Investigation of Genetic Variation Underlying Central Obesity amongst South Asians

Adiposity and metabolic health in Asian populations: an epidemiological study using dual-energy x-ray absorptiometry in Singapore

BACKGROUND

Type 2 diabetes, cardiovascular disease, and related cardiometabolic disturbances are increasing rapidly in the Asia-Pacific region. We investigated the contribution of excess adiposity, a key determinant of type 2 diabetes and cardiovascular risk, to unfavourable cardiometabolic profiles among Asian ethnic subgroups.

METHODS

The Health for Life in Singapore (HELIOS) Study is a population-based cohort comprising multiethnic Asian men and women living in Singapore, aged 30-84 years. We performed a cross-sectional analysis of data from individuals who had assessment of body composition by dual-energy x-ray absorptiometry and metabolic characterisation. In a subset of participants on no medication for type 2 diabetes, hypertension, and hypercholesterolaemia, we tested the relationship of BMI and visceral fat mass index (vFMI) with cardiometabolic phenotypes (glycaemic indices, lipid levels, and blood pressure), disease outcomes (type 2 diabetes, hypercholesterolaemia, and hypertension), and metabolic syndrome score with multivariable regression analyses.

FINDINGS

Between April 2, 2018, and Jan 28, 2022, 10 004 individuals consented to be part of the HELIOS cohort, of whom 9067 were included in the study (5404 [59·6%] female, 3663 [40·4%] male; 6224 [68·6%] Chinese, 1169 [12·9%] Malay, 1674 [18·5%] Indian; mean age 52·8 years [SD 11·8]). The prevalence of type 2 diabetes, hypercholesterolaemia, and hypertension was 8·2% (n=744), 27·2% (n=2469), and 18·0% (n=1630), respectively. Malay and Indian participants had 3-4-times higher odds of obesity and type 2 diabetes, and showed adverse metabolic and adiposity profiles, compared with Chinese participants. Excess adiposity was associated with adverse cardiometabolic health indices including type 2 diabetes (p<0·0001). However, while vFMI explained the differences in triglycerides and blood pressure between the Asian ethnic groups, increased vFMI did not explain higher glucose levels, reduced insulin sensitivity, and increased risk of type 2 diabetes among Indian participants.

INTERPRETATION

Visceral adiposity is an independent risk factor for metabolic disease in Asian populations, and accounts for a large fraction of type 2 diabetes cases in each of the ethnic groups studied. However, the variation in insulin resistance and type 2 diabetes risk between Asian subgroups is not consistently explained by adiposity, indicating an important role for additional mechanisms underlying the susceptibility to cardiometabolic disease in Asian populations.

FUNDING

Nanyang Technological University-the Lee Kong Chian School of Medicine, National Healthcare Group, and National Medical Research Council, Singapore.

Adiposity and cancer: meta-analysis, mechanisms, and future perspectives

Obesity is a recognised risk factor for many cancers and with rising global prevalence, has become a leading cause of cancer. Here we summarise the current evidence from both population-based epidemiologic investigations and experimental studies on the role of obesity in cancer development. This review presents a new meta-analysis using data from 40 million individuals and reports positive associations with 19 cancer types. Utilising major new data from East Asia, the meta-analysis also shows that the strength of obesity and cancer associations varies regionally, with stronger relative risks for several cancers in East Asia. This review also presents current evidence on the mechanisms linking obesity and cancer and identifies promising future research directions. These include the use of new imaging data to circumvent the methodological issues involved with body mass index and the use of omics technologies to resolve biologic mechanisms with greater precision and clarity.

Obesity and Cardiovascular Risk among South Asian Americans

Purpose of review

South Asian Americans experience higher cardiometabolic risk and disproportionately high rates of cardiovascular disease (CVD) compared to other racial and ethnic groups in the United States. The purpose of this review is to summarize recent evidence about the role of obesity in CVD risk in South Asian Americans and identify key evidence gaps and future directions for research and interventions for obesity in this group.

Recent findings

South Asian Americans are predisposed to abdominal obesity and have a higher distribution of visceral fat, intermuscular fat, and intrahepatic fat compared to adults of other race and ethnic groups. In this population, the risk for cardiometabolic disease appears to be elevated even at a normal body mass index. Social, cultural, religious, interpersonal, and environmental factors are related to obesity and obesity-related behaviors among South Asian Americans.

Summary

There is a relatively high prevalence of obesity in South Asian-origin populations in the United States, who have unique socio-cultural determinants of overweight and obesity. Future research should clarify why the risk for metabolic disease and CVD is elevated at normal BMI in the South Asian American population, and environmental and other structural factors that may influence obesity in this group. Interventions must be adapted to the social and cultural context of South Asian Americans to improve effectiveness and implementation.

Food environments and obesity: A geospatial analysis of the South Asia Biobank, income and sex inequalities

INTRODUCTION

In low-middle income countries (LMICs) the role of food environments on obesity has been understudied. We address this gap by 1) examining the effect of food environments on adults' body size (BMI, waist circumference) and obesity; 2) measuring the heterogeneity of such effects by income and sex.

METHODS

This cross-sectional study analysed South Asia Biobank surveillance and environment mapping data for 12,167 adults collected between 2018 and 2020 from 33 surveillance sites in Bangladesh and Sri Lanka. Individual-level data (demographic, socio-economic, and health characteristics) were combined with exposure to healthy and unhealthy food environments measured with geolocations of food outlets (obtained through ground-truth surveys) within 300 m buffer zones around participants' homes. Multivariate regression models were used to assess association of exposure to healthy and unhealthy food environments on waist circumference, BMI, and probability of obesity for the total sample and stratified by sex and income.

FINDINGS

The presence of a higher share of supermarkets in the neighbourhood was associated with a reduction in body size (BMI, β = - 3∙23; p < 0∙0001, and waist circumference, β = -5∙99; p = 0∙0212) and obesity (Average Marginal Effect (AME): -0∙18; p = 0∙0009). High share of fast-food restaurants in the neighbourhood was not significantly associated with body size, but it significantly increased the probability of obesity measured by BMI (AME: 0∙09; p = 0∙0234) and waist circumference (AME: 0∙21; p = 0∙0021). These effects were stronger among females and low-income individuals.

INTERPRETATION

The results suggest the availability of fast-food outlets influences obesity, especially among female and lower-income groups. The availability of supermarkets is associated with reduced body size and obesity, but their effects do not outweigh the role of fast-food outlets. Policies should target food environments to promote better diets and reduce obesity.

Genetics of Body Fat Distribution: Comparative Analyses in Populations with European, Asian and African Ancestries

Preferential fat accumulation in visceral vs. subcutaneous depots makes obese individuals more prone to metabolic complications. Body fat distribution (FD) is regulated by genetics. FD patterns vary across ethnic groups independent of obesity. Asians have more and Africans have less visceral fat compared with Europeans. Consequently, Asians tend to be more susceptible to type 2 diabetes even with lower BMIs when compared with Europeans. To date, genome-wide association studies (GWAS) have identified more than 460 loci related to FD traits. However, the majority of these data were generated in European populations. In this review, we aimed to summarize recent advances in FD genetics with a focus on comparisons between European and non-European populations (Asians and Africans). We therefore not only compared FD-related susceptibility loci identified in three ethnicities but also discussed whether known genetic variants might explain the FD pattern heterogeneity across different ancestries. Moreover, we describe several novel candidate genes potentially regulating FD, including NID2, HECTD4 and GNAS, identified in studies with Asian populations. It is of note that in agreement with current knowledge, most of the proposed FD candidate genes found in Asians belong to the group of developmental genes.

Obesity and Metabolic Care of Children of South Asian Ethnicity in Western Society

South Asians constitute one-fourth of the world’s population and are distributed significantly in western countries. With exponentially growing numbers, childhood obesity is of global concern. Children of South Asian ancestry have a higher likelihood of developing obesity and associated metabolic risks. The validity of commonly used measures for quantifying adiposity and its impact on metabolic outcomes differ by race and ethnicity. In this review we aim to discuss the validity of body mass index (BMI) and other tools in screening for adiposity in South Asian children. We also discuss the prevalence of overweight and obesity amongst South Asian children in western countries and the differences in body fat percentage, adiposity distribution, and metabolic risks specific to these children compared to Caucasian children. South Asian children have a characteristic phenotype: lower lean mass and higher body fat percentage favoring central fat accumulation. Hence, BMI is a less reliable predictor of metabolic status in these children than it is for Caucasian children. Furthermore, the relatively lower birth weight and rapid growth acceleration in early childhood of South Asian children increase the risk of their developing cardiometabolic disorders at a younger age than that of Caucasians. We emphasize the need to use modified tools for assessment of adiposity, which take into consideration the ethnic differences and provide early and appropriate intervention to prevent obesity and its complications.

Diabetes and cardiometabolic risk in South Asian youth: A review

South Asians are at increased risk for developing type 2 diabetes and cardiovascular disease at lower body mass index compared to other ancestral groups. Many factors contribute to this increased risk, including genetics, maternal-fetal factors, diet, fitness, body composition, and unique pathophysiology. Increased cardiometabolic risk is also seen at younger ages in South Asian individuals as compared to their White counterparts. This risk persists in migrant communities outside of South Asia. With the growing prevalence of obesity, diabetes, and cardiovascular disease in the South Asian population, it is imperative that we had better understand the mechanisms underlying this increased risk and implement strategies to address this growing public health problem during childhood and adolescence.

Genetics of Obesity in East Asians

Obesity has become a public health problem worldwide. Compared with Europe, people in Asia tend to suffer from type 2 diabetes with a lower body mass index (BMI). Genome-wide association studies (GWASs) have identified over 750 loci associated with obesity. Although the majority of GWAS results were conducted in individuals of European ancestry, a recent GWAS in individuals of Asian ancestry has made a significant contribution to the identification of obesity susceptibility loci. Indeed, owing to the multifactorial character of obesity with a strong environmental component, the revealed loci may have distinct contributions in different ancestral genetic backgrounds and in different environments as presented through diet and exercise among other factors. Uncovering novel, yet unrevealed genes in non-European ancestries may further contribute to explaining the missing heritability for BMI. In this review, we aimed to summarize recent advances in obesity genetics in individuals of Asian ancestry. We therefore compared proposed mechanisms underlying susceptibility loci for obesity associated with individuals of European and Asian ancestries and discussed whether known genetic variants might explain ethnic differences in obesity risk. We further acknowledged that GWAS implemented in individuals of Asian ancestries have not only validated the potential role of previously specified obesity susceptibility loci but also exposed novel ones, which have been missed in the initial genetic studies in individuals of European ancestries. Thus, multi-ethnic studies have a great potential not only to contribute to a better understanding of the complex etiology of human obesity but also potentially of ethnic differences in the prevalence of obesity, which may ultimately pave new avenues in more targeted and personalized obesity treatments.

A low intensity dietary intervention for reducing excessive gestational weight gain in an overweight and obese pregnant cohort

PURPOSE

Excessive gestational weight gain is associated with detrimental outcomes to both the mother and baby. Currently, the best approach to prevent excessive gestational weight gain in overweight and obese women is undetermined. The present study aimed to evaluate the effectiveness of a group-based outpatient dietary intervention in pregnancy to reduce excessive gestational weight gain.

METHODS

In this retrospective study, overweight and obese pregnant women who attended a single 90-min group education session were compared to women who received standard care alone. Total gestational weight gain, maternal and neonatal outcomes were compared between the intervention and control groups. Data were analysed using Student t, Mann-Whitney and Chi-squared tests as appropriate. A 24-h dietary recall was analysed and compared to the Australian National Nutrition Survey.

RESULTS

A significant reduction in gestational weight gain was observed with this intervention (P = 0.010), as well as in the rate of small for gestational age births (P = 0.043). Those who attended the intervention had saturated fat and sodium intake levels that exceeded recommendations. Intake of pregnancy-specific micronutrients including folate, calcium and iron were poor from diet alone.

CONCLUSIONS

A low-intensity antenatal dietary intervention may be effective in reducing excessive gestational weight gain, although multi-disciplinary interventions yield the best success. Further research is required to identify the optimal modality and frequency to limit excessive gestational weight gain. Dietary interventions tailored to ethnicity should also be explored.

LEVEL OF EVIDENCE

Level II, controlled trial without randomization.

Evolutionary history of disease-susceptibility loci identified in longitudinal exome-wide association studies

Background

Our longitudinal exome‐wide association studies previously detected various genetic determinants of complex disorders using ~26,000 single‐nucleotide polymorphisms (SNPs) that passed quality control and longitudinal medical examination data (mean follow‐up period, 5 years) in 4884–6022 Japanese subjects. We found that allele frequencies of several identified SNPs were remarkably different among four ethnic groups. Elucidating the evolutionary history of disease‐susceptibility loci may help us uncover the pathogenesis of the related complex disorders.

Methods

In the present study, we conducted evolutionary analyses such as extended haplotype homozygosity, focusing on genomic regions containing disease‐susceptibility loci and based on genotyping data of our previous studies and datasets from the 1000 Genomes Project.

Results

Our evolutionary analyses suggest that derived alleles of rs78338345 of GGA3, rs7656604 at 4q13.3, rs34902660 of SLC17A3, and six SNPs closely located at 12q24.1 associated with type 2 diabetes mellitus, obesity, dyslipidemia, and three complex disorders (hypertension, hyperuricemia, and dyslipidemia), respectively, rapidly expanded after the human dispersion from Africa (Out‐of‐Africa). Allele frequencies of GGA3 and six SNPs at 12q24.1 appeared to have remarkably changed in East Asians, whereas the derived alleles of rs34902660 of SLC17A3 and rs7656604 at 4q13.3 might have spread across Japanese and non‐Africans, respectively, although we cannot completely exclude the possibility that allele frequencies of disease‐associated loci may be affected by demographic events.

Conclusion

Our findings indicate that derived allele frequencies of nine disease‐associated SNPs (rs78338345 of GGA3, rs7656604 at 4q13.3, rs34902660 of SLC17A3, and six SNPs at 12q24.1) identified in the longitudinal exome‐wide association studies largely increased in non‐Africans after Out‐of‐Africa.

Ethnicity and Type 2 diabetes in the UK

Type 2 diabetes is a major UK public health priority. Among minority ethnic communities, the prevalence is alarmingly high, approximately three to five times higher than in the white British population. Particularly striking is the earlier onset of Type 2 diabetes, which occurs some 10-12 years younger, with a significant proportion of cases being diagnosed before the age of 40 years. This review focuses on the UK context and Type 2 diabetes in adult populations, exploring the available evidence regarding the complex interplay of biological, lifestyle, social, clinical and healthcare system factors that are known to drive these disparities.

Systems Genomics of Thigh Adipose Tissue From Asian Indian Type-2 Diabetics Revealed Distinct Protein Interaction Hubs

We performed a systematic analysis of genes implicated in thigh subcutaneous adipose tissue of Asian Indian Type 2 Diabetes Mellitus (AIT2DM) and created a phenome-interactome network. This analysis was performed on 60 subjects specific to limb thigh fat by integrating phenotypic traits and similarity scores associated with AIT2DM. Using a phenotypic attribute, a contextual neighbor was identified across all the traits, viz. body mass index (BMI) statistics, adipocyte size, lipid parameters, homeostatic model assessment- insulin resistance (HOMA-IR), HOMA-ß. In this work, we have attempted to characterize transcription signatures using the phenome-interactome maps where each of the traits under study including the intermediary phenotypes has a distinct set of genes forming the hubs. Furthermore, we have identified various clinical, biochemical, and radiological parameters which show significant correlation with distinct hubs. We observed a number of novel pathways and genes including those that are non-coding RNAs implicated in AIT2DM.We showed that they appear to be associated with pathways, viz. tyrosine kinase JAK2, NOTCH thereby recruiting signaling molecules such as STAT5 and Src family kinases on the cell surface regulated them and our analyses comprising significant hubs suggest that thigh subcutaneous adipose tissue plays a role in pathophysiology of AIT2DM.

Atherosclerotic Cardiovascular Disease in South Asians in the United States: Epidemiology, Risk Factors, and Treatments: A Scientific Statement From the American Heart Association

South Asians (from Bangladesh, Bhutan, India, the Maldives, Nepal, Pakistan, and Sri Lanka) make up one quarter of the world's population and are one of the fastest-growing ethnic groups in the United States. Although native South Asians share genetic and cultural risk factors with South Asians abroad, South Asians in the United States can differ in socioeconomic status, education, healthcare behaviors, attitudes, and health insurance, which can affect their risk and the treatment and outcomes of atherosclerotic cardiovascular disease (ASCVD). South Asians have higher proportional mortality rates from ASCVD compared with other Asian groups and non-Hispanic whites, in contrast to the finding that Asian Americans (Asian Indian, Chinese, Filipino, Japanese, Korean, and Vietnamese) aggregated as a group are at lower risk of ASCVD, largely because of the lower risk observed in East Asian populations. Literature relevant to South Asian populations regarding demographics and risk factors, health behaviors, and interventions, including physical activity, diet, medications, and community strategies, is summarized. The evidence to date is that the biology of ASCVD is complex but is no different in South Asians than in any other racial/ethnic group. A majority of the risk in South Asians can be explained by the increased prevalence of known risk factors, especially those related to insulin resistance, and no unique risk factors in this population have been found. This scientific statement focuses on how ASCVD risk factors affect the South Asian population in order to make recommendations for clinical strategies to reduce disease and for directions for future research to reduce ASCVD in this population.

Identification of three genetic variants as novel susceptibility loci for body mass index in a Japanese population

Recent genome-wide association studies have identified various obesity or metabolic syndrome (MetS) susceptibility loci. However, most studies were conducted in a cross-sectional manner. To address this gap, we performed a longitudinal exome-wide association study to identify susceptibility loci for obesity and MetS in a Japanese population. We traced clinical data of 6,022 Japanese subjects who had annual health check-ups for several years (mean follow-up period, 5 yr) and genotyped ~244,000 genetic variants. The association of single nucleotide polymorphisms (SNPs) with body mass index (BMI) or the prevalence of obesity and MetS was examined in a generalized estimating equation model. Our longitudinal exome-wide association studies detected 21 BMI- and five MetS-associated SNPs (false discovery rate, FDR <0.01). Among these SNPs, 16 have not been previously implicated as determinants of BMI or MetS. Cross-sectional data for obesity- and MetS-related phenotypes in 7,285 Japanese subjects were examined in a replication study. Among the 16 SNPs, three ( rs9491140 , rs145848316 , and rs7863248 ) were related to BMI in the replication cohort ( P < 0.05). In conclusion, three SNPs [ rs9491140 of NKAIN2 (FDR = 0.003, P = 1.9 × 10-5), rs145848316 of KMT2C (FDR = 0.007, P = 4.5 × 10-5), and rs7863248 of AGTPBP1 (FDR = 0.006, P = 4.2 × 10-5)] were newly identified as susceptibility loci for BMI.