A population-based study of bronchial asthma in adult twin pairs

Circulating MicroRNAs associated with Bronchodilator Response in Childhood Asthma

Rationale

Bronchodilator response (BDR) is a measure of improvement in airway smooth muscle tone, inhibition of liquid accumulation and mucus section into the lumen in response to short-acting beta-2 agonists that varies among asthmatic patients. MicroRNAs (miRNAs) are well-known post-translational regulators. Identifying miRNAs associated with BDR could lead to a better understanding of the underlying complex pathophysiology.

Objective

The purpose of this study is to identify circulating miRNAs associated with bronchodilator response in asthma and decipher possible mechanism of bronchodilator response variation.

Methods

We used available small RNA sequencing on blood serum from 1,134 asthmatic children aged 6 to 14 years who participated in the Genetics of Asthma in Costa Rica Study (GACRS). We filtered the participants into high and low bronchodilator response (BDR) quartiles and used DeSeq2 to identify miRNAs with differential expression (DE) in high (N= 277) vs low (N= 278) BDR group. Replication was carried out in the Leukotriene modifier Or Corticosteroids or Corticosteroid-Salmeterol trial (LOCCS), an adult asthma cohort. The putative target genes of DE miRNAs were identified, and pathway enrichment analysis was performed.

Results

We identified 10 down-regulated miRNAs having odds ratios (OR) between 0.37 and 0.76 for a doubling of miRNA counts and one up-regulated miRNA (OR=2.26) between high and low BDR group. These were assessed for replication in the LOCCS cohort, where two miRNAs (miR-200b-3p and miR-1246) were associated. Further, functional annotation of 11 DE miRNAs were performed as well as of two replicated miRs. Target genes of these miRs were enriched in regulation of cholesterol biosynthesis by SREBPs, ESR-mediated signaling, G1/S transition, RHO GTPase cycle, and signaling by TGFB family pathways.

Conclusion

MiRNAs miR-1246 and miR-200b-3p are associated with both childhood and adult asthma BDR. Our findings add to the growing body of evidence that miRNAs play a significant role in the difference of asthma treatment response among patients as it points to genomic regulatory machinery underlying difference in bronchodilator response among patients.

Trial registration

LOCCS cohort [ClinicalTrials.gov number: NCT00156819], GACRS cohort [ClinicalTrials.gov number: NCT00021840].

Immunogenetics and pharmacogenetics of allergic asthma in Africa

Asthma is a common chronic condition in children and in an African setting is often highly prevalent in urban areas as compared to rural areas. Asthma is a heritable disease and the genetic risk is often exacerbated by unique localised environmental factors. The Global Initiative for Asthma (GINA) recommendation for the control of asthma includes inhaled corticosteroids (ICS) alone or together with short-acting β₂-agonists (SABA) or long-acting β₂-agonists (LABA). While these drugs can relieve asthma symptoms, there is evidence of reduced efficacy in people of African ancestry. Whether this is due to immunogenetics, genomic variability in drug metabolising genes (pharmacogenetics) or genetics of asthma-related traits is not well defined. Pharmacogenetic evidence of first-line asthma drugs in people of African ancestry is lacking and is further compounded by the lack of representative genetic association studies in the continent. In this review, we will discuss the paucity of data related to the pharmacogenetics of asthma drugs in people of African ancestry, mainly drawing from African American data. We will further discuss how this gap can be bridged to improve asthma health outcomes in Africa.

Role of thymic stromal lymphopoietin in allergy and beyond

Thymic stromal lymphopoietin (TSLP) is a pleiotropic cytokine that acts on multiple cell lineages, including dendritic cells, T cells, B cells, neutrophils, mast cells, eosinophils and innate lymphoid cells, affecting their maturation, survival and recruitment. It is best known for its role in promoting type 2 immune responses such as in allergic diseases and, in 2021, a monoclonal antibody targeting TSLP was approved for the treatment of severe asthma. However, it is now clear that TSLP has many other important roles in a variety of settings. Indeed, several genetic variants for TSLP are linked to disease severity, and chromosomal alterations in TSLP are common in certain cancers, indicating important roles of TSLP in disease. In this Review, we discuss recent advances in TSLP biology, highlighting how it regulates the tissue environment not only in allergic disease but also in infectious diseases, inflammatory diseases and cancer. Encouragingly, therapies targeting the TSLP pathway are being actively pursued for several diseases.

[Genetic aspects involved in asthma]

Asthma is an etiologically heterogeneous disease resulting from a complex interaction between genetic. The genetic aspects involved in asthma, which were analyzed from the perspective of the traditional model of multifactorial inheritance, were susceptibility, host factors, and environmental exposures. In the present paper, studies on their family aggregation, concordance in twins, and heritability were analized; as well as the current knowledge about candidate genes, genome wide association studies, and epigenomics contributions and other omic studies that have increased our knowledge about their pathophysiology and environmental interactions.

CC16 polymorphisms in asthma, asthma subtypes, and asthma control in adults from the Agricultural Lung Health Study

BACKGROUND

The club cell secretory protein (CC16) has anti-inflammatory and antioxidant effects and is a potential early biomarker of lung damage. The CC16 single nucleotide polymorphism (SNP) rs3741240 risk allele (A) has been inconsistently linked to asthma; other tagging SNPs in the gene have not been explored. The aim was to determine whether CC16 tagging polymorphisms are associated with adult asthma, asthma subtypes or asthma control in the Agricultural Lung Health Study (ALHS).

METHODS

The ALHS is an asthma case-control study nested in the Agricultural Health Study cohort. Asthma cases were individuals with current doctor diagnosed asthma, likely undiagnosed asthma, or asthma-COPD overlap defined by questionnaire. We also examined asthma subtypes and asthma control. Five CC16 tagging SNPs were imputed to 1000 Genomes Integrated phase 1 reference panel. Logistic regression was used to estimate associations between CC16 SNPs and asthma outcomes adjusted for covariates.

RESULTS

The sample included 1120 asthma cases and 1926 controls of European ancestry, with a mean age of 63 years. The frequency of the risk genotype (AA) for rs3741240 was 12.5% (n = 382). CC16 rs3741240 was not associated with adult asthma outcomes. A tagging SNP in the CC16 gene, rs12270961 was associated with uncontrolled asthma (n = 208, OR_adj= 1.4, 95% CI 1.0, 1.9; p = 0.03).

CONCLUSION

This study, the largest study to investigate associations between CC16 tagging SNPs and asthma phenotypes in adults, did not confirm an association of rs3741240 with adult asthma. A tagging SNP in CC16 suggests a potential relationship with asthma control.

Pharmacogenetics of Bronchodilator Response: Future Directions

PURPOSE OF REVIEW

Several genome-wide association studies (GWASs) of bronchodilator response (BDR) to albuterol have been published over the past decade. This review describes current knowledge gaps, including pharmacogenetic studies of albuterol response in minority populations, effect modification of pharmacogenetic associations by age, and relevance of BDR phenotype characterization to pharmacogenetic findings. New approaches, such as leveraging additional "omics" data to focus pharmacogenetic interrogation, as well as developing polygenic risk scores in asthma treatment responses, are also discussed.

RECENT FINDINGS

Recent pharmacogenetic studies of albuterol response in minority populations have identified genetic polymorphisms in loci (DNAH5, NFKB1, PLCB1, ADAMTS3, COX18, and PRKG1), that are associated with BDR. Additional studies are needed to replicate these findings. Modification of the pharmacogenetic associations for SPATS2L and ASB3 polymorphisms by age has also been published. Evidence from metabolomic and epigenomic studies of BDR may point to new pharmacogenetic targets. Lastly, a polygenic risk score for response to albuterol has been developed but requires validation in additional cohorts. In order to expand our knowledge of pharmacogenetics of BDR, additional studies in minority populations are needed. Consideration of effect modification by age and leverage of other "omics" data beyond genomics may also help uncover novel pharmacogenetic loci for use in precision medicine for asthma treatment.

Single Nucleotide Polymorphisms (SNPs) in PRKG1 & SPATA13-AS1 are associated with bronchodilator response: a pilot study during acute asthma exacerbations in African American children

OBJECTIVE

Inhaled bronchodilators are the first-line treatment for asthma exacerbations, but individual bronchodilator response (BDR) varies by race and ethnicity. Studies have examined BDR's genetic underpinnings, but many did not include children or were not conducted during an asthma exacerbation. This pilot study tested single-nucleotide polymorphisms' (SNPs') association with pediatric African American BDR during an acute asthma exacerbation.

METHODS

This was a study of pediatric asthma patients in the age group 2-18 years treated in the emergency department for an asthma exacerbation. We measured BDR before and after inhaled bronchodilator treatments using both the Pediatric Asthma Severity Score (PASS) and asthma severity score. We collected genomic DNA and examined whether 21 candidate SNPs from a review of the literature were associated with BDR using crude odds ratios (OR) and adjusted analysis.

RESULTS

The final sample population was 53 children, with an average age of 7.2 years. The average initial PASS score (scale of ascending severity from 0 to 6) was 2.5. After adjusting for BMI, age category, gender and smoke exposure, rs912142 was associated with decreased odds of having low BDR (OR, 0.20; 95% confidence interval (CI), 0.02-0.92), and rs7081864 and rs7903366 were associated with decreased odds of having high BDR (OR, 0.097; 95% CI, 0.009-0.62).

CONCLUSIONS

We found three SNPs significantly associated with pediatric African American BDR that provide information regarding a child's potential response to emergency asthma exacerbation treatment. Once validated in larger studies, such information could guide pharmacogenomic evidence-based emergency asthma treatment to improve patient outcomes.

Machine learning approach to single nucleotide polymorphism-based asthma prediction

Machine learning (ML) is poised as a transformational approach uniquely positioned to discover the hidden biological interactions for better prediction and diagnosis of complex diseases. In this work, we integrated ML-based models for feature selection and classification to quantify the risk of individual susceptibility to asthma using single nucleotide polymorphism (SNP). Random forest (RF) and recursive feature elimination (RFE) algorithm were implemented to identify the SNPs with high implication to asthma. K-nearest neighbor (kNN) and support vector machine (SVM) algorithms were trained to classify the identified SNPs whether associated with non-asthmatic or asthmatic samples. Feature selection step showed that RF outperformed RFE and the feature importance score derived from RF was consistently high for a subset of SNPs, indicating the robustness of RF in selecting relevant features associated with asthma. Model comparison showed that the integration of RF-SVM obtained the highest model performance with an accuracy, precision, and sensitivity of 62.5%, 65.3%, and 69%, respectively, when compared to the baseline, RF-kNN, and an external MeanDiff-kNN models. Furthermore, results show that the occurrence of asthma can be predicted with an Area under the Curve (AUC) of 0.62 and 0.64 for RF-SVM and RF-kNN models, respectively. This study demonstrates the integration of ML models to augment traditional methods in predicting genetic predisposition to multifactorial diseases such as asthma.

How does race and ethnicity effect the precision treatment of asthma?

Introduction

Asthma is a common condition that affects large numbers of children and adults, yet the burden of disease is not equally distributed amongst groups. In the United States, African Americans and Puerto Ricans have higher rates of asthma and its complications when compared with European Americans. However, clinical trials and genetic studies have largely focused on the latter group.

Areas covered

Here we examine what is known regarding differences in asthma treatment response by race-ethnicity. We also review existing genetic studies related to the use of asthma medications, paying special attention to studies that included substantial numbers of non-white population groups. Publicly accessible search engines of the medical literature were queried using combinations of the terms asthma, race, ethnicity, pharmacogenomics, and pharmacogenetics, as well as the names of individual asthma medication classes. The list of articles reviewed was supplemented by bibliographies and expert knowledge.

Expert opinion

A substantial and coordinated effort is still needed to both identify and validate genetic biomarkers of asthma medication response, as currently there are no clinically actionable genetic markers available for this purpose. The path to identifying such markers in non-white populations is even more formidable, since these groups are underrepresented in existing data.

Blocking IL-19 Signaling Ameliorates Allergen-Induced Airway Inflammation

Asthma is a chronic inflammatory disease of the airway. Its major symptoms are reversible breathing problems causing airway narrowing and obstruction. IL-19 is a member of the IL-10 family cytokines. We previously showed that IL-19 induces T-helper 2 (Th2) cytokines and that asthma patients had higher serum IL-19 levels. To further examine whether inhibiting IL-19 and its receptor (IL-20R1) protected rodents against asthma, we used Dermatophagoides pteronyssinus (Der p; house dust mites) to induce chronic airway inflammation in wild-type C57BL/6 and IL-20R1-deficient mice and then analyzed the effect of the IL-20R1 deficiency on the pathogenesis of asthma. We also examined whether inhibiting IL-19 and IL-20R1 ameliorated Der p-induced chronic asthma. Der p induced IL-19 in lung airway epithelial cells, type 2 alveolar cells, and alveolar macrophages. An IL-20R1 deficiency abolished IL-19-induced Th2 cell differentiation in vitro. Th2 cytokine expression, immune cell infiltration in the bronchoalveolar lavage, airway hyperresponsiveness (AHR), and bronchial wall thickening were lower in Der p-challenged IL-20R1-deficient mice. Anti-IL-20R1 monoclonal antibody (mAb) 51D and IL-19 polyclonal antibody (pAb) both ameliorated Der p-induced AHR, lung immune cell infiltration, bronchial wall thickening, and Th2 cytokine expression. Moreover, we confirmed that anti-IL-19 mAb (1BB1) attenuated lung inflammation in a rat ovalbumin-induced asthma model. This is the first report to show that inhibition of IL-19 by targeting IL-19 or IL-20R1 protected rodents from allergic lung inflammation. Our study suggests that targeting IL-19 signaling might be a novel therapeutic strategy for treating allergic asthma.

Genomic mosaicism: A neglected factor that promotes variability in asthma diagnosis

To elucidate the genetic architecture of asthma continues to be a challenge for molecular biologists and medical researchers. However, powerful genomic technologies are at disposal to help decipher complete human genomes; the genetic variability in asthma hinders the discovery of common molecular markers for this disease. In this context, we purpose to explore genomic mosaicism on asthma cells' biology as a strategy to discover key mechanisms, which can complement or re-define asthma diagnosis. Recent evidences showed that genomic mosaicism could be a normal event. In brains, each neuron may harbor hundreds of genetic alterations, which may contribute to neuronal diversity. Thus, can mosaicism be a natural motor of diversity in asthma? Why this genetic event is little described in scientific literature? To discuss these questions, we perform a critical review about the normality of genomic mosaicism; moreover, we examine the difficulty of current experimental approaches to detect different genotypes in cell populations of one individual.

Identification of deleterious and regulatory genomic variations in known asthma loci

Background

Candidate gene and genome-wide association studies have identified hundreds of asthma risk loci. The majority of associated variants, however, are not known to have any biological function and are believed to represent markers rather than true causative mutations. We hypothesized that many of these associated markers are in linkage disequilibrium (LD) with the elusive causative variants.

Methods

We compiled a comprehensive list of 449 asthma-associated variants previously reported in candidate gene and genome-wide association studies. Next, we identified all sequence variants located within the 305 unique genes using whole-genome sequencing data from the 1000 Genomes Project. Then, we calculated the LD between known asthma variants and the sequence variants within each gene. LD variants identified were then annotated to determine those that are potentially deleterious and/or functional (i.e. coding or regulatory effects on the encoded transcript or protein).

Results

We identified 10,130 variants in LD (r² > 0.6) with known asthma variants. Annotations of these LD variants revealed that several have potentially deleterious effects including frameshift, alternate splice site, stop-lost, and missense. Moreover, 24 of the LD variants have been reported to regulate gene expression as expression quantitative trait loci (eQTLs).

Conclusions

This study is proof of concept that many of the genetic loci previously associated with complex diseases such as asthma are not causative but represent markers of disease, which are in LD with the elusive causative variants. We hereby report a number of potentially deleterious and regulatory variants that are in LD with the reported asthma loci. These reported LD variants could account for the original association signals with asthma and represent the true causative mutations at these loci.

Electronic supplementary material

The online version of this article (10.1186/s12931-018-0953-2) contains supplementary material, which is available to authorized users.

Whole-Genome Sequencing of Pharmacogenetic Drug Response in Racially Diverse Children with Asthma

RATIONALE

Albuterol, a bronchodilator medication, is the first-line therapy for asthma worldwide. There are significant racial/ethnic differences in albuterol drug response.

OBJECTIVES

To identify genetic variants important for bronchodilator drug response (BDR) in racially diverse children.

METHODS

We performed the first whole-genome sequencing pharmacogenetics study from 1,441 children with asthma from the tails of the BDR distribution to identify genetic association with BDR.

MEASUREMENTS AND MAIN RESULTS

We identified population-specific and shared genetic variants associated with BDR, including genome-wide significant (P < 3.53 × 10-7) and suggestive (P < 7.06 × 10-6) loci near genes previously associated with lung capacity (DNAH5), immunity (NFKB1 and PLCB1), and β-adrenergic signaling (ADAMTS3 and COX18). Functional analyses of the BDR-associated SNP in NFKB1 revealed potential regulatory function in bronchial smooth muscle cells. The SNP is also an expression quantitative trait locus for a neighboring gene, SLC39A8. The lack of other asthma study populations with BDR and whole-genome sequencing data on minority children makes it impossible to perform replication of our rare variant associations. Minority underrepresentation also poses significant challenges to identify age-matched and population-matched cohorts of sufficient sample size for replication of our common variant findings.

CONCLUSIONS

The lack of minority data, despite a collaboration of eight universities and 13 individual laboratories, highlights the urgent need for a dedicated national effort to prioritize diversity in research. Our study expands the understanding of pharmacogenetic analyses in racially/ethnically diverse populations and advances the foundation for precision medicine in at-risk and understudied minority populations.

A meta-analysis of genome-wide association studies of asthma in Puerto Ricans

Puerto Ricans are disproportionately affected with asthma in the USA. In this study, we aim to identify genetic variants that confer susceptibility to asthma in Puerto Ricans.We conducted a meta-analysis of genome-wide association studies (GWAS) of asthma in Puerto Ricans, including participants from: the Genetics of Asthma in Latino Americans (GALA) I-II, the Hartford-Puerto Rico Study and the Hispanic Community Health Study. Moreover, we examined whether susceptibility loci identified in previous meta-analyses of GWAS are associated with asthma in Puerto Ricans.The only locus to achieve genome-wide significance was chromosome 17q21, as evidenced by our top single nucleotide polymorphism (SNP), rs907092 (OR 0.71, p=1.2×10^-12) at IKZF3 Similar to results in non-Puerto Ricans, SNPs in genes in the same linkage disequilibrium block as IKZF3 (e.g. ZPBP2, ORMDL3 and GSDMB) were significantly associated with asthma in Puerto Ricans. With regard to results from a meta-analysis in Europeans, we replicated findings for rs2305480 at GSDMB, but not for SNPs in any other genes. On the other hand, we replicated results from a meta-analysis of North American populations for SNPs at IL1RL1, TSLP and GSDMB but not for IL33Our findings suggest that common variants on chromosome 17q21 have the greatest effects on asthma in Puerto Ricans.

Asthma Genetics in the Post-GWAS Era

Genome-wide association studies (GWAS) of asthma have yielded exciting results and identified novel risk alleles and loci. But, like other common complex diseases, asthma-associated alleles have small effect sizes and account for little of the prevalence of asthma. In this review, I discuss the limitations of GWAS approaches and the major challenges facing geneticists in the post-GWAS era and propose alternative strategies to address these challenges. In particular, I propose that focusing on genetic variations that influences gene expression and using cell models of gene-environment interactions in cell types that are relevant to asthma will allow us to more completely characterize the genetic architecture of asthma.

Severe Asthma: Have We Made Progress?

Tremendous efforts have been invested in research to (1) discover risk factors, biomarkers, and clinical characteristics; (2) understand the pathophysiology and treatment response variability in severe asthma; and (3) design new therapies. However, to combat severe asthma, many questions concerning the pathogenesis of severe asthma, including its natural history, genetic and environmental risk factors, and disease mechanisms, must be answered. In this article we highlight some of the major discoveries concerning the pathogenesis of severe asthma and its therapeutic development. We conclude that discoveries on numerous fronts of severe asthma, from disease heterogeneity, features of airway remodeling, cytokine mediators and signaling pathways underlying disease pathogenesis, disease mechanisms, potential biomarkers, to new therapeutic targets, demonstrate that progress has been made in understanding and developing more effective treatments for this difficult-to-treat disease.

Novel genetic risk factors for asthma in African American children: Precision Medicine and the SAGE II Study

Asthma, an inflammatory disorder of the airways, is the most common chronic disease of children worldwide. There are significant racial/ethnic disparities in asthma prevalence, morbidity, and mortality among US children. This trend is mirrored in obesity, which may share genetic and environmental risk factors with asthma. The majority of asthma biomedical research has been performed in populations of European decent. We sought to identify genetic risk factors for asthma in African American children. We also assessed the generalizability of genetic variants associated with asthma in European and Asian populations to African American children. Our study population consisted of 1227 (812 asthma cases, 415 controls) African American children with genome-wide single nucleotide polymorphism (SNP) data. Logistic regression was used to identify associations between SNP genotype and asthma status. We identified a novel variant in the PTCHD3 gene that is significantly associated with asthma (rs660498, p = 2.2 × 10(-7)) independent of obesity status. Approximately 5 % of previously reported asthma genetic associations identified in European populations replicated in African Americans. Our identification of novel variants associated with asthma in African American children, coupled with our inability to replicate the majority of findings reported in European Americans, underscores the necessity for including diverse populations in biomedical studies of asthma.

Public and Population Health Genomics

Public health seeks to improve health at a population level through interventions that increase the net health benefit to the population as a whole. Advances in genomics knowledge and technologies can add to this endeavor, but also pose a challenge when faced with often conflicting public health (population) and genomic medicine (individual) perspectives. Combining the fields of genomic, population, and social sciences, population genomics or public health genomics looks at the promotion of health and prevention of disease using genomic knowledge through the lens of populations rather than individuals. In this chapter we will survey the three major disciplines contributing to population genomics (genomics, population, and social sciences) and explore two cross-cutting issues: global health and population versus individual health, using specific examples from diseases such as asthma, colon cancer, and cystic fibrosis.

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.

The contribution of twin studies to the understanding of the aetiology of asthma and atopic diseases

The prevalence of asthma and other atopic diseases has increased markedly during the past decades and the reasons for this are not fully understood. Asthma is still increasing in many parts of the world, notably in developing countries, and this emphasizes the importance of continuing research aimed at studying the aetiological factors of the disease and the causes of its increase in prevalence. Twin studies enable investigations into the genetic and environmental causes of individual variation in multifactorial diseases such as asthma. Thorough insight into these causes is important as this will ultimately guide the development of preventive strategies and targeted therapies. This review explores the contribution of twin studies to the understanding of the aetiology of asthma and atopic diseases.

Asthma risk factors

BACKGROUND

Bronchial asthma is one of the most common chronic diseases in childhood, with a current prevalence of 6% to 9%, but a prevalence that is increasing at an alarming rate. Asthma is a complex genetic disorder with strong environmental influence. It imposes a growing burden on our society in terms of morbidity, quality of life, and healthcare costs. Despite large-scale efforts, only a few asthma genes have been confirmed, suggesting that the genetic underpinning of asthma is highly complex.

METHODS

A review of the literature was performed regarding atopic and nonatopic asthma risk factors, including environmental risk factors and genetic studies in adults and children.

RESULTS

Several environmental risk factors have been identified to increase the risk of developing asthma such as exposure to air pollution and tobaccos smoke as well as occupational risk factors. In addition atopy, stress, and obesity all can increases the risk for asthma in genetically susceptible persons.

CONCLUSION

Asthma represents a dysfunctional interaction with our genes and the environment to which they are exposed, especially in fetal and early infant life. The increasing prevalence of asthma in all age groups indicate that our living environment and immunity are in imbalance with each other reacting with airway inflammation to the environmental exposures and often non-harmful proteins, such as allergens causing the current "asthma and allergy epidemic." Because of the close relationship between asthma and chronic rhinosinusitis, it is important that otolaryngologists have a good understanding of asthma, the etiologic factors associated with disease, and its evaluation and management.

Epithelial function and dysfunction in asthma

Asthma was previously defined as an allergic Th2-mediated inflammatory immune disorder. Recently, this paradigm has been challenged because not all pathological changes observed in the asthmatic airways are adequately explained simply as a result of Th2-mediated processes. Contemporary thought holds that asthma is a complex immune disorder involving innate as well as adaptive immune responses, with the clinical heterogeneity of asthma perhaps a result of the different relative contribution of these two systems to the disease. Epidemiological studies show that exposure to certain environmental substances is strongly associated with the risk of developing asthma. The airway epithelium is first barrier to interact with, and respond to, environmental agents (pollution, viral infection, allergens), suggesting that it is a key player in the pathology of asthma. Epithelial cells play a key role in the regulation of tissue homeostasis by the modulation of numerous molecules, from antioxidants and lipid mediators to growth factors, cytokines, and chemokines. Additionally, the epithelium is also able to suppress mechanisms involved in, for example, inflammation in order to maintain homeostasis. An intrinsic alteration or defect in these regulation mechanisms compromises the epithelial barrier, and therefore, the barrier may be more prone to environmental substances and thus more likely to exhibit an asthmatic phenotype. In support of this, polymorphisms in a number of genes that are expressed in the bronchial epithelium have been linked to asthma susceptibility, while environmental factors may affect epigenetic mechanisms that can alter epithelial function and response to environmental insults. A detailed understanding of the regulatory role of the airway epithelium is required to develop new therapeutic strategies for asthma that not only address the symptoms but also the underlining pathogenic mechanism(s) and prevent airway remodelling.

Exploring the origins of asthma: Lessons from twin studies

This thesis explores the contribution of twin studies, particularly those studies originating from the Danish Twin Registry, to the understanding of the aetiology of asthma. First, it is explored how twin studies have established the contribution of genetic and environmental factors to the variation in the susceptibility to asthma, and to the variation in several aspects of the clinical expression of the disease such as its age at onset, its symptomatology, its intermediate phenotypes, and its relationship with other atopic diseases. Next, it is explored how twin studies have corroborated theories explaining asthma's recent increase in prevalence, and last, how these fit with the explanations of the epidemiological trends in other common chronic diseases of modernity.

Epistasis between serine protease inhibitor Kazal-type 5 (SPINK5) and thymic stromal lymphopoietin (TSLP) genes contributes to childhood asthma

BACKGROUND

Epithelial genes have previously been associated with asthma but only explain a small fraction of heritability. In part, this might be due to epistasis, which is often not considered.

OBJECTIVE

We sought to determine independent and epistatic associations between filaggrin (FLG), serine protease inhibitor Kazal-type 5 (SPINK5), and thymic stromal lymphopoietin (TSLP) gene variants and childhood asthma.

METHODS

Using a candidate gene approach, we genotyped 29 variants in FLG, SPINK5, and TSLP in asthmatic, allergic, and nonallergic nonasthmatic white and black children participating in the well-phenotyped Greater Cincinnati Pediatric Clinic Repository. Associations with asthma were also assessed in 6 replication populations.

RESULTS

We observed independent associations of variants in SPINK5 (P = .003) and TSLP (P = .006) with childhood asthma; a SPINK5 single nucleotide polymorphism was replicated. In subjects with 1 or more SPINK5 risk alleles, the absence of the TSLP protective minor alleles was associated with a significant increase in asthma (67% vs 53%, P = .0017). In contrast, the presence or absence of TSLP minor alleles did not affect asthma risk in subjects without the SPINK5 risk alleles. The SPINK5 and TSLP epistasis was replicated in a black population (P = .036) who did not display independent association with variants in these genes.

CONCLUSIONS

Our results support epistasis between SPINK5 and TSLP, which contributes to childhood asthma. These findings emphasize the importance of using biology to inform analyses to identify genetic susceptibility to complex diseases. The results from our study have clinical relevance and support that the therapeutic effects of anti-TSLP therapy in asthmatic patients might be dependent on SPINK5 genotype.

Functional Fcgamma receptor polymorphisms are associated with human allergy

Objective

IgG Fc receptors (FcγRs) play important roles in immune responses. It is not clear whether FcγR receptors play a role in human asthma and allergy. The aim of current study was to investigate whether functional single nucleotide polymorphisms (SNPs) of FcγR genes (FCGR) are associated with human asthma and allergy.

Methods

Functional SNPs of FCGR2A (FcγRIIA-131His>Arg, rs1801274), FCGR2B (FcγRIIB-187Ile>Thr, rs1050501), FCGR2C (FcγRIIC-13Gln>Stop, rs10917661), FCGR3A (FcγRIIIA-158Val>Phe, rs396991), and FCGR3B variants (FcγRIIIB NA1 and NA2) were genotyped in an asthma family cohort including 370 atopy positive, 239 atopy negative, and 169 asthma positive subjects. The genotype and phenotype data (asthma, bronchial hyper-responsiveness, and atopy) of subjects were analyzed using family-based association tests (FBAT) and logistic regression adjusted for age and sex.

Result

The FcγRIIA-131His>Arg SNP is significantly associated with atopy in a family-based association test (P = 0.00287) and in a logistic regression analysis (P = 0.0269, OR 0.732, 95% CI: 0.555–0.965). The FcγRIIA-131His (or rs1801274-A) allele capable of binding human IgG2 has a protective role against atopy. In addition, the rare FcγRIIB-187Thr (or rs1050501-C) allele defective for the receptor-mediated inhibitory signals is a risk factor for atopy (P = 0.0031, OR 1.758, 95% CI: 1.209–2.556) and IgE production (P<0.001). However, variants of activating FcγRIIIA (rs396991), and FcγRIIIB (NA1 and NA2), and FcγRIIC (rs10917661) are not associated with asthma, BHR, and atopy (P>0.05).

Conclusions

FcγRIIA and FcγRIIB functional polymorphisms may have a role in the pathogenesis of allergy.

A genome-wide association study of atopic dermatitis identifies loci with overlapping effects on asthma and psoriasis

Atopic dermatitis (AD) is the most common dermatological disease of childhood. Many children with AD have asthma and AD shares regions of genetic linkage with psoriasis, another chronic inflammatory skin disease. We present here a genome-wide association study (GWAS) of childhood-onset AD in 1563 European cases with known asthma status and 4054 European controls. Using Illumina genotyping followed by imputation, we generated 268 034 consensus genotypes and in excess of 2 million single nucleotide polymorphisms (SNPs) for analysis. Association signals were assessed for replication in a second panel of 2286 European cases and 3160 European controls. Four loci achieved genome-wide significance for AD and replicated consistently across all cohorts. These included the epidermal differentiation complex (EDC) on chromosome 1, the genomic region proximal to LRRC32 on chromosome 11, the RAD50/IL13 locus on chromosome 5 and the major histocompatibility complex (MHC) on chromosome 6; reflecting action of classical HLA alleles. We observed variation in the contribution towards co-morbid asthma for these regions of association. We further explored the genetic relationship between AD, asthma and psoriasis by examining previously identified susceptibility SNPs for these diseases. We found considerable overlap between AD and psoriasis together with variable coincidence between allergic rhinitis (AR) and asthma. Our results indicate that the pathogenesis of AD incorporates immune and epidermal barrier defects with combinations of specific and overlapping effects at individual loci.

Genetic polymorphisms and associated susceptibility to asthma

As complex common diseases, asthma and allergic diseases are caused by the interaction of multiple genetic variants with a variety of environmental factors. Candidate-gene studies have examined the involvement of a very large list of genes in asthma and allergy, demonstrating a role for more than 100 loci. These studies have elucidated several themes in the biology and pathogenesis of these diseases. A small number of genes have been associated with asthma or allergy through traditional linkage analyses. The publication of the first asthma-focused genome-wide association (GWA) study in 2007 has been followed by nearly 30 reports of GWA studies targeting asthma, allergy, or associated phenotypes and quantitative traits. GWA studies have confirmed several candidate genes and have identified new, unsuspected, and occasionally uncharacterized genes as asthma susceptibility loci. Issues of results replication persist, complicating interpretation and making conclusions difficult to draw, and much of the heritability of these diseases remains undiscovered. In the coming years studies of complex diseases like asthma and allergy will probably involve the use of high-throughput next-generation sequencing, which will bring a tremendous influx of new information as well as new problems in dealing with vast datasets.

Further replication studies of the EVE Consortium meta-analysis identifies 2 asthma risk loci in European Americans

BACKGROUND

Genome-wide association studies of asthma have implicated many genetic risk factors, with well-replicated associations at approximately 10 loci that account for only a small proportion of the genetic risk.

OBJECTIVES

We aimed to identify additional asthma risk loci by performing an extensive replication study of the results from the EVE Consortium meta-analysis.

METHODS

We selected 3186 single nucleotide polymorphisms for replication based on the P values from the EVE Consortium meta-analysis. These single nucleotide polymorphisms were genotyped in ethnically diverse replication samples from 9 different studies, totaling 7202 cases, 6426 controls, and 507 case-parent trios. Association analyses were conducted within each participating study, and the resulting test statistics were combined in a meta-analysis.

RESULTS

Two novel associations were replicated in European Americans: rs1061477 in the KLK3 gene on chromosome 19 (combined odds ratio = 1.18; 95% CI, 1.10-1.25) and rs9570077 (combined odds ratio =1.20; 95% CI, 1.12-1.29) on chromosome 13q21. We could not replicate any additional associations in the African Americans or Latinos.

CONCLUSIONS

This extended replication study identified 2 additional asthma risk loci in populations of European descent. The absence of additional loci for African Americans and Latinos highlights the difficulty in replicating associations in admixed populations.

Genome-wide association studies of asthma in population-based cohorts confirm known and suggested loci and identify an additional association near HLA

RATIONALE

Asthma has substantial morbidity and mortality and a strong genetic component, but identification of genetic risk factors is limited by availability of suitable studies.

OBJECTIVES

To test if population-based cohorts with self-reported physician-diagnosed asthma and genome-wide association (GWA) data could be used to validate known associations with asthma and identify novel associations.

METHODS

The APCAT (Analysis in Population-based Cohorts of Asthma Traits) consortium consists of 1,716 individuals with asthma and 16,888 healthy controls from six European-descent population-based cohorts. We examined associations in APCAT of thirteen variants previously reported as genome-wide significant (P<5 x 10(-8)) and three variants reported as suggestive (P<5× 10(-7)). We also searched for novel associations in APCAT (Stage 1) and followed-up the most promising variants in 4,035 asthmatics and 11,251 healthy controls (Stage 2). Finally, we conducted the first genome-wide screen for interactions with smoking or hay fever.

MAIN RESULTS

We observed association in the same direction for all thirteen previously reported variants and nominally replicated ten of them. One variant that was previously suggestive, rs11071559 in RORA, now reaches genome-wide significance when combined with our data (P = 2.4 × 10(-9)). We also identified two genome-wide significant associations: rs13408661 near IL1RL1/IL18R1 (P(Stage1+Stage2) = 1.1x10(-9)), which is correlated with a variant recently shown to be associated with asthma (rs3771180), and rs9268516 in the HLA region (P(Stage1+Stage2) = 1.1x10(-8)), which appears to be independent of previously reported associations in this locus. Finally, we found no strong evidence for gene-environment interactions with smoking or hay fever status.

CONCLUSIONS

Population-based cohorts with simple asthma phenotypes represent a valuable and largely untapped resource for genetic studies of asthma.

Asthma Research for All of the United States

Asthma disproportionally affects different ethnic/racial groups, with Puerto Ricans and African Americans suffering the highest asthma prevalence and morbidity, Mexicans the lowest, and non-Hispanic whites in between. Genome-wide association studies of asthma have found both shared and race/ethnic-specific genetic risks factors for asthma. However, the majority of genetic asthma research is performed in populations of European descent, which limits the benefits of genetic research to European populations. It is important to biomedical and clinical research to include more diverse and underrepresented populations. The rich genetic diversity of all populations can be leveraged to scientific advantage. For example, admixture mapping provides a more powerful approach than traditional genome-wide allelic association studies in discovering genetic associations for complex diseases. By being more inclusive we can achieve a better understanding of the genetics of asthma, address health disparities, and ensure that scientific advances will benefit populations worldwide.

Human leucocyte antigen-G: expression and function in airway allergic disease

Human leucocyte antigen-G (HLA-G) is a non-classical HLA class I molecule demonstrated originally in placental trophoblast cells. Recognition of the importance of HLA-G to the maternal immune accommodation of the semi-allogeneic fetus has led to investigations of its role in the suppression of immune responses and induction of tolerance. More recently, HLA-G has been shown to have increased expression in several immunological diseases including asthma and allergic rhinitis. The focus of this review is the potential role of HLA-G in immunological airway diseases.

Meta-analysis of genome-wide association studies of asthma in ethnically diverse North American populations

Asthma is a common disease with a complex risk architecture including both genetic and environmental factors. We performed a meta-analysis of North American genome-wide association studies of asthma in 5,416 individuals with asthma (cases) including individuals of European American, African American or African Caribbean, and Latino ancestry, with replication in an additional 12,649 individuals from the same ethnic groups. We identified five susceptibility loci. Four were at previously reported loci on 17q21, near IL1RL1, TSLP and IL33, but we report for the first time, to our knowledge, that these loci are associated with asthma risk in three ethnic groups. In addition, we identified a new asthma susceptibility locus at PYHIN1, with the association being specific to individuals of African descent (P = 3.9 × 10(-9)). These results suggest that some asthma susceptibility loci are robust to differences in ancestry when sufficiently large samples sizes are investigated, and that ancestry-specific associations also contribute to the complex genetic architecture of asthma.

The lung: the natural boundary between nature and nurture

Common lung diseases such as asthma, COPD, and pulmonary fibrosis cause significant morbidity and mortality in the U.S. and worldwide. Research investigating the mechanisms of disease etiology has clearly indicated that genetic attributes and environmental exposures each play important roles in the development of these diseases. Emerging evidence underscores the importance of the interplay between genetic predisposition and environmental factors in fully understanding the development of lung disease. Herein we discuss recent advances in knowledge and technology surrounding the role of genetics, the environment, and gene-environment interactions in these common lung diseases.

The genetics of asthma and allergic disease: a 21st century perspective

Asthma and allergy are common conditions with complex etiologies involving both genetic and environmental contributions. Recent genome-wide association studies (GWAS) and meta-analyses of GWAS have begun to shed light on both common and distinct pathways that contribute to asthma and allergic diseases. Associations with variation in genes encoding the epithelial cell-derived cytokines, interleukin-33 (IL-33) and thymic stromal lymphopoietin (TSLP), and the IL1RL1 gene encoding the IL-33 receptor, ST2, highlight the central roles for innate immune response pathways that promote the activation and differentiation of T-helper 2 cells in the pathogenesis of both asthma and allergic diseases. In contrast, variation at the 17q21 asthma locus, encoding the ORMDL3 and GSDML genes, is specifically associated with risk for childhood onset asthma. These and other genetic findings are providing a list of well-validated asthma and allergy susceptibility genes that are expanding our understanding of the common and unique biological pathways that are dysregulated in these related conditions. Ongoing studies will continue to broaden our understanding of asthma and allergy and unravel the mechanisms for the development of these complex traits.

Multi-locus models of genetic risk of disease

Background

Evidence for genetic contribution to complex diseases is described by recurrence risks to relatives of diseased individuals. Genome-wide association studies allow a description of the genetics of the same diseases in terms of risk loci, their effects and allele frequencies. To reconcile the two descriptions requires a model of how risks from individual loci combine to determine an individual's overall risk.

Methods

We derive predictions of risk to relatives from risks at individual loci under a number of models and compare them with published data on disease risk.

Results

The model in which risks are multiplicative on the risk scale implies equality between the recurrence risk to monozygotic twins and the square of the recurrence risk to sibs, a relationship often not observed, especially for low prevalence diseases. We show that this theoretical equality is achieved by allowing impossible probabilities of disease. Other models, in which probabilities of disease are constrained to a maximum of one, generate results more consistent with empirical estimates for a range of diseases.

Conclusions

The unconstrained multiplicative model, often used in theoretical studies because of its mathematical tractability, is not a realistic model. We find three models, the constrained multiplicative, Odds (or Logit) and Probit (or liability threshold) models, all fit the data on risk to relatives. Currently, in practice it would be difficult to differentiate between these models, but this may become possible if genetic variants that explain the majority of the genetic variance are identified.

Genome-wide association studies in the genetics of asthma

The field of asthma genetics has progressed rapidly over the past decade, implicating many genes and variants in the etiology of this complex disease. However, many of these factors have failed to replicate consistently, indicating a high false-positive rate and/or insufficient power for the detection of small effects. Technological limitations also have restricted the potential to detect novel mechanisms, fostering a dependence on existing knowledge. Since its inception almost 4 years ago, genome-wide association (GWA) has transformed genetic studies of multifactorial traits and yielded unprecedented insights into mechanisms of causation. Asthma is at the forefront of this revolution, as it uses GWA to map not only genetic determinants of clinical status but also transcript and protein abundance and structural (copy number) variants that may underlie disease susceptibility. In this review, we consider the applications of GWA data to asthma and describe the factors likely to influence the procedure's success.

Gene-environment interactions and airway disease in children

Asthma is the most common chronic disease of childhood in the United States, affecting nearly 6.5 million children. The prevalence and severity of childhood asthma have continued to increase over the past 2 decades, despite major advances in the recognition and treatment of this condition. Representing a heterogeneous collection of airway diseases, asthma has multiple pathologic processes resulting from the interactions of genetic susceptibility and environmental exposures. Preventing and treating airway disease in children will require new research approaches to understanding these complex interactions.

Repeatability of response to asthma medications

BACKGROUND

Pharmacogenetic studies of drug response in asthma assume that patients respond consistently to a treatment but that treatment response varies across patients; however, no formal studies have demonstrated this.

OBJECTIVE

To determine the repeatability of commonly used outcomes for treatment response to asthma medications: bronchodilator response, FEV(1), and PC(20).

METHODS

The Childhood Asthma Management Program was a multicenter clinical trial of children randomized to receiving budesonide, nedocromil, or placebo. We determined the intraclass correlation coefficient (ICC) for each outcome over repeated visits over a period of 4 years in the Childhood Asthma Management Program by using mixed-effects regression models. We adjusted for the covariates age, race/ethnicity, height, family income, parental education, and symptom score. We incorporated each outcome for each child as repeated outcome measurements and stratified by treatment group.

RESULTS

The ICC for bronchodilator response was 0.31 in the budesonide group, 0.35 in the nedocromil group, and 0.40 in the placebo group, after adjusting for covariates. The ICC for FEV(1) was 0.71 in the budesonide group, 0.60 in the nedocromil group, and 0.69 in the placebo group, after adjusting for covariates. The ICC for PC(20) was 0.67 in the budesonide and placebo groups and 0.73 in the nedocromil group, after adjusting for covariates.

CONCLUSION

The within-treatment group repeatability of FEV(1) and PC(20) is high; thus, these phenotypes are heritable. FEV(1) and PC(20) may be better phenotypes than bronchodilator response for studies of treatment response in asthma.

A note on twin-singleton differences in asthma

Twins constitute a valuable resource for genetic studies of asthma. However, critics argue that twins are 'special' in terms of prenatal environment and upbringing and therefore nonrepresentative. In respect to asthma a small range of studies report differential morbidity in twins compared with singletons. We review some of the possible explanations for these findings and conclude that results from twin studies of asthma can be extrapolated to the general population.

Heritability and shared genetic effects of asthma and hay fever: an Italian study of young twins

A number of studies have provided evidence of a significant familial aggregation for both asthma and hay fever, and have reported a substantial comorbidity between the two conditions. However, far fewer, especially in Italy, have aimed at clarifying the origins of such comorbidity. The main aims of the present study were (a) to estimate heritability of asthma and hay fever, (b) to measure the association between asthma and hay fever at the individual level, and (c) to assess the extent to which genetic and environmental factors, shared by the two conditions, mediate this association. The twin method was used. The study sample was derived from the Italian Twin Registry, and included 392 twin pairs aged 8 to 17 years. Data collection was performed through parent self-administered questionnaire. Bivariate structural equation twin modeling was applied to asthma and hay fever. Genetic factors accounted for 92% and 78% of the variance in liability to asthma and hay fever, respectively, with the remaining contributions due to unique environmental influences. The within-individual association between asthma and hay fever was substantial. The genetic correlation between the two conditions was .58, whereas no evidence of overlapping unique environmental effects was found. In conclusion, this study showed a high heritability of asthma and hay fever in the Italian child and adolescent population. It also indicated that asthma and hay fever share, to a large extent, a common genetic background, and environmental factors are not relevant to explain the comorbidity.

Characterizing community-based asthma knowledge in Chicago and its high risk neighborhoods

The goal of this study was to characterize asthma knowledge in high risk neighborhoods compared to a random sample of residents in the Chicago area. The Chicago Community Asthma Survey-32 (CCAS-32) was administered to 1006 Chicago-area residents and 388 residents in 4 high-risk Chicago inner-city neighborhoods. There was a significant difference in asthma knowledge between groups. The general Chicago-area respondents have an average desirable response rate of 71.6% versus 64.7% for respondents in high-risk communities (p < 0.0001). For some aspects of asthma knowledge, e.g., nocturnal cough, cockroach allergen, and vaporizer use, general knowledge was similarly low. For other aspects, such as the need for asymptomatic asthma visits and chest tightness, there were larger gaps between residents of high risk communities and the general community. High-risk neighborhoods in Chicago had lower asthma knowledge compared to the general Chicago community. This discrepancy may be contributing to the disparities seen in asthma morbidity. Public health efforts to increase asthma knowledge in these high risk minority communities may help reduce these disparities. Important misconceptions exist about asthma triggers, signs and symptoms, especially among lower income African American communities, that should be addressed by physicians.

Recent advances in asthma genetics

There are over 100 genes that have been reported to be associated with asthma or related phenotypes. In 2006–2007 alone there were 53 novel candidate gene associations reported in the literature. Replication of genetic associations and demonstration of a functional mechanism for the associated variants are needed to confirm an asthma susceptibility gene. For most of the candidate genes there is little functional information. In a previous review by Hoffjan et al. published in 2003, functional information was reported for 40 polymorphisms and here we list another 22 genes which have such data. Some important genes such as filaggrin, interleukin-13, interleukin-17 and the cysteinyl leukotriene receptor-1 which not only were replicated by independent association studies but also have functional data are reviewed in this article.

Genetics of asthma: potential implications for reducing asthma disparities

Although genetic factors may partly explain the differences in asthma prevalence, morbidity, and mortality among ethnic groups in the United States, few studies of the genetics of asthma have included members of ethnic minority groups. Only one genome-wide linkage analysis of asthma and/or asthma-related phenotypes (conducted by the Collaborative Study on the Genetics of Asthma) has included any members of ethnic minority populations. The interpretation of the findings of genetic association studies of asthma in ethnic minority groups is complicated by reduced statistical power due to small sample sizes; the failure to correct for multiple comparisons; a lack of homogeneity of the populations studied with regard to area of residence, ancestral background, and/or country of origin; a lack of measurement of relevant environmental exposures; and (for case-control studies of genetic association) a lack of detection and control of potential population stratification. Genetic studies may improve our understanding of asthma and lead to new methods to prevent, diagnose, and treat this disease. Limited study of asthma genetics in ethnic minority populations is unacceptable, as it may prevent these groups from benefiting from future developments in asthma management and thus widen existing disparities in asthma care. Future genetic association studies of asthma among ethnic minorities in the United States should include large samples of populations that have been adequately defined with regard to area of residence, self-designated ancestry, and country of origin. These studies should also include an adequate assessment of potentially relevant environmental exposures and (for case-control association studies) population stratification.

The potential for reducing asthma disparities through improved family and social function and modified health behaviors

The National Workshop To Reduce Asthma Disparities assembled a multidisciplinary group comprised of scientists, clinicians, and community representatives to examine factors related to asthma disparities. Attention was given to the importance of discerning family, social, and behavioral factors that facilitate or impede the use of health-care services suitable to the medical status of an individual. This review highlights select biopsychosocial factors that contribute to these disparities, the manner in which they may contribute or protect persons affected by asthma, and recommended directions for future research.

Genetic effects in common on maximal walking speed and muscle performance in older women

The purpose was to examine whether maximal walking speed, maximal isometric knee extensor strength, and leg extensor power share genetic or environmental effects in common. The data was collected from 103 monozygotic and 114 dizygotic female twin pairs aged 63-76 years. Maximal walking speed over 10 m was measured in the laboratory corridor using photocells for timing. Isometric knee extensor strength and leg extensor power were measured using an adjustable dynamometer. The genetic models showed that strength, power, and walking speed had a genetic effect in common which accounted for 52% of the variance in strength, 36% in power, and 34% in walking speed. Strength and power had a non-shared environmental effect in common explaining 13% of variation in strength and 14% in power. The remaining variance was accounted for by trait-specific effects. Some people may be more prone to functional limitation in old age due to their genetic disposition, but this does not rule out that changes in the lifestyle of predisposed subjects may also have a major effect. Approximately half of the variation in each trait was explained by environmental effects, which suggests the importance of the physical activity to improve performance and prevent functional limitation.