How Can Genetic Studies Help Us to Understand Links Between Birth Weight and Type 2 Diabetes?

Interaction effect between low birthweight and resistin gene rs1862513 variant on insulin resistance and type 2 diabetes mellitus in adulthood: Toon Genome Study

AIMS/INTRODUCTION

Gene-environment interactions are considered to critically influence type 2 diabetes mellitus development; however, the underlying mechanisms and specific interactions remain unclear. Given the increasing prevalence of low birthweight (LBW) influenced by the intrauterine environment, we sought to investigate genetic factors related to type 2 diabetes development in individuals with LBW.

MATERIALS AND METHODS

The interaction between 20 reported type 2 diabetes susceptibility genes and the development of type 2 diabetes in LBW (<2,500 g) individuals in a population-based Japanese cohort (n = 1,021) was examined by logistic regression and stratified analyses.

RESULTS

Logistic regression analyses showed that only the G/G genotype at the rs1862513 locus of the resistin gene (RETN), an established initiator of insulin resistance, was closely related to the prevalence of type 2 diabetes in individuals with LBW. Age, sex and current body mass index-adjusted stratified analyses showed a significant interaction effect of LBW and the RETN G/G genotype on fasting insulin, homeostatic model assessment 2-insulin resistance, Matsuda index and the prevalence of type 2 diabetes (all P-values for interaction <0.05). The adjusted odds ratio for type 2 diabetes in the LBW + G/G genotype group was 7.33 (95% confidence interval 2.43-22.11; P = 0.002) compared with the non-LBW + non-G/G genotype group. Similar results were obtained after excluding the influence of malnutrition due to World War II.

CONCLUSIONS

Simultaneous assessment of LBW and the RETN G/G genotype can more accurately predict the risk of future type 2 diabetes than assessing each of these factors alone, and provide management strategies, including early lifestyle intervention in LBW population.

Effects of folic acid supplementation in pregnant mice on glucose metabolism disorders in male offspring induced by lipopolysaccharide exposure during pregnancy

The DOHaD theory suggests that adverse environmental factors in early life may lead to the development of metabolic diseases including diabetes and hypertension in adult offspring through epigenetic mechanisms such as DNA methylation. Folic acid (FA) is an important methyl donor in vivo and participates in DNA replication and methylation. The preliminary experimental results of our group demonstrated that lipopolysaccharide (LPS, 50 µg/kg/d) exposure during pregnancy could lead to glucose metabolism disorders in male offspring, but not female offspring; however, the effect of folic acid supplementation on glucose metabolism disorders in male offspring induced by LPS exposure remains unclear. Therefore, in this study, pregnant mice were exposed to LPS on gestational day (GD) 15-17 and were given three doses of FA supplementation (2 mg/kg, 5 mg/kg, or 40 mg/kg) from mating to lactation to explore its effect on glucose metabolism in male offspring and the potential mechanism. This study confirmed that FA supplementation of 5 mg/kg in pregnant mice improved glucose metabolism in LPS-exposed offspring during pregnancy by regulating gene expression.

Investigation of maternal polymorphisms in genes related to glucose homeostasis and the influence on birth weight: a cohort study

OBJECTIVES

To contribute to a better understanding of the maternal genetic mechanisms that influence obstetric outcomes and that are involved in maternal and child health, this study aimed to evaluate the association between maternal genetic variants and the offspring birth weight by analyzing single-nucleotide polymorphisms (SNPs) in genes related to glucose homeostasis.

METHODS

Three polymorphisms were analyzed (GCK rs1799884, TCF7L2 rs7903146 and LEPR rs1137101) in 250 pregnant women who participated in a Brazilian prospective cohort study. Genotyping was performed by Real-Time Polymerase Chain Reaction (qPCR) using pre-designed TaqMan® SNP genotyping assays. Vitamin D dosage was performed by chemiluminescence. Variance, Pearson's chi-square test and multiple linear regression were used for the statistical analysis.

RESULTS

It was possible to verify a significant association between birth weight and maternal GCK rs1799884 when obstetric outcomes, clinical and anthropometric characteristics were taken into consideration. The children of homozygous women for the minor allele GCK rs1799884 presented lower birth weight (β = -335.25, 95% CI = -669.39; -1.17, p = 0.04). Furthermore, a direct link between a leptin receptor variant and gestational duration was found (p = 0.037).

CONCLUSION

The variant GCK rs1799884 (mm) was associated with a reduction in newborn weight in the miscegenated Brazilian population.

Maternal vitamin D status in relation to infant BMI growth trajectories up to 2 years of age in two prospective pregnancy cohorts

Background

Early childhood growth can affect the child's health status later in life. Maternal vitamin D status has been suggested to affect early childhood growth. However, there is a lack of studies investigating the role of maternal vitamin D status on growth trajectories during infancy. By using growth mixture modeling (GMM), maternal vitamin D status during pregnancy can be investigated in relation to different classes of infant growth trajectories.

Objectives

To examine the association between maternal 25‐hydroxyvitamin D (25OHD) and classes of infant body mass index (BMI) growth trajectories.

Methods

Mother–child pairs were included from the Norwegian Mother, Father, and Child Cohort Study (MoBa, n = 2522) and the Swedish GraviD cohort (n = 862). Maternal 25OHD in pregnancy was analyzed by liquid chromatography tandem mass spectrometry. Children's weights and heights were registry‐based. GMM identified classes of infant BMI growth trajectories up to 2 years. The association between maternal 25OHD and infant BMI class by cohort was estimated using a log‐link generalized linear model. Mixed model analysis estimated the pooled association including both cohorts.

Results

Two infant BMI classes were identified, stable normal and stable high. In MoBa, maternal 25OHD <50 and 50–75 nmol/L were associated (RR 2.70, 95% CI 1.26–5.77 and RR 2.56, 95% CI 1.20–5.47) with a higher risk of the infant stable high BMI class, compared with 25OHD >75 nmol/L. In GraviD, no association was found. In pooled analysis, maternal 25OHD ≤75 nmol/L was non‐significantly associated with a higher risk of the stable high BMI growth class.

Conclusions

Maternal 25OHD ≤75 nmol/L may be associated with a higher class of BMI growth trajectory during infancy.

Association of diabetes-related variants in ADCY5 and CDKAL1 with neonatal insulin, C-peptide, and birth weight

BACKGROUND AND PURPOSE

Neonates at the highest and lowest percentiles of birth weight present an increased risk of developing metabolic diseases in adult life. While environmental events in utero may play an important role in this association, some genetic variants are associated both with birth weight and type 2 diabetes mellitus (T2DM), suggesting a genetic link between intrauterine growth and metabolism in adult life. Variants rs11708067 in ADCY5 and rs7754840 in CDKAL1 are associated with low birth weight, risk of T2DM, and lower insulin secretion in adults. We aimed to investigate whether, besides birth weight, these polymorphisms were related to insulin secretion at birth.

METHODS

A cohort of 218 healthy term newborns from uncomplicated pregnancies were evaluated for anthropometric and biochemical variables. Cord blood insulin and C-peptide were analyzed by ELISA. Genotyping of rs11708067 in ADCY5 and rs7754840 in CDKAL1 was performed.

RESULTS

Newborns carrying the A allele of ADCY5 rs11708067 had lower cord blood insulin and C-peptide, even after adjusting by maternal glycemia, HbA1c, and pregestational BMI. Lower birth weight was found for AA-AG genotypes compared to GG, but no differences were seen in adjusted birth weight or z-score. Variant rs7754840 in CDKAL1 was not associated with birth weight, neonatal insulin, or C-peptide for any genotype or genetic model.

CONCLUSIONS

The variant rs11708067 in ADCY5 is associated with lower neonatal insulin and C-peptide concentrations. Our results suggest that the genetic influence on insulin secretion may be evident from birth, even in healthy newborns, independently of maternal glycemia and BMI.

Risk factors for left ventricular dysfunction in adulthood: role of low birth weight

Aims

This study aimed to determine the relationship of low birth weight (LBW) with adult cardiac structure and function and investigate potential causal pathways.

Methods and results

A population‐based sample of 925 Australians (41.3% male) were followed from childhood (aged 7–15 years) to young adulthood (aged 26–36 years) and mid‐adulthood (aged 36–50 years). Left ventricular (LV) global longitudinal strain (GLS, %), LV mass index (LVMi, g/m^2.7), LV filling pressure (E/e′), and left atrial volume index (g/m²) were measured by transthoracic echocardiography in mid‐adulthood. Birth weight category was self‐reported in young adulthood and classified as low (≤5 lb or ≤2270 g), normal (5–8 lb or 2271–3630 g), and high (>8 lb or >3630 g). Of the 925 participants, 7.5% (n = 69) were classified as LBW. Compared with participants with normal birth weight, those with LBW had 2.01‐fold (95% confidence interval: 1.19, 3.41, P = 0.009) higher risks of impaired GLS (GLS > −18%) and 2.63‐fold (95% confidence interval: 0.89, 7.81, P = 0.08) higher risks of LV hypertrophy (LVMi > 48 g/m^2.7 in men or >44 g/m^2.7 in women) in adulthood, independent of age, sex, and any socio‐economic factors. Participants with LBW significantly increased body fat from childhood to adulthood relative to their peers and had greater levels of triglycerides, fasting glucose, and arterial stiffness in adulthood. These risk factors were the strongest mediators and explained 54% of the LBW effect size on adult GLS and 33% of the LBW effect size on LVMi. The remaining of these associations was independent of any of the measured risk factors.

Conclusions

Low birth weight was associated with impaired cardiac structure and function in mid‐adulthood. This association was only partially explained by known risk factors.

Comparing the Predictivity of Human Placental Gene, microRNA, and CpG Methylation Signatures in Relation to Perinatal Outcomes

Molecular signatures are being increasingly integrated into predictive biology applications. However, there are limited studies comparing the overall predictivity of transcriptomic vs. epigenomic signatures in relation to perinatal outcomes. This study set out to evaluate mRNA and microRNA (miRNA) expression and cytosine-guanine dinucleotide (CpG) methylation signatures in human placental tissues and relate these to perinatal outcomes known to influence maternal/fetal health; namely, birth weight, placenta weight, placental damage, and placental inflammation. The following hypotheses were tested: (1) different molecular signatures will demonstrate varying levels of predictivity towards perinatal outcomes, and (2) these signatures will show disruptions from an example exposure (i.e., cadmium) known to elicit perinatal toxicity. Multi-omic placental profiles from 390 infants in the Extremely Low Gestational Age Newborns cohort were used to develop molecular signatures that predict each perinatal outcome. Epigenomic signatures (i.e., miRNA and CpG methylation) consistently demonstrated the highest levels of predictivity, with model performance metrics including R^2 (predicted vs. observed) values of 0.36-0.57 for continuous outcomes and balanced accuracy values of 0.49-0.77 for categorical outcomes. Top-ranking predictors included miRNAs involved in injury and inflammation. To demonstrate the utility of these predictive signatures in screening of potentially harmful exogenous insults, top-ranking miRNA predictors were analyzed in a separate pregnancy cohort and related to cadmium. Key predictive miRNAs demonstrated altered expression in association with cadmium exposure, including miR-210, known to impact placental cell growth, blood vessel development, and fetal weight. These findings inform future predictive biology applications, where additional benefit will be gained by including epigenetic markers.

Genetic architecture of type 2 diabetes and its shared genetic component with low birth weight in African Americans

PURPOSE OF REVIEW

Recent large-scale multiancestry efforts has contributed to our knowledge of the hereditary basis of type 2 diabetes (T2D). The present review will summarize findings of the genetic basis of T2D in African Americans, a population group with a disproportionate burden of this disease.

RECENT FINDINGS

To date, >400 risk genetic variants have been found to be associated with the risk of T2D across populations of different ancestries. Although these findings are based on primarily European-ancestry populations, most of the identified loci show similar associations in African Americans. Ancestry-specific analyses including genome-wide associations studies (GWAS) in African Americans, Africans; as well as admixture mapping scans in African Americans have identified additional risk variants and genomic loci associate with the risk of T2D. These efforts have also uncovered new genetic links between low birth weight and T2D. In particular, admixture mapping approaches have identified a shared genetic ancestry component of both phenotypic traits in African Americans.

SUMMARY

Recent findings have helped us to better understand the genetic basis of T2D in African Americans. Of particular interest are new genetic discoveries linking low birth weight and T2D, two conditions with a much higher prevalence in African Americans compared to U.S. whites. Continuing work, including large-scale sequencing efforts would add to our knowledge of the genetic architecture of T2D in African Americans, as well as genetic links with other conditions.

Developing Novel Tests to Screen for Fetal Growth Restriction

Fetal growth restriction (FGR) is a major determinant of global morbidity and mortality. There is an unmet need for methods to stratify the pregnant population on the basis of FGR risk. Despite evolutionary divergence in mammalian reproduction, studies of genetically modified mice have identified biomarkers that have been validated in women, and a systematic screen for genes that control fetal growth in animals could help identify novel clinical biomarkers. Current approaches to biomarker identification using human samples include both targeted and discovery approaches (omics). Application of omic methods to the placenta and maternal blood has yielded promising results, but comes with logistical, experimental, and analytical challenges and all studies are limited by the lack of a gold standard for disease.

Autocrine IGF2 programmes β-cell plasticity under conditions of increased metabolic demand

When exposed to nutrient excess and insulin resistance, pancreatic β-cells undergo adaptive changes in order to maintain glucose homeostasis. The role that growth control genes, highly expressed in early pancreas development, might exert in programming β-cell plasticity in later life is a poorly studied area. The imprinted Igf2 (insulin-like growth factor 2) gene is highly transcribed during early life and has been identified in recent genome-wide association studies as a type 2 diabetes susceptibility gene in humans. Hence, here we investigate the long-term phenotypic metabolic consequences of conditional Igf2 deletion in pancreatic β-cells (Igf2βKO) in mice. We show that autocrine actions of IGF2 are not critical for β-cell development, or for the early post-natal wave of β-cell remodelling. Additionally, adult Igf2βKO mice maintain glucose homeostasis when fed a chow diet. However, pregnant Igf2βKO females become hyperglycemic and hyperinsulinemic, and their conceptuses exhibit hyperinsulinemia and placentomegalia. Insulin resistance induced by congenital leptin deficiency also renders Igf2βKO females more hyperglycaemic compared to leptin-deficient controls. Upon high-fat diet feeding, Igf2βKO females are less susceptible to develop insulin resistance. Based on these findings, we conclude that in female mice, autocrine actions of β-cell IGF2 during early development determine their adaptive capacity in adult life.

Nutritional and developmental programming effects of insulin

The discovery of insulin in 1921 was a major breakthrough in medicine and for therapy in patients with diabetes. The dramatic rise in the prevalence of overweight and obesity has been tightly linked to an increased prevalence of gestational diabetes mellitus (GDM), which poses major health concerns. Babies born to GDM mothers are more likely to develop obesity, type 2 diabetes and cardiovascular disease later in life. Evidence accumulated during the past two decades has revealed that high levels insulin, such as those observed during GDM, can have a widespread effect on the development and function of a variety of organs. This review summarises our current knowledge on the role of insulin in the placenta, cardiovascular system and brain during critical periods of development, as well as how it can contribute to lifelong metabolic regulation. We also discuss possible intervention strategies to ameliorate and hopefully reverse the developmental defects associated with obesity and GDM.

Placental genomic and epigenomic signatures associated with infant birth weight highlight mechanisms involved in collagen and growth factor signaling

Birth weight (BW) represents an important clinical and toxicological measure, indicative of the overall health of the newborn as well as potential risk for later-in-life outcomes. BW can be influenced by endogenous and exogenous factors and is known to be heavily impacted in utero by the health and function of the placenta. An aspect that remains understudied is the influence of genomic and epigenomic programming within the placenta on infant BW. To address this gap, we set out to test the hypothesis that genes involved in critical placental cell signaling are associated with infant BW, and are likely regulated, in part, through epigenetic mechanisms based on microRNA (miRNA) mediation. This study leveraged a robust dataset based on 390 infants born at low gestational age (ranged 23-27 weeks) to evaluate genome-wide expression profiles of both mRNAs and miRNAs in placenta tissues and relate these to infant BW. A total of 254 mRNAs and 268 miRNAs were identified as associated with BW, the majority of which showed consistent associations across placentas derived from both males and females. BW-associated mRNAs were found to be enriched for important biological pathways, including glycoprotein VI (the major receptor for collagen), human growth, and hepatocyte growth factor signaling, a portion of which were predicted to be regulated by BW-associated miRNAs. These miRNA-regulated pathways highlight key mechanisms potentially linking endogenous/exogenous factors to changes in birth outcomes that may be deleterious to infant and later-in-life health.

Why and How Imprinted Genes Drive Fetal Programming

Imprinted genes mediate fetal and childhood growth and development, and early growth patterns drive fetal programming effects. However, predictions and evidence from the kinship theory of imprinting have yet to be directly integrated with data on fetal programming and risks of metabolic disease. I first define paternal-gene and maternal-gene optima with regard to early human growth and development. Next, I review salient evidence with regard to imprinted gene effects on birth weight, body composition, trajectories of feeding and growth, and timing of developmental stages, to evaluate why and how imprinted gene expression influences risks of metabolic disease in later life. I find that metabolic disease risks derive primarily from maternal gene biases that lead to reduced placental efficacy, low birth weight, low relative muscle mass, high relative white fat, increased abdominal adiposity, reduced pancreatic β-cell mass that promotes insulin resistance, reduced appetite and infant sucking efficacy, catch-up fat deposition from family foods after weaning, and early puberty. Paternal gene biases, by contrast, may contribute to metabolic disease via lower rates of brown fat thermiogenesis, and through favoring more rapid postnatal catch-up growth after intrauterine growth restriction from environmental causes. These disease risks can be alleviated through dietary and pharmacological alterations that selectively target imprinted gene expression and relevant metabolic pathways. The kinship theory of imprinting, and mother-offspring conflict more generally, provide a clear predictive framework for guiding future research on fetal programming and metabolic disease.

The association between birthweight and grandparental type 2 diabetes and cardiovascular disease in a multiethnic population

Intergenerational links of chronic disease have been suggested, as birthweight (BW) is associated with cardiovascular disease (CVD) and type 2 diabetes (T2D) in both parents and grandparents. However, most studies investigating these relationships have used relatively homogenous, white, majority populations. This study aimed to investigate the association between BW and CVD and T2D in a multiethnic population, that is, where the parents and grandparents often developed in a different environment from that where the child was born. Participants were women from a population-based cohort study of pregnant women (STORK Groruddalen), attending Child Health Clinics for antenatal care in three administrative city districts in Oslo, Norway, 2008-2010. Information about socioeconomic and lifestyle factors were collected among mothers and fathers. Parents reported history of CVD or T2D among grandparents. In logistic regressions, higher BW z-scores were associated with lower odds of T2D among maternal (OR 0.71 (95% CI 0.53, 0.97) and paternal (0.68 (0.49, 0.94) grandmothers after adjustments for parental and grandmothers' characteristics. BW was not associated with CVD, but the association in maternal grandfathers was borderline significant. Our results indicate intergenerational transmission of chronic diseases like T2D in a multiethnic population.

Maternal and Offspring Genetic Risk of Type 2 Diabetes and Offspring Birthweight Among African Ancestry Populations

OBJECTIVES

Maternal genetic risk of type 2 diabetes (T2D) can influence offspring birthweight through shared offspring genetic risk and by altering intrauterine glycemic status. The aim of this study was to estimate the independent effects of maternal and offspring genetic risk scores (GRSs) of T2D on offspring birthweight and the extent to which intrauterine glycemic traits mediate the effect of maternal GRSs on offspring birthweight.

DESIGN

The study involved 949 mother-offspring pairs of African ancestry from the Hyperglycemia Adverse Pregnancy Outcome study. GRSs of T2D were calculated separately for mothers and offspring as the weighted sum of 91 T2D risk alleles identified in a genome-wide association study meta-analysis in African Americans. Linear regression models were fit to estimate changes in birthweight by quartiles of GRSs. Mediation analysis was implemented to estimate the direct and indirect effects of maternal GRS on offspring birthweight through cord blood C-peptide and maternal fasting and postchallenge glucose levels.

RESULTS

Maternal and offspring GRSs were independently and differentially associated with offspring birthweight. Changes (95% CI) in birthweight across increasing quartiles of maternal GRSs were 0 g (reference), 83.1 g (6.5, 159.6), 103.1 g (26.0, 180.2), and 92.7 g (12.6, 172.8) (P trend = 0.041) and those of offspring GRSs were 0 (reference), -92.0 g (-169.2, -14.9), -64.9 g (-142.4, 12.6), and 2.0 g (-77.8, 81.7) (P trend = 0.032). Cord blood C-peptide mediated the effect of maternal GRS on offspring birthweight, whereas maternal postchallenge glucose levels showed additive effects with maternal GRS on birthweight.

CONCLUSIONS

Maternal and offspring GRSs of T2D were independently and differentially associated with offspring birthweight.

Causal Association Between Birth Weight and Adult Diseases: Evidence From a Mendelian Randomization Analysis

Purpose: Birth weight has a profound long-term impact on individual’s predisposition to various diseases at adulthood—a hypothesis commonly referred to as the fetal origins of adult diseases. However, it is not fully clear to what extent the fetal origins of adult diseases hypothesis holds and it is also not completely known what types of adult diseases are causally affected by birth weight.

Materials and methods: Mendelian randomization using multiple genetic instruments associated with birth weight was performed to explore the causal relationship between birth weight and adult diseases. The causal relationship between birth weight and 21 adult diseases as well as 38 other complex traits was examined based on data collected from 37 large-scale genome-wide association studies with up to 340,000 individuals of European ancestry. Causal effects of birth weight were estimated using inverse-variance weighted methods. The identified causal relationships between birth weight and adult diseases were further validated through extensive sensitivity analyses, bias calculation, and simulations.

Results: Among the 21 adult diseases, three were identified to be inversely causally affected by birth weight after the Bonferroni correction. The measurement unit of birth weight was defined as its standard deviation (i.e., 488 g), and one unit lower birth weight was causally related to an increased risk of coronary artery disease (CAD), myocardial infarction (MI), type 2 diabetes (T2D), and BMI-adjusted T2D, with the estimated odds ratios of 1.34 [95% confidence interval (CI) 1.17–1.53], 1.30 (95% CI 1.13–1.51), 1.41 (95% CI 1.15–1.73), and 1.54 (95% CI 1.25–1.89), respectively. All these identified causal associations were robust across various sensitivity analyses that guard against various confounding due to pleiotropy or maternal effects as well as reverse causation. In addition, analysis on 38 additional complex traits did not identify candidate traits that may mediate the causal association between birth weight and CAD/MI/T2D.

Conclusions: The results suggest that lower birth weight is causally associated with an increased risk of CAD, MI, and T2D in later life, supporting the fetal origins of adult diseases hypothesis.

Birth weight and risk of type 2 diabetes: A dose-response meta-analysis of cohort studies

The association between birth weight and type 2 diabetes mellitus has been debated for several decades. The objective of this systematic review and meta-analysis was to quantitatively clarify the association between birth weight and risk of type 2 diabetes mellitus based on cohort studies. We searched PubMed, Web of Science, and Embase databases for cohort study articles on the association between birth weight and risk of type 2 diabetes mellitus published up to 1 March 2018. Random effects of generalized least square regression models were used to estimate relative risk (RR). Restricted cubic splines were conducted to model the dose-response relationship. We included 21 studies (19 articles) involving 1 041 879 individuals and 35 699 cases of type 2 diabetes mellitus, with follow-up ranged from 6 to 47 years. We identified significant decreasing trend for the highest versus lowest category of birth weight for the association with type 2 diabetes mellitus risk: The risk was reduced by 35% (RR, 0.65; 95% confidence interval [CI], 0.53-0.81) and by 12% (RR 0.88; 95% CI, 0.85-0.91) per 500-g increment in birth weight. Our results showed a dose-response relationship between birth weight and diabetes risk, which was nonlinear (P_nonlinearity  < 0.001) and L-shaped. With increasing birth weight (<5000 g), the risk of type 2 diabetes mellitus decreased substantially. The association between birth weight and type 2 diabetes mellitus was curvilinear and L-shaped.

Using structural equation modelling to jointly estimate maternal and fetal effects on birthweight in the UK Biobank

Background

To date, 60 genetic variants have been robustly associated with birthweight. It is unclear whether these associations represent the effect of an individual's own genotype on their birthweight, their mother's genotype, or both.

Methods

We demonstrate how structural equation modelling (SEM) can be used to estimate both maternal and fetal effects when phenotype information is present for individuals in two generations and genotype information is available on the older individual. We conduct an extensive simulation study to assess the bias, power and type 1 error rates of the SEM and also apply the SEM to birthweight data in the UK Biobank study.

Results

Unlike simple regression models, our approach is unbiased when there is both a maternal and a fetal effect. The method can be used when either the individual's own phenotype or the phenotype of their offspring is not available, and allows the inclusion of summary statistics from additional cohorts where raw data cannot be shared. We show that the type 1 error rate of the method is appropriate, and that there is substantial statistical power to detect a genetic variant that has a moderate effect on the phenotype and reasonable power to detect whether it is a fetal and/or a maternal effect. We also identify a subset of birthweight-associated single nucleotide polymorphisms (SNPs) that have opposing maternal and fetal effects in the UK Biobank.

Conclusions

Our results show that SEM can be used to estimate parameters that would be difficult to quantify using simple statistical methods alone.

Developmental pathways and programming of diabetes: epidemiological aspects

Type 2 diabetes (T2D) is a major, rapidly increasing global public health challenge. The major risk factors for T2D include overweight and obesity, lifestyle related factors and genetic factors. Early life exposures shape the developmental trajectories and alter susceptibility to T2D. Based on epidemiological studies it has been suggested that fetal undernutrition plays a role in the etiology of T2D. A low birth weight has been considered a proxy for fetal undernutrition. A meta-analysis reported that a 1 kg increase in birth weight is associated with a roughly 20% lower risk of T2D. Although fetal life is of major importance for future health, the period spanning the first 1 000 days of life, is characterized by great plasticity and largely influencing later health. Different growth trajectories during this time period have also been associated with an increased risk of T2D. Studies assessing the association between age at BMI rebound in childhood and later risk for T2D have reported a 5-fold difference in T2D according to age at BMI rebound. Developmental and epidemiological cohort studies focusing on T2D have major public health implications supporting a paradigm shift; a shift from focusing upon risk factor modification in adult life to adopting a life course perspective when studying T2D. This paradigm shift will not only help us in getting a better understanding of the pathophysiology underlying T2D, but it will also open new possibilities and opportunities in the prevention of T2D and related disorders.

Population attributable fractions of the main type 2 diabetes mellitus risk factors in women: Findings from the French E3N cohort

BACKGROUND

Although many type 2 diabetes mellitus (T2DM) risk factors have been identified, little is known regarding their contributions to the diabetes burden at the population level.

METHODS

The study included 72 655 French women from the Etude Epidemiologique de Femmes de la Mutuelle Générale de l'Education Nationale (E3N) prospective cohort followed between 1993 and 2011. Cox multivariable models including the main T2DM risk factors (metabolic, dietary, clinical, socioeconomic and hormonal) and a healthy lifestyle index combining five characteristics (smoking, body mass index [BMI], alcohol consumption, fruit and vegetable consumption, and physical activity) were used to estimate hazard ratios and population attributable fractions (PAFs) for T2DM.

RESULTS

In multivariate models, factors with the strongest effect on T2DM risk were, in decreasing order, BMI ≥ 30 kg/m² (PAF = 43%; 95% confidence interval [CI] 37-47), high adherence to a Western dietary pattern (PAF = 30%; 95% CI 20-40), hypertension (PAF = 26%; 95% CI 20-32), an acidogenic diet (PAF = 24%; 95% CI 16-32), a family history of diabetes (PAF = 20%; 95% CI 17-22), and, with a negative correlation, moderate alcohol consumption (PAF-19%; 95% CI -34, -4). The PAF for an unhealthy lifestyle was 57% (95% CI 50-63).

CONCLUSIONS

We have been able to sort out and quantify the effect of various dietary and biological T2DM risk factors simultaneously in a single population, and to highlight the importance of a healthy lifestyle for primary prevention: more than half the T2DM cases could have been prevented through a healthier lifestyle.

Lactoferrin level in maternal serum is related to birth anthropometry - an evidence for an indirect biomarker of intrauterine homeostasis?

Objective: To investigate the relation between level of antibodies against lactoferrin (LfAb) in maternal serum (MS) and birth anthropometry of healthy full-term newborns.Methods: The study included 105 pairs of mother-newborn. MS LfAb level was determined using ELISA kit. Spearman's correlation and Kruskal-Wallis one-way analysis of variance (ANOVA) were applied to establish the relationship between MS LfAb level and birth weight (BW), birth weight-to-birth length ratio (BW/BL), and head circumference (HC) of newborns.Results: The U-shaped relation of MS LfAb and BW was demonstrated (p = .019). Negative correlation between MS LfAb and BW/BL was observed (p = .016). The most optimal birth weight and body proportion were observed in newborns of mothers with MS LfAb level of 49 ± 4 U/ml.Conclusions: Significant relationship between MS LfAb and birth anthropometry suggests serum Lf of pregnant women can be considered as a promising indirect biomarker of intrauterine homeostasis, verifiable noninvasively already during pregnancy and thus allowing predict, or even prevent, potential short- and long-term postnatal health consequences.

Genetic studies of gestational duration and preterm birth

The fine control of birth timing is important to human survival and evolution. A key challenge in studying the mechanisms underlying the regulation of human birth timing is that human parturition is a unique to human event — animal models provide only limited information. The duration of gestation or the risk of preterm birth is a complex human trait under genetic control from both maternal and fetal genomes. Genomic discoveries through genome-wide association (GWA) studies would implicate relevant genes and pathways. Similar to other complex human traits, gestational duration is likely to be influenced by numerous genetic variants of small effect size. The detection of these small-effect genetic variants requires very large sample sizes. In addition, several practical and analytical challenges, in particular the involvement of both maternal and fetal genomes, further complicate the genetic studies of gestational duration and other pregnancy phenotypes. Despite these challenges, large-scale GWA studies have already identified several genomic loci associated with gestational duration or the risk of preterm birth. These genomic discoveries have revealed novel insights about the biology of human birth timing. Expanding genomic discoveries in larger datasets by more refined analytical approaches, together with the functional analysis of the identified genomic loci, will collectively elucidate the biological processes underlying the control of human birth timing.

Birth weight variants are associated with variable fetal intrauterine growth from 20 weeks of gestation

Fetal intrauterine growth is influenced by complex interactions between the maternal genes, environment and fetal genes. The aim of this study was to assess the effect of GWAS-identified genetic variants associated with birth weight on intrauterine fetal growth in 665 children. Fetal growth was estimated by two-dimensional ultrasound scans at 20, 25 and 32 weeks of gestation and growth trajectories were modeled using mixed linear regression. A genetic risk score (GRS) of birth weight-raising variants was associated with intrauterine growth showing an attenuating effect on the unconditional daily reduction in proportional weight gain of 8.92 × 10-6 percentage points/allele/day (p = 2.0 × 10-4), corresponding to a mean difference of 410 g at 40 weeks of gestation between a child with lowest and highest GRS. Eight variants were independently associated with intrauterine growth throughout the pregnancy, while four variants were associated with fetal growth in the periods 20-25 or 25-32 weeks of gestation, indicating that some variants may act in specific time windows during pregnancy. Four of the intrauterine growth variants were associated with type 2 diabetes, hypertension or BMI in the UK Biobank, which may provide basis for further understanding of the link between intrauterine growth and later risk of metabolic disease.

Birth weight and type 2 diabetes: A meta-analysis

The prevalence of T2DM is increasing around the world on a yearly basis. A meta-analysis was conducted to analyze the association between birth weight and incidence of type 2 diabetes mellitus (T2DM). A literature search was performed from January 1990 to June 2016 in PubMed, ScienceDirect, SpringerLink, China National Knowledge Infrastructure and Chinese Biomedical Literature Database. After reviewing characteristics of all the included studies systematically, a meta-analytical method was employed to calculate the pooled odds ratios (ORs) and associated 95% confidence intervals (CI) from random-effects models. Heterogeneity was assessed by Q-statistic test. Funnel plot, Begg's and Egger's linear regression tests were applied to evaluate publication bias. A sensitivity analysis was also performed to assess the robustness of results. According to inclusion and exclusion criteria, 8 studies were selected to be included in the meta-analysis. Compared with normal birth weight (2,500–4,000 g), low birth weight (<2,500 g) was associated with an increased risk of T2DM (OR, 1.55; 95% CI, 1.39–1.73; P<0.001). No significant difference was observed between high birth weight (>4,000 g) and normal birth weight in terms of the risk of T2DM (OR, 0.98; 95% CI, 0.79–1.22). Compared with high birth weight, low birth weight was associated with an increased risk of diabetes mellitus (OR, 1.58; 95% CI, 1.30–1.93; P<0.001). These findings indicated that there may be an inverse linear association between birth weight and T2DM.