Association between Two Polymorphisms of Follicle Stimulating Hormone Receptor G

Lei Qiu, Jing Liu, and Qi-ming Hei*

1Department of Health Management,2Department of Labor and Social Security, School of Management, Hainan Medical University, Haikou 570100, China

Association between Two Polymorphisms of Follicle Stimulating Hormone Receptor Gene and Susceptibility to Polycystic Ovary Syndrome: a Meta-analysis

Lei Qiu1, Jing Liu1, and Qi-ming Hei2*

1Department of Health Management,2Department of Labor and Social Security, School of Management, Hainan Medical University, Haikou 570100, China

follicle stimulating hormone receptor; polycystic ovary syndrome; Meta-analysis; single-nucleotide polymorphism

ObjectiveTo investigate the association between two polymorphisms of follicle stimulating hormone receptor (FSHR) gene and polycystic ovary syndrome (PCOS) susceptibility.

MethodsCase-control studies on relationship of Thr307Ala and Asn680Ser polymorphisms in FSHR gene and PCOS susceptibility were searched from PubMed, ISI web of knowledge, EBSCO, and China National Knowledge Infrastructure (CNKI) databases up to March 21, 2013. The pooled odds ratio (OR) and 95% confidence interval (CI) were calculated using fixed- or random-effect model based on heterogeneity test in 5 genotype models analyses.

ResultsA total of 11 studies were included in the Meta-analysis. The random-effect analysis showed Asn680Ser was significantly associated with the reduced susceptibility to PCOS with dominant model (Asn/Asn+Asn/Ser vs. Ser/Ser, OR=0.83, 95% CI： 0.69-1.00), recessive model (Asn/Asn vs. Asn/Ser+ Ser/Ser, OR=0.84, 95% CI： 0.72-0.98), homozygote comparison (Asn/Asn vs. Ser/Ser, OR=0.79, 95% CI：0.63-0.98), and the allele contrast (Asn vs. Ser, OR=0.87, 95% CI： 0.79-0.97) respectively(p=0.02, I2=56.0%), being protective factors for PCOS. However, no significant associations were found between Thr307Ala and PCOS.

ConclusionThere might be a significant association between Asn680Ser polymorphism and PCOS.

Chin Med Sci J 2015; 30(1)：44-50

P OLYCYSTIC ovary syndrome (PCOS), one of the most common reproductive endocrine disorders among women of reproductive age, affects approximately 4%-12% of this population.1,2It is characterized by a clustering of androgen excess, chronic anovulations, and polycystic ovaries, and is frequently associated with insulin resistance and obesity.3,4To date, although the etiology of PCOS is unclear, the pathogenesis involves both hereditable and environmental factors.5,6

Some evidences have indicated that follicle stimulating hormone (FSH) gene may one of the susceptible genes for PCOS, which plays a central role during folliculogenesis by stimulating granulose-cell estrogen production through induction of aromatase activity.7,8The action of FSH ismediated by the FSH receptor (FSHR). The FSHR gene consists of 10 exons and 9 introns at chromosome 2p21.9Two prevalent polymorphisms of FSHR gene that found within exon 10 at position 307 and 680 are the most clinically relevant. The Thr307Ala (rs6165) and Asn680Ser (rs6166) polymorphisms have an influence upon FSH efficiency,10but it is still unclear whether the polymorphisms within exon 10 predispose one to PCOS. The relationship between two polymorphisms of FSHR gene and PCOS susceptibility has been studied in some ethnic groups, and contradictory results were reported concerning the contribution of certain FSHR variants to PCOS susceptibility. So we need an up-to-date, comprehensive Meta-analysis, which aimed to examine whether the Thr307Ala and Asn680Ser polymorphisms in FSHR gene are associated with PCOS susceptibility.

MATERIALS AND METHODS

Data source

Four databases including PubMed, ISI web of knowledge, EBSCO, and China National Knowledge Infrastructure (CNKI) were electronically searched to retrieve studies on association between PCOS susceptibility and FSHR gene polymorphisms up to March 21, 2013. Searching terms were “FSHR” OR “follicle stimulating hormone receptor”AND “PCOS” OR “polycystic ovary syndrome”. Moreover, we checked the reference lists of retrieved articles to identify more studies.

Inclusion criteria

Included articles met each of the following criteria: (1) case-controlled trial; (2) it evaluated the association between Thr307Ala (rs6165) and Asn680Ser (rs6166) polymorphisms in the FSHR gene and the risk of PCOS; (3) individual genotype frequencies in both the cases and controls were available; (4) both the cases and controls consisted of unrelated subjects; (5) publication language was limited to English and Chinese.

Data extraction and quality assessment

Information was carefully extracted from literatures independently by two of the authors who experienced in conducting systematic reviews. The extracted data included: the frst author, year of publication, country of origin, ethnicity of the studied population, diagnosis criteria of PCOS, mean age of cases, sample size and source of control, genotyping methods, data for Hardy–Weinberg equilibrium (HWE) in the control group.

Quality assessment was done for each article according to a predesigned evaluation form based on Critical Appraisal Skills Programme (CASP) for case–control study11and Strengthening the Reporting of Genetic Association (STREGA) studies,12containing 11 items associated with valid information reported in the study. There were 3 degrees for each item, “yes” (scored 2), “cannot tell”(scored 1) or “no” (scored 0). After evaluating the 11 items, each article could get a total score from 0 to 22. According to the following standards studies would be grouped into 3 grades: Grade A (scored 15-22, high quality), Grade B (scored 8-14, medium quality), or Grade C (scored 0-7, lower quality). Only the studies of Grade A or B would be incorporated into the fnal synthesis.

Statistical analysis

We analyzed data with STATA 11.0 software (Stata Statistical Software, College Station, TX, USA, www.stata. com). Pooled odds ratio (OR) and their 95% confidence interval (CI) were used to identify the strength of association between Thr307Ala and Asn680Ser polymorphisms and PCOS. Statistical heterogeneity among included studies was assessed by Chi-square-based Q test and quantified by I2statistic, which represents the percentage of total variation across studies that is attributable to heterogeneity rather than chance.13If the data showed no heterogeneity (P>0.10, I2<50%), Mantel–Haenszel fixed-effects model was used, otherwise a random-effect model using the DerSimonian and Laird weighting method was used. We adopted 5 comparison genetic models to assess the association. For instance, we calculated genotype distribution of the dominant model (Thr/Thr+Ala/Thr vs. Ala/Ala), recessive model (Thr/Thr vs. Ala/Thr+Ala/Ala), heterozygote comparison (Ala/Thr vs. Ala/Ala), homozygote comparison (Thr/Thr vs. Ala/Ala), and allele contrast (Thr vs. Ala) for Thr307Ala polymorphism; the dominant model (Asn/Asn+ Asn/Ser vs. Ser/Ser), recessive model (Asn/Asn vs. Asn/Ser+Ser/Ser), heterozygote comparison (Asn/Ser vs. Ser/Ser), homozygote comparison (Asn/Asn vs. Ser/Ser), and allele contrast (Asn vs. Ser) respectively for Asn680Ser polymorphism. HWE was also tested for included studies if no relevant information was provided in original research. Moreover, we performed subgroup analysis stratified by ethnicity. To test for publication bias, we formed funnel plots and undertook the Begg's test.14A two-sided P<0.05 was considered statistically significant.

RESULTS

Searching results

We initially identified 287 potentially relevant studies, butmost were excluded because they were not related to the FSHR gene polymorphism and PCOS. After assessing the full texts of 21 potentially relevant articles, 10 publications were excluded. Among them, 4 publications were not case-control studies,15-183 studies were excluded for not relevant to the Thr307Ala or Asn680Ser polymorphism,19-212 studies were reviews,22,231 study did not provide genotype information.24Leaving 11 studies were retrieved for more detailed evaluation.6,25-34The flow chart of article selection process is described in Fig. 1.

Characteristics of studies

The basic characteristics of included studies are presented in Table 1. A total of 11 studies were eligible for Thr307Ala (1326 cases and 3867 controls) and Asn680Ser (1344 cases and 3885 controls). There were 7 studies involving Caucasian participants and 4 studies involving Asian participants. Controls were age and ethnicity-matched healthy populations. Seven studies definitely applied the Rotterdam consensus criteria for the diagnosis of PCOS.35Furthermore, Table 2 and 3 present the genotype frequencies of these studies.

Thr307Ala polymorphism and PCOS susceptibility

The results of 5 different genetic models testing Thr307Ala polymorphism and PCOS susceptibility are presented in for the recessive model, 1.18 (0.98-1.41) for the heterozygote comparison, 1.16 (0.95-1.43) for the homozygote comparison, and 1.15 (0.94-1.40) for the allele contrast, respectively. Overall, there was no evidence for significant association of Thr307Ala polymorphism with PCOS susceptibility.

Asn680Ser polymorphism and PCOS susceptibility

As presented in Table 4, we found a significant association between Asn680Ser polymorphism and PCOS, with the dominant model (OR=0.83, 95% CI=0.69-1.00), the recessive model (OR=0.84, 95% CI=0.72-0.98), the homozygote comparison (OR=0.79, 95% CI=0.63-0.98), and the allele contrast (OR=0.87, 95% CI=0.79-0.97) through the random-effect analysis (P=0.02, I2=56.0%). Thus, Asn680Ser might be a protective factor for PCOS. While no significant associations were observed in heterozygote comparison (OR=0.86, 95% CI=0.71-1.05). In the subgroup analyses stratified by ethnicity (Table 5), no statistical significance was found in the Asian subgroup. However, the homozygote comparison was a protective factor for PCOS in the Caucasian subgroup (OR=0.78, 95% CI=0.61-0.99). Also, P value for heterogeneity was 0.42, and I2was 0%, indicating no heterogeneity.

Publication bias

These 11 articles showed symmetric distribution on funnel plot. Begg's regression test with the P values greater than 0.05 for all of the 5 genetic models suggested there was no publication bias. Table 4. Specifically, the pooled OR (95% CI) were 1.18 (0.99-1.40) for the dominant model, and Z value for testing overall effect was 1.89 (P=0.06), suggesting that no association was found in the dominant model. Furthermore, the pooled OR (95% CI) was 1.05 (0.89-1.22)

Figure 1.Flow chart of data selection.

Table 1.Characteristics of 11 studies included in the Meta-analysis

Table 2.Genotype and allele distributions of FSHR Thr307Ala polymorphism among PCOS case and control (Case number)

Table 3.Genotype and allele distributions of FSHR Asn680Ser polymorphism among PCOS case and control (Case number)

Table 4.Results of analysis of association between Thr307Ala, Asn680Ser polymorphisms and PCOS

Table 5.Results of analysis of association between Asn680Ser polymorphism and PCOS susceptibility stratified by ethnicity

DISCUSSION

The present research revealed significant associations between Asn680Ser polymorphism and PCOS. However, there were no associations between Thr307Ala polymorphism and PCOS. The previous research published in 2010,25based on 8 studies, only analyzed the associations between them in recessive model. And they found the association between Asn680Ser polymorphism and PCOS, for Asn/Asn vs. Asn/Ser+Ser/Ser OR=0.64, 95% CI: 0.42-0.98, and dissociation between Thr307Ala polymorphism and PCOS, which agree with the findings in our research. It is worth mentioning that the present study provided a more comprehensive data analysis by calculating 5 different genetic models to analyze the association, not only with recessive model. Our study also provided evidence of association between Asn680Ser polymorphism and PCOS susceptibility under homozygote model, and Asn allele might have a protective effect for PCOS. However, in the case of Ala307Thr, the variant was negligible and was not associated with PCOS. Of the 11 datasets included in our Meta-analysis providing data on Thr307Ala polymorphism and PCOS susceptibility, only 2 datasets provided significant association.32,34And among them, Laven et al34suggested that the Thr/Thr genotype was significantly less prevalent in PCOS patients compared with controls (23% vs. 52%), whereas in another study conducted by Dolfin et al,32Thr/Ala was significantly more frequent in women with PCOS than in normo-ovulatory subjects (65.0% vs. 33.3%). This deviation may result from ethnicity, sample size or experiment conditions.7Therefore, our Metaanalysis shows that there were lack of associations between Thr307Ala polymorphism and PCOS.

In terms of the subgroup analyses stratified by ethnicity on Asn680Ser polymorphism and PCOS susceptibility, the significant association was found in Caucasian population (Asn/Asn vs. Ser/Ser, OR=0.78, 95% CI=0.61-0.99), but no significant association was found in Asian population. The results implied that among different ethnicities, the same gene polymorphism may act differently on PCOS susceptibility. However, in Asian population, still, there were only 4 studies containing 429 cases and 624 controls in our Meta-analysis.6,25,27,33Also, It is noteworthy that the heterogeneity that existed in our subgroup analyses. In the Caucasian term, significant heterogeneity was detected in the recessive and allele contrast genetic models. While, in the Asian term significant heterogeneity existed in all models. Thus, it is likely that the difference between ethnicities attributed to lack of power and the results related to Asian population should be interpreted with caution.

There are also some limitations that may affect the present conclusions. First, the sample sizes of some included studies are rather small, which may reduce their statistical power. Second, we did not explore the interactions between gene polymorphisms and environmental factors. Third, on the whole, most original studies were based upon Caucasians; only 4 studies were conducted among Asians while none were founded on Africans even.

Despite its limitations, our Meta-analysis had some advantages. First, we assessed the association through 5 comparison genetic models: the dominant model, recessive model, heterozygote comparison, homozygote comparison, and contrast, making our analysis more extensive and valid. Second, the shape of the funnel plot did not reveal any evidence of obvious asymmetry and Begg’s tests still did not detect publication bias, indicating that our results were not biased. Furthermore, generally speaking, all the observed genotype frequencies in the controls agreed with the expected frequencies according to HWE. The 11 studies included in the Meta-analysis were identified as high quality. After quality assessment, most studies clearly articulated characteristics of the case and control, diagnosis criteria for PCOS, and genotyping information.

ACKNOWLEDGMENT

The authors thank Wang Yang and Hang Zhu in the Department of Health Statistics, College of Public Health, Chongqing Medical University for their statistical assistance.

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for publication July 5, 2014.

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