Relationship between melatonin receptor 1B and insulin receptor substrate 1 polymorphisms with gestational diabetes mellitus: a systematic review and meta-analysis.

Studies have investigated the relationship between genetic variants and risk of gestational diabetes mellitus (GDM). However, the results remain inconclusive. The aim of this study was to investigate the association of rs10830963 and rs1387153 variants in melatonin receptor 1B (MTNR1B) and rs1801278 variant in insulin receptor substrate 1 (IRS1) with GDM susceptibility. Electronic database of PubMed, Medline, Embase, and CNKI (China National Knowledge Infrastructure) were searched for relevant studies between 2005 and 2014. The odds ratio (OR) with its 95% confidence interval (CI) were employed to estimate the association. Total ten case-control studies, including 3428 GDM cases and 4637 healthy controls, met the inclusion criteria. Our results showed a significant association between the three genetic variants and GDM risk, rs10830963 with a P-value less than 0.0001, rs1387153 with a P-value of 0.0002, and rs1801278 with a P-value of 0.001. Furthermore, all the genetic models in these three polymorphisms were associated with increased risks of GDM as well (P< = 0.009). In conclusion, our study found that the genetic polymorphisms rs10830963 and rs1387153 in MTNR1B and rs1801278 in IRS1 were associated with an increased risk of developing GDM. However, further studies with gene-gene and gene-environmental interactions should be considered.

Gestational diabetes mellitus (GDM), defined as glucose intolerance with onset or first recognition during pregnancy, is one of the most common medical problems and a growing public health concern12. It causes by an increase in the insulin resistance, and the condition is also aggravated by insulin secretion from the β cells of the pancreas3. GDM affects 1–14% of all pregnant women depending on the population studied4: it complicates about 1–3% of all pregnancies in the western world5, whereas 5–10% among Asian women6. GDM is often more common in populations with a high frequency of type 2 diabetes (T2D)7. Furthermore, it increases risk of adverse pregnancy outcomes and has substantial long-term adverse health impacts on both mothers and their offspring. Though the WHO current guidelines for GDM were published in 1999 and are widely used worldwide8, to date, there is still no universal recommendation for the ideal approach for screening and diagnosis of GDM. Thus, identifying patients at a higher risk of GDM has become an important goal.

Recently, extraordinary progress was made in identifying susceptible genes of complicated diseases through genome-wide association strategy910. Melatonin receptor 1B (MTNR1B) and insulin receptor substrate 1 (IRS1) were two of diabetogenic genes associated with the developing of GDM. Melatonin is a circulating hormone secreted mainly from the pineal gland11, and acts mostly through G-protein-coupled plasma membrane receptors12. MTNR1B, located on human chromosome 11q21–2213, is a member of the G-protein-coupled receptor family, and one of the functional and high-affinity melatonin membrane receptors14. MTNR1B is expressed in human and rodent pancreatic islets. Studies have shown that MTNR1B is a novel candidate gene for T2D15. Variants rs10830963 (C/G) and rs1387153 (C/T) in MTNR1B have been shown with an increased risk of developing T2D16. They may have a possible link in the etiology and pathophysiology of GDM. IRS1 gene, located on chromosome 2q3617, is expressed in insulin-sensitive tissues. It is an endogenous substrate of the insulin receptor18, and plays a crucial role in the insulin signaling pathway. The IRS1 gene variant rs1801278, a nucleotide T/C substitution in codon 972 (Gly972Arg), has been identified to be associated with increased risk of T2D and GDM19.

Although numerous studies have demonstrated the association between genetic polymorphisms and the developing of GDM, inconsistent results were presented for each polymorphism among study populations. The purpose of this meta-analysis is to summarize the existing evidence on the prevalence of the genetic polymorphisms in patients diagnosed with GDM.

Results

Study selection and characteristics

The electronic database search identified 107 references. After applying the inclusion criteria, 10 articles including 3428 GDM cases and 4637 healthy controls were ultimately included in the systematic review and meta-analysis. The study selection process is shown in Figure 1.

Figure 1

Flow chart of literature screening.

All the 10 reports, one in Chinese20 and nine in English212223242526272829, included cases and controls from 7 countries concerning 3 genetic variants in 2 genes (MTNR1B and IRS1). The detailed characteristics of the studies included were shown in Table 1. The distributions of genotypes and alleles in the individual studies were presented in Table 2.

Table 1

Main characteristics of studies included in this meta-analysis

			Mean age	Total		Definition		BMI
First author's Last name	Year	Country	Case/Control	Cases Controls		Cases	Controls	Case/Control	Genotype method
MTNR1B
Deng	2011	China	31.8/29.7	87	91	OGTT confirmed	Normal glucose tolerant	23.6/21.5	Sequencing
Kim	2011	Korea	33.1/32.2	928	990	OGTT confirmed	Normal glucose tolerant	23.32/21.40	TaqMan
Wang	2011	China	32/30	725	1039	OGTT confirmed	Normal glucose tolerant	21.72/21.48	TaqMan
Vlassi	2012	Greece	35.4/31.3	77	98	ADA criteria	Normal glucose tolerant	25.83/26.76	PCR-RFLP
Li	2013	China	32.4/31.9	350	480	OGTT and IADPSG	Normal glucose tolerant	25.34/24.69	PCR-RFLP
IRS1
Shaat	2005	Sweden	32.2/30.5	587	1189	EASD-DPSG criteria	Normal glucose tolerant	24.5/23.1	TaqMan
Fallucca	2006	Italy	34.1/32.7	309	277	OGTT confirmed	Normal glucose tolerant	23.4/22.8	PCR-RFLP
Tok	2006	Turkey	-	62	100	NDDG criteria	Normal glucose tolerant	25.1/24.7	PCR-RFLP
Pappa	2011	Greece	32.5/26.6	148	107	Fourth IWCGDM criteria	Normal glucose tolerant	26/24	PCR-RFLP
Alharbi	2014	Saudi	32.4/31.3	200	300	OGTT confirmed	Normal glucose tolerant	34.4/33.3	PCR-RFLP

OGTT, the oral glucose tolerance test; ADA, the American Diabetes Association; IADPSG, the International Association of Diabetes in Pregnancy Study Groups;

EASD-DPSG, the European Association for the Study of Diabetes-Diabetic Pregnancy Study Group; IWCGDM, International Workshop-Conferences on Gestational Diabetes Mellitus.

Table 2

Distribution of genotypes and alleles in the individual studies

First author's last name	Cases					Controls
MTNR1B rs10830963 (C/G)	GG	GC	CC	G	C	GG	GC	CC	G	C
Deng	26	38	23	90	84	15	45	31	75	107
Kim	256	435	217	947	869	203	469	294	875	1057
Wang	137	364	199	638	762	191	509	329	891	1167
Vlassi	16	31	30	63	91	12	30	56	54	142
Li	79	158	113	316	384	75	233	172	383	577
MTNR1B rs1387153 (C/T)	TT	TC	CC	T	C	TT	TC	CC	T	C
Kim	241	433	235	915	903	204	455	313	863	1081
Vlassi	12	26	39	50	104	11	35	52	57	139
IRS1 rs1801278 (C/T)	TT	TC	CC	T	C	TT	TC	CC	T	C
Shaat	4	49	534	57	1117	0	111	1078	111	2267
Fallucca	4	34	271	42	576	0	22	255	22	532
Tok	0	9	53	9	115	0	11	89	11	189
Pappa	17	73	58	107	189	7	40	60	54	160
Alharbi	1	10	189	12	388	0	5	295	5	595

Association between MTNR1B rs10830963 variant and GDM

For MTNR1B rs10830963 variant, five studies, containing 2122 GDM cases and 2664 healthy controls, were included. The results of each allele and genetic models in this meta-analysis were listed in Table S1. The heterogeneity between studies was assessed, and the fixed-effects model and the random-effects model were employed for calculating the pooled odds ratio (OR). Overall, this meta-analysis showed that the frequency of MTNR1B rs10830963 G allele is higher in GDM patients than that in the healthy controls (48.4% vs. 42.3%), and demonstrated a statistically significant positive association between the risk factor G allele carriers and GDM susceptibility [OR = 1.24, 95% confidence interval (CI) = 1.14–1.35, P<0.00001)], as shown in Figure 2. This significant association was found in other genetic models as well in a fixed-effects model (GG vs. CC: OR = 1.53, 95% CI = 1.30–1.80, P<0.00001; GG+GC vs. CC: OR = 1.30, 95% CI = 1.14–1.47, P<0.0001; GG vs. GC+CC: OR = 1.37, 95% CI = 1.19–1.57, P<0.0001). As shown in Figure 3.

Figure 2

Forest plot on the association for allelic model (G vs. C) of MTNR1B rs10830963 and risk of GDM in a fixed-effects model.

Figure 3

Forest plot on the association for the dominant model (GG+GC vs. CC) of MTNR1B rs10830963 and GDM in a fixed-effects model.

Association between MTNR1B rs1387153 variant and GDM

Two studies including 986 cases and 1070 controls focused on the relationship between rs1387153 variant and GDM. The frequency of the T allele was higher in GDM cases than that in controls (48.9% vs. 43.0%). As shown in Figure 4, our result demonstrated that the T allele had a positive relationship between rs1387153 variant and GDM risk (OR = 1.26, 95% CI = 1.12–1.43, P = 0.0002). Various genetic models also demonstrated that the T allele was associated with an increased risk of GDM (TT vs. CC: OR = 1.56, 95% CI = 1.23–1.99, P = 0.0003; TT+TC vs. CC: OR = 1.33, 95% CI = 1.10–1.61, P = 0.003; TT vs. TC+CC: OR = 1.36, 95% CI = 1.11–1.68, P = 0.003) (Figure 5). No significant heterogeneity was found between these two studies (I2 = 0%).

Figure 4

Forest plot on the association for allelic model (T vs. C) of MTNR1B rs1387153 and GDM risk in a fixed-effects model.

Figure 5

Forest plot on the association for the dominant model (TT+TC vs. CC) of MTNR1B rs1387153 and GDM in a fixed-effects model.

Association between IRS1 rs1801278 variant and GDM

The association between rs1801278 and GDM has been examined in five studies, including 1306 GDM cases and 1973 controls. Our meta-analysis of these studies showed that the frequency of the T allele of rs1801278 was higher in GDM than that in controls (8.7% vs. 5.1%), and indicated a significant association with an increased risk of GDM (OR = 1.42, 95% CI = 1.15–1.75, P = 0.001) (Figure 6). As shown in Figure 7 and Figure S1, the dominant model and recessive model were also significant with GDM susceptibility, respectively (TT+TC vs. CC: OR = 1.54, 95% CI = 1.02–2.32, P = 0.04; TT vs. TC+CC: OR = 3.01, 95% CI = 1.38–6.56, P = 0.006).

Figure 6

Forest plot on the association for allelic model (T vs. C) of IRS1 rs1801278 and GDM risk in a fixed-effects model.

Figure 7

Forest plot on the association for the dominant model (TT+TC vs. CC) of IRS1 rs1801278 and GDM in a random-effects model.

Sensitivity analysis and publication bias

The influence of each study on the overall meta-analysis estimate was assessed by eliminating one study at a time, respectively. The OR was not significantly influenced by omitting any single study.

Begger's funnel plot was used to identify individual studies in relation to their respective standard deviation, as shown in Figure 8 and Figure S2, which revealed no evidence of asymmetry. Egger's test was employed to provide further statistical evidence, similarly, no significant publication bias was found for all these three polymorphisms (P = 0.263 for MTNR1B rs10830963, P = 0.378 for MTNR1B rs1387153, P = 0.149 for IRS1 rs1801278). Thus, there does not appear to be a publication bias risk in the meta-analysis.

Figure 8

Funnel plot on the association for allelic model (G vs. C) of MTNR1B rs10830963 and risk of GDM in a fixed-effects model (P = 0.263 for Egger's test).

Discussion

GDM is usually recognized as a temporary form of diabetes that occurs during pregnancy, and is associated with an increased risk of complications during pregnancy and birth30. Women with GDM are at a high risk of developing T2D later in life31, and the risk of developing type 1 diabetes (T1D) is also increased32. Moreover, GDM increases the risk of macrosomia and caesarean delivery33. Therefore, there is an urgent need to study the pathogenesis and establish diagnosis criteria for GDM.

Many studies have shown that gene polymorphisms could provide insight into underlying pathogenetic mechanisms and the relationship between candidate genes and complex diseases. Functional studies showed that those diabetogenic genes took part in many steps of the process of developing GDM. For instance, impaired β-cell function (MTNR1B), insulin resistance (IRS1), and abnormal utilization of glucose. In our meta-analysis, we found that the frequency of G allele in rs10830963, and T alleles in both rs1387153 and rs1801278 respectively, were higher in GDM cases than that in healthy controls, demonstrating strong statistical association with an increased risk of GDM.

GDM is associated with both insulin resistance and an impaired insulin secretion34. GDM could develop when a genetic predisposition of pancreatic islet β-cell impairment is unmasked by an increased insulin resistance during pregnancy35. MTNR1B variants are related to insulin secretion and impaired β-cell function. Liao et al. have showed that MTNR1B is likely to be involved in the regulation of glucose homeostasis during pregnancy36. MTNR1B rs10830963 has been shown to influence the fasting plasma glucose (FPG)37 and to be associated with T2D38; rs1387153 has been reported to be associated with an increased FPG and a higher risk of T2D39. In our study, we found that the SNPs rs1387153 and rs10830963 in MTNR1B occur more frequently in women with GDM than in normal pregnant women, supporting a potential association of these polymorphisms with an increased risk of developing GDM. This may due to the observation that MTNR1B down-regulates GCK expression and glucose-stimulated insulin secretion by lowering intracellular cAMP level40. An increased expression of MTNR1B on β-cells leads to impaired insulin secretion. Previous studies have shown that the G allele of rs10830963 polymorphism in the MTNR1B exhibits a higher expression of this melatonin receptor on the β-cell as compared with that of the C allele41.

IRS1, a substrate of the insulin receptor tyrosine kinase and a participant in insulin signaling42, is related to insulin resistance. It plays a crucial role in the signal transduction pathway43. Epidemiological studies confirmed that the prevalence of GDM is in direct proportion to the prevalence of T2D. A meta-analysis conducted by Jellema et al. has shown that carriers of the R972 variant of the IRS1 gene are at a 25% increased risk of having T2D compared with non-carriers44. While Morini et al. investigating 32 studies found that the relatively infrequent R972 variant was not significantly associated with T2D45. Our result showed a significant association between IRS1 rs1801278 polymorphism and GDM risk. IRS1 protein is expressed in many insulin-sensitive tissues, and its tyrosine phosphorylation can elicit the downstream effects of insulin, such as activation of phosphatidylinositol 3-kinase (PI3K) and translocation of glucose transporter 446. Previous studies have shown that the IRS1 G972R polymorphism, which reduces insulin content and impairs insulin secretion in isolated human islets, is associated with impaired β-cell function29. Evidence suggests that susceptibility to GDM has a genetic component, family studies indicate that GDM aggregates within families and is associated with a history of T2D47.

Several limitations were presented in this meta-analysis. Firstly, the number of studies included was relatively small. For MTNR1B rs1387153 variant, only two studies were included. Secondly, studies were mainly focused on Asian populations or Caucasian populations, other populations should also be included. Thirdly, these polymorphisms may interact with other risk factors which should be considered. Fourthly, the selected studies could be more subject to bias and artifact than prospective studies.

In conclusion, our meta-analysis demonstrated that genetic polymorphisms rs10830963 and rs1387153 in MTNR1B and rs1801278 in IRS1 were associated with an increased risk of developing GDM. However, further studies with large sample sizes and accounting for the interaction of genetic and environmental risk factors are needed to understand associations between the genetic polymorphisms and risk of GDM.

Methods

Identification and eligibility of relevant studies

A comprehensive literature search was conducted for relevant articles published between January 2005 and March 2014 using the electronic database of PubMed, Medline, Embase, Wanfang and CNKI (China National Knowledge Infrastructure). We retrieved the related articles using the following terms: “gestational diabetes mellitus”, “melatonin receptor 1B or MTNR 1B”, “insulin receptor substrate 1 or IRS1”, “polymorphisms or variants” as well as their combinations. The corresponding Chinese terms were used in the Chinese library. References of retrieved articles were searched with no language restrictions. The search was focused on studies that had been conducted in humans. Only full-text articles and the most recent studies were included in this meta-analysis.

Criteria for inclusion

The inclusion criteria were as follows: 1) the paper should be case-control or cohort studies; 2) identification of gestational diabetes mellitus cases was confirmed pathologically and the controls should be non-diabetic; 3) each study included at least one of the three polymorphisms, rs10830963 and rs1387153 in MTNR1B, rs1801278 in IRS1; 4) genotype distribution information and OR with its 95% CI were available; and 5) genotype distribution of control for a certain polymorphism must be in Hardy-Weinberg equilibrium.

Data extraction

Two investigators independently assessed the quality of the included studies according to the descriptions provided by the authors of the included studies. Any disagreement was subsequently resolved by discussion with a third author. The following information was extracted from each article: first author, year of publication, country, ethnicity, mean age, body mass index (BMI), total numbers, definition and genotype distributions in GDM cases and controls.

Statistical analysis

The overall association between genetic polymorphisms and GDM risk was measured by OR and its 95% CI. The Z test was employed to determine the significance of the pooled ORs, and a P value less than 0.05 was considered statistically significant. For rs10830963, the allelic model (G vs. C) and genotype genetic models (co-dominant effects: GG vs. CC; dominant effect: GG+GC vs. CC; and recessive effect: GG vs. GC+CC) were examined; for rs1387153 and rs1801278, the allelic model (T vs. C) and genotype genetic models (co-dominant effects: TT vs. CC; dominant effect: TT+TC vs. CC; and recessive effect: TT vs. TC+CC) was identified. The I2 test was used to assess the proportion of statistical heterogeneity and the Q-statistic test was used to define the degree of heterogeneity. A P-value less than 0.10 for the Q-test and I2 more than 50% was considered significant among the studies. Data were combined using both a fixed-effects model (the inverse variance-weighted method) and a random-effects model (DerSimonian and Laird method)4849. The fixed-effects model is used when the effects are assumed to be homogenous, while the random-effects model is used when they are heterogenous. The evidence of publication bias was assessed by visual funnel plot inspection. Egger's regression test was also conducted to identify study effects (P-value less than 0.10 was considered significant). To evaluate whether our results were influenced by the presence of any individual study, we conducted a sensitivity analysis by systematically removing each study and reassessing the significance of the result. Statistical analyses were conducted in Review Manager (RevMan version 5.2, the Cochrane Collaboration, Oxford, England; available at: http://ims.cochrane.org/revman). All the tests were two-sided.

Author Contributions

Conceived and designed the study: Y.Z., C.M.S., X.Q. and Y.Z.; Performed the experiments: Y.Z., C.M.S., X.Q. and Y.Z.; Statistical analyses and paper writing: Y.Z., C.M.S., X.Q. and Y.Z.