Genetic Loci and Physiologic Pathways Involved in Gestational Diabetes Mellitus Implicated Through Clustering

Individualized nutritional intervention compared with routine care for gestational diabetes prevention: a randomized controlled trial

BACKGROUND

Gestational diabetes mellitus (GDM) affects millions of females and their children. Effective dietary strategies for early prevention are controversial.

OBJECTIVES

This study aims to investigate whether an individualized nutritional intervention reduced GDM incidence in high-risk females.

METHODS

A randomized trial was conducted at 3 tertiary hospitals in Shanghai, China. We randomly assigned (1:1) pregnant females in the first trimester who were identified to be at high risk of GDM by a prediction model to either an individualized nutritional intervention or usual care. The intervention consisted of 3 dietary consultations by dietitians based on Chinese dietary guidelines before the oral glucose tolerance test (OGTT) at 24-28 wk of gestation. The control group received usual care. All participants provided 3-d food records at each follow-up. The primary outcome was GDM incidence using the International Association of Diabetes and Pregnancy Study Group criteria. Key secondary outcomes were dietary alterations, gestational weight gain (GWG), maternal metabolic profile, perinatal and pregnancy outcomes. Intention-to-treat analyses were conducted.

RESULTS

A total of 519 females were enrolled, of whom 261 were assigned to the intervention and 258 to usual care. GDM was diagnosed in 85/245 (34.7%) females in the intervention group compared with 89/244 (36.5%) in the control group [adjusted relative risk 0.91 (95% confidence interval: 0.73, 1.15), P = 0.44]. More females in the intervention group had an appropriate GWG than the control group [1.38 (1.06, 1.79)] and lower levels of fasting and 2-h insulin during the OGTT (P < 0.001). We observed a reduction in the rate of small for gestational age in the intervention group compared with the control group [0.11 (0.01, 0.80)] and neonatal hypoglycemia [0.14 (0.04, 0.57)].

CONCLUSIONS

Among females at risk of GDM, an individualized nutritional intervention based on Chinese dietary guidelines provided before the OGTT did not prevent GDM but helped to manage GWG appropriately and improved pregnancy outcomes. This trial was registered on 27 October, 2019, with initial participant enrollment on 5 May, 2020 at ChiCTR as 1900026963 (https://www.chictr.org.cn/searchproj.html?regno=1900026963).

Genetics and epigenetics in gestational diabetes contributing to type 2 diabetes

Gestational diabetes mellitus (GDM) is a common pregnancy complication and a risk factor for the subsequent development of type 2 diabetes (T2D) in mothers and of several metabolic diseases in offspring. However, the molecular underpinnings of these risks are not well understood. Genome-wide association studies (GWAS) and epigenetic studies may provide complementary insights into the causal relationships between GDM exposure and maternal/offspring metabolic outcomes. In this review we discuss the potential pathophysiological roles of specific genetic variants and commonly reported differentially methylated loci in GDM development, and their link to the progression to T2D in both the mother and the offspring in later life, pointing to the potential for tailored interventional strategies based on these genetic and epigenetic mechanisms.

Cohort profile: the Genetics of Glucose regulation in Gestation and Growth (Gen3G) - a prospective prebirth cohort of mother-child pairs in Sherbrooke, Canada, 3-year and 5-year follow-up visits

PURPOSE

Initiated in 2010, the Genetics of Glucose regulation in Gestation and Growth (Gen3G) prospective cohort investigates the pathophysiology of impaired glycaemic regulation in pregnancy and evaluates its impact on both the mothers and her offspring health trajectory. Follow-up visits 3 and 5 years after delivery aimed to investigate pregnancy-related risk factors such as maternal obesity and gestational hyperglycaemia in relation to the mother's metabolic health after pregnancy, and with offspring health outcomes such as risk of obesity and neurodevelopmental problems in early childhood. We also investigated molecular mechanisms involved in the fetal programming of these later health outcomes.

PARTICIPANTS

Of the 1024 women originally recruited in the first trimester of pregnancy, we have targeted the 854 who had complete glucose tolerance test data and the 724 newborns who provided placenta and/or cord blood samples for follow-up recruitment. Of these, 695 mother-child dyads agreed to be contacted for the prospective follow-up visits. 448 and 521 mother-child dyads completed the research visits at 3 and 5 years after delivery respectively.

FINDINGS TO DATE

At both visits, we collected the mother's and child's medical history, lifestyle (using validated questionnaires), sociodemographic status, anthropometric measurements, mother's blood samples, child's saliva samples and growth charts. At the 5-year-old visit, we additionally collected the mother's and child's urine and stool samples and the child's blood samples; we performed a 75 g oral glucose tolerance test in the mothers and assessed the body composition in children using dual-energy X-ray absorptiometry. Using the Gen3G rich longitudinal data set, we have enhanced the understanding of the pathophysiology and characterisation of the heterogeneity of gestational diabetes mellitus, and we have shown that gestational hyperglycaemia and insulin resistance are associated with offspring epigenetics (DNA methylation) variations in the placenta, cord blood and blood at 5 years of age, as well as with offspring anthropometric, metabolic and neurodevelopmental outcomes in early childhood.

FUTURE PLANS

We are currently conducting a prospective follow-up of mothers and their children 12 years after delivery to study how prenatal and early-life metabolic factors may programme childhood adiposity and obesogenic dietary behaviours. This follow-up should be completed by the end of 2026.

Polycystic Ovary Syndrome Physiologic Pathways Implicated Through Clustering of Genetic Loci

CONTEXT

Polycystic ovary syndrome (PCOS) is a heterogeneous disorder, with disease loci identified from genome-wide association studies (GWAS) having largely unknown relationships to disease pathogenesis.

OBJECTIVE

This work aimed to group PCOS GWAS loci into genetic clusters associated with disease pathophysiology.

METHODS

Cluster analysis was performed for 60 PCOS-associated genetic variants and 49 traits using GWAS summary statistics. Cluster-specific PCOS partitioned polygenic scores (pPS) were generated and tested for association with clinical phenotypes in the Mass General Brigham Biobank (MGBB, N = 62 252). Associations with clinical outcomes (type 2 diabetes [T2D], coronary artery disease [CAD], and female reproductive traits) were assessed using both GWAS-based pPS (DIAMANTE, N = 898,130, CARDIOGRAM/UKBB, N = 547 261) and individual-level pPS in MGBB.

RESULTS

Four PCOS genetic clusters were identified with top loci indicated as following: (i) cluster 1/obesity/insulin resistance (FTO); (ii) cluster 2/hormonal/menstrual cycle changes (FSHB); (iii) cluster 3/blood markers/inflammation (ATXN2/SH2B3); (iv) cluster 4/metabolic changes (MAF, SLC38A11). Cluster pPS were associated with distinct clinical traits: Cluster 1 with increased body mass index (P = 6.6 × 10-29); cluster 2 with increased age of menarche (P = 1.5 × 10-4); cluster 3 with multiple decreased blood markers, including mean platelet volume (P = 3.1 ×10-5); and cluster 4 with increased alkaline phosphatase (P = .007). PCOS genetic clusters GWAS-pPSs were also associated with disease outcomes: cluster 1 pPS with increased T2D (odds ratio [OR] 1.07; P = 7.3 × 10-50), with replication in MGBB all participants (OR 1.09, P = 2.7 × 10-7) and females only (OR 1.11, 4.8 × 10-5).

CONCLUSION

Distinct genetic backgrounds in individuals with PCOS may underlie clinical heterogeneity and disease outcomes.

Towards Precision Medicine in Gestational Diabetes: Pathophysiology and Glycemic Patterns in Pregnant Women With Obesity

AIMS

Precision medicine has revolutionized our understanding of type 1 diabetes and neonatal diabetes but has yet to improve insight into gestational diabetes mellitus (GDM), the most common obstetric complication and strongly linked to obesity. Here we explored if patterns of glycaemia (fasting, 1 hour, 2 hours) during the antenatal oral glucose tolerance test (OGTT), reflect distinct pathophysiological subtypes of GDM as defined by insulin secretion/sensitivity or lipid profiles.

METHODS

867 pregnant women with obesity (body mass index ≥ 30 kg/m2) from the UPBEAT trial (ISRCTN 89971375) were assessed for GDM at 28 weeks' gestation (75 g oral glucose tolerance test OGTT; World Health Organization criteria). Lipid profiling of the fasting plasma OGTT sample was undertaken using direct infusion mass spectrometry and analyzed by logistic/linear regression, with and without adjustment for confounders. Insulin secretion and sensitivity were characterized by homeostatic model assessment 2b and 2s, respectively.

RESULTS

In women who developed GDM (n = 241), patterns of glycaemia were associated with distinct clinical and biochemical characteristics and changes to lipid abundance in the circulation. Severity of glucose derangement, rather than pattern of postload glycaemia, was most strongly related to insulin action and lipid abundance/profile. Unexpectedly, women with isolated postload hyperglycemia had comparable insulin secretion and sensitivity to euglycemic women, potentially indicative of a novel mechanistic pathway.

CONCLUSIONS

Patterns of glycemia during the OGTT may contribute to a precision approach to GDM as assessed by differences in insulin resistance/secretion. Further research is indicated to determine if isolated postload hyperglycemia reflects a different mechanistic pathway for targeted management.

Genetics and Epigenetics: Implications for the Life Course of Gestational Diabetes

Gestational diabetes (GDM) is one of the most common complications of pregnancy, affecting as many as one in six pregnancies. It is associated with both short- and long-term adverse outcomes for the mother and fetus and has important implications for the life course of affected women. Advances in genetics and epigenetics have not only provided new insight into the pathophysiology of GDM but have also provided new approaches to identify women at high risk for progression to postpartum cardiometabolic disease. GDM and type 2 diabetes share similarities in their pathophysiology, suggesting that they also share similarities in their genetic architecture. Candidate gene and genome-wide association studies have identified susceptibility genes that are shared between GDM and type 2 diabetes. Despite these similarities, a much greater effect size for MTNR1B in GDM compared to type 2 diabetes and association of HKDC1, which encodes a hexokinase, with GDM but not type 2 diabetes suggest some differences in the genetic architecture of GDM. Genetic risk scores have shown some efficacy in identifying women with a history of GDM who will progress to type 2 diabetes. The association of epigenetic changes, including DNA methylation and circulating microRNAs, with GDM has also been examined. Targeted and epigenome-wide approaches have been used to identify DNA methylation in circulating blood cells collected during early, mid-, and late pregnancy that is associated with GDM. DNA methylation in early pregnancy had some ability to identify women who progressed to GDM, while DNA methylation in blood collected at 26-30 weeks gestation improved upon the ability of clinical factors alone to identify women at risk for progression to abnormal glucose tolerance post-partum. Finally, circulating microRNAs and long non-coding RNAs that are present in early or mid-pregnancy and associated with GDM have been identified. MicroRNAs have also proven efficacious in predicting both the development of GDM as well as its long-term cardiometabolic complications. Studies performed to date have demonstrated the potential for genetic and epigenetic technologies to impact clinical care, although much remains to be done.

Evolution of the diagnostic value of "the sugar of the blood": hitting the sweet spot to identify alterations in glucose dynamics

In this paper, we provide an overview of the evolution of the definition of hyperglycemia during the past century and the alterations in glucose dynamics that cause fasting and postprandial hyperglycemia. We discuss how extensive mechanistic, physiological research into the factors and pathways that regulate the appearance of glucose in the circulation and its uptake and metabolism by tissues and organs has contributed knowledge that has advanced our understanding of different types of hyperglycemia, namely prediabetes and diabetes and their subtypes (impaired fasting plasma glucose, impaired glucose tolerance, combined impaired fasting plasma glucose, impaired glucose tolerance, type 1 diabetes, type 2 diabetes, gestational diabetes mellitus), their relationships with medical complications, and how to prevent and treat hyperglycemia.

Genetic Risk Factors and Gene-Lifestyle Interactions in Gestational Diabetes

Paralleling the increasing trends of maternal obesity, gestational diabetes (GDM) has become a global health challenge with significant public health repercussions. In addition to short-term adverse outcomes, such as hypertensive pregnancy disorders and fetal macrosomia, in the long term, GDM results in excess cardiometabolic morbidity in both the mother and child. Recent data suggest that women with GDM are characterized by notable phenotypic and genotypic heterogeneity and that frequencies of adverse obstetric and perinatal outcomes are different between physiologic GDM subtypes. However, as of yet, GDM treatment protocols do not differentiate between these subtypes. Mapping the genetic architecture of GDM, as well as accurate phenotypic and genotypic definitions of GDM, could potentially help in the individualization of GDM treatment and assessment of long-term prognoses. In this narrative review, we outline recent studies exploring genetic risk factors of GDM and later type 2 diabetes (T2D) in women with prior GDM. Further, we discuss the current evidence on gene-lifestyle interactions in the development of these diseases. In addition, we point out specific research gaps that still need to be addressed to better understand the complex genetic and metabolic crosstalk within the mother-placenta-fetus triad that contributes to hyperglycemia in pregnancy.

Altered Lipid Metabolism in Obese Women With Gestational Diabetes and Associations With Offspring Adiposity

CONTEXT

Gestational diabetes (GDM) affects 20 million women/year worldwide and is associated with childhood obesity. Infants of affected mothers have increased adiposity from birth, which leads to obesity in later life. However, it remains unknown whether the effect of GDM upon neonatal body composition is due to hyperglycemia alone or is mediated by other pathways.

OBJECTIVE

To investigate plasma lipid profiles in obese women according to GDM diagnosis, infant birthweight percentiles, and adiposity.

DESIGN

Prospective cohort from UPBEAT trial (ISRCTN 89971375).

SETTING

Hospital and community.

PATIENTS

867 obese pregnant women recruited in early pregnancy, assessed at 28 weeks for GDM. Offspring anthropometry was assessed at birth.

OUTCOME (PRESPECIFIED)

Neonatal birth percentile and abdominal circumference.

METHODS

Lipidomic profiling in the fasting plasma oral glucose tolerance test sample using direct infusion mass spectrometry. Analysis included logistic/linear regression, unadjusted and adjusted for maternal age, body mass index, parity, ethnicity, UPBEAT trial arm, and fetal sex. The limit of significance was P = 0.05 for offspring anthropometry and P = 0.002 for lipidomic data.

RESULTS

GDM in obese women was associated with elevated plasma concentrations of specific diglycerides [DG(32:0)] and triglycerides [TG(48:0), (50:1), (50:2)] containing fatty acids (16:0), (16:1), (18:0), and (18:1), consistent with increased de novo lipogenesis. In the whole cohort, these species were associated with birthweight percentile and neonatal abdominal circumference. Effects upon infant abdominal circumference remained significant after adjustment for maternal glycemia.

CONCLUSIONS

Increased de novo lipogenesis-related species in pregnant women with obesity and GDM are associated with measures of offspring adiposity and may be a target for improving lifelong health.

Axon Guidance Molecules in the Islets of Langerhans

The islets of Langerhans, responsible for regulating blood glucose in vertebrates, are clusters of endocrine cells distributed throughout the exocrine pancreas. The spatial architecture of the different cell types within the islets controls cell-cell communication and impacts their ability to collectively regulate glucose. Islets rely on a range of chemotactic and adhesive cues to establish and manage intercellular relationships. Growing evidence indicates that axon guidance molecules such as Slit-Robo, Semaphorin-Neuropilin, Ephrin-Eph, and Netrins, influence endocrine progenitors' cell migration to establish correct architecture during islet morphogenesis, as well as directly regulating physical cell-cell communication in the mature islet to coordinate hormone secretion. In this mini-review, we discuss what is known and not yet known about how axon guidance molecules contribute to islet morphogenesis and function.