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No association between APOE epsilon 4 allele and multiple sclerosis susceptibility: A meta-analysis from 5472 cases and 4727 controls
Journal of the Neurological Sciences 308 (2011) 110–116
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Journal of the Neurological Sciences j o u r n a l h o m e p a g e : w w w. e l s ev i e r. c o m / l o c a t e / j n s
No association between APOE epsilon 4 allele and multiple sclerosis susceptibility: A meta-analysis from 5472 cases and 4727 controls Chao Xuan a,⁎, Bei-Bei Zhang b, Ming Li c, Kai-Feng Deng d, Tao Yang e, Xiang-E Zhang f a
Medical College of NanKai University, Tianjin, China Basic Medical College, Guangxi Medical University, Nanning, China The Affiliated Hospital of Taishan Medical College, Tai'an, China d The Fourth Affiliated Hospital of Guangxi Medical University, Liuzhou, China e The Second Affiliated Hospital of Chongqing Medical University, Chongqing, China f Fujian Provincial Hospital, Fujian Medical University, Fuzhu, China b c
a r t i c l e
i n f o
Article history: Received 22 March 2011 Received in revised form 22 May 2011 Accepted 25 May 2011 Available online 15 June 2011 Keywords: Multiple sclerosis Apolipoprotein E Allele Meta-analysis
a b s t r a c t Background: Apolipoprotein E (APOE) gene ε4, 2 alleles have been reported to be associated with multiple sclerosis (MS), but results were conflicting. In order to derive a more precise estimation of the associations, a meta-analysis was performed. Methods: The PubMed, EBSCO and BIOSIS databases were searched to identify eligible studies published in English before March, 2011. Data were extracted using standardized forms. The association was assessed by odds ratio (OR) with 95% confidence intervals (CIs). Begg's test was used to measure publication bias. Results: A total of 20 case–control studies, containing 5472 patients/4727 controls for ε4 allele and 4636 patients/4047 controls for ε2 allele were included. The associations between APOE ε4, 2 alleles and MS were not found in overall population (ORε4 = 0.997, 95% CI = 0.861–1.156; ORε2 = 1.097, 95% CI = 0.940–1.279). Subgroup analysis revealed that APOE ε4, 2 alleles were not associated with an increased risk of MS in Caucasian population (ORc-ε4 = 0.924, 95% CI = 0.819–1.041; ORc-ε2 = 1.127, 95% CI = 0.955–1.331). There was no evidence of publication bias according to Begg's regression test. Conclusions: This meta-analysis suggests that APOE ε4, 2 alleles are not associated with MS susceptibility. However, large sample, representative population-based studies with homogeneous MS patients, and well matched controls are warranted to confirm this finding. © 2011 Elsevier B.V. All rights reserved.
1. Introduction Multiple sclerosis (MS) is a common inflammatory disease of the central nervous system (CNS) characterized by myelin loss, varying degrees of axonal pathology, and progressive neurological dysfunction [1]. The causes of MS are largely unknown. However, epidemiologic studies reveal a significant environmental contribution to the pathogenesis of MS [2,3]. Familial aggregation and twin studies indicate the presence of genetic factors for susceptibility to this condition [4,5]. Several genomic screens have been performed to find genetic linkage to MS. The chromosome 19q13 region showed genetic linkage to MS [6,7]. In various genes, the apolipoprotein E (APOE) gene, which is located in the chromosome 19q13.2 region and codes for ApoE, has been one of the most studied in the past [8,9]. ApoE is a glycoprotein synthesized in the CNS by glial cells which has a crucial role in membrane remodeling and repair, as well as an immunomodulatory ⁎ Corresponding author at: Medical College of NanKai University, No. 94, The Weijin Road, Tianjin, 300071, PR China. Tel.: + 86 13821176150. E-mail address: [email protected] (C. Xuan). 0022-510X/$ – see front matter © 2011 Elsevier B.V. All rights reserved. doi:10.1016/j.jns.2011.05.040
effect [10]. The APOE gene exists in three common allelic forms (ε2, ε3, ε4) and the corresponding protein isoforms Apo E2, E3 and E4 are distinguishable by having different combinations of the amino acids arginine and cysteine at positions 112 and 158. The amino acid changes result in distinctive physical and biochemical properties [11]. Additionally, the APOE gene exists in two minor allelic forms (ε1, ε5) which are present in less than 0.1% of the population [12–14]. ApoE is one of the proteins associated with cholesterol haemostasis, E1 and E2 decreases the plasma level of the cholesterol but E4 and E5 increases it [13,15]. E2 and E3 activities for the clearance of the β-amyloid plaques in Alzheimer diseases are 20 times more than E4 [16]. In addition, ApoE has antioxidant activities that ranked E2 N E3 N E4 [17]. According to these associations, it seems that ε4 allele is a hazardous allelic form in comparison with ε3 and ε2 alleles, but it is noteworthy that some associations with ε2 allele were reported [18]. The relationship between the APOE ε4 allele and MS has been studied over the last two decades. Many studies found a positive association between APOE ε4 allele and the risk of disease progression [19–21]. However, several other retrospective studies found no association [22–24]. Partially, because of the APOE gene is a minor gene and/or the relatively small sample-size in each published
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Table 1 Characteristics of case–control studies included in meta-analysis. First author
Year
Lee et al. [35] Losonczi et al. [49] Bonetti et al. [40] Mustafina et al. [39] Koutsis et al. [34] Ramsaransing et al. [33] Cocco et al. [31] Al-Shammri et al. [30] Pinholt et al. [32] Zakrzewska-Pniewska et al. [37] Zwemmer et al. [38] Niino et al. [29] Savettieri et al. [24] Ballerini et al. [27] Hogh et al. [20] Weatherby et al. [36] Ferri et al. [28] Oliveri et al. [48] Gaillard et al. [41] Rubinsztein et al. [41]
2010 2010 2009 2008 2007 2005 2005 2005 2005 2004 2004 2003 2003 2000 2000 2000 1999 1999 1998 1994
Country (ethnicity)
Genotyping method
South Korea (EA) Hungary (M) Finland (C) Russian (C) Greek (M) Netherlands (C) Italy (C) Kuwait (AR) Denmark (C) Poland (C) Netherlands (C) Japan (EA) Italy (C) Italy (C) Denmark (C) UK (C) Italy (C) Italy (C) France (C) UK (C)
Sample size (case/control)
NA PCR-RFLP Sequenced PCR-RFLP PCR-RFLP NA NA PCR-RFLP PCR-RFLP PCR-RFLP Mutation Detection Kit PCR-RFLP PCR-RFLP PCR-RFLP PCR-RFLP PCR-RFLP NA PCR-RFLP NA NA
836/680 90/45 737/1156 120/263 212/216 82/29 871/348 39/106 385/361 99/100 408/144 135/134 428/107 66/67 238/361 370/159 161/153 89/107 70/100 36/91
Allele carrier (n) MS
Control
ε2+
ε4+
ε2+
ε4+
NA 26 43 12 26 11 59 1 63 14 67 11 53 15 10 65 18 7 9 2
141 35 132 34 35 24 88 8 109 20 115 16 62 6 76 88 15 12 14 9
NA 17 72 34 23 6 18 10 48 9 16 10 15 11 8 20 16 14 15 7
104 4 212 61 26 9 37 19 115 21 52 17 9 15 115 43 18 9 22 34
NA: not available; MS: multiple sclerosis; EA: East Asian; C: Caucasian; M: mixed population; AR: Arabs.
studies. Therefore, we performed a meta-analysis of the published studies to derive a more precise estimation of the association. Concurrently, the relationship between the APOE ε2 allele and MS will also be analyzed.
2.3. Data extraction Two investigators extracted the data independently, and the result was reviewed by a third investigator. The following information was extracted from a study: first author, year of publication, study population (country, ethnicity), the number of patients and controls for a study, genotyping method, and genotype information.
2. Materials and methods 2.1. Search strategy
2.4. Statistical analysis All studies reporting the association between the APOE ε4, 2 alleles and MS susceptibility published in English before March, 2011 were identified by comprehensive computer based on searches of Medline, EBSCO and BIOSIS. The following keywords were used for searching: (“multiple sclerosis” OR “MS”) AND ("polymorphism*" OR "variant*") AND (“ApoE” OR “APOE” OR “apolipoprotein E”). The most complete and recent results were used when there were multiple publications from the same study group. We only recruited data from published papers. Hand searches for related articles were also performed.
The number of allele carrier at ε2 and ε4 from each respective study were calculated. We examined the contrast of the ε4 carriers (ε4+) vs. ε4 non-carriers (ε4−), and ε2+ vs. ε2−. The associations between APOE ε2, 4 alleles and MS susceptibility were estimated by odd risk (OR) and its 95% confidence intervals (95% CIs). Heterogeneity across the eligible studies was tested using Q-test, and it was considered statistically significant when P b 0.1. Heterogeneity was also quantified with I 2 metric [25] (I 2 = (Q − df) / Q × 100%. I 2 b 25%, no heterogeneity; I 2 = 25–50%, moderate heterogeneity; I 2 = 50–75%, large heterogeneity, I 2 N 75%, extreme heterogeneity). When the effects were assumed to be homogeneous (P N 0.1, I 2 b 50%), the fixed-effects model was used; otherwise, the random-effects model was more appropriate. To evaluate the ethnicity-specific effects, subgroup analyses was performed in ethnic group. Sensitivity analysis was performed to evaluate the stability of the results. Individual studies included in the meta-analysis were deleted one at a time to determine the contribution of the individual data to the pooled ORs. Begg's test was used to measure publication bias, which
2.2. Inclusion criteria Two investigators reviewed all identified studies independently to determine whether an individual study was eligible for inclusion. The selection criteria for studies to be considered for this meta-analysis were as follows: 1) APOE polymorphisms in MS; 2) case–control studies; 3) proper MS diagnosis criteria; 4) not republished data; 5) not animal studies. The study would be excluded if the information could not be obtained.
Table 2 Main results of pooled ORs in the meta-analysis. Genetic model
ε4+ vs. ε4− ε2+ vs. ε2−
Ethnicity
Overall Caucasian Overall Caucasian
Sample size
Test of heterogeneity
Test of association
Test of publication bias
Case
Control
Q
P
I2 (%)
OR
95% CI
z
P
5472 4160 4636 4160
4727 3546 4047 3546
30.22 15.00 16.06 12.36
0.049 0.378 0.589 0.577
37.1 6.7 0.0 0.0
0.997 0.924 1.097 1.127
0.861–1.156 0.819–1.041 0.940–1.279 0.955–1.331
0.55 0.49 1.75 0.59
0.681 0.621 0.080 0.553
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A %
Study ID
OR (95% CI)
Weight
Lee et al (2010)
1.12 (0.85, 1.48)
10.17
Losonczi et al (2010)
6.52 (2.15, 19.81)
1.59
Bonetti et al (2009)
0.97 (0.76, 1.24)
11.15
Mustafina et al (2008)
1.31 (0.80, 2.14)
5.77
Koutsis et al (2007)
1.45 (0.84, 2.50)
4.98
Ramsaransing et al (2005)
0.92 (0.37, 2.31)
2.22
Cocco et al (2005)
0.94 (0.63, 1.42)
7.20
Al Shammriet al (2005)
1.18 (0.47, 2.97)
2.21
Pinholt et al (2005)
0.84 (0.62, 1.16)
9.23
Zakrzewska-Pniewskaet al (2004)
0.95 (0.48, 1.89)
3.57
Zwemmer et al (2004)
0.69 (0.46, 1.04)
7.27
Niino et al (2003)
0.93 (0.45, 1.92)
3.26
Savettieri et al (2003)
1.84 (0.89, 3.84)
3.22
Ballerini et al (2000)
0.35 (0.13, 0.96)
1.86
Hogh et al (2000)
1.00 (0.71, 1.43)
8.35
Weatherby et al (2000)
0.84 (0.55, 1.29)
6.86
Ferri et al (1999)
0.77 (0.37, 1.59)
3.29
Oliveri et al (1999)
1.70 (0.68, 4.23)
2.24
Gaillard et al (1998)
0.89 (0.42, 1.88)
3.09
Rubinsztein et al (1994)
0.56 (0.24, 1.33)
2.46
Overall (I-squared = 37.1%, p = 0.049)
1.00 (0.86, 1.16)
100.00
NOTE: Weights are from random effects analysis
.0505
1
19.8
B Study
%
ID
OR (95% CI)
Weight
Bonetti et al (2009)
0.97 (0.76, 1.24)
24.80
Mustafina et al (2008)
1.31 (0.80, 2.14)
5.97
Ramsaransing et al (2005)
0.92 (0.37, 2.31)
1.69
Cocco et al (2005)
0.94 (0.63, 1.42)
8.68
Pinholt et al (2005)
0.84 (0.62, 1.16)
14.56
Zakrzewska-Pniewskaet al (2004)
0.95 (0.48, 1.89)
3.03
Zwemmer et al (2004)
0.69 (0.46, 1.04)
8.82
Savettieri et al (2003)
1.84 (0.89, 3.84)
2.65
Ballerini et al (2000)
0.35 (0.13, 0.96)
1.38
Hogh et al (2000)
1.00 (0.71, 1.43)
11.60
Weatherby et al (2000)
0.84 (0.55, 1.29)
7.95
Ferri et al (1999)
0.77 (0.37, 1.59)
2.73
Oliveri et al (1999)
1.70 (0.68, 4.23)
1.71
Gaillard et al (1998)
0.89 (0.42, 1.88)
2.52
Rubinsztein et al (1994)
0.56 (0.24, 1.33)
1.91
Overall (I-squared = 6.7%, p = 0.378)
0.92 (0.82, 1.04)
100.00
.125
1
7.98
C. Xuan et al. / Journal of the Neurological Sciences 308 (2011) 110–116
was shown as funnel plot (P b 0.05 was considered representative of statistically significant publication bias) [26]. All analyses were performed using STATA software, version 10.0 (Stata Corporation, College Station, TX, USA). 3. Results 3.1. Studies included in meta-analysis A total of 27 [19–21,24,27–49] relevant studies concerning the APOE ε2, 4 alleles and MS were identified. Seven studies [19,21,43–47] were excluded due to the number of alleles that couldn't be extracted. Thus, 20 studies which met the inclusion consisted of 5472 patients/4727 controls for ε4 allele and 4636 patients/4047 controls for ε2 allele were considered in meta-analysis. In subgroup analyses, 15 (4160 patients/3546 controls for ε4 and ε2 allele) different studies with specific focus on Caucasian populations were included in ethnic group. Main characteristics of the included studies were listed in Table 1. 3.2. Meta-analysis results In overall analysis, the combination of 20 comparisons showed heterogeneity for ε4+ vs. ε4− (Q = 30.22, df = 19, P = 0.049; I 2 = 37.1%), but not for ε2+ vs. ε2− (Q = 16.06, df = 18, P = 0.589; I 2 = 0.0%). No significant associations were found between APOE ε2, 4 alleles and MS susceptibility when all studies pooled with randomeffects model for ε4+ vs. ε4− (ORε4 = 0.997, 95% CI = 0.861–1.156) and fixed-effects model for ε2+ vs. ε2− (ORε2 = 1.097, 95% CI = 0.940–1.279). In the stratified analysis by ethnicity, no significant associations were found among Caucasian population when all 15 studies pooled with fixed-effects model for ε4+ vs. ε4− (ORc-ε4 = 0.924, 95% CI = 0.819–1.041; P = 0.378 for heterogeneity), and ε2+ vs. ε2− (ORc-ε2 = 1.127, 95% CI = 0.955–1.331; P = 0.577 for heterogeneity). The main results of meta-analysis were shown in Table 2 and Figs. 1–2. 3.3. Sensitivity analysis A single study involved in the meta-analysis was deleted each time to reflect the influence of the individual data-set to the pooled ORs, and the corresponding pooled ORs were not materially altered (data not shown), indicating that our results were statistically robust. 3.4. Publication bias Begg's test and funnel plot were performed to access the publication bias of literatures. The results suggest no evidence of publication biases (Table 2, Fig. 3). 4. Discussion Although MS is the most common demyelinating diseases, its pathogenesis and etiology are as yet poorly understood. MS is a major cause of morbidity and disability in young adults (aged 16–35), with a prevalence of 0.1% in individuals of northern European origin [50]. Recently, interest has also focused on genetic factors that may influence the outcome and prognosis of MS. One of the regions of interest identified through linkage analysis was chromosome 19q13, near the APOE gene locus [51]. Three other
113
linkage analysis [52–54] have shown some support for linkage to this region, and a meta-analysis of all four genomic screens identified 19q13 as the second most significant region after the major histocompatibility complex (MHC) [55]. The APOE gene consists of four exons and three introns spanning 3597 nucleotides, and produces ApoE which is a 299 amino acid polypeptide [56]. In humans, the APOE gene exists in three common allelic forms (APOE ε2, ε3, ε4) and 2 rare allelic forms (APOE ε1, ε5) [12–14]. APOE ε3 is the most (77%) and ε2 is the least (8%) common alleles. The frequency of the ε4 allele is approximately 15% in general population [57]. Three common APOE alleles (ε2, ε3 and ε4) encode three corresponding protein isoforms, Apo E2, E3 and E4. Apo E, a 35-kDa plasma protein synthesized mainly in the liver, is involved in cholesterol transport and metabolism [58]. APOE is also expressed in other tissues, notably the brain, the second most prolific tissue in terms of ApoE production [59]. ApoE3 seems to be the normal form, while ApoE2 and ApoE4 can each be dysfunctional. Some studies have indeed found an association between APOE ε4 allele and an increased brain damage [11]. It is suggested that APOE ε4 allele may be associated with accelerated neurodegeneration and plays a role in the development and progression of MS, Alzheimer's disease [60], and several other diseases [61,62]. On the other hand, some publications report a protective effect from the ε2 allele of the APOE gene [9,24]. The first meta-analysis in association between APOE ε4, 2 alleles and MS susceptibility was performed by Burwick et al. in 2006 [63]. After the meta-analysis from 3299 patients and 2532 controls, they concluded there were no relation between the ε4, 2 alleles and MS susceptibility [63]. In the last five years, 5 case–control studies were performed to investigate the associations. Therefore, it is essential for us to re-perform a new meta-analysis to evaluate the associations. There is no doubt that the new results will be more credible. As a result, our meta-analysis form 5472 patients/4727 controls for ε4 allele and 4636 patients/4047 controls for ε2 allele demonstrated that no association between the APOE ε4, 2 alleles and MS susceptibility. Some limitations of this meta-analysis should be discussed. First, this meta-analysis only focused on papers published in English language and reported in other languages might bias the present results, even though the publication bias were not detected with Begg's test presently. Additionally, there might be eligible studies that were not published, not indexed by electronic databases, or published in the journals we did not cover. Second, moderate heterogeneity was observed in association between APOE ε4 allele and MS susceptibility in overall population analysis. Although we use random-effect model to pool ORs, it may affect the precision of results. Large sample and representative population-based studies with homogeneous MS patients and well matched controls are warranted to confirm this finding. Any heterogeneity was not observed in subgroup analysis for Caucasian population. Therefore, the source of heterogeneity might come from ethnicity classification. At last, the lack of individual participants' data has restricted further adjustments by other covariables, such as specific outcome, sex, smoking, diabetes, etc. Despite these limitations, our results do not support APOE ε2, 4 alleles as susceptibility factors for MS. The effect of the variants on the expression levels and the possible functional role of the variants in MS should be addressed in further studies. References [1] Noseworthy JH, Lucchinetti C, Rodriguez M, Weinshenker BG. Multiple sclerosis. N Engl J Med 2000;343:938–52. [2] Pugliatti M, Harbo HF, Holmoy T, Kampman MT, Myhr KM, Riise T, et al. Environmental risk factors in multiple sclerosis. Acta Neurol Scand Suppl 2008;188:34–40.
Fig. 1. Pooled OR and 95% confidence intervals (CIs) of individual studies and pooled data for the association between APOE ε4 allele and multiple sclerosis in (A) overall, and (B) Caucasian population.
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A Study
%
ID
OR (95% CI)
Weight
Losonczi et al (2010)
0.67 (0.31, 1.42)
4.13
Bonetti et al (2009)
0.93 (0.63, 1.38)
15.53
Mustafina et al (2008)
0.75 (0.37, 1.50)
4.86
Koutsis et al (2007)
1.17 (0.65, 2.13)
6.64
Ramsaransing et al (2005)
0.59 (0.20, 1.78)
1.95
Cocco et al (2005)
1.33 (0.77, 2.29)
7.99
Al-Shammri et al (2005)
0.25 (0.03, 2.04)
0.54
Pinholt et al (2005)
1.28 (0.85, 1.92)
14.27
Zakrzewska-Pniewska et al (2004)
1.67 (0.69, 4.05)
2.99
Zwemmer et al (2004)
1.57 (0.88, 2.81)
6.96
Niino et al (2003)
1.10 (0.45, 2.68)
2.96
Savettieri et al (2003)
0.87 (0.47, 1.61)
6.19
Ballerini et al (2000)
1.50 (0.63, 3.56)
3.15
Hogh et al (2000)
1.94 (0.75, 4.98)
2.64
Weatherby et al (2000)
1.48 (0.86, 2.54)
8.09
Ferri et al (1999)
1.08 (0.53, 2.20)
4.64
Oliveri et al (1999)
0.57 (0.22, 1.47)
2.59
Gaillard et al (1998)
0.84 (0.34, 2.03)
2.98
Rubinsztein et al (1994)
0.71 (0.14, 3.57)
0.90
Overall (I squared = 0.0%, p = 0.589)
1.10 (0.94, 1.28)
100.00
.0313
1
32
B Study
%
ID
OR (95% CI)
Weight
Bonetti et al (2009)
0.93 (0.63, 1.38)
18.12
Mustafina et al (2008)
0.75 (0.37, 1.50)
5.66
Ramsaransing et al (2005)
0.59 (0.20, 1.78)
2.27
Cocco et al (2005)
1.33 (0.77, 2.29)
9.33
Pinholt et al (2005)
1.28 (0.85, 1.92)
16.65
Zakrzewska-Pniewskaet al (2004)
1.67 (0.69, 4.05)
3.49
Zwemmer et al (2004)
1.57 (0.88, 2.81)
8.12
Savettieri et al (2003)
0.87 (0.47, 1.61)
7.23
Ballerini et al (2000)
1.50 (0.63, 3.56)
3.67
Hogh et al (2000)
1.94 (0.75, 4.98)
3.08
Weatherby et al (2000)
1.48 (0.86, 2.54)
9.44
Ferri et al (1999)
1.08 (0.53, 2.20)
5.41
Oliveri et al (1999)
0.57 (0.22, 1.47)
3.02
Gaillard et al (1998)
0.84 (0.34, 2.03)
3.48
Rubinsztein et al (1994)
0.71 (0.14, 3.57)
1.05
Overall (I-squared = 0.0%, p = 0.577)
1.13 (0.96, 1.33)
100.00
.14
1
7.17
C. Xuan et al. / Journal of the Neurological Sciences 308 (2011) 110–116 2
Begg's funnel plot with pseudo 95% confidence limits
[23] [24] 1
logor
[25] [26] 0
[27]
[28] -1
[29] 0
.2
.4
.6
s.e. of: logor Fig. 3. Begg's funnel plot for publication bias in selection of studies on the APOE ε4 allele in overall population.
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No major association of ApoE genotype with disease characteristics and MRI findings in multiple sclerosis. Mult Scler 2004;10:272–7. Mustafina OE, Bakhtiiarova KZ, Mikhailova AM, Tuktarova IA, Khusainova AN, Nasibullin TR, et al. Analysis of the association of allelic variants of apolypoprotein E and interleukin 1 beta genes with multiple sclerosis in ethnic Tatars. Genetika 2008;44:407–13. Bonetti A, Koivisto K, Pirttila T, Elovaara I, Reunanen M, Laaksonen M, et al. A follow-up study of chromosome 19q13 in multiple sclerosis susceptibility. J Neuroimmunol 2009;208:119–24. Gaillard O, Gervais A, Meillet D, Plassart E, Fontaine B, Lyon-Caen O, et al. Apolipoprotein E and multiple sclerosis: a biochemical and genetic investigation. J Neurol Sci 1998;158:180–6. Rubinsztein DC, Hanlon CS, Irving RM, Goodburn S, Evans DG, Kellar-Wood H, et al. Apo E genotypes in multiple sclerosis, Parkinson's disease, schwannomas and lateonset Alzheimer's disease. Mol Cell Probes 1994;8:519–25. Enzinger C, Ropele S, Strasser-Fuchs S, Kapeller P, Schmidt H, Poltrum B, et al. Lower levels of N-acetylaspartate in multiple sclerosis patients with the apolipoprotein E epsilon4 allele. Arch Neurol 2003;60:65–70. Carlin C, Murray L, Graham D, Doyle D, Nicoll J. Involvement of apolipoprotein E in multiple sclerosis: absence of remyelination associated with possession of the APOE epsilon2 allele. J Neuropathol Exp Neurol 2000;59:361–7. Pirttila T, Haanpaa M, Mehta PD, Lehtimaki T. Apolipoprotein E (APOE) phenotype and APOE concentrations in multiple sclerosis and acute herpes zoster. Acta Neurol Scand 2000;102:94–8. Gervais A, Gaillard O, Plassart E, Reboul J, Fontaine B, Schuller E. Apolipoprotein E polymorphism in multiple sclerosis. Ann Clin Biochem 1998;35(Pt 1):135–6. Koutsis G, Panas M, Giogkaraki E, Potagas C, Karadima G, Sfagos C, et al. APOE epsilon4 is associated with impaired verbal learning in patients with MS. Neurology 2007;68:546–9. Oliveri RL, Cittadella R, Sibilia G, Manna I, Valentino P, Gambardella A, et al. APOE and risk of cognitive impairment in multiple sclerosis. Acta Neurol Scand 1999;100:290–5. Losonczi E, Bencsik K, Fricska Nagy Z, Honti V, Szalczer E, Rajda C, et al. APOE epsilon status in Hungarian patients with primary progressive multiple sclerosis. Swiss Med Wkly 2010;140 w13119 LID-10.4414/smw.2010.13119 [doi] LID-20. Hader WJ, Elliot M, Ebers GC. Epidemiology of multiple sclerosis in London and Middlesex County, Ontario, Canada. Neurology 1988;38:617–21.
Fig. 2. Pooled OR and 95% CI of individual studies and pooled data for the association between APOE ε2 allele and multiple sclerosis in (A) overall, and (B) Caucasian population.
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[58] Mahley RW. Apolipoprotein E: cholesterol transport protein with expanding role in cell biology. Science 1988;240:622–30. [59] Elshourbagy NA, Liao WS, Mahley RW, Taylor JM. Apolipoprotein E mRNA is abundant in the brain and adrenals, as well as in the liver, and is present in other peripheral tissues of rats and marmosets. Proc Natl Acad Sci U S A 1985;82:203–7. [60] Bertram L, Tanzi RE. Thirty years of Alzheimer's disease genetics: the implications of systematic meta-analyses. Nat Rev Neurosci 2008;9:768–78. [61] Burt TD, Agan BK, Marconi VC, He W, Kulkarni H, Mold JE, et al. Apolipoprotein (apo) E4 enhances HIV-1 cell entry in vitro, and the APOE epsilon4/epsilon4 genotype accelerates HIV disease progression. Proc Natl Acad Sci U S A 2008;105:8718–23. [62] Martinez M, Brice A, Vaughan JR, Zimprich A, Breteler MM, Meco G, et al. Apolipoprotein E4 is probably responsible for the chromosome 19 linkage peak for Parkinson's disease. Am J Med Genet B Neuropsychiatr Genet 2005;136B:72–4. [63] Burwick RM, Ramsay PP, Haines JL, Hauser SL, Oksenberg JR, Pericak-Vance MA, et al. APOE epsilon variation in multiple sclerosis susceptibility and disease severity: some answers. Neurology 2006;66:1373–83.
Contents lists available at ScienceDirect
Journal of the Neurological Sciences j o u r n a l h o m e p a g e : w w w. e l s ev i e r. c o m / l o c a t e / j n s
No association between APOE epsilon 4 allele and multiple sclerosis susceptibility: A meta-analysis from 5472 cases and 4727 controls Chao Xuan a,⁎, Bei-Bei Zhang b, Ming Li c, Kai-Feng Deng d, Tao Yang e, Xiang-E Zhang f a
Medical College of NanKai University, Tianjin, China Basic Medical College, Guangxi Medical University, Nanning, China The Affiliated Hospital of Taishan Medical College, Tai'an, China d The Fourth Affiliated Hospital of Guangxi Medical University, Liuzhou, China e The Second Affiliated Hospital of Chongqing Medical University, Chongqing, China f Fujian Provincial Hospital, Fujian Medical University, Fuzhu, China b c
a r t i c l e
i n f o
Article history: Received 22 March 2011 Received in revised form 22 May 2011 Accepted 25 May 2011 Available online 15 June 2011 Keywords: Multiple sclerosis Apolipoprotein E Allele Meta-analysis
a b s t r a c t Background: Apolipoprotein E (APOE) gene ε4, 2 alleles have been reported to be associated with multiple sclerosis (MS), but results were conflicting. In order to derive a more precise estimation of the associations, a meta-analysis was performed. Methods: The PubMed, EBSCO and BIOSIS databases were searched to identify eligible studies published in English before March, 2011. Data were extracted using standardized forms. The association was assessed by odds ratio (OR) with 95% confidence intervals (CIs). Begg's test was used to measure publication bias. Results: A total of 20 case–control studies, containing 5472 patients/4727 controls for ε4 allele and 4636 patients/4047 controls for ε2 allele were included. The associations between APOE ε4, 2 alleles and MS were not found in overall population (ORε4 = 0.997, 95% CI = 0.861–1.156; ORε2 = 1.097, 95% CI = 0.940–1.279). Subgroup analysis revealed that APOE ε4, 2 alleles were not associated with an increased risk of MS in Caucasian population (ORc-ε4 = 0.924, 95% CI = 0.819–1.041; ORc-ε2 = 1.127, 95% CI = 0.955–1.331). There was no evidence of publication bias according to Begg's regression test. Conclusions: This meta-analysis suggests that APOE ε4, 2 alleles are not associated with MS susceptibility. However, large sample, representative population-based studies with homogeneous MS patients, and well matched controls are warranted to confirm this finding. © 2011 Elsevier B.V. All rights reserved.
1. Introduction Multiple sclerosis (MS) is a common inflammatory disease of the central nervous system (CNS) characterized by myelin loss, varying degrees of axonal pathology, and progressive neurological dysfunction [1]. The causes of MS are largely unknown. However, epidemiologic studies reveal a significant environmental contribution to the pathogenesis of MS [2,3]. Familial aggregation and twin studies indicate the presence of genetic factors for susceptibility to this condition [4,5]. Several genomic screens have been performed to find genetic linkage to MS. The chromosome 19q13 region showed genetic linkage to MS [6,7]. In various genes, the apolipoprotein E (APOE) gene, which is located in the chromosome 19q13.2 region and codes for ApoE, has been one of the most studied in the past [8,9]. ApoE is a glycoprotein synthesized in the CNS by glial cells which has a crucial role in membrane remodeling and repair, as well as an immunomodulatory ⁎ Corresponding author at: Medical College of NanKai University, No. 94, The Weijin Road, Tianjin, 300071, PR China. Tel.: + 86 13821176150. E-mail address: [email protected] (C. Xuan). 0022-510X/$ – see front matter © 2011 Elsevier B.V. All rights reserved. doi:10.1016/j.jns.2011.05.040
effect [10]. The APOE gene exists in three common allelic forms (ε2, ε3, ε4) and the corresponding protein isoforms Apo E2, E3 and E4 are distinguishable by having different combinations of the amino acids arginine and cysteine at positions 112 and 158. The amino acid changes result in distinctive physical and biochemical properties [11]. Additionally, the APOE gene exists in two minor allelic forms (ε1, ε5) which are present in less than 0.1% of the population [12–14]. ApoE is one of the proteins associated with cholesterol haemostasis, E1 and E2 decreases the plasma level of the cholesterol but E4 and E5 increases it [13,15]. E2 and E3 activities for the clearance of the β-amyloid plaques in Alzheimer diseases are 20 times more than E4 [16]. In addition, ApoE has antioxidant activities that ranked E2 N E3 N E4 [17]. According to these associations, it seems that ε4 allele is a hazardous allelic form in comparison with ε3 and ε2 alleles, but it is noteworthy that some associations with ε2 allele were reported [18]. The relationship between the APOE ε4 allele and MS has been studied over the last two decades. Many studies found a positive association between APOE ε4 allele and the risk of disease progression [19–21]. However, several other retrospective studies found no association [22–24]. Partially, because of the APOE gene is a minor gene and/or the relatively small sample-size in each published
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Table 1 Characteristics of case–control studies included in meta-analysis. First author
Year
Lee et al. [35] Losonczi et al. [49] Bonetti et al. [40] Mustafina et al. [39] Koutsis et al. [34] Ramsaransing et al. [33] Cocco et al. [31] Al-Shammri et al. [30] Pinholt et al. [32] Zakrzewska-Pniewska et al. [37] Zwemmer et al. [38] Niino et al. [29] Savettieri et al. [24] Ballerini et al. [27] Hogh et al. [20] Weatherby et al. [36] Ferri et al. [28] Oliveri et al. [48] Gaillard et al. [41] Rubinsztein et al. [41]
2010 2010 2009 2008 2007 2005 2005 2005 2005 2004 2004 2003 2003 2000 2000 2000 1999 1999 1998 1994
Country (ethnicity)
Genotyping method
South Korea (EA) Hungary (M) Finland (C) Russian (C) Greek (M) Netherlands (C) Italy (C) Kuwait (AR) Denmark (C) Poland (C) Netherlands (C) Japan (EA) Italy (C) Italy (C) Denmark (C) UK (C) Italy (C) Italy (C) France (C) UK (C)
Sample size (case/control)
NA PCR-RFLP Sequenced PCR-RFLP PCR-RFLP NA NA PCR-RFLP PCR-RFLP PCR-RFLP Mutation Detection Kit PCR-RFLP PCR-RFLP PCR-RFLP PCR-RFLP PCR-RFLP NA PCR-RFLP NA NA
836/680 90/45 737/1156 120/263 212/216 82/29 871/348 39/106 385/361 99/100 408/144 135/134 428/107 66/67 238/361 370/159 161/153 89/107 70/100 36/91
Allele carrier (n) MS
Control
ε2+
ε4+
ε2+
ε4+
NA 26 43 12 26 11 59 1 63 14 67 11 53 15 10 65 18 7 9 2
141 35 132 34 35 24 88 8 109 20 115 16 62 6 76 88 15 12 14 9
NA 17 72 34 23 6 18 10 48 9 16 10 15 11 8 20 16 14 15 7
104 4 212 61 26 9 37 19 115 21 52 17 9 15 115 43 18 9 22 34
NA: not available; MS: multiple sclerosis; EA: East Asian; C: Caucasian; M: mixed population; AR: Arabs.
studies. Therefore, we performed a meta-analysis of the published studies to derive a more precise estimation of the association. Concurrently, the relationship between the APOE ε2 allele and MS will also be analyzed.
2.3. Data extraction Two investigators extracted the data independently, and the result was reviewed by a third investigator. The following information was extracted from a study: first author, year of publication, study population (country, ethnicity), the number of patients and controls for a study, genotyping method, and genotype information.
2. Materials and methods 2.1. Search strategy
2.4. Statistical analysis All studies reporting the association between the APOE ε4, 2 alleles and MS susceptibility published in English before March, 2011 were identified by comprehensive computer based on searches of Medline, EBSCO and BIOSIS. The following keywords were used for searching: (“multiple sclerosis” OR “MS”) AND ("polymorphism*" OR "variant*") AND (“ApoE” OR “APOE” OR “apolipoprotein E”). The most complete and recent results were used when there were multiple publications from the same study group. We only recruited data from published papers. Hand searches for related articles were also performed.
The number of allele carrier at ε2 and ε4 from each respective study were calculated. We examined the contrast of the ε4 carriers (ε4+) vs. ε4 non-carriers (ε4−), and ε2+ vs. ε2−. The associations between APOE ε2, 4 alleles and MS susceptibility were estimated by odd risk (OR) and its 95% confidence intervals (95% CIs). Heterogeneity across the eligible studies was tested using Q-test, and it was considered statistically significant when P b 0.1. Heterogeneity was also quantified with I 2 metric [25] (I 2 = (Q − df) / Q × 100%. I 2 b 25%, no heterogeneity; I 2 = 25–50%, moderate heterogeneity; I 2 = 50–75%, large heterogeneity, I 2 N 75%, extreme heterogeneity). When the effects were assumed to be homogeneous (P N 0.1, I 2 b 50%), the fixed-effects model was used; otherwise, the random-effects model was more appropriate. To evaluate the ethnicity-specific effects, subgroup analyses was performed in ethnic group. Sensitivity analysis was performed to evaluate the stability of the results. Individual studies included in the meta-analysis were deleted one at a time to determine the contribution of the individual data to the pooled ORs. Begg's test was used to measure publication bias, which
2.2. Inclusion criteria Two investigators reviewed all identified studies independently to determine whether an individual study was eligible for inclusion. The selection criteria for studies to be considered for this meta-analysis were as follows: 1) APOE polymorphisms in MS; 2) case–control studies; 3) proper MS diagnosis criteria; 4) not republished data; 5) not animal studies. The study would be excluded if the information could not be obtained.
Table 2 Main results of pooled ORs in the meta-analysis. Genetic model
ε4+ vs. ε4− ε2+ vs. ε2−
Ethnicity
Overall Caucasian Overall Caucasian
Sample size
Test of heterogeneity
Test of association
Test of publication bias
Case
Control
Q
P
I2 (%)
OR
95% CI
z
P
5472 4160 4636 4160
4727 3546 4047 3546
30.22 15.00 16.06 12.36
0.049 0.378 0.589 0.577
37.1 6.7 0.0 0.0
0.997 0.924 1.097 1.127
0.861–1.156 0.819–1.041 0.940–1.279 0.955–1.331
0.55 0.49 1.75 0.59
0.681 0.621 0.080 0.553
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A %
Study ID
OR (95% CI)
Weight
Lee et al (2010)
1.12 (0.85, 1.48)
10.17
Losonczi et al (2010)
6.52 (2.15, 19.81)
1.59
Bonetti et al (2009)
0.97 (0.76, 1.24)
11.15
Mustafina et al (2008)
1.31 (0.80, 2.14)
5.77
Koutsis et al (2007)
1.45 (0.84, 2.50)
4.98
Ramsaransing et al (2005)
0.92 (0.37, 2.31)
2.22
Cocco et al (2005)
0.94 (0.63, 1.42)
7.20
Al Shammriet al (2005)
1.18 (0.47, 2.97)
2.21
Pinholt et al (2005)
0.84 (0.62, 1.16)
9.23
Zakrzewska-Pniewskaet al (2004)
0.95 (0.48, 1.89)
3.57
Zwemmer et al (2004)
0.69 (0.46, 1.04)
7.27
Niino et al (2003)
0.93 (0.45, 1.92)
3.26
Savettieri et al (2003)
1.84 (0.89, 3.84)
3.22
Ballerini et al (2000)
0.35 (0.13, 0.96)
1.86
Hogh et al (2000)
1.00 (0.71, 1.43)
8.35
Weatherby et al (2000)
0.84 (0.55, 1.29)
6.86
Ferri et al (1999)
0.77 (0.37, 1.59)
3.29
Oliveri et al (1999)
1.70 (0.68, 4.23)
2.24
Gaillard et al (1998)
0.89 (0.42, 1.88)
3.09
Rubinsztein et al (1994)
0.56 (0.24, 1.33)
2.46
Overall (I-squared = 37.1%, p = 0.049)
1.00 (0.86, 1.16)
100.00
NOTE: Weights are from random effects analysis
.0505
1
19.8
B Study
%
ID
OR (95% CI)
Weight
Bonetti et al (2009)
0.97 (0.76, 1.24)
24.80
Mustafina et al (2008)
1.31 (0.80, 2.14)
5.97
Ramsaransing et al (2005)
0.92 (0.37, 2.31)
1.69
Cocco et al (2005)
0.94 (0.63, 1.42)
8.68
Pinholt et al (2005)
0.84 (0.62, 1.16)
14.56
Zakrzewska-Pniewskaet al (2004)
0.95 (0.48, 1.89)
3.03
Zwemmer et al (2004)
0.69 (0.46, 1.04)
8.82
Savettieri et al (2003)
1.84 (0.89, 3.84)
2.65
Ballerini et al (2000)
0.35 (0.13, 0.96)
1.38
Hogh et al (2000)
1.00 (0.71, 1.43)
11.60
Weatherby et al (2000)
0.84 (0.55, 1.29)
7.95
Ferri et al (1999)
0.77 (0.37, 1.59)
2.73
Oliveri et al (1999)
1.70 (0.68, 4.23)
1.71
Gaillard et al (1998)
0.89 (0.42, 1.88)
2.52
Rubinsztein et al (1994)
0.56 (0.24, 1.33)
1.91
Overall (I-squared = 6.7%, p = 0.378)
0.92 (0.82, 1.04)
100.00
.125
1
7.98
C. Xuan et al. / Journal of the Neurological Sciences 308 (2011) 110–116
was shown as funnel plot (P b 0.05 was considered representative of statistically significant publication bias) [26]. All analyses were performed using STATA software, version 10.0 (Stata Corporation, College Station, TX, USA). 3. Results 3.1. Studies included in meta-analysis A total of 27 [19–21,24,27–49] relevant studies concerning the APOE ε2, 4 alleles and MS were identified. Seven studies [19,21,43–47] were excluded due to the number of alleles that couldn't be extracted. Thus, 20 studies which met the inclusion consisted of 5472 patients/4727 controls for ε4 allele and 4636 patients/4047 controls for ε2 allele were considered in meta-analysis. In subgroup analyses, 15 (4160 patients/3546 controls for ε4 and ε2 allele) different studies with specific focus on Caucasian populations were included in ethnic group. Main characteristics of the included studies were listed in Table 1. 3.2. Meta-analysis results In overall analysis, the combination of 20 comparisons showed heterogeneity for ε4+ vs. ε4− (Q = 30.22, df = 19, P = 0.049; I 2 = 37.1%), but not for ε2+ vs. ε2− (Q = 16.06, df = 18, P = 0.589; I 2 = 0.0%). No significant associations were found between APOE ε2, 4 alleles and MS susceptibility when all studies pooled with randomeffects model for ε4+ vs. ε4− (ORε4 = 0.997, 95% CI = 0.861–1.156) and fixed-effects model for ε2+ vs. ε2− (ORε2 = 1.097, 95% CI = 0.940–1.279). In the stratified analysis by ethnicity, no significant associations were found among Caucasian population when all 15 studies pooled with fixed-effects model for ε4+ vs. ε4− (ORc-ε4 = 0.924, 95% CI = 0.819–1.041; P = 0.378 for heterogeneity), and ε2+ vs. ε2− (ORc-ε2 = 1.127, 95% CI = 0.955–1.331; P = 0.577 for heterogeneity). The main results of meta-analysis were shown in Table 2 and Figs. 1–2. 3.3. Sensitivity analysis A single study involved in the meta-analysis was deleted each time to reflect the influence of the individual data-set to the pooled ORs, and the corresponding pooled ORs were not materially altered (data not shown), indicating that our results were statistically robust. 3.4. Publication bias Begg's test and funnel plot were performed to access the publication bias of literatures. The results suggest no evidence of publication biases (Table 2, Fig. 3). 4. Discussion Although MS is the most common demyelinating diseases, its pathogenesis and etiology are as yet poorly understood. MS is a major cause of morbidity and disability in young adults (aged 16–35), with a prevalence of 0.1% in individuals of northern European origin [50]. Recently, interest has also focused on genetic factors that may influence the outcome and prognosis of MS. One of the regions of interest identified through linkage analysis was chromosome 19q13, near the APOE gene locus [51]. Three other
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linkage analysis [52–54] have shown some support for linkage to this region, and a meta-analysis of all four genomic screens identified 19q13 as the second most significant region after the major histocompatibility complex (MHC) [55]. The APOE gene consists of four exons and three introns spanning 3597 nucleotides, and produces ApoE which is a 299 amino acid polypeptide [56]. In humans, the APOE gene exists in three common allelic forms (APOE ε2, ε3, ε4) and 2 rare allelic forms (APOE ε1, ε5) [12–14]. APOE ε3 is the most (77%) and ε2 is the least (8%) common alleles. The frequency of the ε4 allele is approximately 15% in general population [57]. Three common APOE alleles (ε2, ε3 and ε4) encode three corresponding protein isoforms, Apo E2, E3 and E4. Apo E, a 35-kDa plasma protein synthesized mainly in the liver, is involved in cholesterol transport and metabolism [58]. APOE is also expressed in other tissues, notably the brain, the second most prolific tissue in terms of ApoE production [59]. ApoE3 seems to be the normal form, while ApoE2 and ApoE4 can each be dysfunctional. Some studies have indeed found an association between APOE ε4 allele and an increased brain damage [11]. It is suggested that APOE ε4 allele may be associated with accelerated neurodegeneration and plays a role in the development and progression of MS, Alzheimer's disease [60], and several other diseases [61,62]. On the other hand, some publications report a protective effect from the ε2 allele of the APOE gene [9,24]. The first meta-analysis in association between APOE ε4, 2 alleles and MS susceptibility was performed by Burwick et al. in 2006 [63]. After the meta-analysis from 3299 patients and 2532 controls, they concluded there were no relation between the ε4, 2 alleles and MS susceptibility [63]. In the last five years, 5 case–control studies were performed to investigate the associations. Therefore, it is essential for us to re-perform a new meta-analysis to evaluate the associations. There is no doubt that the new results will be more credible. As a result, our meta-analysis form 5472 patients/4727 controls for ε4 allele and 4636 patients/4047 controls for ε2 allele demonstrated that no association between the APOE ε4, 2 alleles and MS susceptibility. Some limitations of this meta-analysis should be discussed. First, this meta-analysis only focused on papers published in English language and reported in other languages might bias the present results, even though the publication bias were not detected with Begg's test presently. Additionally, there might be eligible studies that were not published, not indexed by electronic databases, or published in the journals we did not cover. Second, moderate heterogeneity was observed in association between APOE ε4 allele and MS susceptibility in overall population analysis. Although we use random-effect model to pool ORs, it may affect the precision of results. Large sample and representative population-based studies with homogeneous MS patients and well matched controls are warranted to confirm this finding. Any heterogeneity was not observed in subgroup analysis for Caucasian population. Therefore, the source of heterogeneity might come from ethnicity classification. At last, the lack of individual participants' data has restricted further adjustments by other covariables, such as specific outcome, sex, smoking, diabetes, etc. Despite these limitations, our results do not support APOE ε2, 4 alleles as susceptibility factors for MS. The effect of the variants on the expression levels and the possible functional role of the variants in MS should be addressed in further studies. References [1] Noseworthy JH, Lucchinetti C, Rodriguez M, Weinshenker BG. Multiple sclerosis. N Engl J Med 2000;343:938–52. [2] Pugliatti M, Harbo HF, Holmoy T, Kampman MT, Myhr KM, Riise T, et al. Environmental risk factors in multiple sclerosis. Acta Neurol Scand Suppl 2008;188:34–40.
Fig. 1. Pooled OR and 95% confidence intervals (CIs) of individual studies and pooled data for the association between APOE ε4 allele and multiple sclerosis in (A) overall, and (B) Caucasian population.
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C. Xuan et al. / Journal of the Neurological Sciences 308 (2011) 110–116
A Study
%
ID
OR (95% CI)
Weight
Losonczi et al (2010)
0.67 (0.31, 1.42)
4.13
Bonetti et al (2009)
0.93 (0.63, 1.38)
15.53
Mustafina et al (2008)
0.75 (0.37, 1.50)
4.86
Koutsis et al (2007)
1.17 (0.65, 2.13)
6.64
Ramsaransing et al (2005)
0.59 (0.20, 1.78)
1.95
Cocco et al (2005)
1.33 (0.77, 2.29)
7.99
Al-Shammri et al (2005)
0.25 (0.03, 2.04)
0.54
Pinholt et al (2005)
1.28 (0.85, 1.92)
14.27
Zakrzewska-Pniewska et al (2004)
1.67 (0.69, 4.05)
2.99
Zwemmer et al (2004)
1.57 (0.88, 2.81)
6.96
Niino et al (2003)
1.10 (0.45, 2.68)
2.96
Savettieri et al (2003)
0.87 (0.47, 1.61)
6.19
Ballerini et al (2000)
1.50 (0.63, 3.56)
3.15
Hogh et al (2000)
1.94 (0.75, 4.98)
2.64
Weatherby et al (2000)
1.48 (0.86, 2.54)
8.09
Ferri et al (1999)
1.08 (0.53, 2.20)
4.64
Oliveri et al (1999)
0.57 (0.22, 1.47)
2.59
Gaillard et al (1998)
0.84 (0.34, 2.03)
2.98
Rubinsztein et al (1994)
0.71 (0.14, 3.57)
0.90
Overall (I squared = 0.0%, p = 0.589)
1.10 (0.94, 1.28)
100.00
.0313
1
32
B Study
%
ID
OR (95% CI)
Weight
Bonetti et al (2009)
0.93 (0.63, 1.38)
18.12
Mustafina et al (2008)
0.75 (0.37, 1.50)
5.66
Ramsaransing et al (2005)
0.59 (0.20, 1.78)
2.27
Cocco et al (2005)
1.33 (0.77, 2.29)
9.33
Pinholt et al (2005)
1.28 (0.85, 1.92)
16.65
Zakrzewska-Pniewskaet al (2004)
1.67 (0.69, 4.05)
3.49
Zwemmer et al (2004)
1.57 (0.88, 2.81)
8.12
Savettieri et al (2003)
0.87 (0.47, 1.61)
7.23
Ballerini et al (2000)
1.50 (0.63, 3.56)
3.67
Hogh et al (2000)
1.94 (0.75, 4.98)
3.08
Weatherby et al (2000)
1.48 (0.86, 2.54)
9.44
Ferri et al (1999)
1.08 (0.53, 2.20)
5.41
Oliveri et al (1999)
0.57 (0.22, 1.47)
3.02
Gaillard et al (1998)
0.84 (0.34, 2.03)
3.48
Rubinsztein et al (1994)
0.71 (0.14, 3.57)
1.05
Overall (I-squared = 0.0%, p = 0.577)
1.13 (0.96, 1.33)
100.00
.14
1
7.17
C. Xuan et al. / Journal of the Neurological Sciences 308 (2011) 110–116 2
Begg's funnel plot with pseudo 95% confidence limits
[23] [24] 1
logor
[25] [26] 0
[27]
[28] -1
[29] 0
.2
.4
.6
s.e. of: logor Fig. 3. Begg's funnel plot for publication bias in selection of studies on the APOE ε4 allele in overall population.
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Fig. 2. Pooled OR and 95% CI of individual studies and pooled data for the association between APOE ε2 allele and multiple sclerosis in (A) overall, and (B) Caucasian population.
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