Lack of support for a role of the insulin gene variable number of tandem repeats minisatellite (INS-VNTR) locus in fetal growth or type 2 diabetes-related intermediate traits in United Kingdom populations

Fetal growth is associated with CpG methylation in the P2 promoter of the IGF1 gene

Background

There are many reasons to think that epigenetics is a key determinant of fetal growth variability across the normal population. Since IGF1 and INS genes are major determinants of intrauterine growth, we examined the methylation of selected CpGs located in the regulatory region of these two genes.

Methods

Cord blood was sampled in 159 newborns born to mothers prospectively followed during their pregnancy. A 142-item questionnaire was filled by mothers at inclusion, during the last trimester of the pregnancy and at the delivery. The methylation of selected CpGs located in the promoters of the IGF1 and INS genes was measured in cord blood mononuclear cells collected at birth using bisulfite-PCR-pyrosequencing.

Results

Methylation at IGF1 CpG-137 correlated negatively with birth length (r = 0.27, P = 3.5 × 10⁻⁴). The same effect size was found after adjustment for maternal age, parity, and smoking: a 10% increase in CpG-137 methylation was associated with a decrease of length by 0.23 SDS.

Conclusion

The current results suggest that the methylation of IGF1 CpG-137 contributes to the individual variation of fetal growth by regulating IGF1 expression in fetal tissues.

Electronic supplementary material

The online version of this article (10.1186/s13148-018-0489-9) contains supplementary material, which is available to authorized users.

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.

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.

Relationship between birth head circumference and adulthood quality of life in Chinese people

AIM

To determine the relationship between birth size and later QOL for Chinese people.

METHODS

Birth data of 1074 subjects were obtained from obstetric birth records of Peking Union Medical College Hospital. All subjects are interviewed face to face with the 36-Item Short-Form Health Survey scale by trained investigators. Linear regression model was used to analyse the relationship between QOL and birth head circumference of the subjects after adjusting for the childhood and adulthood characteristics. The relationship was described with regression coefficients (B) and its 95% confidence interval (CI).

RESULTS

The mean weighted score of QOL was 88.1 ± 9.1, ranging from 76.8 to 100. Larger birth head circumference meant higher adulthood QOL total score (P= 0.001). After controlling the adulthood confounders, as compared to larger head circumference (≥33 cm), small (<31 cm) and medium head circumferences (31-33 cm) meant lower adulthood QOL scores (B=-2.356, P= 0.005 and B=-1.645, P= 0.014, respectively). The increase of head circumference by 1 cm was associated with 0.480 (95% CI: 0.141, 0.820) increase of QOL score after adjusting adulthood confounders (P= 0.006).

CONCLUSIONS

This study validated the relationship between birth head circumference and QOL in later life. Smaller head circumference at birth could predict worse adulthood QOL at above 50 years old.

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.

Insulin gene variable number of tandem repeats is associated with increased fat mass during adolescence in non‐obese girls

Obesity and related disorders have become a major health problem. Understanding the interaction between genetic and environmental factors influencing the susceptibility to develop obesity is important when pinpointing people at risk. In a longitudinal study of 256 non-obese adolescents, the influence of the insulin gene (INS) variable number of tandem repeats (VNTR) on anthropometric measures and fat mass was investigated. The adolescents were examined at the age of 12.4 (2.3) (mean, SD) and 16.2 (2.3) years, and at follow-up with dual x-ray absorptiometry (DXA) for measurement of body composition. INS VNTR classes I and III alleles were investigated using the -23T/A single nucleotide polymorphism as a surrogate marker. There was a non-significant trend towards increased body mass index (BMI) and fat mass with the class III allele in girls. Homozygotes for the INS VNTR class III allele had a greater increase in BMI compared with those that were homozygous or heterozygous for the class I allele (3.8 (1.6) versus 2.4 (1.9) kg/m2, p = 0.03), and they had higher fat mass (36.4 (3.9) versus 31.3 (6.8)%, p = 0.02) at follow-up. Our finding that homozygosity of the INS VNTR class III allele seems to predispose to increased weight gain and fat mass raises the possibility that this genotype may be one of the important factors in the gene-environment interaction that eventually results in overweight and insulin resistance.

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.

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.

The Genetic Basis of Type 2 Diabetes

Type 2 Diabetes results from a complex physiologic process that includes the pancreatic beta cells, peripheral glucose uptake in muscle, the secretion of multiple cytokines and hormone-like molecules from adipocytes, hepatic glucose production, and likely the central nervous system. Consistent with the complex web of physiologic defects, the emerging picture of the genetics will involve a large number of risk susceptibility genes, each individually with relatively small effect (odds ratios below 1.2 in most cases). The challenge for the future will include cataloging and confirming the genetic risk factors, and understanding how these risk factors interact with each other and with the known environmental and lifestyle risk factors that increase the propensity to type 2 diabetes.

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.

Single-nucleotide polymorphisms and haplotype LD analysis of the 29-kb IGF2 region on chromosome 11p15.5 in the Korean population

OBJECTIVE

We investigated sequence variations of the 29-kb insulin-like growth factor 2 (IGF2) region in human chromosome region 11p15.5 in the Korean population. This region consists of IGF2, insulin-like growth factor 2 antisense (IGF2AS), and the insulin gene, all important candidate genes for various diseases, including cancer, obesity, diabetes, and coronary disease. While single nucleotide polymorphisms (SNPs) have been identified for this region and used in association studies, ethnic differences in genetic variation at this site have not been addressed. To date, SNPs for the entire 29-kb region in the Korean population have not been reported.

METHODS

We surveyed a population of 108 Koreans for SNPs in the 29-kb IGF2 region.

RESULTS

We identified 62 SNPs, consisting of 6 SNPs in the promoter region, 17 in the untranslated region, 19 in introns, and 20 in the intergenic region. We also analyzed linkage disequilibrium (LD) patterns and haplotypes using 36 high-frequency (> 5%)SNPs and found a well-defined LD block spanning about 13 kb that includes 8 kb of the IGF2AS gene, with two hot-spot regions flanking the LD block.

CONCLUSION

These SNPs may be useful as genetic markers in disease association studies in the Korean population.

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.

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.

The insulin gene variable number tandem repeat and risk of type 2 diabetes in a population-based sample of families and unrelated men and women

Abnormalities in insulin regulation are central to the pathogenesis of type 2 diabetes. We assessed variation in the insulin gene variable number tandem repeat (INS VNTR) minisatellite (using the -23Hph1 A/T single nucleotide polymorphism) as a risk factor for 92 cases of incident type 2 diabetes in 883 unrelated Framingham Heart Study (FHS) subjects and in a separate sample of 698 members of 282 FHS nuclear families with 62 diabetes cases. In the unrelated sample, the -23Hph1 TT genotype frequency was 8.0% and was associated with a diabetes hazard ratio of 1.89 [95% confidence interval (CI), 1.01-3.52; P = 0.045] compared with the AA genotype using diabetes age of onset as the time failure variable in a proportional hazards model adjusted for age, offspring sex, body mass index, parental diabetes, and sex by parental diabetes interactions. In sex-stratified analyses, TT increased risk for diabetes in women (hazard ratio, 4.25; 95% CI, 1.76-10.3), but not men (hazard ratio, 1.01; 95% CI, 0.39-2.60). Using a family-based association test to assess transmission disequilibrium in the sample of related subjects, the age- and sex-adjusted z-score for diabetes associated with the T allele was 2.07 (P = 0.04), and a family-based association test using age of onset in a proportional hazards model was also statistically significant (P = 0.03), indicating that increased risk of diabetes was not attributable to population admixture. These data support the hypothesis that the INS VNTR is a genetic risk factor for type 2 diabetes, with the TT genotype accounting for about 6.6% of cases in the FHS population.

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

Variation at the insulin gene (INS-)VNTR (variable number of tandem repeats) minisatellite polymorphism has been reported to be associated with both early growth and adult metabolic phenotypes. However, the samples studied have been small and the relationship between INS-VNTR variation and parameters of early growth inconsistent, with four previous studies producing conflicting results. We have studied the relationship between INS-VNTR class (measured by genotyping the nearby -23HphI variant with which it is in tight linkage disequilibrium) and early growth in 5,646 members of the Northern Finnish Birth Cohort of 1966. Comparing class III homozygotes with other genotypes using multivariate linear regression analysis, we found no significant associations with any early growth measure (birth weight, birth length, ponderal index, and head circumference at 1 year), even after stratifying subjects by growth trajectory during infancy and/or birth order. For example, among infants with limited postnatal growth realignment (n = 2,470), class III/III infants were no heavier at birth (difference [+/-SE] in the means [fully adjusted], 58 +/- 51 g; P = 0.26) than class I/- infants. No significant associations were detected following reanalysis with an additive model (for example, for birth weight, beta = 20 g [95% CI -3 to 44], P = 0.09). Studies of this large population-based cohort have failed to generate convincing evidence that INS-VNTR variation influences early growth.