Birthweight, early environment, and genetics: a study of twins discordant for acute myocardial infarction

MTHFR gene polymorphisms and susceptibility to myocardial infarction: Evidence from meta-analysis and trial sequential analysis

Background

This meta-analysis aimed to provide a comprehensive assessment of the association between Methylenetetrahydrofolate reductase (MTHFR) gene polymorphisms, specifically C677T and A1298C, and the susceptibility to myocardial infarction (MI).

Methods

A systematic literature search was conducted in MEDLINE, Web of Science, and Scopus until April 2023 to identify studies investigating the relationship between MTHFR gene polymorphisms (C677T and A1298C) and the risk of MI.

Results

The analysis included 66 studies involving 16,860 cases and 20,403 controls for the C677T polymorphism and 18 studies comprising 3162 cases and 3632 controls for the A1298C polymorphism. Significant associations were observed between the C677T polymorphism and MI risk in various genetic models: dominant (OR = 1.16, 95 % CI = 1.06-1.28, P = 0.008), recessive (OR = 1.20, 95 % CI = 1.12-1.28, P < 0.001), allelic (OR = 1.13, 95 % CI = 1.06-1.21, P < 0.001), TT vs. CC (OR = 1.19, 95 % CI = 1.05-1.36, P < 0.001), and CT vs. CC (OR = 1.11, 95 % CI = 1.02-1.21, P = 0.01). Furthermore, an overall analysis indicated a marginally significant association between the A1298C polymorphism and MI risk in the recessive model (OR = 1.27, 95 % CI = 1.06-1.51, P = 0.008), allelic model (OR = 1.18, 95 % CI = 1.01-1.39, P = 0.03), and CC vs. AA model (OR = 1.22, 95 % CI = 1.01-1.47, P = 0.04). Meta-regression analysis revealed that none of the potential factors contributed to the observed heterogeneity.

Conclusions

This meta-analysis revealed an association between MTHFR gene C677T and A1298C polymorphisms and the risk of MI.

Birthweight, genetic risk, and gastrointestinal cancer incidence: a prospective cohort study

BACKGROUND

The epidemiologic studies investigating the association of birthweight and genetic factors with gastrointestinal cancer remain scarce. The study aimed to prospectively assess the interactions and joint effects of birthweight and genetic risk levels on gastrointestinal cancer incidence in adulthood.

METHODS

A total of 254,997 participants were included in the UK Biobank study. We used multivariate restricted cubic splines and Cox regression models to estimate the hazard ratios (HRs) and 95% confidential intervals (CI) for the association between birthweight and gastrointestinal cancer risk, then constructed a polygenic risk score (PRS) to assess its interaction and joint effect with birthweight on the development of gastrointestinal cancer.

RESULTS

We documented 2512 incident cases during a median follow-up of 8.88 years. Compare with participants reporting a normal birthweight (2.5-4.5 kg), multivariable-adjusted HR of gastrointestinal cancer incidence for participants with high birthweight (≥4.5 kg) was 1.17 (95%CI: 1.01-1.36). Such association was remarkably observed in pancreatic cancer, with an HR of 1.82 (95%CI: 1.26-2.64). No statistically significant association was observed between low birth weight and gastrointestinal cancers. Participants with high birthweight and high PRS had the highest risk of gastrointestinal cancer (HR: 2.95, 95%CI: 2.19-3.96).

CONCLUSION

Our findings highlight that high birthweight is associated with a higher incidence of gastrointestinal cancer, especially for pancreatic cancer. Benefits would be obtained from birthweight control, particularly for individuals with a high genetic risk.KEY MESSAGESThe epidemiologic studies investigating the association of birthweight and genetic factors with gastrointestinal cancer remain scarce.This cohort study of 254,997 adults in the United Kingdom found an association of high birthweight with the incidence of gastrointestinal cancer, especially for pancreatic cancer, and also found that participants with high birthweight and high polygenic risk score had the highest risk of gastrointestinal cancer.Our data suggests a possible effect of in utero or early life exposures on adulthood gastrointestinal cancer, especially for those with a high genetic risk.

Expression Profiles and Functional Analysis of Plasma Exosomal Circular RNAs in Acute Myocardial Infarction

Acute myocardial infarction (AMI) is a common cardiovascular disease with high rates of morbidity and mortality globally. The dysregulation of circular RNAs (circRNAs) has been shown to be closely related to various pathological aspects of AMI. However, the function of exosomal circRNAs in AMI has yet to be investigated. The purpose of this study was to investigate the expression profiles of plasma exosomal circRNAs in AMI and explore their potential functionality. The expression profiles of plasma exosomal circRNAs in patients with AMI, stable coronary heart atherosclerotic disease (CAD), and healthy controls were obtained from a GEO expression dataset (GSE159657). We also analyzed bioinformatics functionality, potential pathways, and interaction networks related to the microRNAs associated with the differentially expressed circRNAs. A total of 253 exosomal circRNAs (184 up- and 69 down-regulated) and 182 exosomal circRNAs (94 up- and 88 down-regulated) were identified as being differentially expressed between the control group and the AMI and CAD patients, respectively. Compared with the CAD group, 231 different exosomal circRNAs (177 up- and 54 down-regulated) were identified in the AMI group. Functional analysis suggested that the parental genes of exosomal has_circ_0061776 were significantly enriched in the biological process of lysine degradation. Pathway interaction network analysis further indicated that exosomal has_circ_0061776 was associated with has-miR-133a, has-miR-214, has-miR-423, and has-miR-217 and may play a role in the pathogenesis of AMI through the MAPK signaling pathway. This study identified the differential expression and functionality of exosomal circRNAs in AMI and provided further understanding of the potential pathogenesis of an exosomal circRNA-related competing endogenous RNA (ceRNA) network in AMI.

Single-Cell Sequencing Revealed Pivotal Genes Related to Prognosis of Myocardial Infarction Patients

Objectives

Myocardial infarction (MI) is a common cardiovascular disease. Histopathology is a main molecular characteristic of MI, but often, differences between various cell subsets have been neglected. Under this premise, MI-related molecular biomarkers were screened using single-cell sequencing.

Methods

This work examined immune cell abundance in normal and MI samples from GSE109048 and determined differences in the activated mast cells and activated CD4 memory T cells, resting mast cells. Weighted gene coexpression network analysis (WGCNA) demonstrated that activated CD4 memory T cells were the most closely related to the turquoise module, and 10 hub genes were screened. Single-cell sequencing data (scRNA-seq) of MI were examined. We used t-distributed stochastic neighbor embedding (t-SNE) for cell clustering.

Results

We obtained 8 cell subpopulations, each of which had different marker genes. 7 out of the 10 hub genes were detected by single-cell sequencing analysis. The expression quantity and proportion of the 7 genes were different in 8 cell clusters.

Conclusion

In general, our study revealed the immune characteristics and determined 7 prognostic markers for MI at the single-cell level, providing a new understanding of the molecular characteristics and mechanism of MI.

Serum miR-96-5p is a novel and non-invasive marker of acute myocardial infarction associated with coronary artery disease

Acute myocardial infarction (AMI) is a severe cardiovascular disease. AMI associated with coronary artery disease (AMI-CAD) is a subtype of AMI, composed of AMI patients caused by CAD. This study aimed to evaluate the diagnostic value of miR-96-5p in AMI induced by coronary artery disease. Expression of miR-96-5p and BCL2L13 was evaluated by serum samples and cells utilizing Western blot and RT-qPCR assays. The diagnostic value of miR-96-5p in AMI-CAD was analyzed with a receiver operating characteristic (ROC) curves. The correlation between miR-96-5p and BCL2L13 was examined by Spearman's correlation analysis. The level of oxidative stress and apoptosis were estimated via relative commercial kit, flow cytometry apoptosis assay and TUNEL staining assay. Our study discovered that miR-96-5p was down-regulated while BCL2L13 was up-regulated in patients with AMI-CAD. miR-96-5p was a potential diagnostic parameter, which may help distinguish AMI-CAD patients from healthy controls. In vitro experiments, miR-96-5p expression was down regulated while BCL2L13 was up-regulated in hypoxic cardiomyocytes. After confirming the targeted link of miR-96-5p to BCL2L13 using luciferase reporter and RNA pull down assays, we discovered that miR-96-5p overexpression may restore oxidative stress and cell apoptosis induced by hypoxia treatment in H9c2 cells; meanwhile, co-transfection with BCL2L13 overexpressing plasmid might partly countervail the ameliorative effects of miR-96-5p on oxidative stress and apoptosis. Collectively, miR-96-5p may function as a potential diagnostic biomarker for AMI-CAD patients, and the up-regulation of miR-96-5p would ameliorate AMI-associated cardiomyocytes injury by targeting BCL2L13, hence contributing to the clinical treatment of AMI-CAD.

Influence of strain, age, origin, and anesthesia on the cardioprotective efficacy by local and remote ischemic conditioning in an ex vivo rat model

Background

Local ischemic preconditioning (IPC) and remote ischemic conditioning (RIC) induced by brief periods of ischemia and reperfusion protect against ischemia‐reperfusion injury.

Methods

We studied the sensitivity to IR‐injury and the influence of strain, age, supplier, and anesthesia upon the efficacy of IPC and RIC in 7‐ and 16‐weeks‐old Sprague‐Dawley and Wistar rats from three different suppliers. The influence of sedation with a hypnorm and midazolam mixture (rodent mixture) and pentobarbiturate was compared.

Results

IPC attenuated infarct size in both 7‐weeks‐old Sprague–Dawley (48.4 ± 17.7% vs. 20.3 ± 6.9, p < 0.001) and 7‐weeks‐old Wistar (55.6 ± 10.9% vs. 26.8 ± 5.0%, p < 0.001) rats. Infarct size was larger in 16‐weeks‐old Sprague–Dawley rats, however, IPC still lowered infarct size (78.8 ± 9.2% vs. 58.3 ± 12.3%, p < 0.01). RIC reduced infarct sizes in 7‐weeks‐old Sprague–Dawley (75.3 ± 11.8% vs. 58.6 ± 8.9%, p < 0.05), but not in 7‐weeks‐old Wistar rats (31.7 ± 17.6% and 24.0 ± 12.6%, p = 0.2). In 16‐weeks‐old Sprague–Dawley rats, RIC did not induce protection (76.4 ± 5.5% and 73.2 ± 14.7%, p = 0.6). However, RIC induced protection in 16‐weeks‐old Wistar rats (45.2 ± 8.5% vs. 14.7 ± 10.8%, p < 0.001). RIC did not reduce infarct size in 7‐weeks‐old Sprague–Dawley rats from Charles River (62.0 ± 13.5% and 69.4 ± 10.4% p = 0.3) or 16‐weeks‐old Wistar rats from Janvier (50.7 ± 11.3 and 49.2 ± 16.2, p = 0.8). There was no difference between sedation with rodent mixture or pentobarbiturate.

Conclusion

The cardioprotective effect of IPC is consistent across rat strains independent of age, strain, and supplier. RIC seems to be less reproducible, but still yields protection across different rat strains. However, age, animal supplier, and anesthetics may modulate the sensitivity of IR‐injury and the response to RIC.

Developmental origins of cardiometabolic health outcomes in twins: A systematic review and meta-analysis

BACKGROUND AND AIMS

Studies of twins can reduce confounding and provide additional evidence about the causes of disease, due to within-pair matching for measured and unmeasured factors. Although findings from twin studies are typically applicable to the general population, few studies have taken full advantage of the twin design to explore the developmental origins of cardiometabolic health outcomes. We aimed to systematically review the evidence from twin studies and generate pooled estimates for the effects of early-life risk factors on later-life cardiometabolic health.

METHODS AND RESULTS

An initial search was conducted in March 2018, with 55 studies of twins included in the review. Risk of bias was assessed using the Newcastle-Ottawa Scale, and eligible studies were included in a meta-analysis, where pooled estimates were calculated. Twenty-six studies analysed twins as individuals, and found that higher birthweight was associated with lower SBP (β = -2.02 mmHg, 95%CI: -3.07, -0.97), higher BMI (β = 0.52 kg/m², 95%CI: 0.20, 0.84) and lower total cholesterol (β = -0.07 mmol/L, 95%CI: -0.11, -0.04). However, no associations were reported in studies which adjusted for gestational age. Few of the included studies separated their analyses into within-pair and between-pair associations.

CONCLUSIONS

Early-life risk factors were associated with cardiometabolic health outcomes in twin studies. However, many estimates from studies in this review were likely to have been confounded by gestational age, and few fully exploited the twin design to assess the developmental origins of cardiometabolic health outcomes.

Birthweight in offspring and cardiovascular mortality in their parents, aunts and uncles: a family-based cohort study of 1.35 million births

Background

A link between suboptimal fetal growth and higher risk of cardiovascular disease (CVD) is well documented. It has been difficult to assess the contribution of environmental versus genetic factors to the association, as these factors are closely connected in nuclear families. We investigated the association between offspring birthweight and CVD mortality in parents, aunts and uncles, and examined whether these associations are explained by CVD risk factors.

Methods

We linked Norwegian data from the Medical Birth Registry, the Cause of Death Registry and cardiovascular surveys. A total of 1 353 956 births (1967–2012) were linked to parents and one maternal and one paternal aunt/uncle. Offspring birthweight and CVD mortality association among all relationships was assessed by hazard ratios (HR) from Cox regressions. The influence of CVD risk factors on the associations was examined in a subgroup.

Results

Offspring birthweight was inversely associated with CVD mortality among parents and aunts/uncles. HR of CVD mortality for one standard deviation (SD) increase in offspring birthweight was 0.72 (0.69–0.75) in mothers and 0.89 (0.86–0.92) in fathers. In aunts/uncles, the HRs were between 0.90 (0.86–0.95) and 0.93 (0.91–0.95). Adjustment for CVD risk factors in a subgroup attenuated all the associations.

Conclusions

Birthweight was associated with increased risk of CVD in parents and in aunts/uncles. These associations were largely explained by CVD risk factors. Our findings suggest that associations between offspring birthweight and CVD in adult relatives involve both behavioural variables (especially smoking) and shared genetics relating to established CVD risk factors.

Long-term cardiovascular hospitalizations of small for gestational age (SGA) offspring born to women with and without gestational diabetes mellitus (GDM) ‡

OBJECTIVE

To assess whether delivery of small for gestational age (SGA) neonates to mothers with gestational diabetes mellitus (GDM) increases the risk of long-term cardiovascular offspring hospitalizations compared to SGA neonates born to mothers without GDM.

STUDY DESIGN

This is a population-based retrospective cohort study. The study group was SGA offspring born to mothers with GDM (n = 259), while the control group was SGA offspring born to mothers without GDM (n = 9053). The main factor evaluated was offspring cardiovascular hospitalizations up to the age of 18 years. Kaplan-Meier survival curve was used to estimate cumulative incidence of cardiovascular hospitalizations. A Cox proportional hazards model was used to estimate the adjusted hazard ratios (HR) for cardiovascular hospitalizations.

RESULTS

SGA children born to mothers with GDM had significantly higher rates of cardiovascular-related hospitalizations (1.9% vs. 0.7%, p = .026). A Kaplan-Meier survival curve demonstrated that SGA children born to GDM mothers had a higher cumulative incidence of cardiovascular hospitalizations (log-rank p = .037). The Cox regression model, while controlling for confounders, demonstrated that delivery of SGA neonates to mothers with GDM is independently associated with long-term cardiovascular offspring hospitalizations (adjusted HR =2.6; 95% CI 1.02-6.55 p = .045).

CONCLUSION

Delivery of SGA neonates born to mothers with GDM is independently associated with long-term cardiovascular offspring hospitalizations.

The Impact of Kidney Development on the Life Course: A Consensus Document for Action

Hypertension and chronic kidney disease (CKD) have a significant impact on global morbidity and mortality. The Low Birth Weight and Nephron Number Working Group has prepared a consensus document aimed to address the relatively neglected issue for the developmental programming of hypertension and CKD. It emerged from a workshop held on April 2, 2016, including eminent internationally recognized experts in the field of obstetrics, neonatology, and nephrology. Through multidisciplinary engagement, the goal of the workshop was to highlight the association between fetal and childhood development and an increased risk of adult diseases, focusing on hypertension and CKD, and to suggest possible practical solutions for the future. The recommendations for action of the consensus workshop are the results of combined clinical experience, shared research expertise, and a review of the literature. They highlight the need to act early to prevent CKD and other related noncommunicable diseases later in life by reducing low birth weight, small for gestational age, prematurity, and low nephron numbers at birth through coordinated interventions. Meeting the current unmet needs would help to define the most cost-effective strategies and to optimize interventions to limit or interrupt the developmental programming cycle of CKD later in life, especially in the poorest part of the world.

Familial Factors, Low Birth Weight, and Development of ESRD: A Nationwide Registry Study

BACKGROUND

Previous studies have demonstrated that low birth weight (LBW) is associated with higher risk for end-stage renal disease (ESRD). However, both LBW and ESRD cluster in families. The present study investigates whether familial factors explain the association between LBW and ESRD.

STUDY DESIGN

Retrospective registry-based cohort study.

SETTING & PARTICIPANTS

Since 1967, the Medical Birth Registry of Norway has recorded medical data for all births in the country. Sibling data are available through the Norwegian Population Registry. Since 1980, all patients with ESRD in Norway have been registered in the Norwegian Renal Registry. Individuals registered in the Medical Birth Registry with at least 1 registered sibling were included.

PREDICTOR

LBW in the participant and/or LBW in at least 1 sibling.

OUTCOME

ESRD.

RESULTS

Of 1,852,080 included individuals, 527 developed ESRD. Compared with individuals without LBW and with no siblings with LBW, individuals without LBW but with a sibling with LBW had an HR for ESRD of 1.20 (95% CI, 0.91-1.59), individuals with LBW but no siblings with LBW had an HR of 1.59 (95% CI, 1.18-2.14), and individuals with LBW and a sibling with LBW had an HR of 1.78 (95% CI, 1.26-2.53). Similar results were observed for individuals who were small for gestational age (SGA). Separate analyses for the association of age 18 to 42 years and noncongenital ESRD showed stronger associations for SGA than for LBW, and the associations were not statistically significant for age 18 to 42 years for LBW.

LIMITATIONS

Follow-up only until 42 years of age.

CONCLUSIONS

LBW and SGA are associated with higher risk for ESRD during the first 40 years of life, and the associations were not explained by familial factors. Our results support the hypothesis that impaired intrauterine nephron development may be a causal risk factor for progressive kidney disease.

Skin capillary density in infants born to normotensive mothers: a comparison between singleton and twin infants

OBJECTIVE

Twin infants tend to have LBW and microvascular alterations but do not appear to have an increase in cardiovascular mortality later in life as singleton infants. We hypothesized that twin infants born to normotensive mothers would not have capillary rarefaction at birth.

METHODS

We studied 26 dizygotic twin infants and compared them with 115 consecutive singleton infants to normotensive mothers. We used orthogonal polarized spectroscopy to measure basal (i.e., functional) and maximal (i.e., structural) skin capillary density according to a well-standardized protocol.

RESULTS

Twin infants have significantly higher BCD (mean difference 4.3 capillaries/mm(2) , 95% CI: 0.4, 8.1, p = 0.03) and have marginally significantly higher MCD (mean difference 3.9 capillaries/mm(2) , 95% CI: -0.6, 8.3, p = 0.086) compared to singleton infants. Birth weight was significantly associated with BCD and MCD (p = 0.003 and 0.006).

CONCLUSIONS

Twin infants with low and NBWs tend to have higher functional and structural capillary densities compared to singleton infants. Further longitudinal studies of skin capillary density and of retinal vascular parameters commencing from birth to various stages in early childhood are essential to identify the dynamics and the exact timing, if any, of the remodeling of microcirculation in these individuals.

[Polycystic ovary syndrome: what are the obstetrical risks?]

Polycystic ovary syndrome (PCOS) is the most common endocrine disorder in women of reproductive age and the leading cause of female infertility. This condition is frequently associated with significant metabolic disorders, including obesity and hyperinsulinemia. Therefore, it seems essential to focus on the pregnancy of these patients and possible obstetric complications. Many studies suggest an increase in the risk of obstetric pathology: early miscarriage, gestational hypertension, preeclampsia, gestational diabetes mellitus diagnosed during early pregnancy, prematurity, low birthweight or macrosomia, neonatal complications and cesarean sections. However, it is difficult to conclude clearly about it, because of the heterogeneity of definition of PCOS in different studies. In addition, many confounding factors inherent in PCOS including obesity are not always taken into account and generate a problem of interpretation. However it seems possible to conclude that PCOS does not increase the risk of placental abruption, HELLP syndrome, liver disease, postpartum hemorrhage, late miscarriage and stillbirth.

Age-dependent interaction of apolipoprotein E gene with eastern birthplace in Finland affects severity of coronary atherosclerosis and risk of fatal myocardial infarction--Helsinki Sudden Death Study

BACKGROUND

Mortality from coronary heart disease (CHD) has been constantly higher in eastern late settlement regions compared to western early settlements in Finland, unrelated to classical risk factors. In line with this, eastern birthplace was an age-dependent predictor of severe coronary atherosclerosis and pre-hospital sudden coronary death among male residents of Helsinki. We investigated a possible interaction of apolipoprotein E (APOE) gene with birthplace on the risk of myocardial infarction (MI) and coronary atherosclerosis.

METHOD

APOE genotypes were analyzed in the Helsinki Sudden Death Study series comprising out-of-hospital deaths among males aged 33-70 years (n = 577), who were born in high (east, n = 273) or low (west, n = 304) CHD mortality area.

RESULTS

Eastern-born men ≤ 55 years carried 30% more often (P = 0.017) and older men 40% less often (P = 0.022) the APOE ϵ4 allele compared to western-born men (P = 0.003 for birthplace-by-age interaction). In multivariate analysis, the ϵ4 allele associated with the risk of out-of-hospital MI (odds ratio 2.58; 95% CI 1.20-5.55; P = 0.016) only in eastern-born men and with advanced atherosclerosis in both regions of origin, respectively.

CONCLUSIONS

Birthplace-bound risk of CHD was age-dependently modified by APOE ϵ4 allele, suggesting genetic differences in CHD susceptibility between early and late settlement regions in Finland and providing one explanation for the eastern high mortality.

Solvent exposures and Parkinson disease risk in twins

OBJECTIVE

Several case reports have linked solvent exposure to Parkinson disease (PD), but few studies have assessed associations with specific agents using an analytic epidemiologic design. We tested the hypothesis that exposure to specific solvents is associated with PD risk using a discordant twin pair design.

METHODS

Ninety-nine twin pairs discordant for PD ascertained from the National Academy of Sciences/National Research Council World War II Veteran Twins Cohort were interviewed regarding lifetime occupations and hobbies using detailed job task-specific questionnaires. Exposures to 6 specific solvents selected a priori were estimated by expert raters unaware of case status.

RESULTS

Ever exposure to trichloroethylene (TCE) was associated with significantly increased risk of PD (odds ratio [OR], 6.1; 95% confidence interval [CI] 1.2-33; p = 0.034), and exposure to perchloroethylene (PERC) and carbon tetrachloride (CCl(4) ) tended toward significance (respectively: OR, 10.5; 95% CI, 0.97-113; p = 0.053; OR, 2.3; 95% CI, 0.9-6.1; p = 0.088). Results were similar for estimates of exposure duration and cumulative lifetime exposure.

INTERPRETATION

Exposure to specific solvents may increase risk of PD. TCE is the most common organic contaminant in groundwater, and PERC and CCl(4) are also ubiquitous in the environment. Our findings require replication in other populations with well-characterized exposures, but the potential public health implications are substantial.

Offspring birth weight and cardiovascular risk in parents: a population-based HUNT 2 study

Low birth weight is associated with increased risk of cardiovascular disease and type 2 diabetes in later life. The fetal insulin hypothesis suggests that shared genetic factors partly explain this association. If fetal genes predispose to both low birth weight and cardiovascular disease in adulthood, fathers of offspring with low birth weight should display an unfavorable profile of cardiovascular risk factors. To study this, the authors linked data on more than 14,000 parents, collected from the second Health Study of Nord Trøndelag County, Norway (HUNT 2, 1995-1997), to offspring data from the Norwegian Medical Birth Registry (1967-2005). Linear regression was used to study associations of offspring birth weight for gestational age with the parents' body mass index, waist circumference, blood pressure, glucose, and serum lipids. All analyses were adjusted for shared environment by means of the socioeconomic measures, lifestyle, and cardiovascular risk factors of the partner. The authors found that low offspring birth weight for gestational age was associated with increased paternal blood pressure, body mass index, waist circumference, and unfavorable levels of glucose and lipids. For mothers, associations similar to those for fathers were found for blood pressure, whereas associations in the opposite direction were found for glucose, lipids, and body mass index. The paternal findings strengthen the genetic hypothesis.

Are Twins at Risk of Cancer: Results From the Swedish Family-Cancer Database

A few twin studies on cancer have addressed questions on the possible carcinogenic or protective effects of twining by comparing the occurrence of cancer in twins and singletons. The nationwide Swedish Family-Cancer Database of 10.2 million individuals and 69,654 0- to 70-year-old twin pairs were used to calculate standardized incidence ratios (SIRs) and 95% confidence intervals (CIs) for all main cancers compared to singletons. The overall risk of cancer in same- or different-sex twins was at the same level as the risk for singletons. Testicular cancer, particularly seminoma, was increased among same-sex twins (1.54) and all twins to an SIR of 1.38. Among other tumors, neurinomas and nonthyroid endocrine gland tumors were increased. Colorectal cancers and leukemia were decreased among all twins. Melanoma and squamous cell skin cancer were decreased in male same-sex twins. The data on this unselected population of twins suggest that twinning per se is not a risk factor of cancer. In utero hormonal exposures or postnatal growth stimulation may be related to the risk of testicular cancer and pituitary tumors. Protective effects against colorectal cancer may be related to a beneficial diet, and in melanoma and skin cancer, to socioeconomic factors. The study involved multiple comparisons, and internal consistency between the results was one of the main factors considered for their plausibility. The results should encourage others working on twin and singleton populations to examine the specific associations and emerging hypotheses.

The Foetal Origins of Adult Disease: Interpreting the Evidence From Twin Studies

Twin studies have a contribution to make to the debate concerning the foetal origins of adult disease. Twins are growth retarded compared to singletons and experience post-natal catch-up growth. However, there is no evidence that twins are at increased risk of cardiovascular disease. Studying whether discordance in size at birth within monozygotic twin pairs is predictive of discordance in later life disease should help resolve whether the association between size at birth and later disease is due to common genetic factors. Results from studies of blood pressure in childhood and adult life looking at these within twin effects are far from conclusive. There are, however, methodological problems in the interpretation of these results, not least of which is the relatively small numbers of twin pairs studied. Studies exploring the effect of zygosity and chorion type on later disease provide may provide a useful extension of the research agenda. In summary, twin studies to date have raised more questions about the foetal origins hypothesis than they have resolved.

Birth weight predicts risk of cardiovascular disease within dizygotic but not monozygotic twin pairs: a large population-based co-twin-control study

BACKGROUND

The widely reported inverse association between birth weight and risk of cardiovascular disease (CVD) has sparked theories about early life determinants of adult disease. Within-twin-pair analysis provides a unique opportunity to investigate whether factors shared within twin pairs influence the association.

METHODS AND RESULTS

In a population-based cohort of like-sexed twins with known zygosity born in Sweden from 1926 to 1958, disease-discordant twin pairs were identified through linkage to the National Inpatient and Cause of Death registers between 1973 and 2006. Co-twin-control analyses were performed on twins discordant for cardiovascular disease (n=3884), coronary heart disease (n=2668), and stroke (n=1372). Overall, inverse associations between birth weight and risk of cardiovascular diseases were seen within dizygotic but not monozygotic twin pairs. In dizygotic twins, the odds ratios for a 1-kg within-pair increase in birth weight were 0.74 (95% confidence interval, 0.56 to 0.98) for coronary heart disease and 0.57 (95% confidence interval, 0.37 to 0.88) for stroke. Conversely, no statistically significant associations were found within monozygotic twins (for coronary heart disease: odds ratio, 1.10; 95% confidence interval, 0.73 to 1.68; for stroke: odds ratio, 0.92; 95% confidence interval, 0.48 to 1.80).

CONCLUSIONS

We found an association between birth weight and risk of cardiovascular disease within disease-discordant dizygotic but not monozygotic twin pairs. This indicates that the association between birth weight and cardiovascular disease could be a result of common causes, and that factors that vary within dizygotic but not monozygotic twin pairs may help identify them.

Birth weight effects on children's mental, motor, and physical development: evidence from twins data

OBJECTIVE

To determine the effect of very low birth weight (VLBW; <1500 g) and moderately low birth weight (MLBW; 1500-2499 g) on children's mental and motor development and physical growth during the first 2 years of life and whether VLBW and MLBW babies catch up to normal birth weight (NBW; > or =2500 g) children by age 2.

METHODS

We use data on dizygotic (DZ) and monozygotic (MZ) twins and singleton births from the first two waves of the Early Childhood Longitudinal Study-Birth Cohort (ECLS-B), a nationally representative dataset of children born in the US in 2001. We estimate the effects of VLBW and MLBW on children's mental and motor development scores, weight-for-age, weight-for-length, weight-for-height, and length-for-age z-scores at 9 months and 2 years. We examine whether differences in outcomes within twin pairs are related to differences in their birth weights. The within-twins analysis is conducted on samples of DZ and MZ twins. For comparison, we also estimate birth weight effects on child outcomes from multivariate linear regression models using the full singleton and twins' sample. We also estimate the effect of being small-for-gestational age (SGA; birth weight <10th percentile for gestation) using the same set of models in order to separate out the effects of fetal growth restriction from prematurity.

RESULTS

Evaluation of all births showed that VLBW and MLBW have large negative effects on mental development, motor development, and growth at 9 months and 2 years of age. However, results from within-twin models with DZ twins that control for shared maternal and environmental factors showed much less effect of birth weight on mental or motor development, but continued large effects on growth for the VLBW group. Within-twin models with MZ twins that control for shared maternal, environmental, and genetic factors showed statistically insignificant effects of birth weight on mental and motor development, but continued effects on growth. Similar patterns were found when examining the effects of SGA.

CONCLUSIONS

After controlling for the influence of maternal, environmental, and genetic factors, low birth weight has at most a small negative effect on children's mental and motor development in their first 2 years of life. However, low birth weight is a major risk factor for children's physical growth in the early years and there is no evidence of catch-up by age 2.

Birthplace predicts risk for prehospital sudden cardiac death in middle-aged men who migrated to metropolitan area: The Helsinki Sudden Death Study

BACKGROUND

Eastern-born male Finns, irrespective of their place of residence, have high mortality from coronary heart disease (CHD), and half of such deaths are sudden.

AIM

To study whether eastern birthplace alone or combined with life-style factors predicts risk for prehospital sudden cardiac death (SCD) in the new (west) low-mortality area of residence.

METHOD

Prospective case-control autopsy study of all (700) out-of-hospital deaths of men aged 35-69 years in metropolitan Helsinki during 1981-82 and 1991-92. Data on CHD risk factors were obtained for 405, of whom 149 died of SCD (cases) and 256 of other causes (controls).

RESULTS

A birthplace-by-age interaction with SCD (P=0.024) and with myocardial infarction (P=0.005) appeared. Men < or =54 years born in the east were more often victims of SCD (odds ratio 2.99, 95% confidence interval 1.38-6.49, P=0.006) than were men born in the west, independently of CHD risk factors. SCD was predicted also by alcohol consumption, age, smoking, and hypertension. Amongst older (>54 years) men no association with birthplace was any longer evident, but alcohol and socio-economic status predicted SCD.

CONCLUSIONS

Birthplace-based risk for SCD suggests the contribution of early life environment or genetic east-west differences, reflecting Finns' two-phase settlement history.

Familial (shared environmental and genetic) factors and the foetal origins of cardiovascular diseases and type 2 diabetes: a review of the literature

Several researchers have argued that observed associations between birth weight and cardiovascular diseases, and type 2 diabetes, may be confounded by familial (shared environmental and genetic) factors. However, most studies have found that shared environmental factors, including socio-economic factors, do not influence the foetal origins of adult diseases. Results from two twin studies suggest that genetic factors may be of importance for the association between birth weight and risks of coronary heart disease, but findings from intergenerational studies are not consistent with genetic confounding. More studies have assessed the importance of genetic factors with respect to risk factors of coronary heart, including raised blood pressure and lipid levels. Recent findings suggest that the association between birth weight and hypertension is independent of genetic factors. In contrast, recent twin and intergenerational studies favour the hypothesis that the association between birth weight and risk of type 2 diabetes is confounded by genetic factors.

Perinatal Risk Factors for Ischemic Heart Disease

Background— Several studies have reported an association between low birth weight and ischemic heart disease, but it remains unclear whether the association is mediated through poor fetal growth or short gestational duration.

Methods and Results— In a cohort study, we have identified all subjects born preterm or with a low birth weight at 4 major delivery units in Sweden from 1925 through 1949. For comparison, an equal number of subjects with none of these criteria were identified within the same source population. The study population consists of 6425 subjects, of whom 2931 were born before 37 weeks of gestation and 2176 had a birth weight <2500 g. Fetal growth was estimated through birth weight for gestational age. The cohort was followed up for occurrence of ischemic heart disease through the nationwide Hospital Discharge and Cause of Death Registries during the period of 1987 through 2002. In the cohort, 617 cases of ischemic heart disease occurred. Compared with subjects with a normal fetal growth, those born small for gestational age (birth weight ≤−2 SD below the mean) were at increased risk of ischemic heart disease (adjusted hazard ratio, 1.64; 95% confidence interval, 1.23 to 2.18). The negative association between fetal growth and risk of ischemic heart disease was independent of gestational duration.

Conclusions— The association between low birth weight and adult risk of ischemic heart disease appears to be mediated entirely by poor fetal growth.

Is birth weight a risk factor for ischemic heart disease in later life?

BACKGROUND

An inverse association between birth weight and ischemic heart disease (IHD) has been seen in observational studies.

OBJECTIVE

We wanted to determine the strength and consistency of the association between birth weight and subsequent IHD.

DESIGN

We conducted a systematic review of observational studies.

RESULTS

Seventeen published studies of birth weight and subsequent IHD were identified that included a total of 144,794 singletons. Relative risk estimates for the association between birth weight and IHD were available from 16 of these studies. Additional data from 2 unpublished studies of 3801 persons were also included. In total, the analyses included data from 18 studies on 4210 nonfatal and 3308 fatal IHD events in 147,009 persons. The mean weighted estimate for the association between birth weight and the combined outcome of nonfatal and fatal IHD was 0.84 (95% CI: 0.81, 0.88) per kilogram of birth weight (P<0.0001). No significant heterogeneity was observed between estimates in different studies (P=0.09), nor was there evidence of publication bias (P=0.3, Begg test). Neither restricting the analysis to fatal IHD events nor adjusting for socioeconomic status had any appreciable effect on the findings.

CONCLUSIONS

These findings are consistent with a 1 kg higher birth weight being associated with a 10-20% lower risk of subsequent IHD. However, even if causal, interventions to increase birth weight are unlikely to reduce the incidence of IHD materially. Further studies are needed to determine whether the observed association reflects a stronger underlying association with a related exposure or is due (at least in part) to residual confounding.

Differences in maternal and paternal transmission of coronary heart disease

BACKGROUND

Few studies have investigated the possible differential transmission of maternal and/or paternal coronary heart disease (CHD) to offspring, after accounting for sociodemographic characteristics.

METHODS

The Multigeneration Register was linked to hospital data in this study of all Swedish individuals born since 1932 and their parents. Registered cases of CHD between January 1, 1987, and December 31, 2001, were evaluated. Poisson regression was used to calculate standardized incidence ratios (SIRs) for men and women with mothers and/or fathers affected by CHD compared with men and women whose parents were not affected. All analyses were conducted in 2005.

RESULTS

Maternal transmission was stronger than paternal transmission and the confidence intervals did not overlap. For women, the overall SIRs were 1.43 (95% confidence interval [CI]=1.34-1.51) for maternal transmission and 1.17 (95% CI=1.11-1.23) for paternal transmission. For men, the corresponding SIRs were 1.55 (95% CI=1.50-1.60) and 1.41 (95% CI=1.37-1.45). Even higher SIRs were found in the youngest age groups, among those with both parents affected by coronary heart disease, and among those with premature parental CHD.

CONCLUSIONS

These findings might ultimately influence treatment decisions regarding risk factors and suggest the need for research focusing on genetic and intrauterine risk factors.

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.

Z-velocity in screening for intrauterine growth restriction

OBJECTIVES

Ultrasound scans provide the basis for detection of intrauterine growth restriction (IUGR) but often fail to distinguish IUGR from small-for-gestational age (SGA) fetuses. This study introduces the concept of Z-velocity, calculated as changes in Z-scores over time, as an additional criterion in the diagnosis of IUGR.

METHODS

A computer program simulated 50 000 fetal abdominal circumference (FAC) scans based on published growth formulae. False-positive rates were calculated to determine optimal scan time and scan intervals. Using an independent simulation of 32 500 FAC scans, the two methods were compared using receiver-operating characteristics (ROC) curve analysis.

RESULTS

ROC showed areas under the curve of > 0.74 over the complete range of scan intervals. The positive predictive value of growth arrest as the only diagnostic criterion was, however, too low to recommend it as an exclusive or the first diagnostic criterion.

CONCLUSIONS

Z-velocity can be used to decide whether further investigations for growth abnormality are required in fetuses that fall below the 10(th) percentile. The gain of combined diagnostic approaches should be calculated from large databases that include the neonatal ponderal index as the gold standard.

Embryonic and fetal programming of physiological disorders in adulthood

In the past decade, data from numerous epidemiological studies have indicated strong inverse associations between birth weight and risk of coronary heart disease, hypertension, type 2-diabetes, and other diseases in adulthood. The "Barker hypothesis" thus postulates that a number of organ structures and functions undergo programming during embryonic and fetal life. This developmental programming determines the set points of physiological and metabolic responses in adult life. Alterations of nutrient availability during gestation may lead to developmental adaptations, via hormonal maneuvers by the embryo and fetus that readjust these set points. These adaptive measures have short-term benefits to the embryo and fetus, so that the newborn will be better prepared for the adverse environment (e.g., undernutrition). However, adequate nutritional support during postnatal life that enables catch-up growth may create metabolic conflicts that predispose the adult to aberrant physiological functions and, ultimately, increased risk of disease. It is plausible that other adverse in utero conditions, including exposure to developmental toxicants, may similarly alter adult disease susceptibility. This article provides an overview of the Barker hypothesis, its supporting evidence, the current advances in understanding the biological mechanisms underlying this phenomenon, and its implications for developmental toxicology.

Genetic and environmental influences on birthweight in a sample of Korean twins

This study is the first report of genetic and environmental influences on birthweight using Korean twins. The sample consisted of 255 monozygotic (MZ) and 178 dizygotic (DZ) twin pairs drawn from the Seoul Twin Family Study. Intraclass twin correlations were computed for the twins' birthweights obtained from parents (typically mothers) of the twins. To estimate genetic and shared and nonshared environmental influences on birthweight, standard univariate model-fitting analyses were performed using a software, Mx. For each gender, MZ twin correlations were higher than DZ twin correlations, suggesting existence of genetic influences on birthweight; however, DZ twin correlations were higher than half the MZ twin correlations, indicating that shared environmental factors are also important. For each zygosity, twin correlations were not significantly different between males and females, implicating that genes and environments that cause individual differences in birthweight may not vary between males and females. Model-fitting analyses based on the data pooled across gender yielded estimates of 17% for genetic, 60% for shared environmental, and 23% for nonshared environmental influences on birthweight.

Developmental origins of the metabolic syndrome: prediction, plasticity, and programming

The "fetal" or "early" origins of adult disease hypothesis was originally put forward by David Barker and colleagues and stated that environmental factors, particularly nutrition, act in early life to program the risks for adverse health outcomes in adult life. This hypothesis has been supported by a worldwide series of epidemiological studies that have provided evidence for the association between the perturbation of the early nutritional environment and the major risk factors (hypertension, insulin resistance, and obesity) for cardiovascular disease, diabetes, and the metabolic syndrome in adult life. It is also clear from experimental studies that a range of molecular, cellular, metabolic, neuroendocrine, and physiological adaptations to changes in the early nutritional environment result in a permanent alteration of the developmental pattern of cellular proliferation and differentiation in key tissue and organ systems that result in pathological consequences in adult life. This review focuses on those experimental studies that have investigated the critical windows during which perturbations of the intrauterine environment have major effects, the nature of the epigenetic, structural, and functional adaptive responses which result in a permanent programming of cardiovascular and metabolic function, and the role of the interaction between the pre- and postnatal environment in determining final health outcomes.

Birth weight in offspring of mothers with polycystic ovarian syndrome

BACKGROUND

A relationship between reduced fetal growth and the polycystic ovary syndrome (PCOS) has been proposed in girls with PCOS. However, the birth weight in the offspring of PCOS mothers has not been systematically investigated. The aim of this study was to establish the birth weight of newborns of mothers with PCOS and to compare it with a control group of newborns of normal women matched by age and weight at the beginning of pregnancy.

METHODS

The birth weight of 47 infants born from singleton pregnancies in women with well-documented PCOS was compared with 180 infants born from singleton pregnancies in healthy controls.

RESULTS

The prevalence of small for gestational age (SGA) infants was significantly higher in the PCOS group compared to the control group (12. 8% versus 2.8%, respectively, P<0.02). Moreover, SGA infants born to PCOS mothers were smaller than those born to control mothers (P<0.05). The prevalence of large for gestational age infants (LGA) was similar in both groups, but birth length of LGA newborns was greater in PCOS women than controls (P<0.05).

CONCLUSIONS

PCOS mothers showed a significantly higher prevalence of SGA newborns which cannot be completely attributed to pregnancy complications, and seems to be more related to the PCOS condition of the mother.

Fetal programming: the perspective of single and twin pregnancies

Multiple pregnancy is associated with increased risk of adverse consequences for both mother and fetus(es), including increased rates of maternal hypertension and pre-eclampsia, spontaneous abortion, Caesarean delivery, low birthweight, birth prematurity, perinatal mortality, admission to neonatal intensive care and extended length of care, respiratory distress, cerebral palsy, developmental delay, contact with disability services and mortality to age 5 years. Premature birth, which affects 97% of triplets and 53.3% of twins in Australia, is not the sole factor involved. The rate of multiple pregnancy in Australia is 1.7%. This compares to 22.1% for pregnancies resulting from assisted reproduction technology (ART). As a result, 21.8% of babies born from ART are from a multiple pregnancy, in comparison to the USA where the majority of babies born from ART are from a multiple pregnancy. Additionally, the population rate of multiple births is rising due to the more frequent use of ART and continued multi-embryo transfers, which is operating against a background of rising implantation rates within ART clinics. Twins have been of interest from a programming perspective. However, analysis of associations between crude birthweight and subsequent metabolic risk factors or mortality in adulthood from chronic disease indicate that adaptations in pregnancy to support multi-fetal growth are not identical to fetal growth restriction in singleton pregnancies. Indeed, the process of ‘maternal constraint’ is incompletely understood and confounds such comparisons. From a programming perspective, it is a challenge to identify in twin pregnancies the transition from physiological adaptation to pathological growth restriction. Growth disparity between twins has been more illuminating of subtle adverse effects for the smaller of twin pairs in both blood pressure and insulin resistance in adulthood. Interestingly, these effects can be observed in both dizygotic and to a lesser degree in monozygotic twins, which indicates a role for both genetic and environmental factors in these measures. This suggests that, consistent with experimental studies in other species, the relationship between impaired growth in utero and chronic disease in later life is not simply mediated by a common genetic pathway.

Intrauterine environmental and genetic influences on the association between birthweight and cardiovascular risk factors: studies in twins as a means of testing the fetal origins hypothesis

Evidence has accumulated that low birthweight is associated with several risk factors for cardiovascular disease. However, it is not known whether or not these associations are due to a programmed response to intrauterine malnutrition or genetic factors influencing both birthweight and cardiovascular risk factors. Twin studies offer a unique opportunity to distinguish between intrauterine and genetic origins of the association between birthweight and cardiovascular risk. In our twin cohort, low birthweight was associated with insulin resistance, lower HDL and shorter height within both dizygotic and monozygotic twin pairs, suggesting that these associations are, at least in part, independent of genetic factors. In contrast, low birthweight was associated with blood pressure, total and LDL cholesterol, fibrinogen and sympathetic activation within dizygotic twin pairs, but not within monozygotic twin pairs. These differences between dizygotic and monozygotic twins suggest that these associations are, at least in part, due to genetic factors. Therefore, both intrauterine environmental and genetic factors appear to play a role in the association between birthweight and cardiovascular risk factors. In the future, strategies may be developed targeted at improving or preventing impaired intrauterine growth. However, the effects of interventions that comprise changes in environment within the normal range may be limited due to the possible important role of genetic factors.

The impact of birth weight on coronary heart disease morbidity and mortality in a birth cohort followed up for 85 years: a population-based study of men born in 1913

OBJECTIVES

To analyse whether there is a relationship between birth weight on the one hand and coronary heart disease (CHD) and cardiovascular disease (CVD) mortality and morbidity on the other, whether such a relationship is influenced by potential modifying factors from the time of birth, adult height and the presence of diabetes, and what significance these possible associations might have for the CHD and CVD rates in the general population.

DESIGN

Population-based birth cohort.

SETTING

Sweden.

SUBJECTS

A total of 1319 singleton men born in 1913, surviving until age 20 and from then on followed until 85 years of age.

MAIN OUTCOME MEASURES

CHD and CVD mortality and morbidity events.

RESULTS

The gestational age adjusted CHD and CVD mortality and morbidity hazard ratios were virtually unaffected by birth weight. Taking possible effect-modifying variables into account did not change the results. The population attributable risk percentage for CHD and CVD mortality and morbidity due to a birth weight <or=3000 g was 1% or less.

CONCLUSIONS

Birth weight did not significantly affect CHD or CVD mortality or morbidity. A birth weight <or=3000 g contributes little to the burden of CHD and CVD on a community level.

Birth weight and cardiovascular risk factors in a cohort followed until 80 years of age: the study of men born in 1913

OBJECTIVES

To analyse whether there is a relation-ship between birth weight and cardiovascular risk factors given the influence of potential modifying factors from birth time, former generations and adult life.

DESIGN

Population-based cohort followed until 80 years of age.

SETTING

Sweden.

SUBJECTS

A total of 478 singleton men born in 1913 and participating in a population study in Gothenburg, Sweden, from age 50.

MAIN OUTCOME MEASURES

Systolic blood pressure (SBP), antihypertensive treatment, incident diabetes mellitus, and serum total cholesterol, serum triglycerides and waist circumference as both continuous variables and in the highest quintiles of their distributions.

RESULTS

After adjustment for the influence of birth time variables, hereditary factors and anthropometric and socio-economic adult life variables, SBP decreased by 3.7 mmHg per 1000 g increase of birth weight, the prevalence of antihypertensive treatment decreased by 32%, diabetes decreased by 53%, serum total cholesterol decreased by 0.20 mmol L(-1) and being in the top quintile of serum cholesterol decreased by 23%. The population risk percentage due to a birth weight < or =3000 g was for all three outcomes 3.8% and for antihypertensive treatment, diabetes and cholesterol 0.2, 18 and 2.5%, respectively.

CONCLUSIONS

Low birth weight thus seems to affect the development of increasing SBP, antihypertensive treatment, diabetes and high cholesterol even when potential effect modifiers from birth time, former generations and adult life were taken into account. In the general population, the risk percentage due to a birth weight < or =3000 g was largest for diabetes.

Low birth weight is associated with increased sympathetic activity: dependence on genetic factors

BACKGROUND

Low birth weight may be associated with high blood pressure in later life through genetic factors, an association that may be explained by alterations in sympathetic and parasympathetic activity. We examined the association of birth weight with cardiac pre-ejection period and respiratory sinus arrhythmia (indicators of cardiac sympathetic and parasympathetic activity, respectively) and with blood pressure in 53 dizygotic and 61 monozygotic adolescent twin pairs.

METHODS AND RESULTS

Birth weight of the twins was obtained from the mothers. Pre-ejection period and respiratory sinus arrhythmia were measured with electrocardiography and impedance cardiography at rest, during a reaction time task, and during a mental arithmetic task. In the overall sample, lower birth weight was significantly associated with shorter pre-ejection period at rest, during the reaction time task, and during the mental arithmetic task (P=0.0001, P<0.0001, and P=0.0001, respectively) and with larger pre-ejection period reactivity to the stress tasks (P=0.02 and P=0.06, respectively). In within-pair analyses, differences in birth weight were associated with differences in pre-ejection period at rest and during both stress tasks in dizygotic twin pairs (P=0.01, P=0.06, and P=0.2, respectively) but not in monozygotic twin pairs (P=0.9, P=1.0, and P=0.5, respectively). Shorter pre-ejection period explained approximately 63% to 84% of the birth weight and blood pressure relation.

CONCLUSIONS

Low birth weight is associated with increased sympathetic activity, and this explains a large part of the association between birth weight and blood pressure. In addition, our findings suggest that the association between birth weight and sympathetic activity depends on genetic factors.

The association between birth weight and plasma fibrinogen is abolished after the elimination of genetic influences

Low birth weight is associated with an increased risk of atherothrombosis, which may be related in part to the association between low birth weight and high plasma fibrinogen. The association between birth weight and fibrinogen may be explained by intrauterine, socio-economic or genetic factors. We examined birth weight and fibrinogen in 52 dizygotic and 56 adolescent monozygotic (genetically identical) twin pairs. The dizygotic but not the monozygotic twins with the lowest birth weight from each pair had a fibrinogen level that was higher compared with their co-twins with the highest birth weight [dizygotic twins: 2.62 +/- 0.46 g L(-1) vs. 2.50 +/- 0.41 g L(-1) (P = 0.04); monozygotic twins: 2.42 +/- 0.45 g L(-1) vs. 2.49 +/- 0.39 g L(-1) (P = 0.2)]. These findings suggest that the association between birth weight and plasma fibrinogen is abolished after the elimination of genetic influences and therefore that this association has genetic causes. Improvement of intrauterine nutrition may not lower fibrinogen levels in later life.

The association between low birth weight and high levels of cholesterol is not due to an increased cholesterol synthesis or absorption: analysis in twins

Low birth weight may be associated with high levels of cholesterol in later life through genetic factors that affect both birth weight and cholesterol metabolism. Alterations in cholesterol synthesis and absorption may play an important role in this association. We examined birth weight and plasma ratios of a precursor of cholesterol, lathosterol (an estimate of cholesterol synthesis), and plant sterols, campesterol and beta-sitosterol (estimates of cholesterol absorption), to cholesterol in 53 dizygotic and 58 monozygotic adolescent twin pairs. After adjustment for current weight, birth weight was not associated with the ratios of lathosterol, campesterol, and beta-sitosterol either in the overall sample [+0.07 micro mol/mmol/kg (95% confidence interval: -0.11 to 0.25), p = 0.5; +0.02 micro mol/mmol/kg (-0.33 to 0.37), p = 0.9; and -0.04 micro mol/mmol/kg (-0.23 to 0.15), p = 0.8, respectively] or in the intrapair analysis in dizygotic twins [+0.27 micro mol/mmol/kg (-0.28 to 0.82), p = 0.3; -0.03 micro mol/mmol/kg (-1.07 to 1.01), p = 1.0; and +0.04 micro mol/mmol/kg (-0.56 to 0.64), p = 0.9, respectively] or in the intrapair analysis in monozygotic twins [+0.54 micro mol/mmol/kg (-0.09 to 1.18), p = 0.09; -0.60 micro mol/mmol/kg (-1.59 to 0.39), p = 0.2; and -0.43 micro mol/mmol/kg (-0.99 to 0.14), p = 0.14, respectively]. Plasma levels of lathosterol, campesterol, and beta-sitosterol, which are indicators of cholesterol synthesis and absorption, thus do not explain the association of low birth weight with high levels of total and LDL cholesterol. As an alternative hypothesis, we suggest that a decrease in cholesterol clearance may play an important role.

The influence of maternal BMI and age in twin pregnancies on insulin resistance in the offspring

OBJECTIVE

There is strong evidence that low birth weight is associated with glucose intolerance and diabetes in adults. We have carried out a twin study to distinguish among maternal influences, which affect both twins; fetoplacental influences, which are unique to each twin; and the genetic factors that may underlie this association.

RESEARCH DESIGN AND METHODS

We identified a sample of 423 twin pairs (250 monozygotic and 173 dizygotic) from the East Flanders Prospective Twin Survey who were born between 1964 and 1982. Data collected in this study included the mother's body composition and weight gain during pregnancy, the twins' birth weights, and gestational age. The twins (aged 18-34 years) attended a research center for measurement of height, weight, and waist-to-hip ratio as well as fasting glucose, proinsulin, and insulin concentrations.

RESULTS

Among twin pairs discordant for birth weight, we found little evidence that the lighter twin had abnormal glucose-insulin metabolism in adult life. However, both a low prepregnancy maternal BMI and older maternal age at delivery were associated with hyperinsulinemia and evidence of insulin resistance in the offspring. Fasting insulin increased by 1.3% (95% CI 0.1-2.6%) per unit fall in maternal BMI and by 1.1% (0.02-2.0%) per year increase in maternal age. These associations were independent of the twins' BMI and waist-to-hip ratio and their zygosity.

CONCLUSIONS

These novel findings suggest that in twin pregnancies, maternal factors are more important than fetoplacental factors in determining glucose-insulin metabolism in the offspring.

Genetics, the environment, and lipid abnormalities

Plasma lipid levels have been identified as major risk factors for cardiovascular disease. Multiple behavioral and environmental factors are known to modulate their concentrations in the general population; however, there is dramatic individual variability in the association between risk factors and disease, as well as in the individual response to therapeutic intervention. These differences may be due to the interaction between genetic and nongenetic factors that are ultimately responsible for the individual disease risk and response to intervention. Great strides have been made to characterize the genes involved in the homeostasis of plasma lipoprotein levels and to identify polymorphisms that could contribute to an earlier and more precise individual risk assessment. Especially relevant has been the recent interest and progress on examining the interaction between a number of candidate genes and nongenetic factors, namely smoking, alcohol drinking, physical activity, and sex. The APOE locus continues to be the most thoroughly studied gene in this regard; however, other genes (ie, LPL, APOC3, ADH3) are showing promising results.

The Swedish Twin Registry: a unique resource for clinical, epidemiological and genetic studies

The Swedish Twin Registry (STR), which today has developed into a unique resource, was first established in the late 1950s to study the importance of smoking and alcohol consumption on cancer and cardiovascular diseases whilst controlling for genetic propensity to disease. Since that time, the Registry has been expanded and updated on several occasions, and the focus has similarly broadened to most common complex diseases. In the following, we will summarize the content of the database, describe for the first time recent data collection efforts and review some of the principal findings that have come from the Registry.

Is type 2 diabetes mellitus a disorder of the brain?

I propose that type 2 diabetes mellitus is due to damage to neurons in the ventromedial hypothalamus or to a defect in the action or properties of insulin or insulin receptors in the brain. These neuronal abnormalities are probably secondary to a marginal deficiency of long-chain polyunsaturated fatty acids during the critical periods of brain growth and development. Hence, supplementation of adequate amounts of long-chain polyunsaturated fatty acids during the third trimester of pregnancy to 2 y postterm can prevent or postpone the development of diabetes mellitus.

Fetal growth and systolic blood pressure in young adulthood: the Swedish Young Male Twins Study

The objective was to test the fetal origins hypothesis by examining the association between fetal growth and systolic blood pressure in a large cohort of adult male twins of known zygosity. This cohort study is based on a record linkage of routinely collected data from the Swedish Medical Birth Registry, the Swedish Military Conscription Registry and a mailed questionnaire. It comprises 886 pairs of same-sex male twins born in Sweden in 1973-79 for whom data were available on size at birth and systolic blood pressure, height and weight at age 17-19 years. Based on self-reported similarity of appearance in childhood, 384 twin pairs were classified as monozygotic (MZ), 269 as dizygotic (DZ) and 233 as of uncertain zygosity (XZ). Differences in systolic blood pressure within and between twin pairs were analysed in relation to birthweight and birthweight-for-gestational-age z-score using random effects linear models. Within twin pairs, a 1 kg difference in birthweight was associated with a difference of -1.30 mmHg in systolic blood pressure [95% confidence interval -4.15, +1.54] for MZ twins and +0.14 [-3.49, +3.76] for DZ twins; for all twins combined it was -0.21 [-2.13, +1.71]. Between twin pairs, a 1 kg difference in birthweight was associated with a difference of -2.68 mmHg in systolic blood pressure [-4.95, -0.42] for MZ twins and +0.28 [-2.35, +2.91] for DZ twins; for all twins combined -1.68 [-3.15, -0.22]. All these estimates included adjustment for age, year and conscription centre of examination, gestational age and height and weight at conscription. These results provide little support for the fetal origins hypothesis. The estimates of the within-pair effect in MZ twins and their wide confidence intervals (including zero) cannot exclude the existence of common genetic mechanisms, but are also not inconsistent with an in utero programming effect. This study highlights some methodological problems with twin studies.

Cancer risks in twins: results from the Swedish family-cancer database

Twin studies on cancer have addressed two general questions, one about the possible carcinogenic effects of twinning and the second about heritable effects of cancer. The first question is answered by comparing the occurrence of cancer in twins to that in singletons; the second is answered in probandwise analysis of monozygotic twins compared to dizygotic twins or siblings. We used the nationwide Swedish Family-Cancer Database on 10.2 million individuals and 62,574 0-66-year-old twins to calculate standardized incidence ratios (SIRs) and 95% confidence intervals (CIs) for all main cancer compared to cancer in singletons. In probandwise analysis, the SIR was calculated for the co-twin of an affected twin. The overall risk of cancer in same or opposite sex twins was at the level of the risk for singletons. Testicular cancer was increased among same sex twins and all twins to an SIR of 1.43. Melanoma was decreased in these groups of twins to an SIR of 0.84. Some other cancer sites were increased or decreased in some groups of twins, but none in all twins. The SIR of breast cancer was 1.01 and 1.04 in same and opposite sex twins, respectively. Probandwise analysis showed increased risks for Hodgkin's disease in males and breast cancer and childhood acute lymphoid leukemia among females. The data on this unselected population of twins suggest that twinning per se is not a risk factor of cancer. However, because twins are smaller than singletons at birth, some possible effects could be masked by such differences. In utero hormonal exposures may be related to the risk of testicular cancer. The protective effects in melanoma may be due to socioeconomic factors.