D to VDR regulates the expression of multiple genes associated with inflammation and immune modulation [12–14] Several restriction fragment length polymorphisms (RFLPs) in the VDR gene have been described including BsmI [15], ApaI [16] TaqI [17], and FokI [18]. BsmI and ApaI polymorphisms are located in intron 8 of the VDR gene, and TaqI is located in exon 9 and leads to silent codon changes associated with increased VDR mRNA stability [19]. The FokI polymorphism which is located in the exon 2 leads to a protein with different size, the shorter form of the protein (424 aa) being more active than the longer one (427 aa) [20]. Vitamin D and VDR have significant anti-inflammatory and anti-infectious functions [21–23]. Genetic alterations of VDR gene and poor vitamin D status could lead to the initiation and propagation of several diseases including asthma [24–26]. Important genetic association studies investigated the association between VDR polymorphisms
Methods Identification of Eligible Studies The review process followed the preferred reporting items for systematic reviews and meta-analyses (PRISMA) guidelines [37]. We performed a literature search using the MEDLINE and EMBASE databases to identify articles that examined associations between VDR polymorphisms and asthma. Combinations of keywords, such as VDR polymorphism and asthma, were entered as medical subject heading (MeSH) and text words. The reference lists of the articles retrieved were also reviewed to identify publications on the same topic. Two independent reviewers performed searching in duplicate. Inclusion Criteria and Data Extraction Meta-analyses included case–control studies that reported the number of individual genotypes and/or alleles for VDR
Table 1 Characteristics of reviewed studies on BsmI, ApaI, TaqI, and FokI VDR polymorphisms and asthma risk Reference
VDR polymorphisms
Ethnicity
Country
Latitude
25(OH)D levels ng/ml
Case
Control
Raby et al. [28]
ApaI, TaqI, FokI
Caucasian (European)
Quebec, Canada
48°N
0–24
517
519
Fang et al. [30]
BsmI, FokI
Asian (Chinese Han)
Sichuan, China
34°N
0–24
101
206
Saadi et al. [31] Arababadi et al. [35]
BsmI, ApaI, TaqI, FokI ApaI, TaqI
Asian (Chinese Han) Caucasian (Iranian)
Shandong, China Rafsanjan, Iran
34°N 30°N
0–24 24.1–30.2
567 100
523 100 288
Li et al. [5, 33]
FokI
Asian (Chinese Han)
Peking, China
39°N
0–24
467
Pillai et al. [32]
ApaI, TaqI, FokI
African American
Washington, US
39°N
0–24
139
74
Maalmi et al. [34]
BsmI, ApaI, TaqI, FokI
Caucasian (Tunisian)
Tunis, Tunisia
36°N
24.1–30.2
155
225
Ismail et al. [36]
FokI
Caucasian (Egyptian)
Cairo, Egypt
30°N
30.3–49.9
51
33
2
Reference
Genotyping
Age case/control
Male % case/control
v
Raby et al. [28]
Mass spectrometry
Matched
Women
4.67, 8.85, 0.69
x
–
Fang et al. [30]
PCR–RFLP
35.9
41.58/46.60
2.62, 2.99
–
–
Saadi et al. [31]
PCR–RFLP
41.36/44.18
40.55/66.82
3.14, 9.37, 1.62, 3.65
x
–
Arababadi et al. [35]
PCR–RFLP
48
31/27
5.23, 8.05
–
– –
Haplotypes analysis
Serum VD dosage
Li et al. [5, 33]
PCR–RFLP
40.8 ± 14.1
39.61/54.86
0.19
–
Pillai et al. [32]
Taqman assay
11.2/11.8
58/35
0.86, 2.90, 0.64
–
x
Maalmi et al. [34]
Universal PCR master PCR–RFLP
9.1
61.93
7.44, 1.76, 7.45, 6.34
x
x
Ismail et al. [36]
TaqMan assay
8.6 ± 2.7
54.9
12.55
–
x
BsmI (rs1544410 G [ A), ApaI (rs7975232 A [ C), TaqI (rs731236 T [ C), FokI (rs2228570 C [ T); Estimated 25(OH)Dlevels ng/ml according to Garland et al. [43] PCR Polymerase chain reaction, RFLP restriction fragment length polymorphism, v2 Hardy–Weinberg equilibrium test, x analysis conducted; – analysis not conducted
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polymorphisms in cases and in controls; they had disease outcome definitions that followed accepted GINA guidelines [38]. The following information was extracted from each study: author, publication year, ethnicity, country, gender, age, haplotypes, and serum vitamin D levels for each VDR polymorphism (Table 1). Statistical Analyses Data from studies were combined to give summary odds ratios that were represented as a point estimate with 95 % confidence intervals (CIs) on a forest plot. We used the methodology for meta-analysis of molecular studies described by Thakkinstian et al. [39]. OR1, OR2, and OR3 were calculated for genotypes: (1) TT vs. tt (OR1), Tt vs. tt (OR2), and TT vs. Tt (OR3) for the TaqI polymorphism; (2) BB vs. bb (OR1), Bb vs. bb (OR2), and BB vs. Bb (OR3) for BsmI polymorphism; (3) AA vs. aa (OR1), Aa vs. aa (OR2), and AA vs. Aa (OR3) for ApaI polymorphism; and (4) FF vs. ff (OR1), Ff vs. ff (OR2), and FF vs. Ff (OR3) for FokI polymorphism. The pairwise differences were used to indicate the most appropriate genetic model as follows: if OR1 = OR3 = 1 and OR2 = 1, then a recessive model was suggested; if OR1 = OR2 = 1 and OR3 = 1, then a dominant model was suggested; if OR2 = 1/OR3 = 1 and OR1 = 1, then a complete overdominant model (homozygous) was suggested; if OR1 [ OR2 [ 1 and OR1 [ OR3 [ 1 (or OR1 \ OR2 \ 1 and OR1 \ OR3 \ 1), then a codominant model was suggested [39]. Heterogeneity of data was evaluated by using the Q statistic [40]. I2 values of 25, 50, and 75 % were defined as low, moderate, and high estimates, respectively. The random effects model was used because it accommodates diversity between studies and thus is definitely preferable in the presence or anticipation of any between study heterogeneity [41]. Egger’s regression test was used to search for publication bias [42]. The stability of the summary risk estimate was evaluated using a sensitivity analysis in which each study was individually removed and the odds ratio was recalculated. Subgroup analyses were planned when sufficient information was reported in at least three studies in each subgroup.
Results Characteristics of Studies Appropriate diagnostic criteria and proper genotyping methods were used in all included studies. Ten studies were identified for asthma by the specified search terms. Two studies were ineligible because they were family-based studies [25, 27]. Therefore, 8 studies were considered in the
Fig. 1 Flow diagram of the systematic review and meta-analysis literature search results
analysis [28, 30–36]. Genotype distributions of all single nucleotide polymorphisms (SNPs) in controls and patients exhibited Hardy–Weinberg equilibrium (HWE). Included studies were heterogeneous for study characteristics, and each study characteristic was divided into different subgroups. Publication year was divided into three subgroups: 2001–2005, 2006–2010, and 2011–2013. Ethnicities were Caucasian European, Caucasian, Asian, and African American. Latitude was divided into three subgroups: 20–30°N, 30.1–40°N, and 40.1–50°N. Age was divided into three subgroups: \20 years, 20–40 years, and [40 years. Gender was divided into two subgroups: males \50 % and males [50 %. Estimated 25(OH) D serum levels according to Garland et al. [43] were divided into three subgroups: 0–24, 24.1–30.2, and 30.3-49.9 ng/ml. Results of research are given in Fig. 1 and characteristics of the studies are summarized in Table 1.
Data Analysis TaqI Polymorphism A total of 1,478 cases and 1,441 controls in five case– control studies were included in meta-analysis. We used random effects model for all analyses because we assumed the existence of heterogeneity among studies given the important variation in studies characteristics. Analyses showed that TaqI polymorphism was associated with asthma under Tt vs.tt codominant model [95 % CI, OR 1.488 (1.019–2.174); P = 0.040]. The heterozygote Tt genotype conferred significant asthma risk when compared to the homozygote tt genotype.
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Fig. 2 Forest plot of the association between TaqI polymorphism and asthma with the random effects model: TT ? tt vs. Tt forest plot shows the odds ratio (ORs) and respective 95 % confidence intervals (CIs) for the different studies included in the meta-analysis. For each
study in the forest plot, the area of the black square is proportional to study weight and the horizontal bar represents the 95 % CI. Z score: the standardized expression of a value in terms of its relative position in the full distribution of values
The estimated OR1, OR2, and OR3 were 1.096, 1.488, and 0.870, respectively. These estimates suggested a homozygous genetic model. The pooled OR1 0.886 (95 % CI 0.716–1.098, P = 0.270) (Fig. 2). In the homozygous model, sensitivity analysis by removal of one study [28] modified significantly the association between TaqI polymorphism and asthma. Recalculated OR 0.789 (95 % CI 0.624–0.999; P = 0.049) suggesting a protective effect of TT and tt homozygote genotypes when compared to Tt heterozygote genotype. Heterogeneity was moderate (I2 = 27.93 %) in the homozygous model. Significant publication bias was detected by Egger’s test (Egger P = 0.003). The bias might be caused by unpublished data. Results are summarized in Table 2.
asthma risk OR 1.012 (95 % CI 0.710–1.466; P = 0.913) (Fig. 3). Results are summarized in Table 2.
BsmI Polymorphism A total of 823 cases and 954 controls in three case–control studies were included in meta-analysis. Analyses showed that BsmI polymorphism was significantly associated with asthma under BB vs. bb codominant model. The estimated OR1, OR2, and OR3 were 2.017, 1.055, and 1.047, respectively. These estimates suggested a codominant genetic model. The pooled OR1 2.017 (95 % CI 1.236–3.851; P = 0.017) indicating that the BB homozygote genotype was a significant risk factor for asthma when compared to tt genotype. Heterogeneity was high in BB vs. bb (I2 = 67.50 %) model. Sensitivity analysis by removal of each individual study did not meaningfully change results. Egger’s test was significant in BB vs. bb (Egger P = 0.05) model. The bias might be caused by limited number of studies, as only three studies on BsmI polymorphism were available. Analysis in the allele contrast model showed that the B allele was not associated with
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ApaI Polymorphism A total of 1,478 cases and 1,441 controls in five case– control studies were included in meta-analysis. Preliminary analyses showed that ApaI polymorphism was not associated with asthma under any of the studied genetic models. Sensitivity analysis by removal of one study [31] moderated significantly the association between ApaI polymorphism and asthma risk in the recessive model. Recalculated OR was 0.797 (95 % CI 0.648–0.981; P = 0.032) suggesting that the AA homozygote genotype had a protective effect against asthma when compared to Aa and aa genotypes. Similarly, removal of one study [35] changed significantly results in the allele contrast model. Recalculated OR was 0.823 (95 % CI 0.716–0.948; P = 0.006) suggesting a significant protective effect of the major A allele. The estimated OR1, OR2, and OR3 were 0.858, 0.978, and 0.913, respectively. These estimates suggested a codominant genetic model. The pooled OR1 was 0.858 (95 % CI 0.451–1.635; P = 0.642) (Fig. 4) and OR2 = 0.978 (95 % CI 0.712–1.344; P = 0.892). Heterogeneity was high in AA vs. aa model (I2 = 78.54 %). Sensitivity analysis by removal of each individual study did not meaningfully change results in the codominant model. No evidence of publication bias was detected by Egger’s test in AA vs. aa model (Egger P = 0.38). Results are summarized in Table 2. FokI Polymorphism A total of 1,997 cases and 1,868 controls in seven case– control studies were included in meta-analysis. The association between FokI and asthma was marginal under the
Lung Table 2 Association of TaqI, BsmI, ApaI, and FokI VDR polymorphisms with Asthma risk
TaqI (n = 5)
BsmI (n = 3)
ApaI (n = 5)
Bold significant P value (P \ 0.05); bold* marginal association (0.05 \ P \ 0.1); * best fitted genetic model; n number of studies, OR odds ratio; I2: heterogeneity test TaqI polymorphism: one study removed [28] in the homozygous model: OR 0.789 (0.624–0.999; P = 0.049) ApaI polymorphism: one study removed [31] in the recessive model: OR 0.797 (0.648–0.981; P = 0.032); one study removed [35] in allele contrast model: OR 0.823 (0.716–0.948; P = 0.006)
Fok I (n = 7)
Genetic model
OR (95 % CI)
P value
I2 (%)
EggerP
Recessive
TT vs. Tt ? tt
0.929 (0.643–1.341)
0.692
69.62
0.002
Homozygous*
TT ? tt vs. Tt
0.886 (0.716–1.098)
0.270
27.93
0.003
Dominant
TT ? Tt vs. tt
1.394 (0.895–2.171)
0.141
49.39
0.40
Codominant (OR1)
TT vs. tt
1.096 (0.508–2.368)
0.815
73.766
0.22
Codominant (OR2)
Tt vs. tt
1.488 (1.019–2.174)
0.040
30.210
0.46
Codominant (OR3)
TT vs. Tt
0.870 (0.607–1.247)
0.449
65.558
0.000
Allelecontrast
T allele vs. t allele
1.052 (0.825–1.343)
0.681
64.378
0.030
Recessive
BB vs. Bb ? bb
0.932 (0.298–2.910)
0.903
81.43
0.37
Homozygous
BB ? bb vs. Bb
0.956 (0.738–1.240)
0.736
54.31
0.21
Dominant Codominant* (OR1)
BB ? Bb vs. bb BB vs. bb
1.121 (0.837–1.502) 2.017 (1.236–3.851)
0.443 0.017
0.00 67.50
0.39 0.05
Codominant (OR2)
Bb vs. bb
1.055 (0.679–1.640)
0.810
0.00
0.16
Codominant (OR3) Allelecontrast
BB vs. Bb
1.047 (0.541–2.026)
0.892
79.040
0.39
B allele vs. b allele
1.012 (0.710–1.466)
0.912
61.65
0.001
Recessive
AA vs. Aa ? aa
0.897 (0,617–1.304)
0.570
69.264
0.34
Homozygous
AA ? aa vs. Aa
0.932 (0.802–1.084)
0.361
0.00
0.31
Dominant
AA ? Aa vs. aa
0.935 (0.628–1.393)
0.742
69.08
0.30
Codominant* (OR1)
AA vs. aa
0.858 (0.451–1.635)
0.642
78.540
0.38
Codominant (OR2)
Aa vs. aa
0.978 (0.712–1.344)
0.892
48.329
0.37
Codominant (OR3)
AA vs. Aa
0.913 (0.670–1.244)
0.565
51.236
0.26
Allelecontrast
A allele vs. a allele
0.923 (0.709–1.202)
0.552
77.664
0.25
Recessive
FF vs. Ff ? ff
1.020 (0.812–1.280)
0.867
53.12
0.07
Homozygous Dominant
FF ? ffvs. Ff FF ? Ff vs. ff
0.895 (0.782–1.023)
0.104
0.00
0.18
1.170 (0.906–1.511)
0.228
33.32
0.028
Codominant* (OR1)
FF vs. ff
1.135 (0.799–1.614)
0.479
52.84
0.041
Codominant (OR2)
Ff vs. ff
1.187 (0.975–1.446)
0.088*
1.29
0.044
Codominant (OR3)
FF vs. Ff
0.935 (0.774–1.129)
0.487
28.05
0.12
Allele contrast
F allele vs. f allele
1.099 (0.915–1.320)
0.311
64.27
0.02
codominant model (P = 0.088). The estimated OR1, OR2, and OR3 were 1.135, 1.187, and 0.935, respectively. These estimates suggested a codominant genetic model. The pooled OR1 1.135 (95 % CI 0.799–1.614; P = 0.479) and OR2 1.187 (95 % CI 0.975–1.446; P = 0.088) (Fig. 5). The heterozygote Ff genotype tended to be a significant
asthma risk factor when compared to homozygote ff genotype. Sensitivity analysis by removal of each individual study did not meaningfully change results. Heterogeneity was moderate in FF vs. ff (I2 = 52.84 %) model. A publication bias was detected by Egger’s test in FF vs. ff (Egger P = 0.041) model (Table 2).
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Fig. 3 Forest plot of the association between BsmI polymorphism and asthma with the random effects model: B allele vs. b allele Forest plot shows the odds ratio (ORs) and respective 95 % confidence intervals (CIs) for the different studies included in the meta-analysis.
For each study in the forest plot, the area of the black square is proportional to study weight and the horizontal bar represents the 95 % CI. Z score: the standardized expression of a value in terms of its relative position in the full distribution of values
Fig. 4 Forest plot of the association between ApaI polymorphism and asthma with the random effects model: AA vs. aa Forest plot shows the odds ratio (ORs) and respective 95 % confidence intervals (CIs) for the different studies included in the meta-analysis. For each study
in the forest plot, the area of the black square is proportional to study weight and the horizontal bar represents the 95 % CI. Z-score: the standardized expression of a value in terms of its relative position in the full distribution of values
Sufficient information was available in at least four studies for publication year (2011–2013), latitude (30.1–40°N), 25(OH)D levels (0–24 ng/ml), and gender (males \ 50 %). Gender was found to moderate significantly the association between FokI polymorphism and asthma risk. Pooled ORs were 0.840 (95 % CI 0.713–0.991; P = 0.038) and 0.855 (95 % CI 0.738–0.989; P = 0.035) in codominant and in allele contrast models, respectively. The major F allele and FF homozygote genotype might protect against asthma risk in females (males \ 50 %). Publication year tended to moderate the association between FokI polymorphism and asthma disease in the allele contrast and recessive models [OR 1.394 (95 % CI 0.990–1.963); P = 0.057 and OR 1.300 (95 % CI 0.981–1.723); P = 0.067, respectively]. The major F allele and FF homozygote genotype might be asthma risk factors in ‘2011–2013’ study period. In addition, 25(OH)D level (0–24 ng/ml) tended to modify the association between FokI polymorphism and asthma risk in the
homozygous model [OR 0.874 (95 % CI 0.758–1.007, P = 0.063]. FF and ff homozygote genotypes might have a protective effect against asthma risk in the subgroup where 25(OH)D levels were lower (0–24 ng/ml). Results are summarized in Table 3. Sufficient information was available in three studies for age (\20 years). Age influenced significantly the association between FokI polymorphism and asthma risk. Pooled ORs were 1.525 (95 % CI 1.094–2.126; P = 0.013) and 1.604 (95 % CI (1.092–2.356); P = 0.016) in the recessive and in the allele contrast models, respectively. The major F allele and FF homozygote genotype were significant risk factors in childhood asthma.
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Discussion VDR gene is considered as a pleiotropic gene, associated with multiple autoimmune, inflammatory, and allergic
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Fig. 5 Forest plot of the association between FokI polymorphism and asthma with the random effects model: Ff vs. ff Forest plot shows the odds ratio (ORs) and respective 95 % confidence intervals (CIs) for the different studies included in the meta-analysis. For each study in
the forest plot, the area of the black square is proportional to study weight and the horizontal bar represents the 95 % CI. Z score: the standardized expression of a value in terms of its relative position in the full distribution of values
diseases. Results reported by genetic association studies on VDR polymorphisms and asthma are conflictive, and the role of VDR polymorphisms remains unclear. The reasons for this disparity may be small sample sizes, lifestyle, differences in ethnicities, and extensive geographic variations. Therefore, in order to overcome the limitations of individual studies, we performed meta-analysis. Meta-analysis increases statistical power and resolution by pooling the results of independent analyses. In this meta-analysis, we combined data from published studies to estimate the magnitude of the associations between TaqI, BsmI, ApaI, and FokI polymorphisms in the VDR gene with asthma risk. Our analyses suggested that asthma was significantly associated with TaqI and BsmI polymorphisms and marginally associated with FokI polymorphism. Sensitivity analysis showed that when one study was removed, the ApaI polymorphism was significantly associated with asthma risk. These results suggested that VDR polymorphisms might be, directly or indirectly, involved in mechanisms related to asthma disease. Analyses reported ORs with small levels suggesting modest contribution of VDR polymorphisms to asthma susceptibility. Effectively, the etiology for many of the common complex diseases such as asthma derives from permutations and combinations of common variants. Each variant may only confer a small risk. DNA sequence variations such as polymorphisms exert both modest and subtle biological effects [44]. A number of genes involved in the vitamin D pathway demonstrate modest levels of association with asthma and atopy [45]. Results provided by current analyses are consistent with genome scans which have identified linkage with asthma in several genomic regions, including region q13–23 of chromosome 12, housing the VDR gene [46, 47]. Vitamin D has complex effects on pulmonary cell biology and immunity with impact on inflammation, host
defense, and other processes. High vitamin D levels are associated with better lung function, less airway hyperresponsiveness, and improved glucocorticoid response [48]. The association between VDR polymorphisms and atopy or asthma severity was investigated in several studies. Maalmi et al. [34] found no significant association of VDR polymorphisms with atopy or asthma. In contrast, Poon et al. [27] reported significant association of variants in the VDR gene and atopy. Similarly, Pillai et al. [32] demonstrated that FokI variant was associated with one or more positive aeroallergen skin test, and increased IgE levels. In addition, it was associated with higher nighttime asthma morbidity scores, and lower baseline spirometric measures. More recently, FokI polymorphism was found to be significantly associated with decreased pulmonary functions, increased asthma severity, and uncontrolled disease status in addition to elevated IgE level and hypovitaminosis D [36]. As ApaI, BsmI, and TaqI polymorphisms are silent codon changes [49]; their influence may not be related to changes in the protein structure, but to differences in stability and/or translation efficiency of the RNA. The FokI polymorphism, which is located in translation initiation codon of the VDR, seems to have consequences for both VDR protein structure and transcriptional activity [49, 50]. Our study showed that, although involving silent codon changes, ApaI, BsmI, and TaqI polymorphisms are significantly associated with asthma disease. It has been suggested that VDR RFLPs demonstrate linkage disequilibrium with other relevant polymorphisms in the VDR gene or in its proximity, rather than primary susceptibility loci in autoimmune diseases [51, 52]. The expression and role of VDR to transactivate target genes are determined not only by genetics, but also by ethnicity and environment involving complex interactions [53]. A likely reason
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Lung Table 3 Association of FokI polymorphism and Asthma: Stratification according to study characteristics
Genetic model Codominant FF vs. ff
Codominant Ff vs. ff
Codominant FF vs. Ff
Allele contrast
Recessive
Homozygous
Dominant Bold significant P value (P \ 0.05); bold* marginal association (0.05 \ P \ 0.1); n number of studies, OR odds ratio; 25(OH)D level: ng/ml
Study characteristics
OR (95 % CI)
P value 0.148
Publication year
4
2011–2013
1.884 (0.799–4.445)
Latitude
5
30.1–40°N
0.944 (0.662–1.493)
0.978
Estimated25(OH)D
4
0–24
0.946 (0.764–1.173)
0.614
Gender (male)
4
\50 %
0.944 (0.760–1.172)
0.600
Age (years)
3
\20
2.844 (0.785–10.309)
0.111
Publication year
4
2011–2013
1.495 (0.749–2.985)
0.254
Latitude
5
30.1–40°N
1.164 (0.894–1.514)
0.259
Estimated25(OH)D
4
0–24
1.132 (0.926–1.385)
0.225
Gender (male)
4
\50 %
1.138 (0.929–1.394)
0.210
Age (years)
3
\20
1.902 (0.953–3.797)
0.068* 0.228
Year of study
4
2011–2013
1.173 (0.905–1.520)
Latitude
5
30.1–40°N
0.893 (0.692–1.152)
0.385
Estimated25(OH)D
4
0–24
0.866 (0.730–1.029)
0.102
Gender (male)
4
\50 %
0.840 (0.713–0.991)
0.038
Age (years) Publication year
3 4
\20 2011–2013
1.336 (0.941–1.897) 1.394 (0.990–1.963)
0.105 0.057*
Latitude
5
30.1–40°N
1.053 (0.869–1.277)
0.597
Estimated25(OH)D
4
0–24
0.962 (0.868–1.065)
0.455
Gender (male)
4
\50 %
0.953 (0.858–1.058)
0.367
Age (years)
3
\20
1.604 (1.092–2.356)
0.016
Publication year
4
2011–2013
1.300 (0.981–1.723)
0.067*
Latitude
5
30.1–40°N
0.911 (0.749–1.311)
0.951
Estimated25(OH)D
4
0–24
0.890 (0.765–1.104)
0.129
Gender (male)
4
\50 %
0.868 (0.743–1.015)
0.076*
Age (years)
3
\20
1.525 (1.094–2.126)
0.013
Publication year
4
2011–2013
1.052 (0.828–1.336)
0.681
Latitude
5
30.1–40°N
0.896 (0.752–1.067)
0.217
Estimated25(OH)D
4
0–24
0.874 (0.758–1.007)
0.063*
Gender (male)
4
\50 %
0.855 (0.738–0.989)
0.035
Age (years)
3
\20
1.143 (0.815–1.604)
0.437
Publication year Latitude
4 5
2011–2013 30.1–40°N
1.702 (0.784–3.698) 1.119 (0.899–1.393)
0.179 0.314
Estimated25(OH)D
4
0–24
1.055 (0.873–1.276)
0.580
Gender (male)
4
\50 %
1.056 (0.872–1.279)
0.575
Age (years)
3
\20
2.497 (0.722–8.634)
0.148
that genetic association studies have been largely conflicting and failed to identify specific ‘causal’ genes is that the polymorphisms do not necessarily influence risk directly, but may reflect the effect of environmental exposures [54]. Litonjua and collaborators hypothesized that modern lifestyle leads to decreased cutaneous vitamin D production [55] favoring susceptibility to asthma and allergic diseases. Importantly, the microbial environment has a great influence on development of immune disorders as some microbes have been shown to slow innate immune defenses by deregulating the VDR gene [23]. Multiple environmental factors cited in the literature such as industrialization,
123
n
smoking, air pollution, and geographical location as well as socioeconomic status, diet, fetal growth have been shown to confound asthma susceptibility. Given the importance of environmental factors, we stratified our studies according to study characteristics. Insufficiency of studies was a major limitation to evaluate and compare all interactions between VDR polymorphisms and study characteristics. We found that FokI polymorphism interacts with gender and age to modify asthma risk. Additionally, publication year and 25(OH)D levels tended to moderate the association between FokI polymorphism and asthma susceptibility. Therefore, factors such as gender, age, publication year or study period, and 25(OH)D
Lung
values could be considered as potential moderators of asthma risk. Sex affects many important features of asthma and allergy, including lung growth and development [56], age of symptom onset, and disease severity [57]. The influence of sex and age on the incidence, period of occurrence, severity, and advancement of asthma suggests the possibility of manipulating pathogenetic mechanisms modulated by sex hormones [58]. Experimental observations indicated that sex hormones such as estrogen play a dual role in regulating allergic lung inflammation [59]. Both endogenous and exogenous sex steroids influence asthma in young women. Women had higher levels of enzyme activities than did men, and sex-specific differences were found in the associations between markers of antioxidative defense and asthma [60]. The dual effect of sex hormones on the inflammatory response in the asthmatic lung may explain the conflicting epidemiological and clinical data reported in the literature. The interaction between serum Vitamin D and the disease risk has been explored in other diseases, but findings were inconsistent. VDR polymorphisms were associated with prostate cancer risk only among those with vitamin D deficiency [61, 62]. Latitude gradients of cancer, autoimmune diseases, coronary heart disease, and mental disorders correlate with vitamin D latitude gradients [63, 64]. On molecular basis, Handel and coworkers [65] showed a direct correlation between in vivo vitamin D levels and the number of VDR binding sites. They suggested then, that VDR binding in conditions of vitamin D sufficiency might be more directly related to immune cell function. Recent findings suggested that the inhibitory effect of 25(OH) D3 on the Th17 response was mediated via both T cells and dendritic cells. Dendritic cells pathway is involved in the direct inhibition of 25(OH)D3 on Th17 cell differentiation in young asthmatics [66]. Smolders et al. [67] reported an association between FokI polymorphism and serum vitamin D levels, in multiple sclerosis patients and healthy individuals. However, Hibler et al. [68] did not find any association between VDR genetic variation in VDR and vitamin D serum levels. These discrepancies might be due to the fact that some relationships between genotype and disease will only be seen in conditions of ‘‘high’’ exposure to an environmental factor of interest, whereas others may only be seen in conditions of ‘‘low’’ exposure [69, 70]. Based on Egger’s test, we detected a small publication bias. The bias might be caused essentially by unpublished data. In our meta-analysis, only studies indexed by the selected databases were included. Negative studies were less likely to be published in journals and be available in computerized databases, resulting in potential overestimation of effect sizes. In addition, the bias might be caused by
small numbers of patients as smaller studies are on average conducted and analyzed with less methodological rigor than larger studies [42, 71]. We detected also heterogeneity among studies due to ethnic composition of the studied population, geographic characteristics, and lifestyle. As study characteristics varied widely among studied populations, we used random effects model in our analyses. However, meta-analysis remains a retrospective research, which is subject to the methodological deficiencies of the included studies. Findings from the studies reviewed herein should be interpreted with caution for several reasons. Only four polymorphisms in the VDR gene have been studied, although there are several other functional VDR SNPs in the complex promoter region of the VDR gene. Haplotype analyses are important to identify groups of SNPs linked together. Moreover, studies of epigenetic factors such as methylation, copy number variation (CNV), and post transcriptional modifications will give useful information for both basic and practical research. In conclusion, BsmI, ApaI, and TaqI VDR polymorphisms are significantly associated with asthma. FokI polymorphism interacts with environmental factors to moderate asthma risk. Further genetic association studies along with haplotypes analysis might provide more powerful estimates. Asthma, as complex disease, implicates multiple genetic and environmental factors that interact with each other. Further studies on the interaction between VDR polymorphisms and related risk factors may give useful information to elucidate new approaches for prevention and treatment. Acknowledgments This study was supported by a grant from the Ministry of Higher Education and Scientific Research. Conflict of interest of interest.
The authors declare that they have no conflict
References 1. Brown SD, Calvert HH, Fitzpatrick AM (2012) Vitamin D and asthma. Dermato-Endocrinol 4:137–145 ´ (2012) Effects of vitamin D on immune 2. Sze´kely JI, Pataki A disorders with special regard to asthma, COPD and autoimmune diseases: a short review. Expert Rev Resp Med 6:683–704 3. Hammad H, Lambrecht BN (2008) Dendritic cells and epithelial cells: linking innate and adaptive immunity in asthma. Nat Rev Immunol 8:193–204 4. Brehm JM, Schuemann B, Fuhlbrigge AL et al (2010) Serum vitamin D levels and severe asthma exacerbations in the Childhood Asthma Management Program study. J Allergy Clin Immunol 126:52–58 5. Li F, Peng M, Jiang L, Sun Q, Zhang K, Lian F, Litonjua AA, Gao J, Gao X (2011) Vitamin D deficiency is associated with decreased lung function in Chinese adults with asthma. Respiration 81:469–475
123
Lung 6. Litonjua AA (2009) Childhood asthma may be a consequence of vitamin D deficiency. Curr Opin Allergy Clin Immunol 9:202–207 7. Gupta A, Bush A, Hawrylowicz C, Saglani S (2012) Vitamin D and asthma in children. Pediatr Respir Rev 13:236–243 8. Maalmi H, Berraı¨es A, Tangour E, Ammar J, Abid H, Hamzaoui K, Hamzaoui A (2012) The impact of vitamin D deficiency on immune T cells in asthmatic children: a case-control study. J Asthma Allergy 5:11–19 9. Berraies A, Hamzaoui K, Hamzaoui A (2014) Link between vitamin D and airway remodeling. J Asthma Allergy 7:23–30 10. Poon AH, Mahboob B, Hamid Q (2013) Vitamin D deficiency and severe asthma. PharmacolTher 140:148–155 11. Nagpal S, Rathnachalam (2005) Non calcemic actions of vitamin D receptor ligands. Endocr Rev 26:662–687 12. Wang TT, Tavera-Mendoza LE, Laperriere D, Libby E, MacLeod NB, Nagai Y et al (2005) Large-scale in silico and microarraybased identification of direct 1,25-dihydroxyvitamin D3 target genes. Mol Endocrinol 19:2685–2695 13. Kongsbak M, Levring TB, Geisler C, von Essen MR (2013) The vitamin D receptor and T cell function. Front Immunol 4:1–10 14. Norman AW (2008) A vitamin D nutritional cornucopia: new insights concerning the serum 25-hydroxyvitamin D status of the US population. Am J Clin Nutr 88:1455–1456 15. Morrison NA, Yeoman R, Kelly PJ et al (1992) Contribution of trans-acting factor alleles to normal physiological variability: vitamin D receptor gene polymorphism and circulating osteocalcin. Proc Natl Acad Sci USA 89:6665–6669 16. Faraco JH, Morrison NA, Baker A, Shine J, Frossard PM (1989) ApaI dimorphism at the human vitamin-D receptor gene locus. Nucleic Acids Res 17:2150 17. Morrison NA, Qi JC, Tokita A et al (1994) Prediction of bonedensity from vitamin-D receptor alleles. Nature 367:284–287 18. Gross C, Eccleshall TR, Malloy PJ, Villa ML, Marcus R, Feldman D (1996) The presence of a polymorphism at the translation initiation site of the vitamin D receptor gene is associated with low bone mineral density in postmenopausal Mexican-American women. J Bone Miner Res 11:1850–1855 19. Uitterlinden AG, Fang Y, Bergink AP, van Meurs JBJ, Hans PTM, van Leeuwen HP, Pols HAP (2002) The role of vitamin D receptor gene polymorphisms in bone biology. Mol Cell Endocrinol 197:15–21 20. Whitfield GK, Remus LS, Jurutka PW et al (2001) Functionally relevant polymorphisms in the human nuclear vitamin D receptor gene. Mol Cell Endocrinol 177:145–159 21. Sun J (2010) Vitamin D and mucosal immune function. Curr Opin Gastroenterol 26:591–595 22. Van Belle TL, Gysemans C, Mathieu C (2011) Vitamin D in autoimmune, infectious and allergic diseases: a vital player? Best Pract Res Clin End Metab 25:617–632 23. Khoo AL, Joosten I, Michels M (2011) 1,25-Dihydroxyvitamin D3 inhibits proliferation but not the suppressive function of regulatory T cells in the absence of antigen-presenting cells. Immunology 134:459–468 24. Munger KL, Levin LI, Hollis BW, Howard NS, Ascherio A (2006) Serum 25-hydroxyvitamin D levels and risk of multiple sclerosis. J Am Med Assoc 296:2832–2838 25. Shoenfeld N, Amital H, Shoenfeld Y (2009) The effect of melanism and vitamin D synthesis on the incidence of autoimmune disease. Nat Clin Pract Rheumatol 5:99–105 26. Ben-Zvi I, Aranow C, Mackay M, Stanevsky A, Kamen DL, Marinescu LM et al (2010) The impact of vitamin D on dendritic cell function in patients with systemic lupus erythematosus. PLoS One 5:e 9193 27. Poon AH, Laprise C, Lemire M, Montpetit A, Sinnett D, Schurr E, Hudson TJ (2004) Association of vitamin D receptor genetic
123
28.
29.
30.
31.
32.
33.
34.
35.
36.
37.
38. 39.
40. 41.
42.
43.
44. 45.
46.
47.
variants with susceptibility to asthma and atopy. Am J Respir Crit Care Med 170:967–973 Raby BA, Lazarus R, Silverman EK et al (2004) Association of vitamin D receptor gene polymorphisms with childhood and adult asthma. Am J Respir Crit Care Med 170:1057–1065 Wjst M, Altmu¨ller J, Faus-Kessler T, Braig C, Bahnweg M, Andre´ E (2006) Asthma families show transmission disequilibrium of gene variants in the vitamin D metabolism and signaling pathway. Respir Res 7:60 Fang WL, Gao LB, Liang WB, Xue H, Bai P, Lv ML, Wang YY, Zhou B, Zhang L (2009) Association analysis of vitamin D receptor gene polymorphisms in Chinese population with asthma. Iran J Allergy Asthma Immunol 8(3):141–147 Saadi A, Gao G, Li H, Wei C, Gong Y, Liu Q (2009) Association study between vitamin D receptor gene polymorphisms and asthma in the Chinese Han population: a case–control study. BMC Med Genet 21(10):71 Pillai DK, Iqbal SF, Benton AS et al (2011) Associations between genetic variants in vitamin D metabolism and asthma characteristics in young African Americans: a pilot study. J Investig Med 59(6):938–946 Li F, Jiang L, Willis-Owen SA, Zhang Y, Gao J (2011) Vitamin D binding protein variants associate with asthma susceptibility in the Chinese Han population. BMC Med Genet 12:103 Maalmi H, Haj Sassi F, Berraies A, Ammar J, Hamzaoui K, Hamzaoui A (2013) Association of vitamin D receptor gene polymorphisms with susceptibility to asthma in Tunisian children: a case control study. Hum Immunol 74:234–240 Arababadi MK, Abousaidi H, Hassanshahi G, Pourfathollah AA, Daneshmandi S, Akbarpour V, Hakimi H, Kennedy D (2011) Polymorphisms within Exon 9, but not intron 8, of the vitamin D receptor gene are associated with asthma. Iran J Basic Med Sci 14(3):225–230 Ismail MF, Elnady HG, Fouda EM (2013) Genetic variants in Vitamin D pathway in Egyptian asthmatic children: a pilot study. Hum Immunol 74(12):1659–1664 Moher D, Liberati A, Tetzlaff J, Altman DG (2009) The PRISMA Group: preferred reporting items for systematic reviews and meta-analyses: the PRISMA statement. PLoSMed 6(7):e1000097 Global Initiative for Asthma (GINA) (2014) Global strategy for asthma management and prevention. http://www.ginasthma.org/ Thakkinstian A, Mc Elduff P, D’Este C, Duffy D, Attia J (2005) A method for meta-analysis of molecular association studies. Stat Med 24:1291–1306 Cochran WG (1954) The combination of estimates from different experiments. Biometrics 10:101–129 Kavvoura FK, Ioannidis JPA (2008) Methods for meta-analysis in genetic association studies: a review of their potential and pitfalls. Hum Genet 123:1–14 Egger M, Smith GD, Schneider M, Minder C (1997) Bias in meta-analysis detected by a simple, graphical test. BMJ 315:624–634 Garland CF, Gorham ED, Mohr SB, Garland FC (2009) Vitamin D for cancer prevention: global perspective. Ann Epidemiol 19:468–483 Luong KV, Nguyen LT (2012) The role of vitamin D in asthma. Pulmonary Pharmacol Therapeut 25:137–143 Bosse´ Y, Lemire M, Poon AH, Daley D, He JQ, Sandford A et al (2009) Asthma and genes encoding components of the vitamin D pathway. Resp Res 10:98. doi:10.1186/1465-9921-10-98 Malerba G, Lauciello MC, Scherpbier T et al (2000) Linkage analysis of chromosome 12 markers in Italian families with atopic asthmatic children. Am J Respir Crit Care Med 162:1587–1590 Raby BA, Silverman EK, Lazarus R, Lange C, Kwiatkowski DJ, Weiss ST (2003) Chromosome 12q harbors multiple genetic loci
Lung
48.
49.
50.
51.
52. 53.
54.
55. 56.
57.
58. 59.
60.
related to asthma and asthma-related phenotypes. Hum Mol Genet 12:1973–1979 Sutherland ER, Goleva E, Jackson LP, Stevens AD, Leung DY (2010) Vitamin D levels, lung function, and steroid response in adult asthma. Am J Respir Crit Care Med 181:699–704 Uitterlinden AG, Fang Y, Van Meurs JB, Pols HA, Van Leeuwen JP (2004) Genetics and biology of vitamin D receptor polymorphisms. Gene 338:143–156 Jurutka PW, Remus LS, Whitfield GK et al (2000) The polymorphic N terminus in human vitamin D receptor isoforms influences transcriptional activity by modulating interaction with transcription factor IIB. Mol Endocrinol 14:401–420 Nejentsev S, Cooper JD, Godfrey L, Howson JMM et al (2004) Analysis of the vitamin D receptor gene sequence variants in type 1 diabetes. Diabetes 53:2709–2712 Valdivielso JM, Fernandez E (2006) Vitamin D receptor polymorphisms and diseases. Clin Chim Acta 371:1–12 vanEtten E, Verlinden L, Giulietti A et al (2007) The vitamin D receptor gene FokI polymorphism: functional impact on the immune system. Eur J Immunol 37:395–405 Martinez FD (2008) Gene–environment interaction in complex diseases: asthma as an illustrative case. In: Rutter M (ed) Genetic effects on environmental vulnerability to disease: Novartis foundation symposium, vol 293. Wiley, Chichester Litonjua AA, Weiss ST (2007) Is vitamin D deficiency to blame for the asthma epidemic. J Allergy ClinImmunol 120:1031–1035 Taussig LM, Cota K, Kaltenborn W (1981) Different mechanical properties of the lung in boys and girls. Am Rev Respir Dis 123:640–643 Burrows B, Bloom JW, Traver GA, Cline MG (1987) The course and prognosis of different forms of chronic airways obstruction in a sample from the general population. N Engl J Med 317:1309–1314 Balzano G, Fuschillo S, Melillo G, Bonini S (2001) Asthma and sex hormones. Allergy 56(1):13–20 Riffo-Vasquez Y, Ligeiro de Oliveira AP, Page CP, Spina D, Tavares-de-Lima W (2007) Role of sex hormones in allergic inflammation in mice. Clin Exp Allergy 37(3):459–470 Malling TH, Sigsgaard T, Andersen HR, Deguchi Y, Brandslund I et al (2010) Differences in associations between markers of
61.
62.
63. 64. 65.
66.
67.
68.
69.
70.
71.
antioxidative defense and asthma are sex specific. Gend Med 7:115–124 Li H, Stampfer MJ, Hollis JB, Mucci LA, Gaziano JM, Hunter D et al (2007) A prospective study of plasma vitamin D metabolites, vitamin D receptor polymorphisms, and prostate cancer. PLoS Med 4:e103 Ahn J, Albanes D, Berndt SI, Peters U, Chatterjee N, Freedman ND et al (2009) Vitamin D-related genes, serum vitamin D concentrations and prostate cancer risk. Carcinogenesis 30(5):769–776 Grant WB (2006) Epidemiology of disease risks in relation to vitamin D insufficiency. Prog Biophys Mol Biol 92:65–79 Kimlin MG (2008) Geographic location and vitamin D synthesis. Mol Aspects Med 29:453–461 Handel AE, Sandve GK, Disanto G, Berlanga-Taylor AJ, Gallone G, Hanwell H et al (2013) Vitamin D receptor ChIP-seq in primary CD4? cells: relationship to serum 25-hydroxyvitamin D levels and autoimmune disease. BMC Med 11:163 Hamzaoui A, Berraı¨es A, Hamdi B, Kaabachi W, Ammar J, Hamzaoui K (2014) Vitamin D reduces the differentiation and expansion of Th17 cells in young asthmatic children. Immunobiology. doi:10.1016/j.imbio.2014.07.009 Smolders J, Damoiseaux J, Menheere P, Tervaert JW, Hupperts R (2009) FokI vitamin D receptor gene polymorphism (rs10735810) and vitamin D metabolism inmultiple sclerosis. J Neuroimmunol 207:117–121 Hibler EA, Jurutka PW, Egan JB et al (2010) Association between polymorphic variation in VDR and RXRA and circulating levels of vitamin D metabolites. J Steroid Biochem Mol Biol 121:438–441 Colilla S, Nicolae D, Pluzhnikov A, Blumenthal MN et al (2003) Evidence for gene-environment interactions in a linkage study of asthma and smoking exposure. J Allergy Clin. Immunol 111:840–846 Simpson A, John SL, Jury F, Niven R, Woodcock A, Ollier WE, Custovic A (2006) Endotoxin exposure, CD14, and allergic disease: an interaction between genes and the environment. Am J Respir Crit Care Med 174:386–392 Little J, Higgins JP, Ioannidis JP et al (2009) Strengthening the reporting of genetic association studies (STREGA): an extension of the STROBE statement. Hum Genet 125:131–151
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