Variation at the insulin gene VNTR (variable number tandem repeat) polymorphism and early growth: studies in a large Finnish birth cohort

Environmental health influences in pregnancy and risk of gestational diabetes mellitus: a systematic review

Background

Gestational diabetes mellitus (GDM) is one of the most common pregnancy complications globally. Environmental risk factors may lead to increased glucose levels and GDM, which in turn may affect not only the health of the mother but assuming hypotheses of "fetal programming", also the health of the offspring. In addition to traditional GDM risk factors, the evidence is growing that environmental influences might affect the development of GDM. We conducted a systematic review analyzing the association between several environmental health risk factors in pregnancy, including climate factors, chemicals and metals, and GDM.

Methods

We performed a systematic literature search in Medline (PubMed), EMBASE, CINAHL, Cochrane Library and Web of Science Core Collection databases for research articles published until March 2021. Epidemiological human and animal model studies that examined GDM as an outcome and / or glycemic outcomes and at least one environmental risk factor for GDM were included.

Results

Of n = 91 studies, we classified n = 28 air pollution, n = 18 persistent organic pollutants (POP), n = 11 arsenic, n = 9 phthalate n = 8 bisphenol A (BPA), n = 8 seasonality, n = 6 cadmium and n = 5 ambient temperature studies. In total, we identified two animal model studies. Whilst we found clear evidence for an association between GDM and air pollution, ambient temperature, season, cadmium, arsenic, POPs and phthalates, the findings regarding phenols were rather inconsistent. There were clear associations between adverse glycemic outcomes and air pollution, ambient temperature, season, POPs, phenols, and phthalates. Findings regarding cadmium and arsenic were heterogeneous (n = 2 publications in each case).

Conclusions

Environmental risk factors are important to consider in the management and prevention of GDM. In view of mechanisms of fetal programming, the environmental risk factors investigated may impair the health of mother and offspring in the short and long term. Further research is needed.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12889-022-13965-5.

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.

The association of insertions/deletions (INDELs) and variable number tandem repeats (VNTRs) with obesity and its related traits and complications

BACKGROUND

Despite the fact that insertions/deletions (INDELs) are the second most common type of genetic variations and variable number tandem repeats (VNTRs) represent a large portion of the human genome, they have received far less attention than single nucleotide polymorphisms (SNPs) and larger forms of structural variation like copy number variations (CNVs), especially in genome-wide association studies (GWAS) of complex diseases like polygenic obesity. This is exemplified by the vast amount of review papers on the role of SNPs and CNVs in obesity, its related traits (like anthropometric measurements, biochemical variables, and eating behavior), and its related complications (like hypertension, hypertriglyceridemia, hypercholesterolemia, and insulin resistance-collectively known as metabolic syndrome). Hence, this paper reviews the types of INDELs and VNTRs that have been studied for association with obesity and its related traits and complications. These INDELs and VNTRs could be found in the obesity loci or genes from the earliest GWAS and candidate gene association studies, like FTO, genes in the leptin-proopiomelanocortin pathway, and UCP2/3. Given the important role of the brain serotonergic and dopaminergic reward system in obesity susceptibility, the association of INDELs and VNTRs in these neurotransmitters' metabolism and transport genes with obesity is also reviewed. Next, the role of INS VNTR in obesity and its related traits is questionable, since recent large-scale studies failed to replicate the earlier positive associations. As obesity results in chronic low-grade inflammation of the adipose tissue, the proinflammatory cytokine gene IL1RA and anti-inflammatory cytokine gene IL4 have VNTRs that are implicated in obesity. A systemic proinflammatory state in combination with activation of the renin-angiotensin system and decreased nitric oxide bioavailability as found in obesity leads to endothelial dysfunction. This explains why VNTR and INDEL in eNOS and ACE, respectively, could be predisposing factors of obesity. Finally, two novel genes, DOCK5 and PER3, which are involved in the regulation of the Akt/MAPK pathway and circadian rhythm, respectively, have VNTRs and INDEL that might be associated with obesity.

SHORT CONCLUSION

In conclusion, INDELs and VNTRs could have important functional consequences in the pathophysiology of obesity, and research on them should be continued to facilitate obesity prediction, prevention, and treatment.

Insulin-like growth factor 1 gene (CA)n repeats and a variable number of tandem repeats of the insulin gene in Brazilian children born small for gestational age

OBJECTIVE

To investigate the influence of (CA)n repeats in the insulin-like growth factor 1 gene and a variable number of tandem repeats of the insulin gene on birth size in children who are small or adequate-sized for gestational age and to correlate these polymorphisms with serum insulin-like growth factor 1 levels and insulin sensitivity in children who are small for gestational age, with and without catch-up growth.

PATIENTS AND METHODS

We evaluated 439 infants: 297 that were adequate-sized for gestational age and 142 that were small for gestational age (66 with and 76 without catch-up). The number of (CA)n repeat in the insulin-like growth factor 1 gene and a variable number of tandem repeats in the insulin gene were analyzed using GENESCAN software and polymerase chain reaction followed by enzymatic digestion, respectively. Clinical and laboratory data were obtained from all patients.

RESULTS

The height, body mass index, paternal height, target height and insulin-like growth factor 1 serum levels were higher in children who were small for gestational age with catch-up. There was no difference in the allelic and genotypic distributions of both polymorphisms between the adequate-sized and small infants or among small infants with and without catch-up. Similarly, the polymorphisms were not associated with clinical or laboratory variables.

CONCLUSION

Polymorphisms of the (CA)n repeats of the insulin-like growth factor 1 gene and a variable number of tandem repeats of the insulin gene, separately or in combination, did not influence pre- or postnatal growth, insulin-like growth factor 1 serum levels or insulin resistance.

Diabetic and metabolic programming: mechanisms altering the intrauterine milieu

A wealth of epidemiological, clinical, and experimental studies have been linked to poor intrauterine conditions as well as metabolic and associated cardiovascular changes postnatal. These are novel perspectives connecting the altered intrauterine milieu to a rising number of metabolic diseases, such as diabetes, obesity, and hypercholesterolemia as well as the Metabolic Syndrome (Met S). Moreover, metabolic associated atherosclerotic diseases are connected to perigestational maternal health. The "Thrifty Phenotype Hypothesis" introduced cross-generational links between poor conditions during gestation and metabolic as well as cardiovascular alterations postnatal. Still, mechanisms altering the intrauterine milieu causing metabolic and associated atherosclerotic diseases are currently poorly understood. This paper will give novel insights in fundamental concepts connected to specific molecular mechanisms "programming" diabetes and associated metabolic as well as cardiovascular diseases.

The role of imprinted genes in humans

Genomic imprinting, a process of epigenetic modification which allows the gene to be expressed in a parent-of-origin specific manner, has an essential role in normal growth and development. Imprinting is found predominantly in placental mammals, and has potentially evolved as a mechanism to balance parental resource allocation to the offspring. Therefore, genetic and epigenetic disruptions which alter the specific dosage of imprinted genes can lead to various developmental abnormalities often associated with fetal growth and neurological behaviour. Over the past 20 years since the first imprinted gene was discovered, many different mechanisms have been implicated in this special regulatory mode of gene expression. This review includes a brief summary of the current understanding of the key molecular events taking place during imprint establishment and maintenance in early embryos, and their relationship to epigenetic disruptions seen in imprinting disorders. Genetic and epigenetic causes of eight recognised imprinting disorders including Silver-Russell syndrome (SRS) and Beckwith-Wiedemann syndrome (BWS), and also their association with Assisted reproductive technology (ART) will be discussed. Finally, the role of imprinted genes in fetal growth will be explored by investigating their relationship to a common growth disorder, intrauterine growth restriction (IUGR) and also their potential role in regulating normal growth variation.

Genetic correlates of early accelerated infant growth associated with juvenile-onset type 1 diabetes

OBJECTIVE

We previously showed that accelerated growth predisposing to development of childhood-onset type 1 diabetes (T1D) is restricted to the first year after birth. We assessed whether this phenomenon of increased early growth is associated with variants of two genes, insulin-like growth factor-1 (IGF1) and insulin variable number of tandem repeats (INS-VNTR), whose products are components of the growth axis.

PATIENTS AND METHODS

Patients and their siblings were genotyped for the INS-VNTR and for an IGF1 microsatellite. We tested for difference in first year growth, i.e., increased weight standard deviation score (SDS), a reliable measure of especially first year growth, between carriers and non-carriers of these gene variants, using a repeated measurement and regression analysis.

RESULTS

In patients, growth did not differ between carriers and non-carriers of the INS-VNTR*III allele, while carriership of this allele in siblings was positively associated with increased first year growth. In both patients and siblings, non-carriership of the IGF1*194 allele was positively associated with growth. Birth size was not associated with either variant.

CONCLUSIONS/DISCUSSION

Non-carriership of the IGF1*194 allele was positively associated with accelerated first year growth in both patients and siblings, independent of disease. This IGF1 variant may therefore contribute to increased first year growth, but cannot explain the association of first year growth with diabetes. An effect on growth of the INS-VNTR was detected in healthy siblings, but not in patients, suggesting that disease supersedes a growth effect of INS-VNTR.

Country-specific birth weight and length in type 1 diabetes high-risk HLA genotypes in combination with prenatal characteristics

OBJECTIVE

To examine the relationship between high-risk human leukocyte antigen (HLA) genotypes for type 1 diabetes and birth size in combination with prenatal ch aracteristics in different countries.

STUDY DESIGN

Four high-risk HLA genotypes were enrolled in the Environmental determinants of Diabetes in the Young study newborn babies from the general population in Finland, Germany, Sweden and the United States. Stepwise regression analyses were used to adjust for country, parental physical characteristics and environmental factors during pregnancy.

RESULT

Regression analyses did not reveal differences in birth size between the four type 1 diabetes high-risk HLA genotypes. Compared with DQ 4/8 in each country, (1) DQ 2/2 children were heavier in the United States (P=0.028) mostly explained however, by parental weight; (2) DQ 2/8 (P=0.023) and DQ 8/8 (P=0.046) children were longer in Sweden independent of parents height and as well as (3) in the United States for DQ 2/8 (P=0.023), but again dependent on parental height.

CONCLUSION

Children born with type 1 diabetes high-risk HLA genotypes have comparable birth size. Longitudinal follow-up of these children should reveal whether birth size differences between countries contribute to the risk for islet autoimmunity and type 1 diabetes.

Common polymorphic variation in the genetically diverse African insulin gene and its association with size at birth

The insulin variable number of tandem repeats (INS VNTR) has been variably associated with size at birth in non-African populations. Small size at birth is a major determinant of neonatal mortality, so the INS VNTR may influence survival. We tested the hypothesis, therefore, that genetic variation around the INS VNTR in a rural Gambian population, who experience seasonal variation in nutrition and subsequently birth weight, may be associated with foetal and early growth. Six polymorphisms flanking the INS VNTR were genotyped in over 2,500 people. Significant associations were detected between the maternally inherited SNP 27 (rs689) allele and birth length [effect size 17.5 (5.2-29.8) mm; P = 0.004; n = 361]. Significant associations were also found between the maternally inherited African-specific SNP 28 (rs5506) allele and post-natal weight gain [effect size 0.19 (0.05-0.32) z score points/year; P = 0.005; n = 728). These results suggest that in the Gambian population studied there are associations between polymorphic variation in the genetically diverse INS gene and foetal and early growth characteristics, which contribute to overall polygenic associations with these traits.

Genetic determinants of height growth assessed longitudinally from infancy to adulthood in the northern Finland birth cohort 1966

Recent genome-wide association (GWA) studies have identified dozens of common variants associated with adult height. However, it is unknown how these variants influence height growth during childhood. We derived peak height velocity in infancy (PHV1) and puberty (PHV2) and timing of pubertal height growth spurt from parametric growth curves fitted to longitudinal height growth data to test their association with known height variants. The study consisted of N = 3,538 singletons from the prospective Northern Finland Birth Cohort 1966 with genotype data and frequent height measurements (on average 20 measurements per person) from 0–20 years. Twenty-six of the 48 variants tested associated with adult height (p<0.05, adjusted for sex and principal components) in this sample, all in the same direction as in previous GWA scans. Seven SNPs in or near the genes HHIP, DLEU7, UQCC, SF3B4/SV2A, LCORL, and HIST1H1D associated with PHV1 and five SNPs in or near SOCS2, SF3B4/SV2A, C17orf67, CABLES1, and DOT1L with PHV2 (p<0.05). We formally tested variants for interaction with age (infancy versus puberty) and found biologically meaningful evidence for an age-dependent effect for the SNP in SOCS2 (p = 0.0030) and for the SNP in HHIP (p = 0.045). We did not have similar prior evidence for the association between height variants and timing of pubertal height growth spurt as we had for PHVs, and none of the associations were statistically significant after correction for multiple testing. The fact that in this sample, less than half of the variants associated with adult height had a measurable effect on PHV1 or PHV2 is likely to reflect limited power to detect these associations in this dataset. Our study is the first genetic association analysis on longitudinal height growth in a prospective cohort from birth to adulthood and gives grounding for future research on the genetic regulation of human height during different periods of growth.

Family studies have shown that adult height is largely genetically determined. Identification of common genetic factors has been expedited with recent advances in genotyping techniques. However, factors regulating childhood height growth remain unclear. We investigated genetic variants of adult height for associations with peak height velocity in infancy (PHV1) and puberty (PHV2) and timing of pubertal growth spurt in a population based sample of 3,538 Finns born in 1966. Most variants studied associated with adult height in this sample. Of the 48 genetic variants tested, seven of them associated with PHV1 and five with PHV2. However, only one of these associated with both, and we found suggestive evidence for differential effects at different stages of growth for some of the variants. In this sample, less than half of the variants associated with adult height had a measurable effect on PHV1 or PHV2. However, these differences may reflect lower statistical power to detect associations with height velocities compared to adult height. This study provides a foundation for further biological investigation into the genes acting at each stage of height growth.

Complex signatures of locus-specific selective pressures and gene conversion on Human Growth Hormone/Chorionic Somatomammotropin genes

Reduced birth weight and slow neonatal growth are risks correlated with the development of common diseases in adulthood. The Human Growth Hormone/Chorionic Somatomammotropin (hGH/CSH) gene cluster (48 kb) at 17q22-24, consisting of one pituitary-expressed postnatal (GH1) and four placental genes (GH2, CSH1, CSH2, and CSHL1) may contribute to common variation in intrauterine and infant growth, and also to the regulation of feto-maternal and adult glucose metabolism. In contrast to GH1, there are limited genetic data on the hGH/CSH genes expressed in utero. We report the first survey of sequence variation encompassing all five hGH/CSH genes. Resequencing identified 113 SNPs/indels (ss86217675-ss86217787 in dbSNP) including 66 novel variants, and revealed remarkable differences in diversity patterns among the homologous duplicated genes as well as between the study populations of European (Estonians), Asian (Han Chinese), and African (Mandenkalu) ancestries. A dominant feature of the hGH/CSH region is hyperactive gene conversion, with the rate exceeding tens to hundreds of times the rate of reciprocal crossing-over and resulting in near absence of linkage disequilibrium. The initiation of gene conversion seems to be uniformly distributed because the data do not predict any recombination hotspots. Signatures of different selective constraints acting on each gene indicate functional specification of the hGH/CSH genes. Most strikingly, the GH2 coding for placental growth hormone shows strong intercontinental diversification (F(ST)=0.41-0.91; p<10(-6)) indicative of balancing selection, whereas the flanking CSH1 exhibits low population differentiation (F(ST)=0.03-0.09), low diversity (non-Africans, pi=8-9 x 10(-5); Africans, pi=8.2 x 10(-4)), and one dominant haplotype worldwide, consistent with purifying selection. The results imply that the success of an association study targeted to duplicated genes may be enhanced by prior resequencing of the study population in order to determine polymorphism distribution and relevant tag-SNPs.

INS VNTR is not associated with childhood obesity in 1,023 families: a family-based study

Previous studies have described genetic associations of the insulin gene variable number tandem repeat (INS VNTR) variant with childhood obesity and associated phenotypes. We aimed to assess the contribution of INS VNTR genotypes to childhood obesity and variance of insulin resistance, insulin secretion, and birth weight using family-based design. Participants were either French or German whites. We used transmission disequilibrium tests (TDTs) for assessing binary traits and quantitative pedigree disequilibrium tests for assessing continuous traits. In contrast to previous findings, we did not observe any familial association with childhood obesity (T = 50%, P = 0.77) in the 1,023 families tested. In French obese children, INS VNTR did not associate with fasting insulin levels (P = 0.23) and class I allele showed only borderline association with increased insulin secretion index at 30 min (P = 0.03). INS VNTR did not associate with birth weight in obese children (P = 0.98) and TDT analyses in 350 French families with history of low birth weight (LBW) showed no association with this condition (P = 0.92). In summary, our study, the largest performed so far, does not support the previously reported associations between INS VNTR and childhood obesity, insulin resistance, or birth weight, and does not suggest any major role for this variant in modulating these traits.

Association between small for gestational age and paternally inherited 5' insulin haplotypes

OBJECTIVE

To test the association between small for gestational age and polymorphisms in the insulin gene in newborns and their mothers, as well as the effect of the parental transmission of haplotypes.

SUBJECTS

Pairs of healthy African-American full-term newborns (N=207) and mothers were recruited from Memphis TN and Jackson MS with birth weights ranging from 2210 to 4735 g.

METHODS

Six single nucleotide polymorphisms (SNPs) located in the insulin (INS) and insulin-like growth factor 2 (IGF2) genes were genotyped in mothers and newborns. Haplotypes composed of three SNPs in the 5' region of the INS-IGF2 locus were computationally inferred. Odds ratios for risk of small for gestational age (SGA) birth were calculated for individual SNPs and inferred haplotypes in the newborns and in the mothers using logistic regression. For 162 mother--newborn pairs the parental transmission of the haplotypes could be inferred, and the risks for SGA birth were calculated for the three common haplotypes in this sample.

RESULTS

Three INS SNPs exhibited significant association with risk for SGA birth. The SNP alleles associated with increased risk for SGA were opposite in the maternal and newborn genomes, implying opposing influences on the rate of fetal growth. Consistent with these results, haplotypes composed of complementary nucleotide sequences (CAC at rs3842738, rs689 and rs3842748, respectively, in the newborn versus GTG in the mother) were significantly associated with risk for SGA birth. In analyses of haplotypes according to parental transmission, the same trend in risk for SGA was observed for both maternally and paternally transmitted haplotypes, although a significant difference in risk was observed only for paternally transmitted haplotypes.

CONCLUSION

Polymorphisms near the 5' end of the INS-IGF2 locus are significantly associated with risk for SGA birth with a major effect due to the paternally transmitted haplotype, which is preferentially expressed due to imprinting.

Genetic variations within the insulin gene region are associated with accelerated fetal growth

Size at birth has been proposed to be associated with the risk of type 2 diabetes and cardiovascular disease later in life. It is, however, unclear whether this association is attributed to an unfavorable intrauterine environment or to specific genotypes predisposing both altered fetal growth and common diseases in adult life. The aim of this study was to investigate the associations between the neonatal birth size and the genotypes of polymorphic loci within the insulin gene (INS) region, which is susceptible to diabetes mellitus. We analyzed the genotypes of two polymorphic loci; -23HphI and HUMTH01, in 520 pairs of normal Japanese mothers and their neonates, and compared with the somatoscopic characteristics at birth converted into standard deviation scores (SDS) according to sex, parity and gestational weeks at delivery. It was revealed that neonatal -23HphI T allele and HUMTH01 allele10, which are linked to the INS variable number of tandem repeats (VNTR) class III allele, were associated with increased weight, head circumstance, and length at birth. These associations confirmed that variation within the INS region, most probably at the INS-VNTR, influences fetal growth. Furthermore, the finding that the paternally transmitted -23HphI T allele was exclusively correlated with increased size at birth indicates the involvement of an imprinting mechanism. In conclusion, the INS-VNTR class III allele might accelerate fetal growth in a parent-specific manner.

Type 2 diabetes TCF7L2 risk genotypes alter birth weight: a study of 24,053 individuals

The role of genes in normal birth-weight variation is poorly understood, and it has been suggested that the genetic component of fetal growth is small. Type 2 diabetes genes may influence birth weight through maternal genotype, by increasing maternal glycemia in pregnancy, or through fetal genotype, by altering fetal insulin secretion. We aimed to assess the role of the recently described type 2 diabetes gene TCF7L2 in birth weight. We genotyped the polymorphism rs7903146 in 15,709 individuals whose birth weight was available from six studies and in 8,344 mothers from three studies. Each fetal copy of the predisposing allele was associated with an 18-g (95% confidence interval [CI] 7-29 g) increase in birth weight (P=.001) and each maternal copy with a 30-g (95% CI 15-45 g) increase in offspring birth weight (P=2.8x10-5). Stratification by fetal genotype suggested that the association was driven by maternal genotype (31-g [95% CI 9-48 g] increase per allele; corrected P=.003). Analysis of diabetes-related traits in 10,314 nondiabetic individuals suggested the most likely mechanism is that the risk allele reduces maternal insulin secretion (disposition index reduced by ~0.15 standard deviation; P=1x10-4), which results in increased maternal glycemia in pregnancy and hence increased offspring birth weight. We combined information with the other common variant known to alter fetal growth, the -30G-->A polymorphism of glucokinase (rs1799884). The 4% of offspring born to mothers carrying three or four risk alleles were 119 g (95% CI 62-172 g) heavier than were the 32% born to mothers with none (for overall trend, P=2x10-7), comparable to the impact of maternal smoking during pregnancy. In conclusion, we have identified the first type 2 diabetes-susceptibility allele to be reproducibly associated with birth weight. Common gene variants can substantially influence normal birth-weight variation.

Increased prevalence of VNTR III of the insulin gene in women with gestational diabetes mellitus (GDM)

OBJECTIVE

The VNTR polymorphism in the promoter region of the insulin gene (INS-VNTR) affects transcription rate and has been associated with insulin resistance and DM2. Gestational diabetes mellitus (GDM) is a multifactorial disorder, where both impaired insulin secretion and action may be involved. The aim of the study was to examine the distribution of the INS-VNTRs in women with GDM and to investigate possible associations with features of beta cell function and glycaemic control in this population.

METHODS

One hundred and sixty-one women with GDM and 111 normal pregnant women (n) were genotyped for INS-VNTR during the 24th-32nd pregnancy week. Glucose and insulin levels were determined during the diagnostic OGTT. The majority of the previous GDM women were also examined at 3-6 months post-partum.

RESULTS

VNTR class III/III genotype was significantly more frequent in the GDM group 8.7% versus 2.7%, p=0.02 giving an OR of 3.97 (1.1-14.29). An increased frequency of the VNTR class III allele was found in those GDM women who required insulin for treatment compared to those controlled with diet alone (12.4% versus 4%, p<0.001). Basal insulin levels tended to be lower in GDM women homozygous for the class III allele without reaching statistical significance (p=0.09).

CONCLUSIONS

The INS-VNTR class III is more frequent in women who develop GDM, and may be associated with decreased ability of the beta cell to meet the increased insulin requirements as reflected by the need for insulin supplementation for adequate glycaemic control.

Fetal growth is increased by maternal type 1 diabetes and HLA DR4-related gene interactions

AIMS/HYPOTHESIS

Intrauterine growth in non-diabetic pregnancies is reported to be influenced by type 1 diabetes susceptibility genes. In particular, the high-risk HLA DR4_DQB1*0302 haplotype is associated with increased birthweight. The aim of this study was to determine whether HLA DR4 was associated with increased birthweight in a maternal diabetes environment and whether effects persisted during early childhood.

SUBJECTS AND METHODS

Birthweight and gestational age were obtained in singleton births from mothers with type 1 diabetes (n = 1161) or whose fathers or siblings have type 1 diabetes (n = 872). Weight and height at ages 2 and 5 years were obtained from paediatric records. Data were adjusted for (gestational) age and sex and expressed as percentiles of German reference data. HLA DR typing was obtained for all children and 1090 children also had insulin gene (INS) variable number of tandem repeats (VNTR) typing.

RESULTS

Maternal type 1 diabetes was associated with increased birthweight, gestational age and birthweight percentiles (all p < 0.0001). In children of mothers with type 1 diabetes, birthweight percentile was further related to maternal HbA(1c) during pregnancy (r = 0.26; p < 0.0001) and was independently increased if children had HLA DR4 alleles (76th vs 64th percentile; p < 0.0001). HLA DR4 was not associated with birthweight in children of non-diabetic mothers. Birthweight was not associated with INS VNTR genotypes. High birthweight, but not HLA DR4 was associated with increased weight and BMI at ages 2 and 5 years (p < 0.0001).

CONCLUSIONS/INTERPRETATION

Our findings are consistent with the hypothesis that a diabetic intrauterine environment interacts with gene(s) marked by the type 1 diabetes susceptibility HLA DR4 alleles to increase fetal growth.

Comparative analysis of insulin gene promoters: implications for diabetes research

DNA sequences that regulate expression of the insulin gene are located within a region spanning approximately 400 bp that flank the transcription start site. This region, the insulin promoter, contains a number of cis-acting elements that bind transcription factors, some of which are expressed only in the beta-cell and a few other endocrine or neural cell types, while others have a widespread tissue distribution. The sequencing of the genome of a number of species has allowed us to examine the manner in which the insulin promoter has evolved over a 450 million-year period. The major findings are that the A-box sites that bind PDX-1 are among the most highly conserved regulatory sequences, and that the conservation of the C1, E1, and CRE sequences emphasize the importance of MafA, E47/beta2, and cAMP-associated regulation. The review also reveals that of all the insulin gene promoters studied, the rodent insulin promoters are considerably dissimilar to the human, leading to the conclusion that extreme care should be taken when extrapolating rodent-based data on the insulin gene to humans.

Absence of the wild-type allele (192 base pairs) of a polymorphism in the promoter region of the IGF-I gene but not a polymorphism in the insulin gene variable number of tandem repeat locus is associated with accelerated weight gain in infancy

OBJECTIVE

Our goal was to investigate whether a polymorphism in the insulin-like growth factor I promoter gene (IGF-I, wild-type, 192 base pairs) and in the insulin gene (INS) variable number of tandem repeat locus influence birth weight and weight gain in infancy.

PATIENTS AND METHODS

We obtained genomic DNA from 768 children. Exclusion criteria were multiple births, gestational diabetes, maternal diabetes, gestational age <37 weeks, >42 weeks, or unclear, and any condition potentially influencing weight gain. SD scores were calculated and adjusted for gestational age and gender. A gain in SD scores for weight between birth and 1 year >0.67 SD scores was defined as accelerated weight gain. Genotyping was performed by fragment length analysis (IGF-I) and by fragment length analysis after using a restriction enzyme-based assay (INS variable number tandem repeat).

RESULTS

Accelerated weight gain was present in 205 of 768 children. IGF-I and INS variable number tandem repeat genotype were not associated with birth weight. The IGF-I 192-base pair allele was less frequent in children with accelerated weight gain and was shown to reduce the risk for accelerated weight gain in a logistic regression model.

CONCLUSION

The IGF-I 192-base pair allele may reduce the risk for rapid weight gain in early infancy.

A study of association between common variation in the growth hormone-chorionic somatomammotropin hormone gene cluster and adult fasting insulin in a UK Caucasian population

Background

Reduced growth during infancy is associated with adult insulin resistance. In a UK Caucasian cohort, the CSH1.01 microsatellite polymorphism in the growth hormone-chorionic somatomammotropin hormone gene cluster was recently associated with increases in adult fasting insulin of approximately 23 pmol/l for TT homozygote males compared to D1D1 or D2D2 homozygotes (P = 0.001 and 0.009; n = 206 and 92, respectively), but not for females. TT males additionally had a 547-g lower weight at 1 year (n = 270; P = 0.008) than D2D2 males. We sought to replicate these data in healthy UK Caucasian subjects. We genotyped 1396 subjects (fathers, mothers and children) from a consecutive birth study for the CSH1.01 marker and analysed genotypes for association with 1-year weight in boys and fasting insulin in fathers.

Results

We found no evidence for association of CSH1.01 genotype with adult male fasting insulin concentrations (TT/D1D1 P = 0.38; TT/D2D2 P = 0.18) or weight at 1 year in boys (TT/D1D1 P = 0.76; TT/D2D2 P = 0.85). For fasting insulin, our data can exclude the previously observed effect sizes as the 95 % confidence intervals for the differences observed in our study exclude increases in fasting insulin of 9.0 and 12.6 pmol/l for TT relative to D1D1 and D2D2 homozygotes, respectively. Whilst we have fewer data on boys' 1-year weight than the original study, our data can exclude a reduction in 1-year weight greater than 557 g for TT relative to D2D2 homozygotes.

Conclusion

We have not found association of the CSH1.01 genotype with fasting insulin or weight at 1 year. We conclude that the original study is likely to have over-estimated the effect size for fasting insulin, or that the difference in results reflects the younger age of subjects in this study relative to those in the previous study.

The relation between size at birth and risk of type 1 diabetes is not influenced by adjustment for the insulin gene (-23HphI) polymorphism or HLA-DQ genotype

AIMS/HYPOTHESIS

Associations have been described between higher birthweight and increased risk of type 1 diabetes, and of insulin (INS) and human leucocyte antigen (HLA) genotypes that protect against diabetes with larger size at birth. We studied simultaneously the effects of size at birth, INS and HLA genotypes on the risk of type 1 diabetes to test whether the relation between size at birth and risk of type 1 diabetes would be strengthened after adjustment for INS and HLA genotypes.

SUBJECTS AND METHODS

We designed a population-based case-control study in Norway with 471 cases of childhood-onset type 1 diabetes and 1,369 control subjects who were genotyped for the INS -23HphI polymorphism (surrogate for INS variable number of tandem repeats) and HLA-DQ alleles associated with type 1 diabetes. Data on birthweight and other perinatal factors were obtained from the Medical Birth Registry of Norway by record linkage.

RESULTS

The data fitted a multiplicative model for the protective INS class III allele both within the INS locus and for the model with INS- and HLA-DQ-conferred risk of type 1 diabetes. We found no overall significant association between weight or head circumference at birth and the risk of type 1 diabetes, and adjustment for INS and HLA genotype did not influence this result. There was also no evidence for association of INS or HLA with size at birth among control subjects.

CONCLUSIONS/INTERPRETATION

In contrast to suggestions from previous indirect studies, direct adjustment for INS and HLA genotypes did not lead to a stronger relation between birthweight and the risk of type 1 diabetes.

Association of Single Nucleotide Polymorphisms of the Insulin Gene with Chicken Early Growth and Fat Deposition

Growth rate, body composition, and fat deposition are important traits in chickens. Insulin plays important roles in hepatic cells, muscle cells, and adipose tissue cells. The purpose of the present study was to analyze association of the insulin (INS) gene with chicken growth and body composition traits. Using a F2 design resource population constructed with the crossing of Chinese native Xinghua chickens and White Recessive Rock chickens, the association of 4 single nucleotide polymorphisms (SNP; A+428G, C+1549T, T+3737C, and A+3971G) of INS gene with 13 growth and body composition traits was studied. The T+3737C genotypes were significantly associated with small intestine length (P = 0.0002), and the A+3971G genotypes were significantly associated with early growth (hatch weight and BW at 28 d of age) (P < 0.0001), breast angle (P = 0.0002), and small intestine length (P < 0.0001). None of the 4 SNP was significantly associated with abdominal fat pad weight (P > 0.05). The haplotypes based on the 4 SNP were also significantly associated with early growth (hatch weight and BW at 28 d of age; P < 0.0001) and breast angle (P < 0.0001) but not with small intestine length (P = 0.0505). These results suggested that variation of the insulin gene was significantly associated with chicken early growth but not with fat deposition. In addition, the data from the present study supported the inference that both the one-SNP-at-a-time and the haplotype-based approaches have their own advantages and disadvantages when association analysis of one SNP and haplotypes with chicken complex traits was conducted.

Heterogeneity of class I INS VNTR allele association with insulin secretion in obese children

On the basis of the near-complete linkage disequilibrium of the insulin variable number of tandem repeats ( INS VNTR) allele with the neighboring −23Hph1 A/T single-nucleotide polymorphism, previous studies have documented the association of class I (“short”) and class III (“long”) INS VNTR alleles with metabolic parameters, including circulating insulin levels. Using a new method to sequence class I alleles, we revisited this association in 346 obese children. Class I alleles are made of several types of repeats, whose repartition determines subclasses IC and ID. Fasting insulin was found to be higher in obese children with ID/ID genotypes (135 ± 12 pmol/l, n = 64) than with ID/IC or IC/IC genotypes (91 ± 5 pmol/l, n = 97, P = 0.0005). In response to oral glucose, peak insulin levels and insulin-to-glucose area under the curve ratios were higher in ID/ID (872 ± 122 pmol/l and 109 ± 15, respectively) than in ID/IC or IC/IC patients (586 ± 42 pmol/l and 76 ± 5, P = 0.02 and P = 0.04, respectively). Fasting and postglucose insulin levels were comparable in carriers of IC and of class III alleles. Our results support that the molecular structure of the VNTR allele, not only its overall length, is associated with variations of insulin secretion. ID/ID homozygosity appears responsible for the increased insulin levels previously attributed to the whole class I VNTR group. It will be important to test the ramifications of this observation for class I association with Type 1 (susceptibility) and Type 2 diabetes (protection).

Long-term metabolic consequences of being born small for gestational age

During the last 15 years, a number of long-term health risks associated with reduced fetal growth have been identified, including cardiovascular diseases and the insulin-resistance syndrome or one of its components: hypertension, dyslipidemia, impaired glucose tolerance or Type 2 diabetes. A common feature of these conditions is the presence of high insulin levels, which are thought to play a pathogenic role. However, despite abundant data in the literature, it is still difficult to trace the pathway by which fetal events, environmental or not, may lead to the increased morbidity later in life. To explain this association, several hypotheses have been proposed pointing to the critical role of either a detrimental fetal environment or a genetic susceptibility, or indicating interaction of both. Clearly, not all subjects born small for gestational age are at the same risk of developing these complications. It appears that individuals at particular risk are those who were thin at birth and had a subsequent catch-up in body mass index, irrespective of the degree of adiposity in adulthood. It is suggested that this particular dynamic change in adiposity has a critical role in the development of long-term metabolic complications. Therefore, it is important to consider the relative impact of early postnatal events in relation to fetal growth to the diseases risk throughout life in forming health policy strategies towards eventual early interventions.

Replication of IGF2-INS-TH*5 haplotype effect on obesity in older men and study of related phenotypes

Interindividual variation of the IGF2-INS-TH region influences risk of a variety of diseases and complex traits. Previous studies identified a haplotype (designated IGF2-INS-TH(*)5 and tagged by allele A of IGF2 ApaI, allele 9 of TH01 and class I alleles of INS VNTR) associated with low body mass index (BMI) in a cohort of UK men. We aimed here both to study whether previous findings relating (*)5 with weight are replicated in a different cohort of men (East Hertfordshire) characterised in more phenotypic detail and to test the effect of this haplotype on related subphenotypes. The PHASE program was used to identify (*)5 and not(*)5 haplotypes. A total of 490 haplotypes were derived from 131 men and 114 women, the frequency of (*)5 being around 9%. Specific tests of (*)5 haplotype (vs not(*)5 haplotypes) conducted included Student's t-test and multiple regression analyses. We observed replication of weight effect for the (*)5 haplotype in men: significant associations with lower BMI (-1.81 kg/m(2), P=0.009), lower waist circumference (-6.3 cm, P=0.001) and lower waist-hip ratio (-5%, P<0.001). This haplotype also marks nearly two-fold lower 120 min insulin (P=0.004) as well as low baseline insulin (-11.02 pmol/l, P=0.043) and low 30 min insulin (-64.44 pmol/l, P=0.072) in a glucose tolerance test. No association between (*)5 and these traits was found in women. Our results, taken together with other data on IGFII levels and TH activity, point to the importance of (*)5 as an integrated polygenic haplotype relevant to obesity and insulin response to glucose in men.

Genetic Variations and Normal Fetal Growth

Size at birth is said to be a highly heritable trait, with an estimated 30-70% of the variability a result of genetics. Data from family studies may be confounded, however, by potential interactions between fetal genes and the maternal uterine environment. Overall, the maternal environment tends to restrain fetal growth, and this is most evident in first pregnancies. Restraint of fetal growth appears to be inherited through the maternal line. Potential genetic candidates include the mitochondrial DNA 16189 variant, and common variants of exclusively maternally expressed genes, such as H19, which have been associated with size at birth. Maternal blood glucose levels and blood pressure are also correlated with size at birth, but the degree to which these changes relate to genetic variation in the mother is unclear. Elegant studies in mouse knockout models and rare genetic variants in humans have highlighted the importance of insulin-like growth factor I (IGF-I), IGF-II, insulin and their respective receptors in determining fetal growth. However, data linking common variation in the genes that regulate these proteins and receptors with size at birth are few and inconsistent. Interestingly, common variation in the insulin gene (INS) variable number tandem repeats, which regulates the transcription of insulin and IGF-II, has been associated with size at birth, largely in second and subsequent pregnancies, where maternal restraint is least evident. This suggests that fetal genes, and in particular paternally expressed genes, may have significant effects on fetal growth during pregnancies where maternal restraint of fetal growth is less evident.

Hypotheses on the Fetal Origins of Adult Diseases: Contributions of Epidemiological Studies

Epidemiological studies have demonstrated associations between low birth weight and cardiovascular disease, type 2 diabetes and their risk factors in adult life. These findings have led to sharp debates in the literature concerning potential methodological study flaws and the effect size and causality of the associations. More recent studies seem to have overcome most methodological flaws and suggest a small effect size of low birth weight on adult diseases for the individual. However, the effect size may still be important on a population level. Various causal pathways have been hypothesized as mechanisms underlying these associations. These hypotheses have proposed central roles for (1) fetal undernutrition, (2) increased cortisol exposure, (3) genetic susceptibility and (4) accelerated post-natal growth. These hypotheses have been studied in various epidemiological study designs. Thus far, it is still not known which mechanisms underlie the associations between low birth weight and diseases in adult life. The causal pathways linking low birth weight to diseases in later life seem to be complex and may include combined environmental and genetic mechanisms in various periods of life. Well-designed epidemiological studies are necessary to estimate the population effect size and to identify the underlying mechanisms. This knowledge is needed to develop strategies for identifying groups at risk and prevention focused on early life.

Evidence of genetic regulation of fetal longitudinal growth

BACKGROUND

Genetic as well as environmental factors are important determinants of fetal growth but there have been few studies of the influence of paternal factors on fetal growth.

AIM

To study the influence of paternal anthropometry on detailed measurements of offspring at birth.

DESIGN

A prospective cohort study involving biochemistry, and anthropometry, of mothers and fathers at 28 weeks gestation, and detailed anthropometry of children within 24 h of birth.

SUBJECTS

567 White Caucasian singleton, non-diabetic, full term pregnancies recruited from central Exeter, UK.

RESULTS

Paternal height, but not paternal BMI, was correlated with birth weight (r = 0.19) and with birth length (r = 0.33). This was independent of potential confounders and maternal height. All measurements of fetal skeletal growth including crown-rump, knee-heel and head circumference were associated with paternal height. Maternal height showed similar correlations with birth weight (r = 0.18) and birth length (r = 0.26). Maternal BMI was correlated with birth weight (r = 0.27) and birth length (r = 0.15). In a multifactorial analysis 38% of the variance in fetal height could be explained by gestation, sex, paternal height, maternal height, maternal glucose, maternal BMI, parity and maternal smoking.

CONCLUSION

Paternal height has an independent influence on size at birth. This predominantly influences length and skeletal growth of the baby. In contrast to maternal obesity the degree of paternal obesity does not influence birth weight. This work suggests that there is genetic regulation of skeletal growth while the maternal environment predominantly alters the adiposity of the fetus.

Insights from the developing world: thrifty genotypes and thrifty phenotypes

Few researchers would dispute that the pandemic of obesity is caused by a profound mismatch between humanity's present environmental circumstances and those that have moulded evolutionary selection. This concept was first articulated when gestational diabetes was described as being the result of a 'thrifty genotype rendered detrimental by progress'. More recently, this hypothesis has been extended to the concept of a 'thrifty phenotype' to describe the metabolic adaptations adopted as a survival strategy by a malnourished fetus; changes that may also be inappropriate to deal with a later life of affluence. Both the thrifty genotype and the thrifty phenotype hypotheses would predict that populations in some areas of the developing world would be at greater risk of obesity and its co-morbidities; a proposition to be explored in the present paper. To date thrifty genes remain little more than a nebulous concept propagated by the intuitive logic that man has been selected to survive episodic famine and seasonal hungry periods. Under such conditions those individuals who could lay down extra energy stores and use them most efficiently would have a survival advantage. The search for candidate thrifty genes needs to cover every aspect of human energy balance from food-seeking behaviour to the coupling efficiency of oxidative phosphorylation. The present paper will describe examples of attempts to find thrifty genes in three selected candidate areas: maternally-transmitted mitochondrial genes; the uncoupling proteins; apoE4, whose geographical distribution has been linked to a possible thrifty role in lipoprotein and cholesterol metabolism.

INS VNTR class genotype and indexes of body size and obesity: population-based studies of 7,999 middle-aged men and women

The relevance of the insulin gene (INS) variable number tandem repeat (VNTR) polymorphism to indexes of body size and adult obesity is inconclusive. Given the equivocal reports on the association between the VNTR class genotype at the insulin gene locus and indexes of body size and obesity, we assessed these associations in a series of cohort studies based on 7,999 middle-aged men and women. We found no convincing evidence that INS VNTR class genotype was associated with indexes of body size and adult obesity. These data suggest that INS VNTR class is not an important determinant of size and body weight regulation in middle-aged men and women.

Association of Kir6.2 and INS VNTR variants with glucose homeostasis in young obese

Although insulin secretion is commonly increased and glucose tolerance decreased in young obese patients, there is a wide individual variability of these parameters. We investigated whether common variants at the Kir6.2 (KCNJ11) and insulin variable number of tandem repeat (INS VNTR) loci are associated with insulin or glucose levels in 388 obese children. The E23K and INS VNTR alleles showed no significant association when each locus was examined individually but a clear effect when the two loci were combined for analysis. In obese children with Kir6.2 KK and class III VNTR alleles, fasting glucose was slightly but consistently greater (4.76 ± 0.05 mM) than in those with Kir6.2 EE and class I/I VNTR alleles (4.63 ± 0.06 mM, P = 6.10−4) or other genotypes (4.64 ± 0.03 mM, P = 1.10−3). Obese children with KK and class III VNTR genotypes also had an early response to oral glucose diminished by ∼36% [insulinogenic index (IGI) = 50 ± 4] compared with Kir6.2 EE and class I/I (IGI = 78 ± 7, P = 0.026) or other genotypes (IGI = 69 ± 3, P = 0.001). In young European obese, the polymorphisms of Kir6.2 and INS VNTR are thus associated with a trend for lower insulin and higher glucose levels, which may reveal a possible epistatic genetic effect that may influence a prediabetic trait in young obese children.

Analysis of multiple data sets reveals no association between the insulin gene variable number tandem repeat element and polycystic ovary syndrome or related traits

CONTEXT

Variation at the insulin gene VNTR (variable number tandem repeat) minisatellite has been reported to be associated with polycystic ovary syndrome (PCOS), but findings have been inconsistent and all studies have featured small sample sizes.

OBJECTIVE

To gain a robust understanding of the role of the INS-VNTR in PCOS susceptibility.

DESIGN

Case-control, family-based association and quantitative trait analyses.

SETTING AND PARTICIPANTS

A UK population comprising 255 parent-offspring trios, 185 additional cases, and 1062 control subjects (cases and controls all British/Irish) as well as 1599 women from a northern Finland population-based birth cohort characterized for PCO symptomatology and testosterone levels. VNTR class was inferred from genotyping of the -23HphI variant.

INTERVENTION(S)

None.

MAIN OUTCOME MEASURE(S)

INS-VNTR genotype frequencies between subject groups, body mass index, and testosterone levels by genotype.

RESULTS

Case-control analyses in both UK and Finnish samples failed to confirm previously reported class III allele associations with PCOS (UK, P = 0.43, Finnish, P = 0.31; Kruskal-Wallis chi2). Transmission analysis in trios showed no excess transmission of either allele (P = 0.62), regardless of parent of origin (maternal: P = 0.73; paternal: P = 0.66). No association between genotype and testosterone levels was seen in any sample (UK PCOS subjects, P = 0.95; Finnish symptomatic cases, P = 0.38; Finnish control women, P = 0.58).

CONCLUSIONS

Despite the strong biological candidacy and supportive data from previous studies, we conclude that variation at the INS-VNTR has no major role in the development of PCOS.

No association between insulin gene variation and adult metabolic phenotypes in a large Finnish birth cohort

AIMS/HYPOTHESIS

Although the variable number tandem repeat (VNTR) minisatellite 5' to the insulin gene is among the most studied polymorphisms in diabetes, the relationships between VNTR variation, diabetes-related traits and predisposition to type 2 diabetes remain unclear. Since inadequate sample size is likely to have been an obstacle to reliable inference, we examined the relationship between VNTR variation and a range of diabetes-related traits in a cohort of 5,753 Finnish adults.

MATERIALS AND METHODS

VNTR genotypes were derived, by typing at the -23HphI variant site, for 5,646 individuals from the Northern Finland Birth Cohort 1966. Associations were sought between these genotypes and a range of anthropometric (BMI, WHR), physiological (blood pressure) and biochemical (fasting glucose, insulin, lipids, indices of insulin sensitivity and beta cell function) measures obtained at clinical examination at 31 years.

RESULTS

We found no evidence that VNTR genotype was significantly associated with measures of insulin secretion, insulin sensitivity, glycaemia, adiposity or blood pressure.

CONCLUSIONS/INTERPRETATION

Despite evidence from several relatively small studies suggesting that INS-VNTR genotypes are associated with predisposition to type 2 diabetes, reduced beta cell function and measures of adiposity, the present study failed to detect any association with a range of diabetes-related traits. Taken with other recent studies in large population-based cohorts, these data suggest that previous studies have, at the very least, overestimated the influence of the INS-VNTR on type 2 diabetes-related traits. The effects of INS-VNTR variation on insulin transcription observed in vitro appear not to translate into detectable differences in basal insulin secretion in humans.