Shared genetic variance between the features of the metabolic syndrome: heritability studies

Interrelationships among metabolic syndrome, bone-derived cytokines, and the most common metabolic syndrome-related diseases negatively affecting bone quality

Metabolic syndrome (MetS), as a set of medical conditions including hyperglycemia, hypertension, abdominal obesity, and dyslipidemia, represents a highly prevalent disease cluster worldwide. The individual components of MetS together increase the risk of MetS-related disorders. Recent research has demonstrated that bone, as an endocrine organ, releases several systemic cytokines (osteokines), including fibroblast growth factor 23 (FGF23), lipocalin 2 (LCN2), and sclerostin (SCL). This review not only summarizes current knowledge about MetS, osteokines and the most common MetS-related diseases with a detrimental impact on bone quality (type 2 diabetes mellitus: T2DM; cardiovascular diseases: CVDs; osteoporosis: OP), but also provides new interpretations of the relationships between osteokines and individual components of MetS, as well as between osteokines and MetS-related diseases mentioned above. In this context, particular emphasis was given on available clinical studies. According to the latest knowledge, FGF23 may become a useful biomarker for obesity, T2DM, and CVDs, as FGF23 levels were increased in patients suffering from these diseases. LCN2 could serve as an indicator of obesity, dyslipidemia, T2DM, and CVDs. The levels of LCN2 positively correlated with obesity indicators, triglycerides, and negatively correlated with high-density lipoprotein (HDL) cholesterol. Furthermore, subjects with T2DM and CVDs had higher LCN2 levels. SCL may act as a potential biomarker predicting the incidence of MetS including all its components, T2DM, CVDs, and OP. Elevated SCL levels were noted in individuals with T2DM, CVDs and reduced in patients with OP. The aforementioned bone-derived cytokines have the potential to serve as promising predictors and prospective treatment targets for MetS and MetS-related diseases negatively affecting bone quality.

Heritability of Protein and Metabolite Biomarkers Associated with COVID-19 Severity: A Metabolomics and Proteomics Analysis

OBJECTIVES

Prior studies have characterized protein and metabolite changes associated with SARS-CoV-2 infection; we hypothesized that these biomarkers may be part of heritable metabolic pathways in erythrocytes.

METHODS

Using a twin study of erythrocyte protein and metabolite levels, we describe the heritability of, and correlations among, previously identified biomarkers that correlate with COVID-19 severity. We used gene ontology and pathway enrichment analysis tools to identify pathways and biological processes enriched among these biomarkers.

RESULTS

Many COVID-19 biomarkers are highly heritable in erythrocytes. Among heritable metabolites downregulated in COVID-19, metabolites involved in amino acid metabolism and biosynthesis are enriched. Specific amino acid metabolism pathways (valine, leucine, and isoleucine biosynthesis; glycine, serine, and threonine metabolism; and arginine biosynthesis) are heritable in erythrocytes.

CONCLUSIONS

Metabolic pathways downregulated in COVID-19, particularly amino acid biosynthesis and metabolism pathways, are heritable in erythrocytes. This finding suggests that a component of the variation in COVID-19 severity may be the result of phenotypic variation in heritable metabolic pathways; future studies will be necessary to determine whether individual variation in amino acid metabolism pathways correlates with heritable outcomes of COVID-19.

Metformin effects on zonulin level in polycystic ovarian women

Zonulin protein is a haptoglobin precursor and functions to modulate the permeability of tight junctions between enterocytes. Local inflammation or systemic inflammation can trigger zonulin expression. While the increased zonulin level causes an increase of intestinal permeability and entrance of foreign antigens, the latter can increase insulin resistance and inflammation. Polycystic ovarian syndrome affects women during their reproductive age characterized by hyperinsulinemia and/or hyperandrogenemia and associated with infertility problems. Changes in gut permeability such as irritable bowel syndrome are often found in PCOS patients. While metformin increases insulin mediates glucose uptake and, acts as an insulin-sensitizing drug used to treat PCOS patients is recently discovered to reshape intestinal bacteria and hence may affect intestinal action. This study was designed to find any association between zonulin level and other parameters in PCOS patients and to find metformin treatment effects on zonulin in PCOS patients. Thirty-one newly diagnosed PCOS women agree to take metformin 850 mg twice daily for three months and, and to give fasting serum samples to measure zonulin, FSH, LH, total testosterone, free testosterone, SHBG, fasting insulin, and fasting serum glucose before and after treatment. The free testosterone and zonulin are determined by the ELISA technique while the other parameters are determined by the Cobas technique. According to patients' Homeostatic Model Assessment (HOMA-IR), the Patients were divided into two sub-groups: the first group consisting of those with initial HOMA-IR less than two and the second group was those of an initial HOMA-IR of between two to four. Whereas the first group showed no significant response to treatment, the second group showed a better response to metformin treatment, as demonstrated by their LH, total testosterone, free testosterone, fasting insulin, zonulin, and glucose levels. These parameters markedly improved after metformin treatment with p-values of 0.08, 0.09, 0.07. 0.04, 0.01 and 0.06, respectively.

Identification of genetic loci simultaneously associated with multiple cardiometabolic traits

BACKGROUND AND AIMS

Cardiometabolic disorders (CMD) arise from a constellation of features such as increased adiposity, hyperlipidemia, hypertension and compromised glucose control. Many genetic loci have shown associations with individual CMD-related traits, but no investigations have focused on simultaneously identifying loci showing associations across all domains. We therefore sought to identify loci associated with risk across seven continuous CMD-related traits.

METHODS AND RESULTS

We conducted separate genome-wide association studies (GWAS) for systolic and diastolic blood pressure (SBP/DBP), hemoglobin A1c (HbA1c), low- and high- density lipoprotein cholesterol (LDL-C/HDL-C), waist-to-hip-ratio (WHR), and triglycerides (TGs) in the UK Biobank (N = 356,574-456,823). Multiple loci reached genome-wide levels of significance (N = 145-333) for each trait, but only four loci (in/near VEGFA, GRB14-COBLL1, KLF14, and RGS19-OPRL1) were associated with risk across all seven traits (P < 5 × 10^-8). We sought replication of these four loci in an independent set of seven trait-specific GWAS meta-analyses. GRB14-COBLL1 showed the most consistent replication, revealing nominally significant associations (P < 0.05) with all traits except DBP.

CONCLUSIONS

Our analyses suggest that very few loci are associated in the same direction of risk with traits representing the full spectrum of CMD features. We identified four such loci, and an understanding of the pathways between these loci and CMD risk may eventually identify factors that can be used to identify pathologic disturbances that represent broadly beneficial therapeutic targets.

Incidence and long-term specific mortality trends of metabolic syndrome in the United States

PURPOSE

Metabolic syndrome (MetS) is extremely prevalent and related to severe diseases and death. This study aims to investigate the incidence and mortality trends among MetS over the past few decades. The gender and age differences of MetS are also explored.

PATIENTS AND METHODS

Adults with MetS were screened in the National Health and Nutrition Examination Survey (NHANES) from 1999 to 2014. The mortality data were also acquired. Then we assessed the incidence and mortality trends of MetS in the United States.

RESULTS

Our study included 14171 participants with a mean age of 46.8 ± 19.3 years, of whom 7354 (51.9%) were women. Among them, 4789 participants were subsequently diagnosed with MetS. From 1999 to 2014, the overall trend of MetS incidence increased (from 27.6 to 32.3%; adjusted odds ratios [aOR], 1.71; 95% confidence interval [CI], 1.42-2.05; P-value <0.001, P for trend <0.001). In more detail, the incidence of MetS rose first but subsequently plateaued and declined. Obvious downward trends were observed from 29.6 to 2.7% for all-cause mortality (aOR, 0.12; 95%CI, 0.07-0.21; P-value <0.001, P for trend <0.001) and 4.8 to 0.8% for cardio-cerebrovascular mortality (aOR, 0.17; 95%CI, 0.05-0.61; P-value =0.007, P for trend <0.001). All-cause mortality decreased yearly, whereas cardio-cerebrovascular death increased briefly before declining and stabilizing. Similarly, the temporal mortality trends in MetS patients of different ages and genders had the same results. Specifically, the incidence of MetS was higher in women than in men (adjusted P =0.003; OR, 1.14; 95%CI, 1.05-1.24), but the mortality was significantly lower after an average of 7.7 years of follow-up (all-cause mortality, adjusted P <0.001; hazard ratio [HR], 0.68; 95%CI, 0.57-0.81; cardio-cerebrovascular mortality, adjusted P =0.004; HR, 0.55; 95%CI, 0.37-0.83).

CONCLUSION

From 1999 to 2014, the incidence of MetS in U.S. adults significantly increased overall, while the mortality rate of MetS had a considerable downward trend. Both trends showed marked gender differences, being more prevalent and at lower risk in women compared with men. It is important to identify the factors that will curb the incidence of MetS and decrease mortality, especially in male patients.

Understanding the Interplay Between Health Disparities and Epigenomics

Social epigenomics has emerged as an integrative field of research focused on identification of socio-environmental factors, their influence on human biology through epigenomic modifications, and how they contribute to current health disparities. Several health disparities studies have been published using genetic-based approaches; however, increasing accessibility and affordability of molecular technologies have allowed for an in-depth investigation of the influence of external factors on epigenetic modifications (e.g., DNA methylation, micro-RNA expression). Currently, research is focused on epigenetic changes in response to environment, as well as targeted epigenetic therapies and environmental/social strategies for potentially minimizing certain health disparities. Here, we will review recent findings in this field pertaining to conditions and diseases over life span encompassing prenatal to adult stages.

Prevalence of metabolic syndrome in sub-Saharan Africa: A systematic review and meta-analysis

BACKGROUND AND AIMS

There are rising levels of cardiovascular diseases (CVDs) and diabetes in Sub-Saharan Africa (SSA). Metabolic syndrome (MS) is a precursor of these conditions, but the data on the prevalence of MS in SSA are fragmented. We conducted a systematic review and meta-analysis to estimate the prevalence of MS in SSA and determine the population groups that are most at risk.

METHODS AND RESULTS

We systematically searched PubMed, Embase and African Journals Online for all published articles reporting MS prevalence in SSA populations. Random effects models were used to calculate the pooled prevalence overall and by major study-level characteristics. A total of 65 studies across fourteen different countries comprising 34,324 healthy participants aged ≥16 years were included in the meta-analysis. The overall prevalence of MS according to the different diagnostic criteria was: IDF: 18.0% (95%CI:13.3-23.3), IDF-ethnic: 16.0% (95%CI:11.3-21.4), JIS: 23.9% (95%CI: 16.5-32.3), NCEP-ATP III: 17.1% (95%CI:12.8-22.0) and WHO: 11.1% (95%CI:5.3-18.9). The prevalence of MS was higher in women than in men, and higher in (semi-)urban than in rural participants. The MS prevalence was highest in Southern Africa, followed by Eastern, Western and Central Africa. Substantial heterogeneity in the prevalence estimates across studies were not explained by major study-level characteristics, while apparent publication biases were likely artefactual.

CONCLUSIONS

MS is not rare in SSA. The prevalence of MS was highest for women, populations in urban areas, and populations in Southern Africa. Public health intervention efforts are needed to prevent further increases in the burden of MS in the region.

Physical Activity, Cardiorespiratory Fitness, and the Metabolic Syndrome

Both observational and interventional studies suggest an important role for physical activity and higher fitness in mitigating the metabolic syndrome. Each component of the metabolic syndrome is, to a certain extent, favorably influenced by interventions that include physical activity. Given that the prevalence of the metabolic syndrome and its individual components (particularly obesity and insulin resistance) has increased significantly in recent decades, guidelines from various professional organizations have called for greater efforts to reduce the incidence of this condition and its components. While physical activity interventions that lead to improved fitness cannot be expected to normalize insulin resistance, lipid disorders, or obesity, the combined effect of increasing activity on these risk markers, an improvement in fitness, or both, has been shown to have a major impact on health outcomes related to the metabolic syndrome. Exercise therapy is a cost-effective intervention to both prevent and mitigate the impact of the metabolic syndrome, but it remains underutilized. In the current article, an overview of the effects of physical activity and higher fitness on the metabolic syndrome is provided, along with a discussion of the mechanisms underlying the benefits of being more fit or more physically active in the prevention and treatment of the metabolic syndrome.

Exome-Derived Adiponectin-Associated Variants Implicate Obesity and Lipid Biology

Circulating levels of adiponectin, an adipocyte-secreted protein associated with cardiovascular and metabolic risk, are highly heritable. To gain insights into the biology that regulates adiponectin levels, we performed an exome array meta-analysis of 265,780 genetic variants in 67,739 individuals of European, Hispanic, African American, and East Asian ancestry. We identified 20 loci associated with adiponectin, including 11 that had been reported previously (p < 2 × 10^-7). Comparison of exome array variants to regional linkage disequilibrium (LD) patterns and prior genome-wide association study (GWAS) results detected candidate variants (r² > .60) spanning as much as 900 kb. To identify potential genes and mechanisms through which the previously unreported association signals act to affect adiponectin levels, we assessed cross-trait associations, expression quantitative trait loci in subcutaneous adipose, and biological pathways of nearby genes. Eight of the nine loci were also associated (p < 1 × 10^-4) with at least one obesity or lipid trait. Candidate genes include PRKAR2A, PTH1R, and HDAC9, which have been suggested to play roles in adipocyte differentiation or bone marrow adipose tissue. Taken together, these findings provide further insights into the processes that influence circulating adiponectin levels.

Effect of Interaction between Early Menarche and Genetic Polymorphisms on Triglyceride

Early menarche has been associated with increased risk of metabolic syndrome. Therefore, investigating the association of each component of metabolic syndrome with age at menarche, and interactions between them, might lead to a better understanding of metabolic syndrome pathogenesis. In this study, we evaluated age at menarche for risk of metabolic syndrome and associations with its components. As a result, the risk of MetS incidence was significantly increased only at ≤12 years of age at menarche (OR = 1.91, P < 0.05). Women with early menarche (≤12 years) had significantly higher levels of triglycerides (β coefficient = 37.83, P = 0.02). In addition, hypertriglyceridemia was significantly increased at early menarche with 1.99 (95% CI: 1.16–3.41, P < 0.01). With GWAS-based pathway analysis, we found the type 2 diabetes mellitus, stress-activated protein kinase signaling, and Jun amino-terminal kinase cascade pathways (all nominal P < 0.001, all FDR < 0.05) to be significantly involved with early menarche on triglyceride levels. These findings may help us understand the role of early menarche on triglyceride and interaction between gene and early menarche on triglyceride for the development of metabolic syndrome.

Genetic and Environmental Influences on the Associations Between Uric Acid Levels and Metabolic Syndrome Over Time

BACKGROUND

The longitudinal associations between serum uric acid (UA) levels and metabolic syndrome (MetS) and its components, as well as the shared genetic and environmental correlations between these traits, were evaluated.

PARTICIPANTS AND METHODS

In a total of 1803 participants (675 men and 1128 women; 695 monozygotic twin individuals, 159 dizygotic twin individuals, and 949 non-twin family members; 44.3 ± 12.8 years old) and 321 monozygotic twin pairs with data on UA levels and MetS components at baseline and follow-up, mixed linear model, conditional logistic regression, and bivariate variance component analysis were conducted.

RESULTS

After 3.7 ± 1.4 years, the incident and persistent prevalence of MetS were 5.3% and 11.6%, respectively. UA was positively associated with the concurrent and future number of MetS criteria, blood pressure (BP), and triglyceride (TG) levels, whereas an inverse association was observed between UA and future high-density lipoprotein cholesterol (HDL-C) levels after adjusting for twin and household effects, demographics, health behaviors at baseline, and other confounders according to outcome variables. In the adjusted bivariate analysis, UA had genetic and environmental correlations with the concurrent and future number of MetS criteria, and had genetic correlations with concurrent BP and TG levels and future diastolic BP and HDL-C levels. In the adjusted co-twin control analysis, twins with a higher UA level were more likely to have concurrent MetS [odds ratio (95% confidence interval) 1.59 (1.00-2.53)], high blood glucose levels [1.84 (1.06-3.17)], future MetS [2.35 (1.19-4.64)], and high TG levels [1.52 (1.03-2.24)] than co-twins with a lower UA level.

CONCLUSION

Genetic and environmental factors affect the concurrent and longitudinal associations between UA and MetS as well as some of its components.

Heritability of the Severity of the Metabolic Syndrome in Whites and Blacks in 3 Large Cohorts

BACKGROUND

Although dichotomous criteria for the metabolic syndrome (MetS) appear heritable, it is not known whether MetS severity as assessed by a continuous MetS score is heritable and whether this varies by race.

METHODS AND RESULTS

We used SOLAR (Sequential Oligogenic Linkage Analysis Routines) to evaluate heritability of Adult Treatment Panel-III MetS and a sex- and race-specific MetS severity Z score among 3 large familial cohorts: the JHS (Jackson Heart Study, 1404 black participants), TOPS (Take Off Pounds Sensibly, 1947 white participants), and PLRS (Princeton Lipid Research Study, 229 black and 527 white participants). Heritability estimates were larger for Adult Treatment Panel-III MetS among black compared with white cohort members (JHS 0.48; 95% confidence interval [CI], 0.28-0.68 and PLRS blacks 0.93 [95% CI, 0.73-1.13] versus TOPS 0.21 [95% CI, -0.18 to 0.60] and PLRS whites 0.27 [95% CI, -0.04 to 0.58]). The difference by race narrowed when assessing heritability of the MetS severity score (JHS 0.52 [95% CI, 0.38, 0.66] and PLRS blacks 0.64 [95% CI, 0.13-1.15] versus TOPS 0.23 [95% CI, 0.15-0.31] and PLRS whites 0.60 [95% CI, 0.33-0.87]). There was a high degree of genetic and phenotypic correlation between MetS severity and the individual components of MetS among all groups, although the genetic correlations failed to reach statistical significance among PLRS blacks. Meta-analyses revealed a combined heritability estimate for Adult Treatment Panel-III MetS of 0.24 (95% CI, 0.11-0.36) and for the MetS severity score of 0.50 (95% CI, -0.05 to 0.99).

CONCLUSIONS

MetS severity seems highly heritable among whites and blacks. This continuous MetS severity Z score may provide a more useful means of characterizing phenotypic MetS in genetic studies by minimizing racial differences.

Associations Between Adiposity and Metabolic Syndrome Over Time: The Healthy Twin Study

BACKGROUND

We evaluated the association between changes in adiposity traits including anthropometric and fat mass indicators and changes in metabolic syndrome traits including metabolic syndrome clustering and individual components over time. We also assessed the shared genetic and environmental correlations between the two traits.

METHODS

Participants were 284 South Korean twin individuals and 279 nontwin family members had complete data for changes in adiposity traits and metabolic syndrome traits of the Healthy Twin study. Mixed linear model and bivariate variance-component analysis were applied.

RESULTS

Over a period of 3.1 ± 0.6 years of study, changes in adiposity traits [body mass index (BMI), waist circumference, total fat mass, and fat mass to lean mass ratio] had significant associations with changes in metabolic syndrome clustering [high blood pressure, high serum glucose, high triglycerides (TG), and low high-density lipoprotein cholesterol] after adjusting for intra-familial and sibling correlations, age, sex, baseline metabolic syndrome clustering, and socioeconomic factors and health behaviors at follow-up. Change in BMI associated significantly with changes in individual metabolic syndrome components compared to other adiposity traits. Change in metabolic syndrome component TG was a better predictor of changes in adiposity traits compared to changes in other metabolic components. These associations were explained by significant environmental correlations but not by genetic correlations.

CONCLUSIONS

Changes in anthropometric and fat mass indicators were positively associated with changes in metabolic syndrome clustering and those associations appeared to be regulated by environmental influences.

The Pathogenesis of Polycystic Ovary Syndrome (PCOS): The Hypothesis of PCOS as Functional Ovarian Hyperandrogenism Revisited

Polycystic ovary syndrome (PCOS) was hypothesized to result from functional ovarian hyperandrogenism (FOH) due to dysregulation of androgen secretion in 1989-1995. Subsequent studies have supported and amplified this hypothesis. When defined as otherwise unexplained hyperandrogenic oligoanovulation, two-thirds of PCOS cases have functionally typical FOH, characterized by 17-hydroxyprogesterone hyperresponsiveness to gonadotropin stimulation. Two-thirds of the remaining PCOS have FOH detectable by testosterone elevation after suppression of adrenal androgen production. About 3% of PCOS have a related isolated functional adrenal hyperandrogenism. The remaining PCOS cases are mild and lack evidence of steroid secretory abnormalities; most of these are obese, which we postulate to account for their atypical PCOS. Approximately half of normal women with polycystic ovarian morphology (PCOM) have subclinical FOH-related steroidogenic defects. Theca cells from polycystic ovaries of classic PCOS patients in long-term culture have an intrinsic steroidogenic dysregulation that can account for the steroidogenic abnormalities typical of FOH. These cells overexpress most steroidogenic enzymes, particularly cytochrome P450c17. Overexpression of a protein identified by genome-wide association screening, differentially expressed in normal and neoplastic development 1A.V2, in normal theca cells has reproduced this PCOS phenotype in vitro. A metabolic syndrome of obesity-related and/or intrinsic insulin resistance occurs in about half of PCOS patients, and the compensatory hyperinsulinism has tissue-selective effects, which include aggravation of hyperandrogenism. PCOS seems to arise as a complex trait that results from the interaction of diverse genetic and environmental factors. Heritable factors include PCOM, hyperandrogenemia, insulin resistance, and insulin secretory defects. Environmental factors include prenatal androgen exposure and poor fetal growth, whereas acquired obesity is a major postnatal factor. The variety of pathways involved and lack of a common thread attests to the multifactorial nature and heterogeneity of the syndrome. Further research into the fundamental basis of the disorder will be necessary to optimally correct androgen levels, ovulation, and metabolic homeostasis.

A new look at the genetic and environmental coherence of metabolic syndrome components

OBJECTIVE

Metabolic syndrome, a clustering of risk factors including insulin resistance, dyslipidemia, central obesity, and hypertension, increases risk for cardiovascular disease and cognitive decline. The etiology of the risk factors' cohesion remains unclear. How genetic and environmental influences explained co-occurrence of metabolic syndrome components was examined.

METHODS

Continuous measures of body mass index (BMI), waist circumference, blood pressure (BP), fasting insulin and glucose, high-density lipoprotein cholesterol (HDL), and triglycerides from 1,193 middle-aged twin men participating in the Vietnam Era Twin Study of Aging at average age 62 (range 56-67) were analyzed using multivariate biometrical modeling.

RESULTS

Four heritable factors were found: adiposity (BMI, waist circumference), insulin resistance (glucose, insulin), lipids (HDL, triglycerides), and BP (systolic, diastolic). Heritabilities were 0.42-0.68. In the best-fitting model, insulin resistance, lipids, and adiposity comprised a higher-order latent genetic factor. Adiposity and BP shared genetic influences independent of the latent genetic factor. All factors aggregated on a latent unique environmental factor.

CONCLUSIONS

Metabolic syndrome components form the equivalent of two genetic factors. BP was genetically unrelated to insulin resistance and lipids. Adiposity was the only characteristic genetically and environmentally related to all other factors. These results inform strategies for gene discovery and prediction of health outcomes.

PPARα gene polymorphisms modulate the association between physical activity and cardiometabolic risk

BACKGROUND AND AIMS

Habitual physical activity is understood to help prevent type 2 diabetes and atherosclerotic cardiovascular disease via beneficial effects on both metabolism and the vascular system. However, individuals do not have uniform cardiometabolic responses to physical activity. Here we explore the extent to which variation in the proliferator-activated receptor-alpha (PPARα) gene, which modulates carbohydrate and lipid metabolism, vascular function, and inflammation, predicts the overall cardiometabolic risk (CMR) profile of individuals engaging in various levels of physical activity.

METHODS AND RESULTS

917 unrelated, community volunteers (52% female, of Non-Hispanic European ancestry) aged 30-54 years, participated in the cross-sectional study. Subjects were genotyped for 5 single nucleotide polymorphisms in the PPARα gene, from which common haplotypes were defined. A continuous measure of CMR was calculated as an aggregate of 5 traditional risk factors: waist circumference, resting blood pressure, fasting serum triglycerides, HDL-cholesterol and glucose. Regression models were used to examine the main and interactive effects of physical activity and genetic variation on CMR. One common PPARα haplotype (H-23) was associated with a higher CMR. This association was moderated by daily physical activity (B = -0.11, SE = 0.053, t = -2.05, P = 0.04). Increased physical activity was associated with a steeper reduction of CMR in persons carrying the otherwise detrimental H-23 haplotype.

CONCLUSIONS

Variations in the PPARα gene appear to magnify the cardiometabolic benefits of habitual physical activity.

A polymorphism of HMGA1 is associated with increased risk of metabolic syndrome and related components

The metabolic syndrome (MetS) is a common disorder, where systemic insulin-resistance is associated with increased risk for type 2 diabetes (T2D) and cardiovascular disease. Identifying genetic traits influencing risk and progression of MetS is important. We and others previously reported a functional HMGA1 gene variant, rs146052672, predisposing to T2D. Here we investigated the association of rs146052672 variant with MetS and related components. In a case-control study from Italy and Turkey, increased risk of MetS was seen among carriers of the HMGA1 variant. In the larger Italian cohort, this variant positively correlated with BMI, hyperglycemia and insulin-resistance, and negatively correlated with serum HDL-cholesterol. Association between rs146052672 variant and MetS occurred independently of T2D, indicating that HMGA1 gene defects play a pathogenetic role in MetS and other insulin-resistance-related conditions. Overall, our results indicate that the rs146052672 variant represents an early predictive marker of MetS, as well as a predictive tool for therapy.

Genetic and Environmental Influences on Cardiovascular Disease Risk Factors: A Study of Chinese Twin Children and Adolescents

We evaluated the genetic and environmental contributions to metabolic cardiovascular risk factors and their mutual associations. Eight metabolic factors (body mass index, waist circumference, waist-to-hip ratio, systolic blood pressure, diastolic blood pressure, total serum cholesterol, serum triglycerides, and serum uric acid) were measured in 508 twin pairs aged 8–17 years from the Qingdao Twin Registry, China. Linear structural equation models were used to estimate the heritability of these traits, as well as the genetic and environmental correlations between them. Among boys, body mass index and uric acid showed consistently high heritability (0.49–0.81), whereas other traits showed moderate to high common environmental variance (0.37–0.73) in children (8–12 years) and adolescents (13–17 years) except total cholesterol. For girls, moderate to high heritability (0.39–0.75) were obtained for six metabolic traits in children, while only two traits showed high heritability and others mostly medium to large common environmental variance in adolescents. Genetic correlations between the traits were strong in both boys and girls in children (rg = 0.64–0.99 between body mass index and diastolic blood pressure; rg = 0.71–1.00 between body mass index and waist circumference), but decreased for adolescent girls (rg = 0.51 between body mass index and waist-to-hip ratio; rg = 0.55 between body mass index and uric acid; rg = 0.61 between body mass index and systolic blood pressure). The effect of genetic factors on most metabolic traits decreased from childhood to adolescence. Both common genetic and specific environmental factors influence the mutual associations among most of the metabolic traits.

Metabolism of plasma cholesterol and lipoprotein parameters are related to a higher degree of insulin sensitivity in high HDL-C healthy normal weight subjects

Background

We have searched if plasma high density lipoprotein-cholesterol (HDL-C) concentration interferes simultaneously with whole-body cholesterol metabolism and insulin sensitivity in normal weight healthy adult subjects.

Methods

We have measured the activities of several plasma components that are critically influenced by insulin and that control lipoprotein metabolism in subjects with low and high HDL-C concentrations. These parameters included cholesteryl ester transfer protein (CETP), phospholipid transfer protein (PLTP), lecithin cholesterol acyl transferase (LCAT), post-heparin lipoprotein lipase (LPL), hepatic lipase (HL), pre-beta-₁HDL, and plasma sterol markers of cholesterol synthesis and intestinal absorption.

Results

In the high-HDL-C group, we found lower plasma concentrations of triglycerides, alanine aminotransferase, insulin, HOMA-IR index, activities of LCAT and HL compared with the low HDL-C group; additionally, we found higher activity of LPL and pre-beta-₁HDL concentration in the high-HDL-C group. There were no differences in the plasma CETP and PLTP activities.

Conclusions

These findings indicate that in healthy hyperalphalipoproteinemia subjects, several parameters that control the metabolism of plasma cholesterol and lipoproteins are related to a higher degree of insulin sensitivity.

Genetic variants of matrix metalloproteinase (MMP2) gene influence metabolic syndrome susceptibility

AIM

Matrix metalloproteinases (MMPs) are suggested to be involved in the development of various clinical factors of metabolic syndrome (MetS). Allelic variants in the promoter region of the MMP2 gene may modulate an individual's susceptibility to MetS. We performed this study to determine whether single-nucleotide polymorphisms (SNPs) -1575 (G>A) and -168 (G>T) of the MMP2 gene are associated with MetS risk.

METHODS

In this hospital-based case-control study, 180 confirmed MetS patients and 190 unrelated healthy controls of similar ethnicity were genotyped for MMP2 (-1575 G>A, -168 G>T) polymorphisms using polymerase chain reaction-restriction fragment length polymorphism.

RESULTS

Variant genotype (AA) of -1575 showed increased risk (odds ratio [OR]=2.72, 95% confidence intervals [CI]=1.19-6.23, p=0.018) of MetS as compared to the wild-type homozygous genotype (GG). Similarly, the variant allele (A) (OR=1.60, 95%CI=1.12-2.26, p=0.009) and combined genotype (GA+AA) (OR=1.51, 95%CI=0.98-2.31, p=0.057) were also significantly associated with MetS risk. High risk of MetS was observed with respect to the haplotype (A-T) (OR=1.83, 95%CI=1.03-3.26, p=0.038) of MMP2 (-1575 and -168) polymorphisms. However, MMP2 (-168 G>T) polymorphism individually did not show any risk with MetS.

CONCLUSIONS

Our results strongly support the notion that common sequence variants and haplotype of MMP2 (-1575 G>A and -168 G>T) might be a genetic risk for the development of MetS in the North Indian population. Additional studies on larger populations are needed to clarify the role of genetic variants of this gene in MetS.

Familial aggregation of metabolic syndrome indicators in Portuguese families

Background and Aims. Family studies are well suited to investigate the genetic architecture underlying the metabolic syndrome (MetS). The purposes of this paper were (i) to estimate heritabilities for each of the MetS indicators, and (ii) to test the significance of familial intratrait and cross-trait correlations in MetS markers. Methods and Results. This study included 1,363 individuals from 515 Portuguese families in which five MetS components, including waist circumference (WC), blood pressure (BP), HDL-cholesterol, triglycerides (TG), and glucose (GLU), were measured. Intratrait and cross-trait familial correlations of these five components were estimated using Generalized Estimating Equations. Each MetS component was significantly heritable (h² ranged from 0.12 to 0.60) and exhibited strong familial resemblance with correlations between biological relatives of similar magnitude to those observed between spouses. With respect to cross-trait correlations, familial resemblance was very weak except for the HDL-TG pair. Conclusions. The present findings confirm the idea of familial aggregation in MetS traits. Spousal correlations were, in general, of the same magnitude as the biological relatives' correlations suggesting that most of the phenotypic variance in MetS traits could be explained by shared environment.

Causal relationship between adiponectin and metabolic traits: a Mendelian randomization study in a multiethnic population

Background

Adiponectin, a secretagogue exclusively produced by adipocytes, has been associated with metabolic features, but its role in the development of the metabolic syndrome remains unclear.

Objectives

We investigated the association between serum adiponectin level and metabolic traits, using both observational and genetic epidemiologic approaches in a multiethnic population assembled in Canada.

Methods

Clinical data and serum adiponectin level were collected in 1,157 participants of the SHARE/SHARE-AP studies. Participants were genotyped for the functional rs266729 and rs1260326 SNPs in ADIPOQ and GCKR genes.

Results

Adiponectin level was positively associated with HDL cholesterol and negatively associated with body mass index, waist-to-hip ratio, triglycerides, fasting glucose, fasting insulin, systolic and diastolic pressure (all P<0.002). The rs266729 minor G allele was associated with lower adiponectin and higher HOMA-IR (P = 0.004 and 0.003, respectively). The association between rs266729 SNP and HOMA-IR was no longer significant after adjustment for adiponectin concentration (P = 0.10). The rs266729 SNP was associated with HOMA-IR to an extent that exceeded its effect on adiponectin level (0.15 SD 95% C.I. [0.06, 0.24], P<0.001). There was no significant interaction between rs266729 SNP and ethnicity on adiponectin or HOMA-IR. In contrast, the SNP rs1260326 in GCKR was associated with HOMA-IR (P<0.001), but not with adiponectin level (P = 0.67).

Conclusion

The association of the functional promoter polymorphism rs266729 with lower serum adiponectin and increased insulin resistance in diverse ethnic groups may suggest a causal relationship between adiponectin level and insulin resistance.

What about non-alcoholic fatty liver disease as a new criterion to define metabolic syndrome?

Non-alcoholic fatty liver disease (NAFLD) is currently not a component of the diagnostic criteria for metabolic syndrome (MetS); however, the development of NAFLD has some common mechanisms with the development of MetS, as they share the pathophysiologic basis of insulin resistance. It is also recognized that NAFLD is the hepatic manifestation of MetS. To define MetS, the presence of at least three of the proposed criteria is required, and sometimes it is sufficient to have only one laboratory value, modified by diet or drugs, for the classification of MetS. Ultrasonographically-detected NAFLD (US-NAFLD) is more stable, only changing during the middle- to long-term. Although controversies over MetS continue, and considering that abdominal ultrasonography for diagnosing NAFLD has high specificity and guidelines to modify the natural course of NAFLD by diet composition or lifestyle have not yet been established, why should we not introduce US-NAFLD as a new criterion to define MetS?

Nonalcoholic fatty liver disease in severely obese adolescent and adult patients

OBJECTIVES

Nonalcoholic fatty liver disease (NAFLD) is increasingly an indication for liver transplantation in adults. While severe obesity (SO, BMI ≥40 kg m(-2) ) in adults is long standing, it is recent in duration in adolescents. With adolescent obesity on the rise, NAFLD is becoming the most frequent liver disease in adolescents. The hypothesis that SO adolescents and adults have different severity of NAFLD because of longer duration of obesity in SO adults was tested.

DESIGN AND METHODS

Preoperative clinical data, NAFLD activity and NASH (Nonalcoholic steatohepatitis) scores from intraoperative liver biopsies were extracted from a prospective database of consecutively operated SO adolescents and adults (n = 24 each). Fasting preoperative serum inflammatory mediators were evaluated by ELISA.

RESULTS

Other than age, baseline BMI, ethnicity and gender distribution, the incidence and extent of dyslipidemia, hypertension, and metabolic syndrome were comparable between groups. Histologic scores for steatosis and inflammation were similar. Adolescents have significantly higher NASH incidence, hepatocyte injury scores and fibrosis. This was associated with higher serum C-reactive protein and sCD14 levels.

CONCLUSION

For comparable BMI and metabolic profile, SO adolescents have more advanced liver damage, more severe systemic inflammation, suggesting differences in NAFLD etiologies and more aggressive disease progression in the young obese population.

Heritability of the metabolic syndrome and its components in the Tehran Lipid and Glucose Study (TLGS)

Growing evidence suggests that metabolic syndrome (MetS) has both genetic and environmental bases. We estimated the heritability of the MetS and its components in the families from the Tehran Lipid and Glucose Study (TLGS). We investigated 904 nuclear families in TLGS with two biological parents and at least one offspring (1565 parents and 2448 children), aged 3–90 years, for whom MetS information was available and had at least two members of family with MetS. Variance component methods were used to estimate age and sex adjusted heritability of metabolic syndrome score (MSS) and MetS components using SOLAR software. The heritability of waist circumference (WC), HDL-cholesterol (HDL-C), triglycerides (TGs), fasting blood sugar (FBS), systolic blood pressure (SBP) and diastolic blood pressure (DBP) as continuous traits after adjusting for age and gender were 27, 46, 36, 29, 25, 26 and 15%, respectively, and MSS had a heritability of 15%. When MetS components were analysed as discrete traits, the estimates of age and gender adjusted heritability for MetS, abdominal obesity, low HDL-C, high TG, high FBS and high blood pressure (BP) were 22, 40, 34, 38 and 23%, respectively (P < 0·05). Three factors were extracted from the six continuous traits of the MetS including factor I (BP), factor II (lipids) and factor III (obesity and FBS). Heritability estimation for these three factors were 7, 13 (P < 0·05) and 2%, respectively. The highest heritability was for HDL-C and TG. The results strongly encourage efforts to identify the underlying susceptibility genes.