Interaction between prenatal growth and high-risk genotypes in the development of type 2 diabetes

Early-life exposure to the Chinese famine, genetic susceptibility and the risk of type 2 diabetes in adulthood

AIMS/HYPOTHESIS

Early famine exposure has been related to the development of type 2 diabetes; however, little is known about whether the genetic background modifies this association. We aimed to investigate the joint effects of famine exposure at different stages of early life and genetic susceptibility on diabetes risk in adulthood.

METHODS

The study included 8350 participants from the Survey on Prevalence in East China for Metabolic Diseases and Risk Factors (SPECT-China) who were born around the time of the Chinese Great Famine. We determined famine exposure subgroups according to the birth year as nonexposed (1963-1974), fetal-exposed (1959-1962), childhood-exposed (1949-1958), and adolescence-exposed (1941-1948). We developed a genetic risk score of 21 variants previously associated with type 2 diabetes in East Asians. Hierarchical logistic models were used to examine the association of famine exposure and genetic risk with diabetes.

RESULTS

The age-standardised prevalence of diabetes in nonexposed, fetal-exposed, childhood-exposed and adolescence-exposed subgroups was 13.0%, 18.2%, 15.1% and 13.2%, respectively. Compared with nonexposed participants, fetal-exposed participants showed an increased risk of diabetes in adulthood (OR 1.47; 95% CI 1.13, 1.93). A higher genetic risk score was associated with an increased risk of diabetes (OR 1.23; 95% CI 1.15, 1.31 per SD increment). The association between famine exposure and diabetes was consistent across genetic risk strata (all p for interaction >0.05). When considered jointly, fetal- or childhood-exposed participants at high genetic risk (highest tertile of genetic risk score) had 2.60-fold (95% CI 1.71, 3.93) and 1.95-fold (95% CI 1.24, 3.05) higher risks of diabetes, respectively, compared with nonexposed participants at low genetic risk (lowest tertile).

CONCLUSIONS/INTERPRETATIONS

Prenatal exposure to famine was associated with an increased risk of type 2 diabetes in Chinese adults independent of genetic risk score using 21 variants common in the East Asian population. Famine exposure and genetic susceptibility may exhibit an additive effect on diabetes development.

The role of genetics in fetal programming of adult cardiometabolic disease

Disturbances affecting early development have broad repercussions on the individual's health during infancy and adulthood. Multiple observational studies throughout the years have shown that alterations of fetal growth are associated with increased cardiometabolic disease risks. However, the genetic component of this association only started to be investigated in the last 40 years, when single genes with distinct effects were investigated. Birth weight (BW), commonly reported as the outcome of developmental growth, has been estimated to be 20% to 60% heritable. Through Genome-Wide Association (GWA) meta-analyses, 190 different loci have been identified being associated with BW, and while many of these loci designate genes involved in glucose and lipid metabolism, with clear ties to fetal development, the role of others is not yet understood. In addition, due to its influence over the intrauterine environment, the maternal genotype also plays an important part in the determination of offspring BW, with the same loci having independent effects of different magnitude or even direction. There is still much to uncover regarding the genetic determinants of BW and the interactions between maternal, offspring, and even paternal genotype. To fully understand these, diverse and novel cohorts from multiple ancestries collecting extensive neonatal phenotype will be needed. This review compiles, chronologically, the main findings in the investigation of the genetics of BW.

Ten SNPs May Affect Type 2 Diabetes Risk in Interaction with Prenatal Exposure to Chinese Famine

Increasing studies have demonstrated that gene and famine may interact on type 2 diabetes risk. The data derived from the cross-sectional 2010-2012 China National Nutrition and Health Survey (CNNHS) was examined to explore whether gene and famine interacted to influence type 2 diabetes risk. In total, 2216 subjects were involved. The subjects born in 1960 and 1961 were selected as the famine-exposed group, whereas subjects born in 1963 were selected as the unexposed group. A Mass Array system was used to detect the genotypes of 50 related single-nucleotide polymorphisms (SNPs). Interactions were found between prenatal exposure to famine and ten SNPs (rs10401969, rs10886471, rs10946398, rs1470579, rs2796441, rs340874, rs3794991, rs5015480, rs7961581, and rs9470794) on type 2 diabetes risk after adjustments. The stratified results showed that famine exposure exacerbated the effect of CILP2-rs10401969 to fasting serum insulin (FINS), GRK5-rs10886471 to fasting plasma glucose (FPG) and FINS, IGF2BP2-rs1470579 to FINS, TLE1-rs2796441 to impaired fasting glucose (IFG), PROX1-rs340874 to impaired glucose tolerance (IGT), GATAD2A-rs3794991 to FINS, TSPAN8/LGR5-rs7961581 to FPG, and ZFAND3-rs9470794 to IGT and FINS. Famine exposure weakened the effect of CDKAL1-rs10946398 to type 2 diabetes. Famine exposure weakened the effect of HHEX-rs5015480 to IFG, but exacerbated the effect of HHEX-rs5015480 to FINS. The present study suggests that ten SNPs may affect type 2 diabetes risk in interaction with prenatal exposure to Chinese famine.

Exome sequencing of Finnish isolates enhances rare-variant association power

Exome-sequencing studies have generally been underpowered to identify deleterious alleles with a large effect on complex traits as such alleles are mostly rare. Because the population of northern and eastern Finland has expanded considerably and in isolation following a series of bottlenecks, individuals of these populations have numerous deleterious alleles at a relatively high frequency. Here, using exome sequencing of nearly 20,000 individuals from these regions, we investigate the role of rare coding variants in clinically relevant quantitative cardiometabolic traits. Exome-wide association studies for 64 quantitative traits identified 26 newly associated deleterious alleles. Of these 26 alleles, 19 are either unique to or more than 20 times more frequent in Finnish individuals than in other Europeans and show geographical clustering comparable to Mendelian disease mutations that are characteristic of the Finnish population. We estimate that sequencing studies of populations without this unique history would require hundreds of thousands to millions of participants to achieve comparable association power.

Renal injury after uninephrectomy in male and female intrauterine growth-restricted aged rats

Epidemiological studies report an inverse association between birth weight and risk for kidney disease that may differ between males and females, but studies investigating this association are limited. This study tested the hypothesis that male intrauterine growth-restricted offspring in a model of low birth weight induced by placental insufficiency in the rat exhibit enhanced renal injury in response to a persistent secondary renal insult while female growth-restricted offspring are protected. For this study, control offspring from sham-operated dams and growth-restricted offspring from reduced uterine perfusion dams underwent uninephrectomy or a sham procedure at 18 months of age. One month later, urinary markers of renal injury, renal function, and histological damage were measured. Results were analyzed using 2-way ANOVA. Male and female offspring were assessed separately. Proteinuria and urinary neutrophil gelatinase-associated lipocalin were significantly elevated in male growth-restricted offspring exposed to uninephrectomy when compared to male uninephrectomized control. Urinary kidney injury marker-1 was elevated in male uninephrectomized growth-restricted offspring relative to male sham growth-restricted but not to male uninephrectomized controls. Likewise, urinary neutrophil gelatinase-associated lipocalin was elevated in female uninephrectomized growth-restricted offspring but only when compared to female sham growth-restricted offspring. Markers of renal function including glomerular filtration rate and serum creatinine were impaired after uninephrectomy in female offspring regardless of birth weight. Histological parameters did not differ between control and growth-restricted offspring. Collectively, these studies suggest that both male and female growth-restricted offspring demonstrate susceptibility to renal injury following uninephrectomy; however, only male growth-restricted offspring exhibited an increase in renal markers of injury in response to uninephrectomy relative to same-sex control counterparts. These findings further suggest that urinary excretion of protein, kidney injury marker-1, and neutrophil gelatinase-associated lipocalin may be early markers of kidney injury in growth-restricted offspring exposed to a secondary renal insult such as reduction in renal mass.

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.

Developmental Origins of Health and Disease - from a small body size at birth to epigenetics

The Developmental Origins of Health and Disease (DOHaD) hypothesis proposes that several non-communicable diseases have their origins in prenatal life and in early childhood. This is believed to work through programming, an insult, taking place at a sensitive period of development, may have lifelong consequences, increasing and programming disease risk later in life. The Helsinki Birth Cohort Study (HBCS) has been focusing upon the importance of factors active during periods in early life and their influence on later health in 20,431 people born 1924-44. This review will focus upon findings from the HBCS over the past 20 years. Early growth patterns associated with coronary heart disease, type 2 diabetes and other health outcomes are described. The long-term health impact of maternal adiposity is also discussed. Potential underlying mechanisms explaining the associations are discussed including epigenetic factors. Key messages Several non-communicable diseases - including coronary heart disease and type 2 diabetes - have their origins in early life. Early life programming during sensitive periods of development may permanently program future health and disease risk. Optimizing the health and lifestyle of women of reproductive age will have positive health consequences for their offspring.

Islet biology, the CDKN2A/B locus and type 2 diabetes risk

Type 2 diabetes, fuelled by the obesity epidemic, is an escalating worldwide cause of personal hardship and public cost. Diabetes incidence increases with age, and many studies link the classic senescence and ageing protein p16(INK4A) to diabetes pathophysiology via pancreatic islet biology. Genome-wide association studies (GWASs) have unequivocally linked the CDKN2A/B locus, which encodes p16 inhibitor of cyclin-dependent kinase (p16(INK4A)) and three other gene products, p14 alternate reading frame (p14(ARF)), p15(INK4B) and antisense non-coding RNA in the INK4 locus (ANRIL), with human diabetes risk. However, the mechanism by which the CDKN2A/B locus influences diabetes risk remains uncertain. Here, we weigh the evidence that CDKN2A/B polymorphisms impact metabolic health via islet biology vs effects in other tissues. Structured in a bedside-to-bench-to-bedside approach, we begin with a summary of the evidence that the CDKN2A/B locus impacts diabetes risk and a brief review of the basic biology of CDKN2A/B gene products. The main emphasis of this work is an in-depth look at the nuanced roles that CDKN2A/B gene products and related proteins play in the regulation of beta cell mass, proliferation and insulin secretory function, as well as roles in other metabolic tissues. We finish with a synthesis of basic biology and clinical observations, incorporating human physiology data. We conclude that it is likely that the CDKN2A/B locus influences diabetes risk through both islet and non-islet mechanisms.

Developmental programming: State-of-the-science and future directions-Summary from a Pennington Biomedical symposium

OBJECTIVE

On December 8-9, 2014, the Pennington Biomedical Research Center convened a scientific symposium to review the state-of-the-science and future directions for the study of developmental programming of obesity and chronic disease. The objectives of the symposium were to discuss: (i) past and current scientific advances in animal models, population-based cohort studies, and human clinical trials, (ii) the state-of-the-science of epigenetic-based research, and (iii) considerations for future studies.

RESULTS

This symposium provided a comprehensive assessment of the state of the scientific field and identified research gaps and opportunities for future research in order to understand the mechanisms contributing to the developmental programming of health and disease.

CONCLUSIONS

Identifying the mechanisms which cause or contribute to developmental programming of future generations will be invaluable to the scientific and medical community. The ability to intervene during critical periods of prenatal and early postnatal life to promote lifelong health is the ultimate goal. Considerations for future research including the use of animal models, the study design in human cohorts with considerations about the timing of the intrauterine exposure, and the resulting tissue-specific epigenetic signature were extensively discussed and are presented in this meeting summary.

Role of high-risk variants in the development of impaired glucose metabolism was modified by birth weight in Han Chinese

BACKGROUND

The aim of this study was to investigate the role of common variants in the genes SLC30A8, KCNQ1, and TCF7L2 in the association between birth weight and increased risk of type 2 diabetes in Han Chinese.

METHODS

Seven variants (SLC30A8-rs13266634 and rs2466293; KCNQ1-rs2237895 and rs2074196; and TCF7L2-rs11196218, rs7903146, and rs290487) were genotyped in 1181 individuals born in Peking Union Medical College Hospital from 1921 to 1954 by Taqman allelic discrimination assay. All the subjects were stratified by birth weight into groups of ≥3000 g and <3000 g. Associations of genetic variants with birth weight and with risk of type 2 diabetes and impaired glucose tolerance (together as impaired glucose metabolism) were analysed.

RESULTS

After adjustment for sex, gestational weeks, parity, and maternal age, the G allele of KCNQ1-rs2074196 was associated with higher birth weight (p = 0.032). KCNQ1-rs2074196, rs2234895, and TCF7L2-rs290487 were associated with increased risk of impaired glucose metabolism. However, the associations were modified by size at birth. The associations above were only found in subjects with birth weights greater than (or equal to) 3000 g. In subjects with birth weights less than 3000 g, impaired glucose metabolism was associated with variants SLC30A8-rs2466293 and TCF7L2-rs11196218.

CONCLUSIONS

The role of common variants in susceptible genes in the development of impaired glucose metabolism was modified by birth weight in Han Chinese. This provides evidence that genetic variants influence birth weight and are involved in development of type 2 diabetes.

Gestational Diabetes – Metabolic Risks of Adult Women With Respect to Birth Weight

Metabolic disorders such as obesity, insulin resistance and other components of metabolic syndrome (MetS) are connected with birth weight. Low and high birth weight is associated with a higher risk of developing type 2 diabetes mellitus, the mechanism is not clear. In this study, we evaluated the association between birth weight and anthropometric as well as biochemical components of MetS in women with a history of gestational diabetes mellitus (GDM) in comparison with control women. In part of the GDM group, we re-evaluated metabolic changes over 5-8 years. Anthropometry, blood pressure, glucose metabolism during the 3-h oGTT, lipid profile, uric acid, thyroid hormones, and liver enzymes were assessed. From the analyzed components of MetS in adult women we proved the association of low birth weight (birth weight <25th percentile) with glucose processing, in particular among women with a history of GDM. Low birth weight GDM women revealed significantly higher postchallenge insulin secretion and lower peripheral insulin sensitivity. Re-examinations indicate this association persists long after delivery.

Does FTO have a paradoxical effect in fetal life?

Background

Low weight at birth is associated with obesity in later life. One hypothesis to explain such an association is that genetic variants that increase the risk of obesity also reduce fetal weight. Recently, obesity in adults was found to be associated with common variants of the fat mass and obesity-associated (FTO) gene. We examined the association between FTO polymorphisms and birth weight in a singleton, full-term birth cohort of 494 newborn-mother pairs without any complications.

Results

The risk alleles for obesity (“A” allele for the rs9939609 FTO variant and “G” allele for the rs9930506 FTO variant) were associated with low weight at birth. The mean differences per risk allele were −79 g (95% CI: −129 to −30; p = 0.002) for rs9939609 and −84 g (95% CI: −131 to −36; P < 0.001) for rs9930506. The level of association remained statistically significant after adjustment for the maternal risk allele and for variables usually associated with birth weight (−50 g, 95% CI: −99 to 0; p = 0.05 for rs9939609 and −48 g, 95% CI: −100 to 0; p = 0.05 for rs9930506). In the follow-up, the allelic difference in weight was attenuated over time.

Conclusions

The FTO variants that confer a predisposition to obesity later in life appear to be associated with low weight at birth. This finding favors the hypothesis of a common genetic denominator that predisposes to a low weight at birth and obesity in adults.

Genetic influences on the association between fetal growth and susceptibility to type 2 diabetes

The fetal insulin hypothesis proposes that low birth weight and susceptibility to type 2 diabetes (T2D) could both be two phenotypes of the same genotype. Insulin is a key growth factor in utero, and T2D is characterized by insulin resistance and/or beta-cell dysfunction. Therefore, genetic variants impacting on insulin secretion and action are likely to alter both fetal growth and susceptibility to T2D. There are three lines of evidence in support of this hypothesis. (1) Studies of rare monogenic diabetes have shown mutations in a single gene, such as GCK or KCNJ11, can cause diabetes by reducing insulin secretion, and these mutations are also associated with reduced birth weight. (2) Epidemiological studies have indicated that children born to fathers with diabetes are born smaller. As the father cannot influence the intrauterine environment, this association is likely to reflect genes inherited by the fetus from the father. (3) The most compelling evidence comes from recent genome-wide association studies. Variants in the CDKAL1 and HHEX-IDE genes that predispose to diabetes, if present in the fetus, are associated with reduced birth weight. These data provide evidence for a genetic contribution to the association between low birth weight and susceptibility to T2D. This genetic background is important to take into consideration when investigating the impact of environmental determinants and developing strategies for intervention and prevention.

Impact of size at birth and prematurity on adult anthropometry in 4744 middle-aged Danes - The Inter99 study

Low birth weight is related to increased risk of developing cardiovascular disease and type 2 diabetes in adult life. Since obesity is closely associated with type 2 diabetes and cardiovascular disease, the relationship between size at birth and adult anthropometry is of interest as a mediator of the relationship between birth weight and metabolic diseases. The aim of this study was, therefore, to examine the effect of size at birth and prematurity on measures of adult anthropometry taking adult socio-economic status and lifestyle variables into account. Midwife records with information on mother's age and parity as well as weight, length and maturity at birth were traced in 4744 Danes born between 1939 and 1970. Measures of adult anthropometry (weight, height, body mass index (BMI), waist circumference, hip circumference and waist/hip ratio) had previously been recorded together with information on socio-economic factors, lifestyle and parental diabetes status. Mother's age, parity and diabetes status were associated with offspring birth weight. Size at birth was positively associated with adult height and weight, but only weakly associated with BMI and not associated with waist/hip ratio when adjusted for socio-economic and lifestyle factors. Infants born preterm were less growth restricted at birth and grew to be taller and heavier compared with term infants born small for gestational age. Altogether, this study does not find evidence that obesity or a central fat distribution is mediating the relationship between low birth weight and risk of cardiovascular disease or type 2 diabetes in later life.

Susceptibility to type 2 diabetes mellitus--from genes to prevention

Knowledge of the genetics of type 2 diabetes mellitus (T2DM) has evolved tremendously over the past few years. Following advances in technology and analytical approaches, collaborative case-control genome-wide association studies have revealed up to 65 loci credibly associated with T2DM. Prospective population studies have demonstrated that aggregated genetic risk scores, so-called because they sum the genetic risk attributed to each locus, can predict incident T2DM among individuals of various age ranges and diverse ethnic backgrounds. With each set of T2DM loci discovered, increasing the number of loci in these scores has improved their predictive ability, although a prediction plateau may already have been reached. The current literature shows that intensive lifestyle interventions are effective for preventing T2DM at any level of genetic risk and might be particularly efficacious among individuals with high genetic susceptibility. By contrast, counselling to inform patients about their personal T2DM genetic risk profiles does not seem to improve motivation or attitudes that lead to positive lifestyle behaviour changes. Future studies should investigate the role of genetics for both T2DM prediction and prevention in young populations in the hope of reducing disease burden for future generations.

JAZF1 can regulate the expression of lipid metabolic genes and inhibit lipid accumulation in adipocytes

JAZF1 is a newly identified gene with unknown functions. A recent genome-wide association study showed that JAZF1 is associated with type 2 diabetes and is highly expressed in liver and adipose tissue. Studies have demonstrated that JAZF1 is the co-repressor for nuclear orphan receptor TAK1, whereas most nuclear orphan receptor family members are involved in the regulation of lipid metabolism. Therefore, JAZF1 could be closely related to glycolipid metabolism. In this study, JAZF1 was significantly upregulated during the induced differentiation process of 3T3-L1 preadipocytes. The overexpression of JAZF1 inhibited lipid accumulation in differentiated mature 3T3-L1 adipocytes and significantly inhibited the expression of SREBPl, ACC, and FAS, which were important in lipid synthesis, while upregulating the expression of key enzyme hormone-sensitive lipase in lipoclasis. Moreover, SREBPl exhibited an inhibitory function on the expression of JAZF1. SREBP1 reversed the inhibitory action on lipid accumulation of JAZF1. SREBP1 and JAZF1 were observed to regulate each other in adipocytes. Therefore, JAZF1 could regulate the expression of particular genes related to lipid metabolism and inhibit lipid accumulation in adipocytes. This result suggests that JAZF1 may be a potential target for the treatment of diseases, such as obesity and lipid metabolism disorders.

Genetic susceptibility to type 2 diabetes and obesity: follow-up of findings from genome-wide association studies

Elucidating the underlying genetic variations influencing various complex diseases is one of the major challenges currently facing clinical genetic research. Although these variations are often difficult to uncover, approaches such as genome-wide association studies (GWASs) have been successful at finding statistically significant associations between specific genomic loci and disease susceptibility. GWAS has been especially successful in elucidating genetic variants that influence type 2 diabetes (T2D) and obesity/body mass index (BMI). Specifically, several GWASs have confirmed that a variant in transcription factor 7-like 2 (TCF7L2) confers risk for T2D, while a variant in fat mass and obesity-associated protein (FTO) confers risk for obesity/BMI; indeed both of these signals are considered the most statistically associated loci discovered for these respective traits to date. The discovery of these two key loci in this context has been invaluable for providing novel insight into mechanisms of heritability and disease pathogenesis. As follow-up studies of TCF7L2 and FTO have typically lead the way in how to follow up a GWAS discovery, we outline what has been learned from such investigations and how they have implications for the myriad of other loci that have been subsequently reported in this disease context.

The architecture of risk for type 2 diabetes: understanding Asia in the context of global findings

The prevalence of Type 2 diabetes is rising rapidly in both developed and developing countries. Asia is developing as the epicentre of the escalating pandemic, reflecting rapid transitions in demography, migration, diet, and lifestyle patterns. The effective management of Type 2 diabetes in Asia may be complicated by differences in prevalence, risk factor profiles, genetic risk allele frequencies, and gene-environment interactions between different Asian countries, and between Asian and other continental populations. To reduce the worldwide burden of T2D, it will be important to understand the architecture of T2D susceptibility both within and between populations. This review will provide an overview of known genetic and nongenetic risk factors for T2D, placing the results from Asian studies in the context of broader global research. Given recent evidence from large-scale genetic studies of T2D, we place special emphasis on emerging knowledge about the genetic architecture of T2D and the potential contribution of genetic effects to population differences in risk.

Birth weight, genetic susceptibility, and adulthood risk of type 2 diabetes

OBJECTIVE

Both stressful intrauterine milieus and genetic susceptibility have been linked to later-life diabetes risk. The current study aims to examine the interaction between low birth weight, a surrogate measure of stressful intrauterine milieus, and genetic susceptibility in relation to risk of type 2 diabetes in adulthood.

RESEARCH DESIGN AND METHODS

The analysis included two independent, nested case-control studies of 2,591 type 2 diabetic case subjects and 3,052 healthy control subjects. We developed two genotype scores: an obesity genotype score based on 32 BMI-predisposing variants and a diabetes genotype score based on 35 diabetes-predisposing variants.

RESULTS

Obesity genotype scores showed a stronger association with type 2 diabetes risk in individuals with low birth weight. In low-birth weight individuals, the multivariable-adjusted odds ratio (OR) was 2.55 (95% CI 1.34-4.84) by comparing extreme quartiles of the obesity genotype score, while the OR was 1.27 (1.04-1.55) among individuals with birth weight >2.5 kg (P for interaction = 0.017). We did not observe significant interaction between diabetes genotype scores and birth weight with regard to risk of type 2 diabetes. In a comparison of extreme quartiles of the diabetes gene score, the multivariable-adjusted OR was 3.80 (1.76-8.24) among individuals with low birth weight and 2.27 (1.82-2.83) among those with high birth weight (P for interaction = 0.16).

CONCLUSIONS

Our data suggest that low birth weight and genetic susceptibility to obesity may synergistically affect adulthood risk of type 2 diabetes.

Early determinants of type-2 diabetes

The global prevalence of type-2 diabetes (T2D) has more than doubled in the last 30 years and is predicted to continue to rise at an alarming rate. The associated health and financial burdens are considerable. The aetiology of common forms of T2D is multifactorial and involves a complex interplay between genetic, epigenetic and environmental factors. The influential role of the environment, in particular our diet and sedentary lifestyles, in diabetes risk is well established. Of major concern is the increasing prevalence of early onset T2D or pre-diabetic characteristics in children. In recent years, the role of the early life environment in programming diabetes risk has been the focus of numerous human and animal studies. Historical studies highlighted an association between low birthweight, a proxy for suboptimal in utero growth, and diabetes risk in adulthood. Over more recent years it has become apparent that a variety of expositions, including maternal obesity and/or maternal diabetes, can have a significant effect on offspring health outcomes. Further complicating matters, paternal and transgenerational transmission of T2D can occur thus mediating a perpetuating cycle of disease risk between generations. It is imperative for the underlying mechanisms to be elucidated so that interventions can be introduced. In doing so, it may be possible to prevent, delay or reverse a pre-programmed risk for T2D induced by pre- and/or postnatal environmental factors to improve health outcomes and curb premature metabolic decline. This review presents evidence for how the early life environment may programme T2D risk and suggests some mechanisms by which this may occur.

Genetics of type 2 diabetes in European populations

Type 2 diabetes (T2D) has become a leading health problem throughout the world. It is caused by environmental and genetic factors, as well as interactions between the two. However, until very recently, the T2D susceptibility genes have been poorly understood. During the past 5 years, with the advent of genome-wide association studies (GWAS), a total of 58 T2D susceptibility loci have been associated with T2D risk at a genome-wide significance level (P < 5 × 10(-8) ), with evidence showing that most of these genetic variants influence pancreatic β-cell function. Most novel T2D susceptibility loci were identified through GWAS in European populations and later confirmed in other ethnic groups. Although the recent discovery of novel T2D susceptibility loci has contributed substantially to our understanding of the pathophysiology of the disease, the clinical utility of these loci in disease prediction and prognosis is limited. More studies using multi-ethnic meta-analysis, gene-environment interaction analysis, sequencing analysis, epigenetic analysis, and functional experiments are needed to identify new susceptibility T2D loci and causal variants, and to establish biological mechanisms.

Factors predicting nongenetic variability in body weight gain induced by a high-fat diet in inbred C57BL/6J mice

Inbred C57BL/6J mice displayed large individual variations in weight gain when fed a high-fat diet (HFD). The objective of this study was to examine whether this predominantly nongenetic variability could be predicted by relevant baseline features and to explore whether variations in these significant features were influenced during pregnancy and/or lactation. Fat mass (FM), fat-free mass (FFM), food intake (FI), resting metabolic rate (RMR), physical activity (PA), and body temperature (T(b)) were all evaluated at baseline in 60 mice (aged 10-12 weeks) before HFD feeding. Regression analyses showed that baseline FM was a strong positive predictor of weight gain between 4 and 16 weeks of HFD. Baseline PA was negatively associated with weight gain at week 8, 12, and 16, and baseline FFM had a positive effect at week 12 and 16. In a second experiment, 40 female mice were mated and litter sizes (LS) were manipulated on day 3 of lactation. Weaning weight and postweaning growth rate (GR) had positive impacts on FM and FFM at age 9 weeks (FM, P = 0.001; FFM, P < 0.001: n = 97). Lactation LS had a negative effect on weaning weight and a positive effect on postweaning GR. In conclusion, our results show that obesity induced by HFD was associated with a higher baseline FM, a higher baseline FFM and a lower baseline PA level before the exposure of HFD. Two of these traits (FM and FFM) were influenced by lactation LS via weaning weight and postweaning GR.

Genetic origins of low birth weight

PURPOSE OF REVIEW

Smaller size at birth is associated with a higher risk of type 2 diabetes in later life, but the mechanisms behind this association are poorly understood. Genetic variants which influence susceptibility to type 2 diabetes via effects on insulin secretion or action are good candidates for association with birth weight because foetal insulin is a key foetal growth factor. This review will focus on recent progress in identifying associations between common genetic variants and birth weight.

RECENT FINDINGS

Foetal genetic variants at two loci (near CCNL1 and in ADCY5) were robustly associated with birth weight via the foetal genotype in the first genome-wide association study of birth weight. The birth weight-lowering allele at ADCY5 also predisposes to type 2 diabetes. In addition, evidence from studies of other type 2 diabetes loci is accumulating for association between the foetal risk alleles at CDKAL1 and HHEX-IDE and lower birth weight, and the maternal risk alleles at GCK and TCF7L2 and higher birth weight.

SUMMARY

The associations with birth weight at ADCY5, CDKAL1 and HHEX-IDE support the foetal insulin hypothesis, which proposed that type 2 diabetes and lower birth weight could be two phenotypes of the same genotype. The associations at GCK and TCF7L2 illustrate that maternal genes are also important determinants of birth weight.

Replication of a genome-wide association study of birth weight in preterm neonates

OBJECTIVE

To examine associations between rs9883204 in ADCY5 and rs900400 near LEKR1 and CCNL1 with birth weight in a preterm population. Both markers were associated with birth weight in a term population in a recent genome-wide association study of Freathy et al.

STUDY DESIGN

A meta-analysis of mother and infant samples was performed for associations of rs900400 and rs9883204 with birth weight in 393 families from the US, 265 families from Argentina, and 735 mother-infant pairs from Denmark. Z-scores adjusted for infant sex and gestational age were generated for each population separately and regressed on allele counts. Association evidence was combined across sites by inverse-variance weighted meta-analysis.

RESULTS

Each additional C allele of rs900400 (LEKR1/CCNL1) in infants was marginally associated with a 0.069 SD lower birth weight (95% CI, -0.159 to 0.022; P = .068). This result was slightly more pronounced after adjusting for smoking (P = .036). No significant associations were identified with rs9883204 or in maternal samples.

CONCLUSIONS

These results indicate the potential importance of this marker on birth weight regardless of gestational age.

Early growth and coronary heart disease and type 2 diabetes: findings from the Helsinki Birth Cohort Study (HBCS)

A slow rate of intrauterine growth is a major risk factor for several common noncommunicable diseases, which include the following: coronary heart disease (CHD), hypertension, and type 2 diabetes. Likewise, growth patterns in infancy and childhood have been identified as important factors linked to the pathogenesis of these disorders. In this overview, patterns of growth associated with CHD, type 2 diabetes, and related metabolic traits in adult life are presented on the basis of findings from the Helsinki Birth Cohort Study (HBCS) 1934-1944. Later risk of CHD was associated with small body size at birth and during infancy, followed by an increase in body size later in childhood. This pattern of growth has been associated with dyslipidemia in later life, which offers an explanation for the observed findings. Type 2 diabetes and CHD share several risk factors. The early growth of persons who later develop type 2 diabetes includes a small body size at birth as well as a small body size during infancy. An early age at adiposity rebound was associated with a markedly increased risk of type 2 diabetes in adulthood. The patterns of growth associated with type 2 diabetes are also associated with alterations in body composition, which predisposes to insulin resistance and the metabolic syndrome. The presented findings suggest that to be able to understand the pathogenesis of several noncommunicable diseases, the diseases need to be studied from a life-course perspective, and prenatal and childhood growth as well as adult characteristics need to be taken into account.

The birth weight lowering C-allele of rs900400 near LEKR1 and CCNL1 associates with elevated insulin release following an oral glucose challenge

Background and Aim

The first genome-wide association study on birth weight was recently published and the most significant associated birth weight lowering variant was the rs900400 C-allele located near LEKR1 and CCNL1. We aimed to replicate the association with birth weight in the Danish Inter99 study and furthermore to evaluate associations between rs900400 and indices of insulin secretion and insulin sensitivity obtained by oral glucose tolerance tests in adults from the Danish Inter99 study and the Finnish, Metabolic Syndrome in Men (METSIM) sample.

Methods

For 4,744 of 6,784 Inter99 participants, midwife journals were traced through the Danish State Archives and association of rs900400 with birth weight was examined. Associations between rs900400 and fasting serum insulin, fasting plasma glucose, insulinogenic index, homeostasis model assessment of insulin resistance (HOMA-IR) and disposition index were studied in 5,484 Danish and 6,915 Finnish non-diabetic individuals and combined in meta-analyses.

Results

The C-allele of rs900400 was associated with a 22.1 g lower birth weight ([−41.3;−3.0], P = 0.024) per allele. Moreover, in combined analyses of the Danish Inter99 study and the Finnish METSIM study we found that the birth weight lowering allele was associated with increased insulin release measured by the insulinogenic index (β = 2.25% [0.59; 3.91], P = 0.008) and with an increased disposition index (β = 1.76% [0.04; 3.49], P = 0.05).

Conclusion

The birth weight lowering effect of the C-allele of rs900400 located near LEKR1 and CCNL1 was replicated in the Danish population. Furthermore the C-allele was associated with increased insulin response following oral glucose stimulation in a meta-analysis based on Danish and Finnish non-diabetic individuals.

Genome-wide association studies (GWAS): impact on elucidating the aetiology of diabetes

It has proven to be challenging to isolate the genes underlying the genetic components conferring susceptibility to type 1 and type 2 diabetes. Unlike previous approaches, 'genome-wide association studies' have extensively delivered on the promise of uncovering genetic determinants of complex diseases, with a number of novel disease-associated variants being largely replicated by independent groups. This review provides an overview of these recent breakthroughs in the context of type 1 and type 2 diabetes, and outlines strategies on how these findings will be applied to impact clinical care for these two highly prevalent disorders.

The effect of ponderal index at birth on the relationships between common LEP and LEPR polymorphisms and adiposity in adolescents

This study examined the effect of ponderal index (PI) at birth on the relationships between eight common polymorphisms of the leptin (LEP) and leptin receptor (LEPR) genes and adiposity in adolescents. A total of 823 European adolescents (45.4% girls) aged 14.8 ± 1.4 years were genotyped for the LEP (rs2167270, rs12706832, rs10244329, rs2071045, and rs3828942) and LEPR (rs1137100, rs1137101, and rs8179183) polymorphisms. The PI was calculated from parental reports of birth weight and length. Fat mass index (FMI) was calculated. Analyses were adjusted for relevant confounders. An "adiposity-risk-allele score" based on genotypes at the three single-nucleotide polymorphisms (SNPs) associated with adolescents' FMI in adolescents within the lower tertile of PI was calculated. The LEP rs10244329 and rs3828942 polymorphisms were associated with higher FMI only in adolescents within the lower PI tertile (+0.55 kg/m(2) per minor T allele, P = 0.040, and +0.58 kg/m(2) per major G allele, P = 0.028, respectively). The LEPR rs8179183 polymorphism was significantly associated with higher FMI in adolescents within the lower PI tertile (+0.87 kg/m(2) per minor C allele, P = 0.006). After correction for multiple comparisons, only the association between the LEPR rs8179183 and FMI persisted. However, each additional risk allele conferred 0.53 kg/m(2) greater FMI in adolescents within the lower tertile of PI (P = 0.008). In conclusion, our results suggest that those adolescents born with lower PI could be more vulnerable to the influence of the LEP rs10244329 and rs3828942 polymorphisms and LEPR rs8179183 polymorphism on total adiposity content. Due to the relatively small sample size, these findings should be replicated in further larger population samples.

Differential nongenetic impact of birth weight versus third-trimester growth velocity on glucose metabolism and magnetic resonance imaging abdominal obesity in young healthy twins

CONTEXT

Low birth weight is associated with type 2 diabetes, which to some extent may be mediated via abdominal adiposity and insulin resistance. Fetal growth velocity is high during the third trimester, constituting a potential critical window for organ programming. Intra-pair differences among monozygotic twins are instrumental in determining nongenetic associations between early environment and adult metabolic phenotype.

OBJECTIVE

Our objective was to investigate the relationship between size at birth and third-trimester growth velocity on adult body composition and glucose metabolism using intra-pair differences in young healthy twins.

METHODS

Fifty-eight healthy twins (42 monozygotic/16 dizygotic) aged 18-24 yr participated. Insulin sensitivity was assessed using hyperinsulinemic-euglycemic clamps. Whole-body fat was assessed by dual-energy x-ray absorptiometry scan, whereas abdominal visceral and sc fat (L1-L4) were assessed by magnetic resonance imaging. Third-trimester growth velocity was determined by repeated ultrasound examinations.

RESULTS

Size at birth was nongenetically inversely associated with adult visceral and sc fat accumulation but unrelated to adult insulin action. In contrast, fetal growth velocity during third trimester was not associated with adult visceral or sc fat accumulation. Interestingly, third-trimester growth was associated with insulin action in a paradoxical inverse manner.

CONCLUSIONS

Abdominal adiposity including accumulation of both sc and visceral fat may constitute primary nongenetic factors associated with low birth weight and reduced fetal growth before the third trimester. Reduced fetal growth during vs. before the third trimester may define distinct adult trajectories of metabolic and anthropometric characteristics influencing risk of developing type 2 diabetes.

Developmental origins of health and disease: experimental and human evidence of fetal programming for metabolic syndrome

The concept of developmental origins of health and disease has been defined as the process through which the environment encountered before birth, or in infancy, shapes the long-term control of tissue physiology and homeostasis. The evidence for programming derives from a large number of experimental and epidemiological observations. Several nutritional interventions during diverse phases of pregnancy and lactation in rodents are associated with fetal and neonatal programming for metabolic syndrome. In this paper, recent experimental models and human epidemiological studies providing evidence for the fetal programming associated with the development of metabolic syndrome and related diseases are revisited.

Type 2 diabetes risk alleles near ADCY5, CDKAL1 and HHEX-IDE are associated with reduced birthweight

AIMS/HYPOTHESIS

The fetal insulin hypothesis suggests that variation in the fetal genotype influencing insulin secretion or action may predispose to low birthweight and type 2 diabetes. We examined associations between 25 confirmed type 2 diabetes risk variants and birthweight in individuals from the Danish Inter99 population and in meta-analyses including Inter99 data and reported studies.

METHODS

Midwife records from the Danish State Archives provided information on mother's age and parity, as well as birthweight, length at birth and prematurity of the newborn in 4,744 individuals of the population-based Inter99 study. We genotyped 25 risk alleles showing genome-wide associations with type 2 diabetes.

RESULTS

Birthweight was inversely associated with the type 2 diabetes risk alleles of ADCY5 rs11708067 (beta = -33 g [95% CI -55, -10], p = 0.004) and CDKAL1 rs7756992 (beta = -22 g [95% CI -43, -1], p = 0.04). The association for the latter locus was confirmed in a meta-analysis (n = 24,885) (beta = -20 g [95% CI -29, -11], p = 5 x 10(-6)). The HHEX-IDE rs1111875 variant showed no significant association among Danes (p = 0.09); however, in a meta-analysis (n = 25,164) this type 2 diabetes risk allele was associated with lower birthweight (beta = -16 g [95% CI -24, -8], p = 8 x 10(-5)). On average, individuals with high genetic risk (>or=25 type 2 diabetes risk alleles) weighed marginally less at birth than those with low genetic risk (<25 type 2 diabetes risk alleles) (beta = -35 g [95% CI -69, -2], p = 0.037).

CONCLUSIONS/INTERPRETATION

We report a novel association between the fetal ADCY5 type 2 diabetes risk allele and decreased birthweight, and confirm in meta-analyses associations between decreased birthweight and the type 2 diabetes risk alleles of HHEX-IDE and CDKAL1. No strong general effect on birthweight can be ascribed to the 25 common type 2 diabetes risk alleles.

Obesity and diabetes genes are associated with being born small for gestational age: results from the Auckland Birthweight Collaborative study

Background

Individuals born small for gestational age (SGA) are at increased risk of rapid postnatal weight gain, later obesity and diseases in adulthood such as type 2 diabetes, hypertension and cardiovascular diseases. Environmental risk factors for SGA are well established and include smoking, low pregnancy weight, maternal short stature, maternal diet, ethnic origin of mother and hypertension. However, in a large proportion of SGA, no underlying cause is evident, and these individuals may have a larger genetic contribution.

Methods

In this study we tested the association between SGA and polymorphisms in genes that have previously been associated with obesity and/or diabetes. We undertook analysis of 54 single nucleotide polymorphisms (SNPs) in 546 samples from the Auckland Birthweight Collaborative (ABC) study. 227 children were born small for gestational age (SGA) and 319 were appropriate for gestational age (AGA).

Results and Conclusion

The results demonstrated that genetic variation in KCNJ11, BDNF, PFKP, PTER and SEC16B were associated with SGA and support the concept that genetic factors associated with obesity and/or type 2 diabetes are more prevalent in those born SGA compared to those born AGA. We have previously determined that environmental factors are associated with differences in birthweight in the ABC study and now we have demonstrated a significant genetic contribution, suggesting that the interaction between genetics and the environment are important.

Genetics of type 2 diabetes

PURPOSE OF REVIEW

To provide an overview of the genetics of type 2 diabetes in the context of recent progress in the understanding of the genetic architecture of the disease and its applicability to the pathogenesis of the disease as well as efforts to individualize therapy in type 2 diabetes. Efforts are underway to understand how these loci alter measurable physiologic processes in nondiabetic humans. However, it is important to understand the potential pitfalls in such studies and the limitations underlying measurement of insulin secretion and action using qualitative methodologies.

RECENT FINDINGS

The availability of large population-based cohorts and the ease with which large numbers of common genetic variants can be genotyped has enabled the discovery of multiple loci and pathways associated with type 2 diabetes. Recent efforts examining quantitative traits such as fasting glucose concentrations have led to the discovery of other genes likely to be important in the development of diabetes.

SUMMARY

The past 4 years have witnessed a significant increase in our understanding of genetic predisposition to type 2 diabetes. Hopefully more progress will be made in applying this knowledge to the pathophysiology of type 2 diabetes in the coming years.

Transcription factor 7-like 2 (TCF7L2) polymorphism and hyperglycemia in an adult Italian population-based cohort

OBJECTIVE

To assess whether TCF7L2 polymorphism has a role in the deterioration of glycemic control.

RESEARCH DESIGN AND METHODS

Metabolic variables were evaluated at baseline and after 6-year follow-up in 1,480 Caucasian subjects from a population-based cohort.

RESULTS

At baseline, T-allele carriers showed significantly lower BMI and homeostasis model assessment for beta-cell function (HOMA-B) values and higher fasting glycemia and diabetes prevalence. At follow-up, fasting glucose and HOMA-B index were increased and reduced, respectively, in carriers of the T-allele. Incident impaired fasting glucose (IFG) and incident diabetes were 5.7, 10.7, 16.9% and 1.6, 1.7, 3.0% in the CC, CT, and TT genotypes, respectively. In a multiple logistic regression model, the association between incident IFG and the T-allele was significant (odds ratio [OR] 2.08 [95% CI 1.35-3.20] and 3.56 [2.11-5.98] in CT and TT genotypes, respectively).

CONCLUSIONS

The T-allele of TCF7L2 rs7903146 polymorphism was independently associated with increasing fasting glucose values toward hyperglycemia in the follow-up.

Novel biological insights emerging from genetic studies of type 2 diabetes and related metabolic traits

PURPOSE OF REVIEW

In the past 3 years, genome-wide association studies have identified many tens of common genetic variants associated with metabolic diseases and traits. Although much further research is needed to identify the target genes, the associations between gene variants and diseases are already providing biological insights. The purpose of this review is to update the reader with the most relevant findings, with a particular emphasis on type 2 diabetes (T2D) and glucose metabolism, and discuss some of the biological implications of the genetic findings.

RECENT FINDINGS

Largely through recent genome-wide association studies, we now know of approximately 20 gene variants associated with T2D, 10 with body mass index (BMI) and obesity, four with fasting glucose levels in the normoglycaemic population and over 30 with lipid levels. These findings are stimulating many new important areas of research related to metabolic diseases. For T2D and glucose metabolism, we discuss a number of aspects and implications of the genetic findings, including the observations that T2D gene variants are not usually in or near obvious candidate genes, highlighting the poor prior knowledge of the biology of the disease; most T2D gene variants are associated with beta-cell function rather than insulin resistance; there is a difference between genes that influence variation in normal glucose levels compared with those influencing onset and progression of diabetes; and there is a genetic link between diabetes and foetal growth.

SUMMARY

Genetic studies in the past 3 years have provided a greatly increased knowledge of the regions of the genome involved in adverse metabolic consequences. There are now over 100 common genetic variants reproducibly associated with metabolic traits, including reduced beta-cell function, obesity, increased lipid levels and increased glucose levels. These genetic findings are already altering perceptions of how these traits develop and interact to result in diseases such as T2D.

Interactions between genetic factors that predict diabetes and dietary factors that ultimately impact on risk of diabetes

PURPOSE OF REVIEW

The purpose of the present review is to summarize recent advances in investigations of interactions between established genetic and dietary risk factors for type 2 diabetes (T2D).

RECENT FINDINGS

Several studies reported that dietary factors related to carbohydrate quality and quantity, such as whole grains and glycemic load, might interact with transcription factor 7-like 2 variants in relation to T2D risk. The genetic predisposition defined by the combination of 10 established T2D risk alleles was found to modulate the association between Western dietary pattern (high intakes of red meat, processed meat, and low fiber) and T2D; a stronger association was observed in those with a high-risk genetic profile. Variants in genes HHEX, CDKN2A/2B, JAZF1, and IGF2BP2 were found to interact with prenatal nutrition in relation to T2D risk and glucose levels in later life.

SUMMARY

The available data provide preliminary support for the gene-diet interactions in determining T2D. However, most findings have yet to be validated. Future studies will need agreed standards of study design and statistical power, dietary measurement, analytical methods, and replication strategies.

Examination of type 2 diabetes loci implicates CDKAL1 as a birth weight gene

OBJECTIVE

A number of studies have found that reduced birth weight is associated with type 2 diabetes later in life; however, the underlying mechanism for this correlation remains unresolved. Recently, association has been demonstrated between low birth weight and single nucleotide polymorphisms (SNPs) at the CDKAL1 and HHEX-IDE loci, regions that were previously implicated in the pathogenesis of type 2 diabetes. In order to investigate whether type 2 diabetes risk-conferring alleles associate with low birth weight in our Caucasian childhood cohort, we examined the effects of 20 such loci on this trait.

RESEARCH DESIGN AND METHODS

Using data from an ongoing genome-wide association study in our cohort of 5,465 Caucasian children with recorded birth weights, we investigated the association of the previously reported type 2 diabetes-associated variation at 20 loci including TCF7L2, HHEX-IDE, PPARG, KCNJ11, SLC30A8, IGF2BP2, CDKAL1, CDKN2A/2B, and JAZF1 with birth weight.

RESULTS

Our data show that the minor allele of rs7756992 (P = 8 x 10(-5)) at the CDKAL1 locus is strongly associated with lower birth weight, whereas a perfect surrogate for variation previously implicated for the trait at the same locus only yielded nominally significant association (P = 0.01; r(2) rs7756992 = 0.677). However, association was not detected with any of the other type 2 diabetes loci studied.

CONCLUSIONS

We observe association between lower birth weight and type 2 diabetes risk-conferring alleles at the CDKAL1 locus. Our data show that the same genetic locus that has been identified as a marker for type 2 diabetes in previous studies also influences birth weight.

Type 2 diabetes gene TCF7L2 polymorphism is not associated with fetal and postnatal growth in two birth cohort studies

Background

An inverse association between birth weight and the risk of developing type 2 diabetes (T2D) in adulthood has been reported. This association may be explained by common genetic variants related to insulin secretion and resistance, since insulin is the most important growth factor in fetal life. The objective of this study was to examine whether T2D gene polymorphism TCF7L2 rs7903146 is associated with growth patterns from fetal life until infancy.

Methods

This study was performed in two independent birth cohort studies, one prospective population-based (Generation R), and one of subjects born small-for-gestational-age (SGA cohort). Fetal growth was assessed by ultrasounds in second and third trimesters of pregnancy in Generation R. Growth in infancy was assessed in both cohorts at birth and at 6, 12 and 24 months postnatally. TCF7L2 genotype was determined in 3,419 subjects in Generation R and in 566 subjects in the SGA cohort.

Results

Minor allele frequency did not differ significantly (p = 0.47) between Generation R (T-allele: 28.7%) and the SGA cohort (T-allele: 29.8%). No differences at birth were found in gestational age or size (head circumference, length, weight) between the genotypes in either cohort. TCF7L2 genotype was also not associated with any pre- or postnatal growth characteristic in either Generation R or the SGA cohort.

Conclusion

We found no evidence for an association between TCF7L2 genotype and fetal and early postnatal growth. Furthermore, this TCF7L2 polymorphism was not associated with an increased risk of SGA.