Abstract
Endometriosis is a complex disease that is influenced by genetic and environmental factors. In endometriosis, WNT4 plays a likely role owing to its biological functions. In this study, the TaqMan allelic discrimination technique was used to investigate the relationship between endometriosis and four single nucleotide polymorphisms in WNT4 (rs7521902 [A/C], rs16826658 [G/T], rs7515106 [C/T] and rs2235529 [A/G]) in Chinese Han women. A total of 646 patients with endometriosis and 766 normal controls were recurited. Regression analyses revealed that rs2235529 was a risk locus for endometriosis (P = 1.80E-03, OR, 95% CI = 1.311, 1.129 to 1.522), particularly in patients with stage III and IV disease. No significant association was found between endometriosis and rs7521902 (A/C), rs16826658 (G/T), or rs7515106 (C/T). For each of the four single nucleotide polymorphisms, no association was found between patients with endometriosis-related infertility or primary infertility and the controls. The results demonstrated that WNT4 rs2235529 is associated with endometriosis in Chinese Han women, which may result in aberrant expression of WNT4, leading to the pathogenesis of endometriosis.
Keywords
Introduction
Endometriosis is defined by the presence of endometrial tissue outside the uterus, and it affects 5–10% of women of reproductive age and up to 50% of infertile women (
Eskenazi, Warner, 1997
, Giudice, Kao, 2004
, Meuleman et al, 2009
). It often results in dysmenorrhoea, chronic pelvic pain, dyspareunia and infertility (Giudice, Kao, 2004
). Epidemiological studies have determined that the risk of endometriosis in women with a family history of the diseaseisincreased by approximately five-fold (Stefansson et al, 2002
, Treloar et al, 1999
). Although the pathogenesis of endometriosis is largely unclear, it is considered to be a multifactorial disease involving environmental and genetic factors and interactions between these factors (Montgomery et al, 2008
).The wingless-type MMTV integration site family member 4 (WNT4) is a protein-coding gene that plays a crucial role in the development of the female reproductive tract, human endometrial stromal cell differentiation and embryonic implantation (
Kobayashi, Behringer, 2003
, Li et al, 2013
, Tulac et al, 2003
, Vainio et al, 1999
). A previous study observed abnormal expression of the WNT4 gene in eutopic endometrium from women with endometriosis (Pabona et al, 2012
). Recently, several genome-wide association studies (GWAS) of endometriosis have detected some endometriosis-related genetic markers in the region close to or within an intron of WNT4 (- Pabona J.M.
- Simmen F.A.
- Nikiforov M.A.
- Zhuang D.
- Shankar K.
- Velarde M.C.
- Zelenko Z.
- Giudice L.C.
- Simmen R.C.
Kruppel-like factor 9 and progesterone receptor coregulation of decidualizing endometrial stromal cells: implications for the pathogenesis of endometriosis.
J. Clin. Endocrinol. Metab. 2012; 97: E376-E392
Nyholt et al, 2012
, - Nyholt D.R.
- Low S.K.
- Anderson C.A.
- Painter J.N.
- Uno S.
- Morris A.P.
- Macgregor S.
- Gordon S.D.
- Henders A.K.
- Martin N.G.
- Attia J.
- Holliday E.G.
- McEvoy M.
- Scott R.J.
- Kennedy S.H.
- Treloar S.A.
- Missmer S.A.
- Adachi S.
- Tanaka K.
- Nakamura Y.
- Zondervan K.T.
- Zembutsu H.
- Montgomery G.W.
Genome-wide association meta-analysis identifies new endometriosis risk loci.
Nat. Genet. 2012; 44: 1355-1359
Painter et al, 2011
, - Painter J.N.
- Anderson C.A.
- Nyholt D.R.
- Macgregor S.
- Lin J.
- Lee S.H.
- Lambert A.
- Zhao Z.Z.
- Roseman F.
- Guo Q.
- Gordon S.D.
- Wallace L.
- Henders A.K.
- Visscher P.M.
- Kraft P.
- Martin N.G.
- Morris A.P.
- Treloar S.A.
- Kennedy S.H.
- Missmer S.A.
- Montgomery G.W.
- Zondervan K.T.
Genome-wide association study identifies a locus at 7p15.2 associated with endometriosis.
Nat. Genet. 2011; 43: 51-54
Uno et al, 2010
). A Japanese GWAS reported an association between endometriosis and rs7521902(A/C) and rs16826658(G/T) (Nyholt et al, 2012
, - Nyholt D.R.
- Low S.K.
- Anderson C.A.
- Painter J.N.
- Uno S.
- Morris A.P.
- Macgregor S.
- Gordon S.D.
- Henders A.K.
- Martin N.G.
- Attia J.
- Holliday E.G.
- McEvoy M.
- Scott R.J.
- Kennedy S.H.
- Treloar S.A.
- Missmer S.A.
- Adachi S.
- Tanaka K.
- Nakamura Y.
- Zondervan K.T.
- Zembutsu H.
- Montgomery G.W.
Genome-wide association meta-analysis identifies new endometriosis risk loci.
Nat. Genet. 2012; 44: 1355-1359
Uno et al, 2010
). In addition, a significant association between rs7521902(A/C) and endometriosis was confirmed in the study by Painter et al, 2011
, as well as an association between rs7515106(C/T) and endometriosis. Some studies have repeatedly investigated associations between these single nucleotide polymorphisms (SNPs) and endometriosis in women of different races (- Painter J.N.
- Anderson C.A.
- Nyholt D.R.
- Macgregor S.
- Lin J.
- Lee S.H.
- Lambert A.
- Zhao Z.Z.
- Roseman F.
- Guo Q.
- Gordon S.D.
- Wallace L.
- Henders A.K.
- Visscher P.M.
- Kraft P.
- Martin N.G.
- Morris A.P.
- Treloar S.A.
- Kennedy S.H.
- Missmer S.A.
- Montgomery G.W.
- Zondervan K.T.
Genome-wide association study identifies a locus at 7p15.2 associated with endometriosis.
Nat. Genet. 2011; 43: 51-54
Albertsen et al, 2013
, Rahmioglu et al, 2014
, Sundqvist et al, 2013
). These results, however, are inconsistent. In a recent study by Albertsen et al, 2013
, an association between one novel SNP (rs2235529[A/G]) and endometriosis was observed in American women. In the present study, therefore, three controversial SNPs were studied (rs7521902[A/C], rs16826658[G/T], and rs7515106[C/T]) and one novel SNP (rs2235529[A/G]) in Chinese Han women with endometriosis.Materials and methods
Patients
In this study, 1412 women were enrolled (646 endometriosis patients and 766 controls). All women had undergone surgery between 2007 and 2013 at Tongji Hospital, Tongji Medical College, Huazhong University of Science and Technology. The following inclusion criteria were applied: members of the Chinese Han population, aged 25–45 years, preoperative 6 months without hormonal therapy, regular menstruation, laparoscopy or laparotomy and with a histologically confirmed presence of endometriosis or absence of endometriosis. Patients with ovarian malignant or benign cysts (except ovarian endometriosis), genital tract anomalies and histories of malignant disease were excluded. The control patients underwent surgery for uterine leiomyomas (231/766 [30.2%]) or infertility (535/766 [69.8%]). The postoperative diagnosis of infertility was hydrosalpinx. According to the revised American Fertility Society classification (
Anonymous, 1985
), 102 (15.8%) stage I-II patients and 544 (84.2%) patients had moderate to severe endometriosis (stage III-IV). In our sample, 39.8% (257/646) women had endometriosis-associated infertility, and 22.5% (172/766) controls had primary infertility.Peripheral blood samples were preoperatively collected into tubes treated with ethylenediaminetetraacetic acid. All patients provided signed informed consent. The study was approved by Tongji Medical College, Huazhong University of Science and Technology on 26 July 2011 (reference number S462).
DNA extraction
Genomic DNA was extracted from leukocytes with the Quickgene DNA whole blood kit (Fuji Film, Japan), according to the manufacturer's protocol.
WNT4 genotyping
Four SNPs were selected for genotyping: rs7521902(A/C), rs16826658(G/T), rs7515106(C/T) and rs2235529(A/G). Detailed information is presented in Table 1. TaqMan allelic discrimination analysis was carried out using the Applied Biosystems protocol. A 384-well plate was prepared with a mixture of 1 × TaqMan SNP Genotyping assay (Applied Biosystems, USA), 1 × TaqMan Universal Master Mix (Applied Biosystems, USA) and 20 ng DNA per well. Polymerase chain reaction (PCR) was carried out using a 7900 HT Fast-Real-Time PCR system (Applied Biosystems, USA). The PCR conditions were denaturation at 95°C for 10 min, followed by 40 cycles of 95°C denaturation for 15 s and a 60°C anneal for 1 min. After PCR, the plates were read, and the data analysed using SDS 2.4 (Applied Biosystems, USA). For quality control, a random 10% of the samples were repeatedly genotyped; the reproducibility rate was 100%. It was determined that a call rate of at least 97% met the standard criteria.
Table 1WNT4 single nucleotide polymorphisms in previous genome-wide association studies of endometriosis.
| SNP | Location | Allele | Distance to WNT4 | P-value | OR (95% CI) | Ethnicity | Reference |
|---|---|---|---|---|---|---|---|
| rs7521902 | Chr1:22164231 | A/C | Upstream 21 kb | 4.23E-05 | 1.25 (1.12 to1.39) | Japanese | Uno et al, 2010 |
| 8.90E-05 | 1.16 (1.08 to 1.25) | White | Painter et al, 2011
Genome-wide association study identifies a locus at 7p15.2 associated with endometriosis. Nat. Genet. 2011; 43: 51-54 | ||||
| rs16826658 | Chr1:22159278 | G/T | Upstream 16 kb | 3.46E-05 | 1.25 (1.12 to 1.39) | White | Painter et al, 2011
Genome-wide association study identifies a locus at 7p15.2 associated with endometriosis. Nat. Genet. 2011; 43: 51-54 |
| rs2235529 | Chr1:22123994 | A/G | Intron 1 | 1.36E-07 | 1.28 (1.16 to 1.41) | White | Albertsen et al, 2013 |
| rs7515106 | Chr1:22146917 | C/T | Upstream 3.9 kb | 3.60E-05 | 1.13 (1.07 to 1.05) | White | Painter et al, 2011
Genome-wide association study identifies a locus at 7p15.2 associated with endometriosis. Nat. Genet. 2011; 43: 51-54 |
CI = confidence interval; OR = odds ratio; SNP = single nucleotide polymorphism.
Statistical analyses
The Statistical Package for Social Sciences (SPSS) version 18.0 for Windows (SPSS, Chicago, IL, USA) was used to conduct statistical analyses. Certain differences (i.e. current age, age at menarche, menstrual cycle and menstrual period) between the patients and controls were evaluated using the non-parametric Kruskal–Wallis test. The chi-squared test was used to test the infertility rate, Hardy–Weinberg equilibrium, and allele and genotype frequencies. Statistically significant values were corrected for multiple tests using the Bonferroni correction, and P < 0.05 was considered to be statistically significant. The odds ratio (OR) and 95% confidence intervals (CI) were calculated by binary logistic regression. A post-hoc power calculation was obtained using Power version 3.0.0 for Windows (Power software, National Cancer Institute, USA). The analysis was based on a disease prevalence of 8% and a relative risk of 1.25. According to these assumptions, the study power for each variant single nucleotide polymorphism (SNP) was as follows: 51.6% for rs7521902(A/C), 57.7% for rs16826658(G/T), 80.0% for rs2235529(A/G) and 72.6% for rs7515106(C/T). The analysis of linkage disequilibrium structures among the four WNT4 SNPs was carried out using Haploview, version 4.2 (http://www.hapmap.org).
Results
Clinical characteristics of study population
The characteristics of the 646 patients with endometriosis and the 766 controls are presented in Table 2. No significant difference was found between the endometriosis patients and controls in age, age at menarche and length of menstrual cycle. The length of the menstrual period in the patients (5.93 ± 1.32 days), however, was longer than that in the controls (5.59 ± 1.68 days P = 0.019). Moreover, infertility in the endometriosis patients was notably higher than in the controls (39.8% versus 22.5%; P < 0.001).
Table 2Characteristics of the study population.
| Characteristic | Endometriosis | Control | P-value |
|---|---|---|---|
| Number of participants | 646 | 766 | |
| Age (years) | 33.25 ± 7.55 | 34.06 ± 7.46 | NS |
| Age at menarche | 13.24 ± 1.42 | 13.40 ± 1.50 | NS |
| Menstrual cycle length | 29.47 ± 4.23 | 29.42 ± 4.41 | NS |
| Menstrual period | 5.93 ± 1.32 | 5.59 ± 1.68 | 0.019 |
| Infertility | 257/646 (39.8) | 172/766 (22.5) | <0.001 |
Values are expressed as the mean ± SD or n (%); P-value: total number of endometriosis patients versus controls. NS = not statistically significant.
Association of WNT4 polymorphism and endometriosis
The genotype frequencies of the four SNPs were in Hardy–Weinberg equilibrium (Table 3) in this study. The call rates for the assays were as follows: 98.4% for rs7521902 (A/C), 98.4% for rs16826658 (G/T), 98.3% for rs7515106 (C/T) and 98.7% for rs2235529 (A/G). The genotypes and allele frequencies of the rs7521902 (A/C), rs16826658 (G/T), rs7515106 (C/T) and rs2235529 (A/G) WNT4 polymorphism in women with and without endometriosis are shown in Table 3. The SNP rs2235529 (A/G) differed significantly between the endometriosis patients and the controls (P = 1.80E-03, OR 95% CI 1.311, 1.129 to 1.522). The other three SNPs did not differ significantly between the patients and the controls. In addition, no linkage disequilibrium was found between any two SNPs (Supplementary Figure S1).
Table 3Comparison of risk allele frequencies in Chinese Han women with endometriosis and controls.
| WNT4 polymorphism | Allele | Population study | N | HWE | RAF | P-value | OR (95% CI) |
|---|---|---|---|---|---|---|---|
| (allele) | |||||||
| rs7521902 | (A/C) | Control | 747 | 0.176 | 0.50 (A) | NS | 1.031 (0.888 to 1.199) |
| Endometriosis | 643 | 0.108 | 0.49 (A) | ||||
| rs16826658 | (G/T) | Control | 748 | 0.242 | 0.50 (G) | NS | 1.044 (0.868 to 1.257) |
| Endometriosis | 642 | 0.507 | 0.52 (G) | ||||
| rs2235529 | (A/G) | Control | 746 | 0.806 | 0.48 (A) | 1.80E-03 | 1.311 (1.129 to 1.522) |
| Endometriosis | 642 | 0.347 | 0.55 (A) | ||||
| rs7515106 | (C/T) | Control | 760 | 0.383 | 0.80 (C) | NS | 1.215 (1.000 to 1.475) |
| Endometriosis | 634 | 0.516 | 0.83 (C) |
CI = confidence intervals; HWE = Hardy-Weinberg equilibrium; NS = not statistically significant; OR = odds ratio; RAF = risk allele frequencies.
In the subgroup analyses, allele frequencies were compared between the patients with stage I-II or stage III-IV endometriosis and the controls. The frequency of rs2235529(A/G) was significantly different between the patients with stage III-IV disease and the control group (P = 0.004, OR 95% CI = 1.322, 1.130 to 1.547), but no differences were observed between the patients with stage I-II disease and the control group. No association was detected between the other three SNPs and the two disease stages (Table 4).
Table 4Analyses of the single nucleotide polymorphisms by severity of endometriosis.
| WNT4 polymorphism | Stage I-II | Stage III-IV |
|---|---|---|
| OR (95% CI) | OR (95% CI) | |
| rs7521902 | 1.087 (0.811 to 1.457) | 1.021 (0.872 to 1.196) |
| rs1682668 | 1.040 (0.776 to 1.394) | 1.069 (0.914 to 1.250) |
| rs2235529 | 1.154 (0.859 to 1.550) | 1.322 (1.130 to 1.547)a |
| rs7515106 | 1.498 (0.985 to 2.278) | 1.172 (0.956 to 1.435) |
CI = confidence intervals; OR = odds ratio.
No statistically significant differences were found, except a difference between rs2235529 and Stage III-IV(aP = 0.004).
Analyses of WNT4 polymorphisms and endometriosis-related infertility or primary infertility
The relationship between four WNT4 SNPs and endometriosis-related infertility or primary infertility is presented in Table 5. No significant difference was observed.
Table 5Distribution of genotype and allele frequencies in infertile women with and without endometriosis and controls.
| WNT4 polymorphism (1/2) | Population study | n | RAF (allele) | OR (95% CI) |
|---|---|---|---|---|
| rs7521902 (A/C) | Fertile controls | 582 | 0.50 (A) | |
| Infertile controls | 165 | 0.49 (A) | 0.976 (0.764 to 1.246) | |
| Infertile endometriosis | 127 | 0.50 (A) | 0.984 (0.750 to 1.291) | |
| rs1682668 (G/T) | Fertile controls | 582 | 0.50 (G) | |
| Infertile controls | 166 | 0.50 (G) | 0.993 (0.778 to 1.267) | |
| Infertile endometriosis | 126 | 0.50 (G) | 0.978 (0.744 to 1.284) | |
| rs2235529 (A/G) | Fertile controls | 578 | 0.48 (A) | |
| Infertile controls | 168 | 0.49 (A) | 1.068 (0.838 to 1.362) | |
| Infertile endometriosis | 130 | 0.53 (A) | 1.257 (0.960 to 1.646) | |
| rs7515106 (C/T) | Fertile controls | 590 | 0.80 (C) | |
| Infertile controls | 170 | 0.79 (C) | 0.916 (0.680 to 1.233) | |
| Infertile endometriosis | 127 | 0.82 (C) | 1.143 (0.803 to 1.626) |
CI = confidence interval; OR = odds ratio; RAF = risk allele frequencies.
No statistically significant differences were found.
Discussion
Because of its biological functions, WNT4 plays a plausible role in endometriosis, including promoting Müllerian-duct differentiation during embryonic development, as well as cell proliferation, migration and invasion in the endometrium (
Biason-Lauber, 2012
, Brosens et al, 2012
, Matsuzaki, Darcha, 2013
, Tulac et al, 2003
). The aberrant expression of WNT4 in eutopic endometrium with endometriosis further indicates that WNT4 may be involved in the pathogenesis of endometriosis (Pabona et al, 2012
). Polymorphisms of the WNT4 gene may change the function or quantity of WNT4. To date, GWAS have identified four SNPs in WNT4 that are associated with the risk of endometriosis in Japanese and white populations (- Pabona J.M.
- Simmen F.A.
- Nikiforov M.A.
- Zhuang D.
- Shankar K.
- Velarde M.C.
- Zelenko Z.
- Giudice L.C.
- Simmen R.C.
Kruppel-like factor 9 and progesterone receptor coregulation of decidualizing endometrial stromal cells: implications for the pathogenesis of endometriosis.
J. Clin. Endocrinol. Metab. 2012; 97: E376-E392
Albertsen et al, 2013
, Painter et al, 2011
, - Painter J.N.
- Anderson C.A.
- Nyholt D.R.
- Macgregor S.
- Lin J.
- Lee S.H.
- Lambert A.
- Zhao Z.Z.
- Roseman F.
- Guo Q.
- Gordon S.D.
- Wallace L.
- Henders A.K.
- Visscher P.M.
- Kraft P.
- Martin N.G.
- Morris A.P.
- Treloar S.A.
- Kennedy S.H.
- Missmer S.A.
- Montgomery G.W.
- Zondervan K.T.
Genome-wide association study identifies a locus at 7p15.2 associated with endometriosis.
Nat. Genet. 2011; 43: 51-54
Uno et al, 2010
). Surprisingly, no endometriosis-related studies of the WNT4 polymorphism in the Chinese Han population have been published.A total of 646 endometriosis patients and 766 controls were enrolled in the present study. No significant differences were found between the two groups in age, age at menarche and menstrual cycle length, whereas a longer menstrual period and a higher proportion of infertility were found in patients with endometriosis. These observations aligned with a clinical manifestation and epidemiological survey (
Giudice, Kao, 2004
).In a recent GWAS,
Albertsen et al, 2013
reported a novel SNP, rs2235529(A/G), that was associated with endometriosis in women in the USA. Our study of 646 patients and 766 controls found a significant association between this SNP and endometriosis. Although no amino acids were changed by the rs2235529(A/G) polymorphism owing to its location in intron 1, genetic mutations in this intron are located in DNase 1 hypersensitive sites (ENCODE Project Consortium, 2012
, http://genome.ucsc.edu/ENCODE/), which may contribute to transcription regulation and aberrant expression, eventually leading to the pathogenesis of endometriosis (Chrysogelos, 1993
, Purugganan, Wessler, 1992
). Since rs2235529 (A/G) was found to be associated with endometriosis in the study by Albertsen et al, 2013
, the relationship between this SNP and endometriosis was first validated. Our results were consistent with those of Albertsen et al, 2013
, which increases the likelihood that this is a true causal association. Therefore, it would be worthwhile to validate an association between rs2235529 (A/G) and endometriosis in different populations in the future. Previous reports, including GWAS, and studies of disease morphology and gene expression, have suggested that endometriosis is a heterogeneous disease that is composed of different entities (Matsuzaki et al, 2006
, Nisolle, Donnez, 1997
, Painter et al, 2011
, - Painter J.N.
- Anderson C.A.
- Nyholt D.R.
- Macgregor S.
- Lin J.
- Lee S.H.
- Lambert A.
- Zhao Z.Z.
- Roseman F.
- Guo Q.
- Gordon S.D.
- Wallace L.
- Henders A.K.
- Visscher P.M.
- Kraft P.
- Martin N.G.
- Morris A.P.
- Treloar S.A.
- Kennedy S.H.
- Missmer S.A.
- Montgomery G.W.
- Zondervan K.T.
Genome-wide association study identifies a locus at 7p15.2 associated with endometriosis.
Nat. Genet. 2011; 43: 51-54
Sundqvist et al, 2011
). In the present study, 84.2% (544/646) of the patients were in stage III/IV, and a significant association was observed between rs2235529(A/G) and stage III/IV, suggesting that the failure to replicate some aspects of Albertsen's study resulted from differences in the genetic backgrounds of the populations. - Sundqvist J.
- Falconer H.
- Seddighzadeh M.
- Vodolazkaia A.
- Fassbender A.
- Kyama C.
- Bokor A.
- Stephansson O.
- Padyukov L.
- Gemzell-Danielsson K.
- D'Hooghe T.M.
Endometriosis and autoimmune disease: association of susceptibility to moderate/severe endometriosis with CCL21 and HLA-DRB1.
Fertil. Steril. 2011; 95: 437-440
Koninckx et al, 1994
demonstrated that endometrial stage I-II is an epiphenomenon rather than a disease, which may partially explain why no association was observed between the patients with stage I/II endometriosis and the controls in our study. It is debateable, however, whether endometriosis stage I-II is a minimal to mild disease or ‘normal’. Because of the small sample size of patients with stage I/II endometriosis in our study (i.e. the sub-analysis was not powerful enough to detect an effect), no association was observed between the patients with stage I-II endometriosis and the controls.The other three SNP (rs7521902 [A/C], rs16826658 [G/T] and rs7515106 [C/T]) were not associated with endometriosis. This result contrasts with the results of other studies that have reported a strong association of rs7521902 (A/C) with susceptibility to endometriosis in Japanese, Australian, British and Italian women (
Pagliardini et al, 2013
, Painter et al, 2011
, - Painter J.N.
- Anderson C.A.
- Nyholt D.R.
- Macgregor S.
- Lin J.
- Lee S.H.
- Lambert A.
- Zhao Z.Z.
- Roseman F.
- Guo Q.
- Gordon S.D.
- Wallace L.
- Henders A.K.
- Visscher P.M.
- Kraft P.
- Martin N.G.
- Morris A.P.
- Treloar S.A.
- Kennedy S.H.
- Missmer S.A.
- Montgomery G.W.
- Zondervan K.T.
Genome-wide association study identifies a locus at 7p15.2 associated with endometriosis.
Nat. Genet. 2011; 43: 51-54
Uno et al, 2010
), but not Belgian women (Sundqvist et al, 2013
). Similarly, a strong relationship between rs16826658 (G/T) and endometriosis was observed in Australian and British women (Painter et al, 2011
), whereas a weak association with rs16826658 (G/T) was found in the USA (- Painter J.N.
- Anderson C.A.
- Nyholt D.R.
- Macgregor S.
- Lin J.
- Lee S.H.
- Lambert A.
- Zhao Z.Z.
- Roseman F.
- Guo Q.
- Gordon S.D.
- Wallace L.
- Henders A.K.
- Visscher P.M.
- Kraft P.
- Martin N.G.
- Morris A.P.
- Treloar S.A.
- Kennedy S.H.
- Missmer S.A.
- Montgomery G.W.
- Zondervan K.T.
Genome-wide association study identifies a locus at 7p15.2 associated with endometriosis.
Nat. Genet. 2011; 43: 51-54
Albertsen et al, 2013
). The inconsistent results of these studies are largely attributed to genetic variations in the different populations studied. In the present study, the lack of an association between these SNPs and endometriosis may also be caused by the different genetic backgrounds of the patients. When comparing the SNPs allele and genotype frequencies from our study with those from the 1000Genomes Consortium (www.1000genomes.org), an approximately coincident distribution of allele and genotype frequencies was observed in a Chinese Han population, which suggests that, although the control patients were recruited from the hospital, the control group bias was small. This bias, however, cannot be completely excluded even though a larger population was analysed in the study. In addition, because the sample size was limited compared with previous GWAS, type II errors may result in the absence of significant association in this study because the analysis had a power of 51.6%. In addition, non-genetic factors might contribute to the conflicting results in various studies (Klein et al, 2012
, Vercellini et al, 2014
). On the basis of the International HapMap Project, different linkage disequilibrium patterns of SNPs exist in different populations (Consortium, 2005
, Consortium et al, 2010
). The failure to find linkage disequilibrum between any two SNPs in the present study may be attributed to population differences.- Consortium I.H.
- Altshuler D.M.
- Gibbs R.A.
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- Sharp R.R.
- Zeng C.
- Brooks L.D.
- McEwen J.E.
Integrating common and rare genetic variation in diverse human populations.
Nature. 2010; 467: 52-58
Given a possible role for WNT4/WNT signalling in infertility in women with endometriosis (
Li et al, 2013
, Matsuzaki et al, 2010
, Tulac et al, 2003
), an attempt was made to analyse the association between WNT4 SNPs and endometriosis-related infertility, which has previously been unreported. No association was found, however, between the examined SNPs and endometriosis-associated infertility and primary infertility in our study, which suggests that WNT4 may not play a role in endometriosis-associated infertility and primary infertility. Meanwhile, it was observed that the small sample size in the sub-analysis may result in an absence of significant association.In conclusion, of the four candidate polymorphisms assessed herein, evidence is provided from Chinese women that the WNT4 rs2235529 polymorphism is associated with the risk of endometriosis, but no association was found between rs7521902 (A/C), rs16826658 or rs7515106 and endometriosis. These findings may lead to a better understanding of mutations in the aetiology of endometriosis in different populations. Our study, however, was limited in sample size; therefore, the results must be validated in an independent cohort. In addition, the function of WNT4 during the pathogenesis of endometriosis is unclear and requires further elucidation.
Acknowledgements
The authors would like to thank the patients for their participation.
Appendix. Supplementary material
The following is the supplementary data to this article:
- Supplementary Figure S1
The linkage disequilibrium structure of rs7521902 (A/C), rs16826658 (G/T), rs7515106 (C/T), and rs2235529 (A/G). The numbers in the squares represent r2.
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Biography
Shi-Xuan Wang, Professor of Gynaecology and Gynaecological Oncology, is Director of the Division of Gynecology and Vice Director of the Cancer Biology Research Centre in Tongji hospital, Huazhong University of Science and Technology. He received his PhD at Tongji Medical University, Wuhan, China in 1996. From 2002 to 2004, he devoted himself to a tumour immunology programme as a postdoctoral researcher at UT Southwestern Medical Centre, Dallas, Texas, USA. His research interests are gynaecology and gynaecological oncology.
Article info
Publication history
Published online: January 07, 2015
Accepted:
December 15,
2014
Received in revised form:
December 12,
2014
Received:
October 6,
2014
Declaration: The authors report no financial or commercial conflicts of interest.Identification
Copyright
© 2014 Reproductive Healthcare Ltd. Published by Elsevier Inc. All rights reserved.
