Polygenic risk and the development and course of asthma: an analysis of data from a four-decade longitudinal study

Methylomic markers of persistent childhood asthma: a longitudinal study of asthma-discordant monozygotic twins

BACKGROUND

Asthma is the most common chronic inflammatory disorder in children. The aetiology of asthma pathology is complex and highly heterogeneous, involving the interplay between genetic and environmental risk factors that is hypothesized to involve epigenetic processes. Our aim was to explore whether methylomic variation in early childhood is associated with discordance for asthma symptoms within monozygotic (MZ) twin pairs recruited from the Environmental Risk (E-Risk) longitudinal twin study. We also aimed to identify differences in DNA methylation that are associated with asthma that develops in childhood and persists into early adulthood as these may represent useful prognostic biomarkers.

RESULTS

We examined genome-wide patterns of DNA methylation in buccal cell samples collected from 37 MZ twin pairs discordant for asthma at age 10. DNA methylation at individual CpG sites demonstrated significant variability within discordant MZ twin pairs with the top-ranked nominally significant differentially methylated position (DMP) located in the HGSNAT gene. We stratified our analysis by assessing DNA methylation differences in a sub-group of MZ twin pairs who remained persistently discordant for asthma at age 18. The top-ranked nominally significant DMP associated with persisting asthma is located in the vicinity of the HLX gene, which has been previously implicated in childhood asthma.

CONCLUSIONS

We identified DNA methylation differences associated with childhood asthma in peripheral DNA samples from discordant MZ twin pairs. Our data suggest that differences in DNA methylation associated with childhood asthma which persists into early adulthood are distinct from those associated with asthma which remits.

Relation of intelligence quotient and body mass index in preschool children: a community-based cross-sectional study

OBJECTIVE

Overweight and obesity in children is a global problem. Besides physical effects, obesity has harmful psychological effects on children.

METHODS

We carried out cross-sectional community-based study to investigate the relation between body mass index (BMI) and cognitive functioning in preschool children. Thirteen socioeconomical elements of 1151 children were measured and analyzed based on their intelligence quotient (IQ) test results. Thirteen out of 33 provinces were selected randomly, and schools were selected as clusters in rural and urban areas. Descriptive statistics, t-test, analysis of variance and regression were used when appropriate.

RESULTS

Our analysis showed that IQ was associated with household income, place of residence, delivery type, type of infant feeding and father's and mother's education level (P<0.001 for all). Using penalized linear regression for eliminating the impact of confounding factor, our study shows that, living in metropolitan (β=2.411) and urban areas (β=2.761), the level of participants' father's education (β=5.251) was positively and BMI (β=-0.594) was negatively related with IQ test results.ConclusionsThe findings of the present study showed that a lower IQ score is associated with higher BMI. However, this relation appears to be largely mediated when the socioeconomic status was considered.

Polygenic Influence on Educational Attainment: New evidence from The National Longitudinal Study of Adolescent to Adult Health

Recent studies have begun to uncover the genetic architecture of educational attainment. We build on this work using genome-wide data from siblings in the National Longitudinal Study of Adolescent to Adult Health (Add Health). We measure the genetic predisposition of siblings to educational attainment using polygenic scores. We then test how polygenic scores are related to social environments and educational outcomes. In Add Health, genetic predisposition to educational attainment is patterned across the social environment. Participants with higher polygenic scores were more likely to grow up in socially advantaged families. Even so, the previously published genetic associations appear to be causal. Among pairs of siblings, the sibling with the higher polygenic score typically went on to complete more years of schooling as compared to their lower-scored co-sibling. We found subtle differences between sibling fixed effect estimates of the genetic effect versus those based on unrelated individuals.

The Dunedin Multidisciplinary Health and Development Study: overview of the first 40 years, with an eye to the future

The Dunedin Multidisciplinary Health and Development Study began more than four decades ago. Unusual at the time, it was founded as a multidisciplinary research enterprise, and was strongly supported by the Dunedin community, both professional and lay, in its early years. Seven research themes have evolved over the past 40 years focusing on mental health and neuro-cognition, cardiovascular risk, respiratory health, oral health, sexual and reproductive health, and psychosocial functioning. A seventh, more applied theme, seeks to maximise the value of the Study findings for New Zealand's indigenous people-Māori (or tangata whenua transl people of the land). The study has published over 1200 papers and reports to date, with almost 2/3 of these being in peer-reviewed journals. Here we provide an overview of the study, its history, leadership structure, scientific approach, operational foci, and some recent examples of work that illustrate the following: (a) the value of multidisciplinary data; (b) how the study is well positioned to address contemporary issues; and (c) how research can simultaneously address multiple audiences-from researchers and theoreticians to policy makers and practitioners. Near-future research plans are described, and we end by reflecting upon the core aspects of the study that portend future useful contributions.

Is the Effect of Parental Education on Offspring Biased or Moderated by Genotype?

Parental education is the strongest measured predictor of offspring education, and thus many scholars see the parent-child correlation in educational attainment as an important measure of social mobility. But if social changes or policy interventions are going to have dynastic effects, we need to know what accounts for this intergenerational association, that is, whether it is primarily environmental or genetic in origin. Thus, to understand whether the estimated social influence of parental education on offspring education is biased owing to genetic inheritance (or moderated by it), we exploit the findings from a recent large genome-wide association study of educational attainment to construct a genetic score designed to predict educational attainment. Using data from two independent samples, we find that our genetic score significantly predicts years of schooling in both between-family and within-family analyses. We report three findings that should be of interest to scholars in the stratification and education fields. First, raw parent-child correlations in education may reflect one-sixth genetic transmission and five-sixths social inheritance. Second, conditional on a child's genetic score, a parental genetic score has no statistically significant relationship to the child's educational attainment. Third, the effects of offspring genotype do not seem to be moderated by measured sociodemographic variables at the parental level (but parent-child genetic interaction effects are significant). These results are consistent with the existence of two separate systems of ascription: genetic inheritance (a random lottery within families) and social inheritance (across-family ascription). We caution, however, that at the presently attainable levels of explanatory power, these results are preliminary and may change when better-powered genetic risk scores are developed.

Have recent investigations into remission from childhood asthma helped in understanding the pathogenesis of this disease?

Studies show that a significant proportion of young people suffering from childhood onset asthma later recovered, usually in adolescence. In this article we argue that an understanding of the differences between children who recover from asthma and those who do not would contribute to increased understanding of the pathogenic mechanisms of the disease and could provide new clues about prevention and treatment. We note that some researchers have recently published results from these kinds of investigations. This paper reports results regarding genetic determinants, distorted mechanisms of inflammation, and mind/body relationships. We also try to integrate findings from these 3 areas to formulate general conclusions about the pathogenesis of asthma.

Personalized respiratory medicine: exploring the horizon, addressing the issues. Summary of a BRN-AJRCCM workshop held in Barcelona on June 12, 2014

This Pulmonary Perspective summarizes the content and main conclusions of an international workshop on personalized respiratory medicine coorganized by the Barcelona Respiratory Network ( www.brn.cat ) and the AJRCCM in June 2014. It discusses (1) its definition and historical, social, legal, and ethical aspects; (2) the view from different disciplines, including basic science, epidemiology, bioinformatics, and network/systems medicine; (3) the bottlenecks and opportunities identified by some currently ongoing projects; and (4) the implications for the individual, the healthcare system and the pharmaceutical industry. The authors hope that, although it is not a systematic review on the subject, this document can be a useful reference for researchers, clinicians, healthcare managers, policy-makers, and industry parties interested in personalized respiratory medicine.

Is chronic asthma associated with shorter leukocyte telomere length at midlife?

RATIONALE

Asthma is prospectively associated with age-related chronic diseases and mortality, suggesting the hypothesis that asthma may relate to a general, multisystem phenotype of accelerated aging.

OBJECTIVES

To test whether chronic asthma is associated with a proposed biomarker of accelerated aging, leukocyte telomere length.

METHODS

Asthma was ascertained prospectively in the Dunedin Multidisciplinary Health and Development Study cohort (n = 1,037) at nine in-person assessments spanning ages 9-38 years. Leukocyte telomere length was measured at ages 26 and 38 years. Asthma was classified as life-course-persistent, childhood-onset not meeting criteria for persistence, and adolescent/adult-onset. We tested associations between asthma and leukocyte telomere length using regression models. We tested for confounding of asthma-leukocyte telomere length associations using covariate adjustment. We tested serum C-reactive protein and white blood cell counts as potential mediators of asthma-leukocyte telomere length associations.

MEASUREMENTS AND MAIN RESULTS

Study members with life-course-persistent asthma had shorter leukocyte telomere length as compared with sex- and age-matched peers with no reported asthma. In contrast, leukocyte telomere length in study members with childhood-onset and adolescent/adult-onset asthma was not different from leukocyte telomere length in peers with no reported asthma. Adjustment for life histories of obesity and smoking did not change results. Study members with life-course-persistent asthma had elevated blood eosinophil counts. Blood eosinophil count mediated 29% of the life-course-persistent asthma-leukocyte telomere length association.

CONCLUSIONS

Life-course-persistent asthma is related to a proposed biomarker of accelerated aging, possibly via systemic eosinophilic inflammation. Life histories of asthma can inform studies of aging.

Trends in the prevalence of asthma

The asthma epidemic of the last few decades may have peaked; studies suggest that the incidence and prevalence of asthma has decreased in some countries in the last few years, although other studies suggest continuing small increases in prevalence. Increasing awareness and changing diagnostic habits make precise evaluation of epidemiologic trends difficult in the absence of a gold-standard test for asthma, and on a global basis uncertainty persists. Trends in prevalence in some populations (eg, immigrants, farming communities) suggest both adverse and beneficial effects of specific environmental factors. Although the effects of indoor allergens, dampness, and mold and of outdoor air pollutants, especially traffic related, have traditionally dominated risk-factor research, more recent epidemiologic and clinical studies have focused on metabolic and nutritional factors, including maternal obesity and vitamin D levels, mode of delivery and its effect on the infant microbiome, fetal and infant growth, the psychosocial environment, and medication use by mother and infant. It is likely that changes in incidence and prevalence are due to multiple factors, each contributing a relatively small effect. Longitudinal studies from pregnancy through childhood to adulthood will yield greater insights into the complex pathways leading to asthma.

Testing the key assumption of heritability estimates based on genome-wide genetic relatedness

Comparing genetic and phenotypic similarity among unrelated individuals seems a promising way to quantify the genetic component of traits while avoiding the problematic assumptions plaguing twin- and other kin-based estimates of heritability. One approach uses a Genetic Relatedness Estimation through Maximum Likelihood (GREML) model for individuals who are related at less than 0.025 to predict their phenotypic similarity by their genetic similarity. Here we test the key underlying assumption of this approach: that genetic relatedness is orthogonal to environmental similarity. Using data from the Health and Retirement Study (and two other surveys), we show two unrelated individuals may be more likely to have been reared in a similar environment (urban versus nonurban setting) if they are genetically similar. This effect is not eliminated by controls for population structure. However, when we include this environmental confound in GREML models, heritabilities do not change substantially and thus potential bias in estimates of most biological phenotypes is probably minimal.

The potential to predict the course of childhood asthma

Many children experience pre-school or early childhood wheezing. In a significant proportion symptoms disappear as the child grows, but others have persistent and troublesome asthma which can be life-long. Tools to predict course of disease in young children are a priority for families and clinicians. This review summarizes evidence from several longitudinal population-based birth-cohort studies that have identified risk factors for persistence and remission of childhood asthma. These factors include clinical characteristics, environmental and other exposures, familial factors, biomarkers of allergic inflammation, measurements of lung function and airway responsiveness, and genetic variants. This review also introduces the concept of polygenic risk and genetic risk scores, and describes results from a recent study that suggests promise for the use of genetic information in predicting the course of childhood asthma. We conclude with a discussion of implications and future directions.

Integrating genetics and social science: genetic risk scores

The sequencing of the human genome and the advent of low-cost genome-wide assays that generate millions of observations of individual genomes in a matter of hours constitute a disruptive innovation for social science. Many public use social science datasets have or will soon add genome-wide genetic data. With these new data come technical challenges, but also new possibilities. Among these, the lowest-hanging fruit and the most potentially disruptive to existing research programs is the ability to measure previously invisible contours of health and disease risk within populations. In this article, we outline why now is the time for social scientists to bring genetics into their research programs. We discuss how to select genetic variants to study. We explain how the polygenic architecture of complex traits and the low penetrance of individual genetic loci pose challenges to research integrating genetics and social science. We introduce genetic risk scores as a method of addressing these challenges and provide guidance on how genetic risk scores can be constructed. We conclude by outlining research questions that are ripe for social science inquiry.