Large scale meta-analyses of fasting plasma glucose raising variants in GCK, GCKR, MTNR1B and G6PC2 and their impacts on type 2 diabetes mellitus risk

Relationship between GCKR gene rs780094 polymorphism and type 2 diabetes with albuminuria

BACKGROUND

Diabetic kidney disease is one of the common complications of type 2 diabetes (T2D). There are no typical symptoms in the early stage, and the disease will progress to moderate and late stage when albuminuria reaches a high level. Treatment is difficult and the prognosis is poor. At present, the pathogenesis of diabetic kidney disease is still unclear, and it is believed that it is associated with genetic and environmental factors.

AIM

To explore the relationship between the glucokinase regulatory protein (GCKR) gene rs780094 polymorphism and T2D with albuminuria.

METHODS

We selected 252 patients (126 males and 126 females) with T2D admitted to our hospital from January 2020 to October 2020, and 66 healthy people (44 females and 22 males). According to the urinary albumin/creatinine ratio, the subjects were divided into group I (control), group II (T2D with normoalbuminuria), group III (T2D with microalbuminuria), and group IV (T2D with macroalbuminuria). Additionly, the subjects were divided into group M (normal group) or group N (albuminuria group) according to whether they developed albuminuria. We detected the GCKR gene rs780094 polymorphism (C/T) of all subjects, and measured the correlation between GCKR gene rs780094 polymorphism (C/T) and T2D with albuminuria.

RESULTS

Gene distribution and genotype distribution among groups I-IV accorded with the Hardy-Weinberg equilibrium. Genotype frequency was significantly different among the four groups (P = 0.048, χ2 = 7.906). T allele frequency in groups II, III, and IV was significantly higher than that in group I. Logistic regression analysis of the risk factors for T2D with albuminuria showed that the CT + TT genotype (odds ratio = 1.710, 95% confidence interval: 1.172-2.493) was a risk factor.

CONCLUSION

CT + TT genotype is a risk factor for T2D with albuminuria. In the future, we can assess the risk of individuals carrying susceptible genes to delay the onset of T2D.

The Association between CDKAL1 Gene rs10946398 Polymorphism and Post-Transplant Diabetes in Kidney Allograft Recipients Treated with Tacrolimus

Post-transplant diabetes mellitus (PTDM) is a common complication that occurs in kidney transplant patients, increasing the risk of infection, cardiovascular disease and loss of graft function. Currently, factors that increase the risk of this complication are being sought, among them polymorphisms in genes that regulate carbohydrate metabolism and influence pancreatic β-cell function. The aim of this study was to evaluate the association of selected polymorphisms of genes affecting carbohydrate metabolism, such as CDKAL1 rs10946398, GCK rs1799884, GCKR rs780094 and DGKB/TMEM195 rs2191349, with the development of post-transplant diabetes in kidney transplant patients. This study included 201 Caucasian patients after kidney transplantation treated with tacrolimus. An association was observed between the CDKAL1 rs10946398 gene polymorphism and PTDM. Among patients with PTDM, there was an increased prevalence of the CC genotype in the PTDM group compared to the group without PTDM. The chance of PTDM in those with the CC genotype was 2.60 times higher compared to those with the AC + AA genotypes (CC vs. AC + AA OR (95% CI): 2.60 (1.02-6.61), p = 0.040). Multivariate logistic regression analysis showed that advanced age and the CC genotype (rare homozygote) of CDKAL1 rs10946398 were risk factors for the development of PTDM at 1 year after transplantation. There was no statistically significant association between GCK rs1799884, GCKR rs780094 or DGKB/TMEM195 rs2191349 polymorphisms and the development of post-transplant diabetes mellitus in kidney transplant patients. The results of this study suggest that the CDKAL1 rs10946398 CC genotype is associated with the increased risk of PTDM development in patients after kidney graft transplantation treated with tacrolimus.

Association of GCK (rs1799884), GCKR (rs780094), and G6PC2 (rs560887) Gene Polymorphisms with Type 2 Diabetes among Malay Ethnics

Background  Type 2 diabetes mellitus (T2DM) is a complex metabolic disorder, and the underlying causes remain unknown and have not been fully elucidated. Several candidate genes have been associated with T2DM in various populations with conflicting results. The variations found in glucokinase ( GCK ), glucokinase regulatory protein ( GCKR ), and glucose-6-phosphatase 2 ( G6PC2 ) genes were not well studied, particularly among Asians. Aims  The main objective of this study was to determine the candidate genetic polymorphisms of GCK (rs1799884), GCKR (rs780094), and G6PC2 (rs560887) genes in T2DM among Malay ethnics. Methods  In this candidate gene association study, a total of 180 T2DM subjects and 180 control subjects were recruited to determine the genotypes using polymerase chain reaction-restriction fragment length polymorphism and Taqman probe assay methods. Genotype and allele frequencies in case and control samples were compared using the chi-squared test to determine a significant difference. Results  The body mass index, fasting blood glucose, hemoglobin A1c, systolic and diastolic blood pressure, and total cholesterol were significantly different ( p  < 0.05) between T2DM and control subjects. The genotypic and allelic frequencies of GCK (rs1799884), GCKR (rs780094), and G6PC2 (rs560887) gene polymorphisms were significantly different between T2DM and controls ( p  < 0.05). Conclusion  Hence, rs1799884 of GCK gene and rs780094 of GCKR gene and rs560887 of the G6PC2 gene are possible genetic biomarkers in T2DM development among Malay ethnics in Malaysia.

Decoding type 2 diabetes mellitus genetic risk variants in Pakistani Pashtun ethnic population using the nascent whole exome sequencing and MassARRAY genotyping: A case-control association study

Genome-wide association studies have greatly increased the number of T2DM associated risk variants but most of them have focused on populations of European origin. There is scarcity of such studies in developing countries including Pakistan. High prevalence of T2DM in Pakistani population prompted us to design this study. We have devised a two stage (the discovery stage and validation stage) case-control study in Pashtun ethnic population in which 500 T2DM cases and controls each have been recruited to investigate T2DM genetic risk variants. In discovery stage Whole Exome Sequencing (WES) was used to identify and suggest T2DM pathogenic SNPs, based on SIFT and Polyphen scores; whereas in validation stage the selected variants were confirmed for T2DM association using MassARRAY genotyping and appropriate statistical tests. Results of the study showed the target positive association of rs1801282/PPARG (OR = 1.24, 95%Cl = 1.20-1.46, P = 0.010), rs745975/HNF4A (OR = 1.30, 95%Cl = 1.06-1.38, P = 0.004), rs806052/GLIS3 (OR = 1.32, 95%Cl = 1.07-1.66, P = 0.016), rs8192552/MTNR1B (OR = 1.53, 95%Cl = 0.56-1.95, P = 0.012) and rs1805097/IRS-2 (OR = 1.27, 95%Cl = 1.36-1.92, P = 0.045), with T2DM; whereas rs6415788/GLIS3, rs61788900/NOTCH2, rs61788901/NOTCH2 and rs11810554/NOTCH2 (P>0.05) showed no significant association. Identification of genetic risk factors/variants can be used in defining high risk subjects assessment, and disease prevention.

The rs10830963 Polymorphism of the MTNR1B Gene: Association With Abnormal Glucose, Insulin and C-peptide Kinetics

BACKGROUND

The MTNR1B gene encodes a receptor for melatonin, a hormone regulating biorhythms. Disruptions in biorhythms contribute to the development of type 2 diabetes mellitus (T2DM). Genetic studies suggest that variability in the MTNR1B gene affects T2DM development. Our aim was to compare the distribution of the genetic variant rs10830963 between persons differing in glucose tolerance in a sample of the Czech population (N=1206). We also evaluated possible associations of the polymorphism with insulin sensitivity, beta cell function, with the shape of glucose, insulin and C-peptide trajectories measured 7 times during a 3-hour oral glucose tolerance test (OGTT) and with glucagon response. In a subgroup of 268 volunteers we also evaluated sleep patterns and biorhythm.

RESULTS

13 persons were diagnosed with T2DM, 119 had impaired fasting blood glucose (IFG) and/or impaired glucose tolerance (IGT). 1074 participants showed normal results and formed a control group. A higher frequency of minor allele G was found in the IFG/IGT group in comparison with controls. The GG constellation was present in 23% of diabetics, in 17% of IFG/IGT probands and in 11% of controls. Compared to CC and CG genotypes, GG homozygotes showed higher stimulated glycemia levels during the OGTT. Homozygous as well as heterozygous carriers of the G allele showed lower very early phase of insulin and C-peptide secretion with unchanged insulin sensitivity. These differences remained significant after excluding diabetics and the IFG/IGT group from the analysis. No associations of the genotype with the shape of OGTT-based trajectories, with glucagon or with chronobiological patterns were observed. However, the shape of the trajectories differed significantly between men and women.

CONCLUSION

In a representative sample of the Czech population, the G allele of the rs10830963 polymorphism is associated with impaired early phase of beta cell function, and this is evident even in healthy individuals.

Membrane Melatonin Receptors Activated Cell Signaling in Physiology and Disease

The pineal hormone melatonin has attracted great scientific interest since its discovery in 1958. Despite the enormous number of basic and clinical studies the exact role of melatonin in respect to human physiology remains elusive. In humans, two high-affinity receptors for melatonin, MT1 and MT2, belonging to the family of G protein-coupled receptors (GPCRs) have been cloned and identified. The two receptor types activate Gi proteins and MT2 couples additionally to Gq proteins to modulate intracellular events. The individual effects of MT1 and MT2 receptor activation in a variety of cells are complemented by their ability to form homo- and heterodimers, the functional relevance of which is yet to be confirmed. Recently, several melatonin receptor genetic polymorphisms were discovered and implicated in pathology-for instance in type 2 diabetes, autoimmune disease, and cancer. The circadian patterns of melatonin secretion, its pleiotropic effects depending on cell type and condition, and the already demonstrated cross-talks of melatonin receptors with other signal transduction pathways further contribute to the perplexity of research on the role of the pineal hormone in humans. In this review we try to summarize the current knowledge on the membrane melatonin receptor activated cell signaling in physiology and pathology and their relevance to certain disease conditions including cancer.

Human and molecular genetics shed lights on fatty liver disease and diabetes conundrum

The causal role of abdominal overweight/obesity, insulin resistance and type 2 diabetes (T2D) on the risk of fatty liver disease (FLD) has robustly been proven. A consensus of experts has recently proposed the novel definition of 'metabolic dysfunction-associated fatty liver disease, MAFLD' instead of 'nonalcoholic fatty liver disease, NAFLD', emphasizing the central role of dysmetabolism in the disease pathogenesis. Conversely, a direct and independent contribution of FLD per se on risk of developing T2D is still a controversial topic. When dealing with FLD as a potential risk factor for T2D, it is straightforward to think of hepatic insulin resistance as the most relevant underlying mechanism. Emerging evidence supports genetic determinants of FLD (eg PNPLA3, TM6SF2, MBOAT7, GCKR, HSD17B13) as determinants of insulin resistance and T2D. However, recent studies highlighted that the key molecular mechanism of dysmetabolism is not fat accumulation per se but the degree of hepatic fibrosis (excess liver fat content-lipotoxicity), leading to reduced insulin clearance, insulin resistance and T2D. A consequence of these findings is that drugs that will ameliorate liver fat accumulation and fibrosis in principle may also exert a beneficial effect on insulin resistance and risk of T2D in individuals with FLD. Finally, initial findings show that these genetic factors might be directly implicated in modulating pancreatic beta-cell function, although future studies are needed to fully understand this relationship.

SNP-Based Genetic Risk Score Modeling Suggests No Increased Genetic Susceptibility of the Roma Population to Type 2 Diabetes Mellitus

BACKGROUND

In a previous survey, an elevated fasting glucose level (FG) and/or known type 2 diabetes mellitus (T2DM) were significantly more frequent in the Roma population than in the Hungarian general population. We assessed whether the distribution of 16 single nucleotide polymorphisms (SNPs) with unequivocal effects on the development of T2DM contributes to this higher prevalence.

METHODS

Genetic risk scores, unweighted (GRS) and weighted (wGRS), were computed and compared between the study populations. Associations between GRSs and FG levels and T2DM status were investigated in separate and combined study populations.

RESULTS

The Hungarian general population carried a greater genetic risk for the development of T2DM (GRS_General = 15.38 ± 2.70 vs. GRS_Roma = 14.80 ± 2.68, p < 0.001; wGRS_General = 1.41 ± 0.32 vs. wGRS_Roma = 1.36 ± 0.31, p < 0.001). In the combined population models, GRSs and wGRSs showed significant associations with elevated FG (p < 0.001) and T2DM (p < 0.001) after adjusting for ethnicity, age, sex, body mass index (BMI), high-density Lipoprotein Cholesterol (HDL-C), and triglyceride (TG). In these models, the effect of ethnicity was relatively strong on both outcomes (FG levels: βethnicity = 0.918, p < 0.001; T2DM status: OR_ethnicity = 2.484, p < 0.001).

CONCLUSIONS

The higher prevalence of elevated FG and/or T2DM among Roma does not seem to be directly linked to their increased genetic load but rather to their environmental/cultural attributes. Interventions targeting T2DM prevention among Roma should focus on harmful environmental exposures related to their unhealthy lifestyle.

New insights into the function of melatonin and its role in metabolic disturbances

INTRODUCTION

Melatonin is a pineal hormone that has acquired several unique modes of regulating the physiological effects in mammals due to its characteristic phylogenetic history. While melatonin exhibits immediate nocturnal effects, it also has next-day prospective effects that take place in the absence of this hormone. Besides that, the daily repetition and the annual variation in the duration of its synthesis determine its circadian and seasonal effects that characterize melatonin as a chronobiotic, a molecule that encodes time to the internal environment. Additionally, it presents transgenerational effects that are important for fetal programming, leading to a balanced energy metabolism in the adult life.

AREAS COVERED

Physiology, pathophysiology and therapeutic value of melatonin in metabolism and metabolic disorders.

EXPERT OPINION

The typical mechanisms of action of melatonin (immediate, prospective, chronobiotic and transgenerational) should be considered to adequately understand its physiological effects on the regulation of metabolism in humans and, as a result, to understand the metabolic pathophysiological consequences caused by its synthesis and/or signaling disturbances. That points to the importance of a broader understanding of melatonin actions, besides the classical endocrinological point of view, that would allow the clinician/research to proper interpret its role in health maintenance.

Genome-Wide Association Study of Serum Fructosamine and Glycated Albumin in Adults Without Diagnosed Diabetes: Results From the Atherosclerosis Risk in Communities Study

Fructosamine and glycated albumin are potentially useful alternatives to hemoglobin A1c (HbA1c) as diabetes biomarkers. The genetic determinants of fructosamine and glycated albumin, however, are unknown. We performed genome-wide association studies of fructosamine and glycated albumin among 2,104 black and 7,647 white participants without diabetes in the Atherosclerosis Risk in Communities (ARIC) Study and replicated findings in the Coronary Artery Risk Development in Young Adults (CARDIA) study. Among whites, rs34459162, a novel missense single nucleotide polymorphism (SNP) in RCN3, was associated with fructosamine (P = 5.3 × 10-9) and rs1260236, a known diabetes-related missense mutation in GCKR, was associated with percent glycated albumin (P = 5.9 × 10-9) and replicated in CARDIA. We also found two novel associations among blacks: an intergenic SNP, rs2438321, associated with fructosamine (P = 6.2 × 10-9), and an intronic variant in PRKCA, rs59443763, associated with percent glycated albumin (P = 4.1 × 10-9), but these results did not replicate. Few established fasting glucose or HbA1c SNPs were also associated with fructosamine or glycated albumin. Overall, we found genetic variants associated with the glycemic information captured by fructosamine and glycated albumin as well as with their nonglycemic component. This highlights the importance of examining the genetics of hyperglycemia biomarkers to understand the information they capture, including potential glucose-independent factors.

Gene-gene interactions lead to higher risk for development of type 2 diabetes in a Chinese Han population: a prospective nested case-control study

Background

The purpose of this study was to evaluate the effect of single-nucleotide polymorphisms (SNPs) of the GCKR and G6PC2 genes on risk for type 2 diabetes and the SNP-SNP and haplotype-based interactions between these genes.

Methods

Subjects of this nested case-control study were selected from a prospective cohort residing in the rural area of Luoyang city in China. Cases (n = 538) were individually matched with controls. Six SNPs in the GCKR and G6PC2 genes were selected and genotyped using an SNPscan™ kit. Stratified Cox proportional hazards regression models were used to generate odds ratios (ORs) and 95% confidence intervals (CI) for different genotype models for the risk of T2DM. Generalized multifactor dimensionality reduction (GMDR) was used to analyze the interactions between two genes with among six SNPs. The linkage disequilibrium (LD) analysis and the haplotype analysis were carried out by SHEsis online.

Results

We found that the C allele of rs780094 was associated with increased risk for T2DM in Han Chinese population. However, the rs492594-C allele in G6PC2 was associated with a decreased risk of T2DM. We also found a significant SNP-SNP interaction between rs2293572 and rs492594, and the CCCCGC and CGCCCA haplotypes significantly increased the risk of T2DM, however, the CCCCCA haplotype had lower susceptibility to T2DM.

Conclusion

The results suggest that the GCKR and G6PC2 genes may contribute to the risk of T2DM independently and/or in an interactive manner in the Han Chinese population.

Electronic supplementary material

The online version of this article (10.1186/s12944-018-0813-6) contains supplementary material, which is available to authorized users.

Genetic determinants of glycated hemoglobin levels in the Greenlandic Inuit population

We previously showed that a common genetic variant leads to a remarkably increased risk of type 2 diabetes (T2D) in the small and historically isolated Greenlandic population. Motivated by this, we aimed at discovering novel genetic determinants for glycated hemoglobin (HbA1C) and at estimating the effect of known HbA1C-associated loci in the Greenlandic population. We analyzed genotype data from 4049 Greenlanders generated using the Illumina Cardio-Metabochip. We performed the discovery association analysis by an additive linear mixed model. To estimate the effect of known HbA1C-associated loci, we modeled the effect in the European and Inuit ancestry proportions of the Greenlandic genome (EAPGG and IAPGG, respectively). After correcting for multiple testing, we found no novel significant associations. When we investigated loci known to associate with HbA1C levels, we found that the lead variant in the GCK locus associated significantly with HbA1C levels in the IAPGG ([Formula: see text]). Furthermore, for 10 of 15 known HbA1C loci, the effects in IAPGG were similar to the previously reported effects. Interestingly, the ANK1 locus showed a statistically significant ancestral population differential effect, with opposing directions of effect in the two ancestral populations. In conclusion, we found only 1 of the 15 known HbA1C loci to be significantly associated with HbA1C levels in the IAPGG and that two-thirds of the loci showed similar effects in Inuit as previously found in European and East Asian populations. Our results shed light on the genetic effects across ethnicities.

Association of melatonin receptor 1 B gene (rs10830963 and rs9192552) polymorphısm with adolescent obesity and related comorbidities in Turkey

Objective

To examine the role of rs10830963 and rs8192552 polymorphisms in melatonin receptor 1 B (MTNR1B) gene on the development of obesity and related comorbidities among adolescents in South-Eastern Turkey.

Methods

The present study included 200 unrelated adolescents (100 obese, 100 normal weight). The rs8192552 and rs10830963 polymorphisms in the MTNR1B gene were genotyped using a PCR SNaPshot assay.

Results

No statistically significant association was observed between MTNR1B gene rs8192552/rs10830963 polymorphisms and adolescent obesity. In adolescents with an rs8192552 E allele, homeostasis model assessment for insulin resistance (IR) level was lower and IR was less common. In morbidly obese adolescents with an rs8192552 E allele, total cholesterol level was lower. In obese adolescents with metabolic syndrome, plasma fasting glucose level was higher in rs10830963G allele carriers. In obese girls, body weight was lower in those with a rs10830963 C allele, whereas in obese boys, body weight and waist circumference were higher in those with a rs10830963 C allele.

Conclusions

The MTNR1B gene was not confirmed as an obesity susceptibility gene in adolescents. However, an association between the MTNR1B gene and IR/hypercholesterolemia/metabolic syndrome was observed in obese adolescents. A sex-specific effect on obesity was also identified.

Association of melatonin &MTNR1B variants with type 2 diabetes in Gujarat population

AIM/HYPOTHESIS

Melatonin is a circadian rhythm regulator and any imbalance in its levels can be related to various metabolic disorders. Melatonin and the genetic variants of Melatonin Receptor 1B (MTNR1B) are reported to be associated with Type 2 Diabetes (T2D) susceptibility. The aim of the present study was to investigate i) plasma melatonin levels ii) Single Nucleotide Polymorphisms (SNPs) of MTNR1B and iii) Genotype-phenotype correlation analysis in T2D patients.

METHODS

Plasma and PBMCs were separated from venous blood of 478 diabetes patients and 502 controls. Genomic DNA was isolated from PBMCs. PCR-RFLP was used for genotyping. Melatonin was estimated from plasma samples by ELISA.

RESULTS

Our study suggests: i) decreased plasma melatonin levels in T2D patients and, ii) association of MTNR1B rs10830963 GG genotype with increased Fasting Blood Glucose (FBG).

CONCLUSION

It can be concluded that reduced titer of melatonin along with altered FBG due to MTNR1B genetic variant could act as a potent risk factor towards T2D in Gujarat population.

Association Between a Melatonin Receptor 1B Genetic Polymorphism and Its Protein Expression in Gestational Diabetes Mellitus

AIMS

This study was conducted to investigate the relationship between a genetic polymorphism and the expression of melatonin receptor 1B (MTNR1B) in the placenta of Han Chinese women with gestational diabetes mellitus (GDM).

METHODS

In this study, 215 patients with GDM and 243 healthy controls were genotyped using direct sequencing for the MTNR1B single-nucleotide polymorphism rs10830963. The expression of MTNR1B in placenta was detected by immunohistochemistry and Western blotting. The association of rs10830963 with the expression of MTNR1B, plasma glucose, and insulin levels as well as blood lipid levels was investigated.

RESULTS

The genotype and allele frequencies of rs10830963 were significantly different between women with GDM and controls (P < .05). Fasting blood glucose, fasting insulin, and homeostasis model assessment for insulin resistance in women with GDM with the GG and GC genotypes were significantly higher than those with the CC genotype (P < .05). The expression level of MTNR1B in placenta was significantly higher in the GDM group than in the control group (P < .05). The expression of MTNR1B was significantly higher in all participants with the GG and GC genotypes (1.31 [0.74]) than in pregnant women with the CC genotype (0.92 [0.52], P < .05).

CONCLUSIONS

The genetic polymorphism rs10830963 in MTNR1B and its protein expression levels in placenta are associated with an increased risk of developing GDM. Furthermore, rs10830963 may tag a molecular mechanism leading to insulin resistance in Han Chinese women with GDM.

Assessing Rare Variation in Complex Traits

While genome-wide association studies have been very successful in identifying associations of common genetic variants with many different traits, the rarer frequency spectrum of the genome has not yet been comprehensively explored. Technological developments increasingly lift restrictions to access rare genetic variation. Dense reference panels enable improved genotype imputation for rarer variants in studies using DNA microarrays. Moreover, the decreasing cost of next generation sequencing makes whole exome and genome sequencing increasingly affordable for large samples. Large-scale efforts based on sequencing, such as ExAC, 100,000 Genomes, and TopMed, are likely to significantly advance this field.The main challenge in evaluating complex trait associations of rare variants is statistical power. The choice of population should be considered carefully because allele frequencies and linkage disequilibrium structure differ between populations. Genetically isolated populations can have favorable genomic characteristics for the study of rare variants.One strategy to increase power is to assess the combined effect of multiple rare variants within a region, known as aggregate testing. A  range of methods have been developed for this. Model performance depends on the genetic architecture of the region of interest.

Transethnic insight into the genetics of glycaemic traits: fine-mapping results from the Population Architecture using Genomics and Epidemiology (PAGE) consortium

AIMS/HYPOTHESIS

Elevated levels of fasting glucose and fasting insulin in non-diabetic individuals are markers of dysregulation of glucose metabolism and are strong risk factors for type 2 diabetes. Genome-wide association studies have discovered over 50 SNPs associated with these traits. Most of these loci were discovered in European populations and have not been tested in a well-powered multi-ethnic study. We hypothesised that a large, ancestrally diverse, fine-mapping genetic study of glycaemic traits would identify novel and population-specific associations that were previously undetectable by European-centric studies.

METHODS

A multiethnic study of up to 26,760 unrelated individuals without diabetes, of predominantly Hispanic/Latino and African ancestries, were genotyped using the Metabochip. Transethnic meta-analysis of racial/ethnic-specific linear regression analyses were performed for fasting glucose and fasting insulin. We attempted to replicate 39 fasting glucose and 17 fasting insulin loci. Genetic fine-mapping was performed through sequential conditional analyses in 15 regions that included both the initially reported SNP association(s) and denser coverage of SNP markers. In addition, Metabochip-wide analyses were performed to discover novel fasting glucose and fasting insulin loci. The most significant SNP associations were further examined using bioinformatic functional annotation.

RESULTS

Previously reported SNP associations were significantly replicated (p ≤ 0.05) in 31/39 fasting glucose loci and 14/17 fasting insulin loci. Eleven glycaemic trait loci were refined to a smaller list of potentially causal variants through transethnic meta-analysis. Stepwise conditional analysis identified two loci with independent secondary signals (G6PC2-rs477224 and GCK-rs2908290), which had not previously been reported. Population-specific conditional analyses identified an independent signal in G6PC2 tagged by the rare variant rs77719485 in African ancestry. Further Metabochip-wide analysis uncovered one novel fasting insulin locus at SLC17A2-rs75862513.

CONCLUSIONS/INTERPRETATION

These findings suggest that while glycaemic trait loci often have generalisable effects across the studied populations, transethnic genetic studies help to prioritise likely functional SNPs, identify novel associations that may be population-specific and in turn have the potential to influence screening efforts or therapeutic discoveries.

DATA AVAILABILITY

The summary statistics from each of the ancestry-specific and transethnic (combined ancestry) results can be found under the PAGE study on dbGaP here: https://www.ncbi.nlm.nih.gov/projects/gap/cgi-bin/study.cgi?study_id=phs000356.v1.p1.

Meta-analyses of the association of G6PC2 allele variants with elevated fasting glucose and type 2 diabetes

Objective

To collectively evaluate the association of glucose-6-phosphatase catalytic unit 2 (G6PC2) allele variants with elevated fasting glucose (FG) and type 2 diabetes (T2D).

Design

Meta-analysis

Data sources

PubMed, Web of Knowledge and Embase databases.

Study selection

Full text articles of studies that identified an association of G6PC2 with T2D and elevated FG.

Patient involvement

There was no T2D patient involvement in the analyses on the association of FG with G6PC2, there were T2D patients and non-diabetes patient involvement in the analyses on the association of T2D with G6PC2.

Statistical analysis

Random-effects meta-analyses were used to calculate the pool effect sizes. I² metric and H² tests were used to calculate the heterogeneity. Begg's funnel plot and Egger’s linear regression test were done to assess publication bias.

Results

Of the 423 studies identified, 21 were eligible and included. Data on three loci (rs560887, rs16856187 and rs573225) were available. The G allele at rs560887 in three ethnicities, the C allele at rs16856187 and the A allele at rs573225 all had a positive association with elevated FG. Per increment of G allele at rs560887 and A allele at rs573225 resulted in a FG 0.070 mmol/l and 0.075 mmol/l higher (ß (95% CI) = 0.070 (0.060, 0.079), p = 4.635e-50 and 0.075 (0.065, 0.085), p = 5.856e-48, respectively). With regard to the relationship of rs16856187 and FG, an increase of 0.152 (95% CI: 0.034–0.270; p = 0.011) and 0.317 (95% CI: 0.193–0.442, p = 6.046e-07) was found in the standardized mean difference (SMD) of FG for the AC and CC genotypes, respectively, when compared with the AA reference genotype. However, the G-allele of rs560887 in Caucasians under the additive model and the C-allele of rs16856187 under the allele and dominant models were associated with a decreased risk of T2D (OR (95% CI) = 0.964 (0.947, 0.981), p = 0.570e-4; OR (95% CI) = 0.892 (0.832, 0.956), p = 0.001; and OR (95% CI) = 0.923(0.892, 0.955), p = 5.301e-6, respectively).

Conclusions

Our meta-analyses demonstrate that all three allele variants of G6PC2 (rs560887, rs16856187 and rs573225) are associated with elevated FG, with two variants (rs560887 in the Caucasians subgroup and rs16856187 under the allele and dominant model) being associated with T2D as well. Further studies utilizing larger sample sizes and different ethnic populations are needed to extend and confirm these findings.

MTNR1A and MTNR1B gene polymorphisms in women with gestational diabetes

Gestational diabetes mellitus (GDM) is glucose intolerance detected during pregnancy. The MTNR1B gene is the genetic locus associated with type 2 diabetes, that may affect insulin secretion and pancreatic glucose sensing. In this study, we examined the association between MTNR1A (rs2119882) and MTNR1B (rs10830963, rs4753426) gene polymorphisms and the risk of GDM. According to the results of their oral glucose tolerance test (OGTT), the women were divided into two groups: 204 pregnant women with GDM and 207 pregnant women with normal glucose tolerance (NGT). There were no statistically significant differences in the distribution of MTNR1A rs2119882 and MTNR1B rs4753426 genotypes and alleles between women with GDM and healthy pregnant women. With regard to the MTNR1B rs10830963 polymorphism, we observed a statistically significant prevalence of GG and CG genotypes and the G allele among pregnant women with GDM (GG + CG vs CC, OR 1.50, 95% CI 1.02-2.22, p = 0.04; G vs C, OR 1.43, 95% CI 1.07-1.90, p = 0.016). In a multivariate logistic regression analysis, a higher number of MTNR1B rs10830963 G alleles was an independent significant predictor of a higher risk of GDM. The results of our study indicate that MTNR1B rs10830963 polymorphism is associated with GDM susceptibility, and women with a higher number of G alleles have an increased risk of GDM development.

Effects of G6pc2 deletion on body weight and cholesterol in mice

Genome-wide association study (GWAS) data have linked the G6PC2 gene to variations in fasting blood glucose (FBG). G6PC2 encodes an islet-specific glucose-6-phosphatase catalytic subunit that forms a substrate cycle with the beta cell glucose sensor glucokinase. This cycle modulates the glucose sensitivity of insulin secretion and hence FBG. GWAS data have not linked G6PC2 to variations in body weight but we previously reported that female C57BL/6J G6pc2-knockout (KO) mice were lighter than wild-type littermates on both a chow and high-fat diet. The purpose of this study was to compare the effects of G6pc2 deletion on FBG and body weight in both chow-fed and high-fat-fed mice on two other genetic backgrounds. FBG was reduced in G6pc2 KO mice largely independent of gender, genetic background or diet. In contrast, the effect of G6pc2 deletion on body weight was markedly influenced by these variables. Deletion of G6pc2 conferred a marked protection against diet-induced obesity in male mixed genetic background mice, whereas in 129SvEv mice deletion of G6pc2 had no effect on body weight. G6pc2 deletion also reduced plasma cholesterol levels in a manner dependent on gender, genetic background and diet. An association between G6PC2 and plasma cholesterol was also observed in humans through electronic health record-derived phenotype analyses. These observations suggest that the action of G6PC2 on FBG is largely independent of the influences of environment, modifier genes or epigenetic events, whereas the action of G6PC2 on body weight and cholesterol are influenced by unknown variables.

The GCKR Gene Polymorphism rs780094 is a Risk Factor for Gestational Diabetes in a Brazilian Population

BACKGROUND

The glucokinase regulatory protein (GCKR) regulates the activity of the glucokinase (GCK), which plays a key role in glucose homeostasis. Genetic variants in GCK have been associated with diabetes and gestational diabetes (GDM). Due to the relationship between GCKRP and GCK, polymorphisms in GCKR are also candidates for genetic association with GDM. The aim of this study was to evaluate the association between the GCKR rs780094 polymorphism and GDM in a Brazilian population.

METHODS

252 unrelated Euro-Brazilian pregnant women were classified as control (healthy pregnant women, n = 125) and GDM (pregnant women with GDM, n = 127) age-matched groups. Clinical and anthropometric data were obtained from all subjects. The GCKR rs780094 polymorphism was genotyped using fluorescent probes (TaqMan® , code C_2862873_10).

RESULTS

Both groups were in Hardy-Weinberg equilibrium. The GCKR rs780094 polymorphism was associated with GDM in codominant and dominant models (P = 0.022 and P = 0.010, respectively). The minor allele (T) frequency for the control group in the study was 38.4% (95% CI: 32-44%), similar to frequencies reported for other Caucasian populations.

CONCLUSION

Carriers of the C allele of rs780094 were 1.41 (odds ratio, 95% CI, 0.97-2.03) times more likely to develop GDM.

Susceptibility to type 2 diabetes may be modulated by haplotypes in G6PC2, a target of positive selection

BACKGROUND

The endoplasmic reticulum enzyme glucose-6-phosphatase catalyzes the common terminal reaction in the gluconeogenic/glycogenolytic pathways and plays a central role in glucose homeostasis. In most mammals, different G6PC subunits are encoded by three paralogous genes (G6PC, G6PC2, and G6PC3). Mutations in G6PC and G6PC3 are responsible for human mendelian diseases, whereas variants in G6PC2 are associated with fasting glucose (FG) levels.

RESULTS

We analyzed the evolutionary history of G6Pase genes. Results indicated that the three paralogs originated during early vertebrate evolution and that negative selection was the major force shaping diversity at these genes in mammals. Nonetheless, site-wise estimation of evolutionary rates at corresponding sites revealed weak correlations, suggesting that mammalian G6Pases have evolved different structural features over time. We also detected pervasive positive selection at mammalian G6PC2. Most selected residues localize in the C-terminal protein region, where several human variants associated with FG levels also map. This region was re-sequenced in ~560 subjects from Saudi Arabia, 185 of whom suffering from type 2 diabetes (T2D). The frequency of rare missense and nonsense variants was not significantly different in T2D and controls. Association analysis with two common missense variants (V219L and S342C) revealed a weak but significant association for both SNPs when analyses were conditioned on rs560887, previously identified in a GWAS for FG. Two haplotypes were significantly associated with T2D with an opposite effect direction.

CONCLUSIONS

We detected pervasive positive selection at mammalian G6PC2 genes and we suggest that distinct haplotypes at the G6PC2 locus modulate susceptibility to T2D.

Functional Analysis of Mouse G6pc1 Mutations Using a Novel In Situ Assay for Glucose-6-Phosphatase Activity and the Effect of Mutations in Conserved Human G6PC1/G6PC2 Amino Acids on G6PC2 Protein Expression

Elevated fasting blood glucose (FBG) has been associated with increased risk for development of type 2 diabetes. Single nucleotide polymorphisms (SNPs) in G6PC2 are the most important common determinants of variations in FBG in humans. Studies using G6pc2 knockout mice suggest that G6pc2 regulates the glucose sensitivity of insulin secretion. G6PC2 and the related G6PC1 and G6PC3 genes encode glucose-6-phosphatase catalytic subunits. This study describes a functional analysis of 22 non-synonymous G6PC2 SNPs, that alter amino acids that are conserved in human G6PC1, mouse G6pc1 and mouse G6pc2, with the goal of identifying variants that potentially affect G6PC2 activity/expression. Published data suggest strong conservation of catalytically important amino acids between all four proteins and the related G6PC3 isoform. Because human G6PC2 has very low glucose-6-phosphatase activity we used an indirect approach, examining the effect of these SNPs on mouse G6pc1 activity. Using a novel in situ functional assay for glucose-6-phosphatase activity we demonstrate that the amino acid changes associated with the human G6PC2 rs144254880 (Arg79Gln), rs149663725 (Gly114Arg) and rs2232326 (Ser324Pro) SNPs reduce mouse G6pc1 enzyme activity without affecting protein expression. The Arg79Gln variant alters an amino acid mutation of which, in G6PC1, has previously been shown to cause glycogen storage disease type 1a. We also demonstrate that the rs368382511 (Gly8Glu), rs138726309 (His177Tyr), rs2232323 (Tyr207Ser) rs374055555 (Arg293Trp), rs2232326 (Ser324Pro), rs137857125 (Pro313Leu) and rs2232327 (Pro340Leu) SNPs confer decreased G6PC2 protein expression. In summary, these studies identify multiple G6PC2 variants that have the potential to be associated with altered FBG in humans.

Nutrigenetics and Nutrimiromics of the Circadian System: The Time for Human Health

Even though the rhythmic oscillations of life have long been known, the precise molecular mechanisms of the biological clock are only recently being explored. Circadian rhythms are found in virtually all organisms and affect our lives. Thus, it is not surprising that the correct running of this clock is essential for cellular functions and health. The circadian system is composed of an intricate network of genes interwined in an intrincated transcriptional/translational feedback loop. The precise oscillation of this clock is controlled by the circadian genes that, in turn, regulate the circadian oscillations of many cellular pathways. Consequently, variations in these genes have been associated with human diseases and metabolic disorders. From a nutrigenetics point of view, some of these variations modify the individual response to the diet and interact with nutrients to modulate such response. This circadian feedback loop is also epigenetically modulated. Among the epigenetic mechanisms that control circadian rhythms, microRNAs are the least studied ones. In this paper, we review the variants of circadian-related genes associated to human disease and nutritional response and discuss the current knowledge about circadian microRNAs. Accumulated evidence on the genetics and epigenetics of the circadian system points to important implications of chronotherapy in the clinical practice, not only in terms of pharmacotherapy, but also for dietary interventions. However, interventional studies (especially nutritional trials) that include chronotherapy are scarce. Given the importance of chronobiology in human health such studies are warranted in the near future.

Association Between a Glucokinase Regulator Genetic Variant and Metabolic Syndrome in Taiwanese Adolescents

AIMS

Variants of the glucokinase regulator (GCKR) gene are associated with metabolic syndrome (MetS). The present study explored the association between a common variant of this gene and MetS and its related traits in Taiwanese adolescents.

METHODS

The frequency of MetS and its features were compared between subjects (n = 962; 468 male, 494 female) with different genotypes or alleles of the GCKR rs780094 single-nucleotide polymorphism. Logistic regression analysis was carried out to explore the interdependence of MetS and metabolic traits.

RESULTS

Low high-density lipoprotein cholesterol (HDL-C) levels and MetS were more prevalent in subjects with the T compared to the C allele of rs780094 (p = 0.009 and 0.044, respectively). T-genotype carriers also exhibited a higher frequency of low HDL-C levels (p = 0.028) than noncarriers, although MetS frequency was similar between the two groups. After adjusting for confounding factors, the odds ratios for low HDL-C levels and MetS incidence in T-genotype carriers were 1.64 (95% confidence interval [CI]: 1.07-2.53) and 2.79 (95% CI: 1.09-7.11), respectively.

CONCLUSIONS

The GCKR rs780094 polymorphism is associated with low HDL-C levels and MetS incidence in Taiwanese adolescents.

Genes, Genetics, and Environment in Type 2 Diabetes: Implication in Personalized Medicine

Type 2 diabetes (T2D) is a multifactorial anomaly involving 57 genes located on 16 different chromosomes and 136 single nucleotide polymorphisms (SNPs). Ten genes are located on chromosome 1, followed by seven genes on chromosome 11 and six genes on chromosomes 3. Remaining chromosomes harbor two to five genes. Significantly, chromosomes 13, 14, 16, 18, 21, 22, X, and Y do not have any associated diabetogenic gene. Genetic components have their own pathways encompassing insulin secretion, resistance, signaling, and β-cell dysfunction. Environmental factors include epigenetic changes, nutrition, intrauterine surroundings, and obesity. In addition, ethnicity plays a role in conferring susceptibility to T2D. This scenario poses a challenge toward the development of biomarker for quick disease diagnosis or for generating a consensus to delineate different categories of T2D patients. We believe, before prescribing a generic drug, detailed genotypic information with the background of ethnicity and environmental factors may be taken into consideration. This nonconventional approach is envisaged to be more robust in the context of personalized medicine and perhaps would cause lot less burden on the patient ensuring better management of T2D.

Identification and functional characterization of G6PC2 coding variants influencing glycemic traits define an effector transcript at the G6PC2-ABCB11 locus

Genome wide association studies (GWAS) for fasting glucose (FG) and insulin (FI) have identified common variant signals which explain 4.8% and 1.2% of trait variance, respectively. It is hypothesized that low-frequency and rare variants could contribute substantially to unexplained genetic variance. To test this, we analyzed exome-array data from up to 33,231 non-diabetic individuals of European ancestry. We found exome-wide significant (P<5×10-7) evidence for two loci not previously highlighted by common variant GWAS: GLP1R (p.Ala316Thr, minor allele frequency (MAF)=1.5%) influencing FG levels, and URB2 (p.Glu594Val, MAF = 0.1%) influencing FI levels. Coding variant associations can highlight potential effector genes at (non-coding) GWAS signals. At the G6PC2/ABCB11 locus, we identified multiple coding variants in G6PC2 (p.Val219Leu, p.His177Tyr, and p.Tyr207Ser) influencing FG levels, conditionally independent of each other and the non-coding GWAS signal. In vitro assays demonstrate that these associated coding alleles result in reduced protein abundance via proteasomal degradation, establishing G6PC2 as an effector gene at this locus. Reconciliation of single-variant associations and functional effects was only possible when haplotype phase was considered. In contrast to earlier reports suggesting that, paradoxically, glucose-raising alleles at this locus are protective against type 2 diabetes (T2D), the p.Val219Leu G6PC2 variant displayed a modest but directionally consistent association with T2D risk. Coding variant associations for glycemic traits in GWAS signals highlight PCSK1, RREB1, and ZHX3 as likely effector transcripts. These coding variant association signals do not have a major impact on the trait variance explained, but they do provide valuable biological insights.

Understanding how FI and FG levels are regulated is important because their derangement is a feature of T2D. Despite recent success from GWAS in identifying regions of the genome influencing glycemic traits, collectively these loci explain only a small proportion of trait variance. Unlocking the biological mechanisms driving these associations has been challenging because the vast majority of variants map to non-coding sequence, and the genes through which they exert their impact are largely unknown. In the current study, we sought to increase our understanding of the physiological pathways influencing both traits using exome-array genotyping in up to 33,231 non-diabetic individuals to identify coding variants and consequently genes associated with either FG or FI levels. We identified novel association signals for both traits including the receptor for GLP-1 agonists which are a widely used therapy for T2D. Furthermore, we identified coding variants at several GWAS loci which point to the genes underlying these association signals. Importantly, we found that multiple coding variants in G6PC2 result in a loss of protein function and lower fasting glucose levels.

Common variant in the glucokinase regulatory gene rs780094 and risk of nonalcoholic fatty liver disease: a meta-analysis

BACKGROUND AND AIM

Although studies have suggested that rs780094, a common variant in the glucokinase regulatory (GCKR) gene to be associated with type 2 diabetes, obesity, and their related traits, the genetic basis of the association between GCKR rs780094 and nonalcoholic fatty liver disease (NAFLD) is still being examined. This meta-analysis was performed to evaluate the effect strength caused by GCKR rs780094 on NAFLD.

METHODS

We searched Medline, PubMed, Scopus, and Embase for relevant articles published up to April 2014. Data were extracted, and summary estimates of the association between GCKR rs780094 and NAFLD were examined. Heterogeneity and publication bias were also examined.

RESULTS

This meta-analysis incorporated a total of 2091 NAFLD cases and 3003 controls from five studies. Overall, the pooled result indicated that the GCKR rs780094 was significantly associated with increased risk of NAFLD (additive: odds ratio (OR) 1.25, 95% confidence interval (CI) 1.14-1.36, P < 0.00001). Analysis also revealed significant associations with different alternative genetic models for the inheritance: dominant, recessive, and homozygote (OR 1.40, 95%CI 1.23-1.61, P < 0.00001; OR 0.79, 95% CI 0.68-0.91, P = 0.001, and; (OR 1.27, 95% CI 1.10-1.47, P = 0.001, respectively), but not the heterozygote model. Population subgroup analysis demonstrated similar effect size in both Asians and non-Asians (OR 1.27, 95%CI 1.12-1.45, P = 0.0003 and OR 1.22, 95%CI 1.10-1.37, P = 0.0003, respectively).

CONCLUSIONS

Our meta-analysis provides evidence of significant association between GCKR rs780094 and risk of NAFLD. Similar effect size was demonstrated in both Asian and non-Asian populations.

MTNR1B Genetic Variability Is Associated with Gestational Diabetes in Czech Women

The gene MTNR1B encodes a receptor for melatonin. Melatonin receptors are expressed in human β-cells, which implies that genetic variants might affect glucose tolerance. Meta-analysis confirmed that the rs10830963 shows the most robust association. The aim of the study was to assess the rs10830963 in Czech GDM patients and controls and to study relations between the SNP and biochemical as well as anthropometric characteristics. Our cohort consisted of 880 women; 458 were diagnosed with GDM, and 422 were normoglycemic controls without history of GDM. Despite similar BMI, the GDM group showed higher WHR, waist circumference, abdominal circumference, and total body fat content. The risk allele G was more frequent in the GDM group (38.3 versus 29.4% in controls, OR 1.49 CI95% [1.22; 1.82]; P OR = 0.0001). In spite of higher frequency, the G allele in the GDM group was not associated with any markers of glucose metabolism. In contrast, controls showed significant association of the allele G with FPG and with postchallenge glycemia during the oGTT. Frequency analysis indicates that rs10830963 is involved in gestational diabetes in Czech women. However, the association of the SNP with glucose metabolism, which is obvious in controls, is covert in women who have experienced GDM.

An interaction effect between glucokinase gene variation and carbohydrate intakes modulates the plasma triglyceride response to a fish oil supplementation

A large inter-individual variability in the plasma triglyceride (TG) response to fish oil consumption has been observed. The objective was to investigate the gene-diet interaction effects between single-nucleotide polymorphisms (SNPs) within glucokinase (GCK) gene and dietary carbohydrate intakes (CHO) on the plasma TG response to a fish oil supplementation. Two hundred and eight participants were recruited in the greater Quebec City area. The participants completed a 6-week fish oil supplementation (5 g fish oil/day: 1.9-2.2 g EPA and 1.1 g DHA). Thirteen SNPs within GCK gene were genotyped using TAQMAN methodology. A gene-diet interaction effect on the plasma TG response was observed with rs741038 and CHO adjusted for age, sex and BMI (p = 0.008). In order to compare the plasma TG response between genotypes according to CHO, participants were divided according to median CHO. Homozygotes of the minor C allele of rs741038 with high CHO >48.59 % had a greater decrease in their plasma TG concentrations following the intake of fish oil (p < 0.05) than C/C homozygotes with low CHO and also than the other genotypes either with high or low CHO. The plasma TG response to a fish oil supplementation may be modulated by gene-diet interaction effects involving GCK gene and CHO.

Association of GCK -30G> a polymorphism with gestational diabetes mellitus and type 2 diabetes mellitus risk: a meta-analysis involving 18 case-control studies

OBJECTIVE

Several studies have examined the association between the GCK -30G>A polymorphism and the risk of gestational diabetes mellitus (GDM) and type 2 diabetes mellitus (T2DM). However, inferences from these studies are hindered by their limited statistical power and conflicting results. The aim of this meta-analysis is to provide a relatively comprehensive picture of the association of the GCK -30G>A polymorphism with GDM and T2DM risk.

METHODS

A literature search for eligible studies published before August 15, 2013, was conducted in PubMed, Embase, Web of Science, Cochrane Library, and CNKI (China National Knowledge Infrastructure). Pooled odds ratios with their corresponding 95% confidence intervals were used to evaluate the strength of the association under a fixed- or random-effect model according to heterogeneity test results. All analyses were performed using Stata software, version 12.0.

RESULTS

Eighteen case-control studies from 17 published reports were included in this meta-analysis with a total of 2011 patients with GDM, 11,057 with T2DM, and 26,102 healthy controls. For GDM, the combined results showed that the risk allele of the -30G>A polymorphism may be associated with an increased risk of GDM. Stratified analyses showed that the magnitude of the effect was especially significant among whites, indicating ethnicity differences for GDM susceptibility. For T2DM, the pooled ORs were not significant in the overall population, although all the ORs >1 suggested an increased risk of T2DM for carriers of the A allele. However, whites seem to be significantly more susceptible to T2DM than Asians.

CONCLUSION

This meta-analysis indicated that the risk allele of the GCK -30G>A polymorphism may increase GDM and T2DM risk in whites, whereas additional studies are needed to confirm the effect of this polymorphism on both diseases in Asians and Africans.

Moving on from GWAS: functional studies on the G6PC2 gene implicated in the regulation of fasting blood glucose

Genome-wide association studies (GWAS) have shown that single-nucleotide polymorphisms (SNPs) in G6PC2 are the most important common determinants of variations in fasting blood glucose (FBG) levels. Molecular studies examining the functional impact of these SNPs on G6PC2 gene transcription and splicing suggest that they affect FBG by directly modulating G6PC2 expression. This conclusion is supported by studies on G6pc2 knockout (KO) mice showing that G6pc2 represents a negative regulator of basal glucose-stimulated insulin secretion that acts by hydrolyzing glucose-6-phosphate, thereby reducing glycolytic flux and opposing the action of glucokinase. Suppression of G6PC2 activity might, therefore, represent a novel therapy for lowering FBG and the risk of cardiovascular-associated mortality. GWAS and G6pc2 KO mouse studies also suggest that G6PC2 affects other aspects of beta cell function. The evolutionary benefit conferred by G6PC2 remains unclear, but it is unlikely to be related to its ability to modulate FBG.