Genetic pleiotropy between asthma and obesity in a community-based sample of twins

A common 16p11.2 inversion underlies the joint susceptibility to asthma and obesity

The prevalence of asthma and obesity is increasing worldwide, and obesity is a well-documented risk factor for asthma. The mechanisms underlying this association and parallel time trends remain largely unknown but genetic factors may be involved. Here, we report on a common ~0.45 Mb genomic inversion at 16p11.2 that can be accurately genotyped via SNP array data. We show that the inversion allele protects against the joint occurrence of asthma and obesity in five large independent studies (combined sample size of 317 cases and 543 controls drawn from a total of 5,809 samples; combined OR = 0.48, p = 5.5 × 10(-6)). Allele frequencies show remarkable worldwide population stratification, ranging from 10% in East Africa to 49% in Northern Europe, consistent with discordant and extreme genetic drifts or adaptive selections after human migration out of Africa. Inversion alleles strongly correlate with expression levels of neighboring genes, especially TUFM (p = 3.0 × 10(-40)) that encodes a mitochondrial protein regulator of energy balance and inhibitor of type 1 interferon, and other candidates for asthma (IL27) and obesity (APOB48R and SH2B1). Therefore, by affecting gene expression, the ~0.45 Mb 16p11.2 inversion provides a genetic basis for the joint susceptibility to asthma and obesity, with a population attributable risk of 39.7%. Differential mitochondrial function and basal energy balance of inversion alleles might also underlie the potential selection signature that led to their uneven distribution in world populations.

Genome-wide association study of body mass index in 23 000 individuals with and without asthma

BACKGROUND

Both asthma and obesity are complex disorders that are influenced by environmental and genetic factors. Shared genetic factors between asthma and obesity have been proposed to partly explain epidemiological findings of co-morbidity between these conditions.

OBJECTIVE

To identify genetic variants that are associated with body mass index (BMI) in asthmatic children and adults, and to evaluate if there are differences between the genetics of BMI in asthmatics and healthy individuals.

METHODS

In total, 19 studies contributed with genome-wide analysis study (GWAS) data from more than 23 000 individuals with predominantly European descent, of whom 8165 are asthmatics.

RESULTS

We report associations between several DENND1B variants (P = 2.2 × 10(-7) for rs4915551) on chromosome 1q31 and BMI from a meta-analysis of GWAS data using 2691 asthmatic children (screening data). The top DENND1B single nucleotide polymorphisms(SNPs) were next evaluated in seven independent replication data sets comprising 2014 asthmatics, and rs4915551 was nominally replicated (P < 0.05) in two of the seven studies and of borderline significance in one (P = 0.059). However, strong evidence of effect heterogeneity was observed and overall, the association between rs4915551 and BMI was not significant in the total replication data set, P = 0.71. Using a random effects model, BMI was overall estimated to increase by 0.30 kg/m(2) (P = 0.01 for combined screening and replication data sets, N = 4705) per additional G allele of this DENND1BSNP. FTO was confirmed as an important gene for adult and childhood BMI regardless of asthma status.

CONCLUSIONS AND CLINICAL RELEVANCE

DENND1B was recently identified as an asthma susceptibility gene in a GWAS on children, and here, we find evidence that DENND1B variants may also be associated with BMI in asthmatic children. However, the association was overall not replicated in the independent data sets and the heterogeneous effect of DENND1B points to complex associations with the studied diseases that deserve further study.

Leptin as regulator of pulmonary immune responses: involvement in respiratory diseases

Leptin is an adipocyte-derived hormone, recognized as a critical mediator of the balance between food intake and energy expenditure by signalling through its functional receptor (Ob-Rb) in the hypothalamus. Structurally, leptin belongs to the long-chain helical cytokine family, and is now known to have pleiotropic functions in both innate and adaptive immunity. The presence of the functional leptin receptor in the lung together with evidence of increased airspace leptin levels arising during pulmonary inflammation, suggests an important role for leptin in lung development, respiratory immune responses and eventually pathogenesis of inflammatory respiratory diseases. The purpose of this article is to review our current understanding of leptin and its functional role on the different resident cell types of the lung in health as well as in the context of three major respiratory conditions being chronic obstructive pulmonary disease (COPD), asthma, and pneumonia.

Asthma and obesity

The prevalence and incidence of asthma have increased among obese children and adults, particularly among women. Obesity seems to be a predisposing factor for the development of asthma, but the underlying mechanisms of its influence are still uncertain. Various hypotheses have been proposed to explain the link between obesity and asthma such as a common genetic predisposition, developmental changes, altered lung mechanics, the presence of a systemic inflammatory process, and an increased prevalence of associated comorbid conditions. Over-diagnosis of asthma does not seem to be more frequent in obese compared to non-obese subjects, but the added effects of obesity on respiratory symptoms can affect asthma control assessment. Obesity can make asthma more difficult to control and is associated with a reduced beneficial effect of asthma medications. This could be due to a change in asthma phenotype, particularly evidenced as a less eosinophilic type of airway inflammation combined to the added effects of changes in lung mechanics. Weight loss is associated with a universal improvement of asthma and should be part of asthma management in the obese patient. Additional research should be conducted to better determine how obesity influences the development and clinical expression of asthma, establish the optimal management of asthma in this population and determine how obesity affects long-term asthma outcomes in these patients.

Impact of maternal obesity on inhaled corticosteroid use in childhood: a registry based analysis of first born children and a sibling pair analysis

BACKGROUND

It has been proposed that maternal obesity during pregnancy may increase the risk that the child develops allergic disease and asthma, although the mechanisms underpinning this relationship are currently unclear. We sought to assess if this association may be due to confounding by genetic or environmental risk factors that are common to maternal obesity and childhood asthma, using a sibling pair analysis.

METHODS

The study population comprised a Swedish national cohort of term children born between 1992 and 2008 to native Swedish parents. Maternal body mass index (BMI) was measured at 8-10 weeks gestation. Unconditional logistic regression models were used to determine if maternal obesity was associated with increased risk of inhaled corticosteroid (ICS) in 431,718 first-born children, while adjusting for potential confounders. An age-matched discordant sib-pair analysis was performed, taking into account shared genetic and environmental risk factors.

RESULTS

Maternal over-weight and obesity were associated with increased risk that the child would require ICS (for BMI≥35 kg/m(2), aOR = 1.30, 95%CI = 1.10-1.52 compared with normal weight mothers) in children aged 6-12 years. Similar effects were seen in younger children, but in children aged 13-16 years, maternal obesity (BMI≥30) was related to increased risk of ICS use in girls (aOR = 1.28, 95%CI = 1.07-1.53) but not boys (OR = 1.05, 95%CI = 0.87-1.26). The sib-pair analysis, which included 2,034 sib-pairs older than six years who were discordant for both ICS use and maternal BMI category, failed to find any evidence that increasing maternal weight was related to increased risk of ICS use.

CONCLUSION

Maternal obesity is associated with increased risk of childhood ICS use up to approximately 12 years of age, but only in girls after this age. These effects could not be confirmed in a sib pair analysis, suggesting either limited statistical power, or the effects of maternal BMI may be due to shared genetic or environmental risk factors.

Obesity and asthma

Asthma is a chronic disorder affecting millions of people worldwide. The prevalence of asthma is around 300 million and is expected to increase another 100 million by 2025. Obesity, on the other hand, also affects a large number of individuals. Overweight in adults is defined when body mass index (BMI) is between 25 to 30 kg/m(2) and obesity when the BMI >30 kg/m(2). It has been a matter of interest for researchers to find a relation between these two conditions. This knowledge will provide a new insight into the management of both conditions. At present, obese asthma patients may be considered a special category and it is important to assess the impact of management of obesity on asthma symptoms.

Obesity and asthma: a coincidence or a causal relationship? A systematic review

BACKGROUND AND AIM

Epidemiological data has established increasing adiposity as a risk factor for incident asthma. However, the mechanisms underlying the association between obesity and asthma are incompletely understood. In the present paper, we review current knowledge of possible mechanisms mediating the observed association between obesity and asthma.

METHODS

Systematic literature review.

RESULTS

Obesity and asthma share some etiological factors, such as a common genetic predisposition and effects of in utero conditions, and may also have common predisposing factors such as physical activity and diet. Obesity results in important changes in the mechanical properties of the respiratory system which could explain the occurrence of asthma. However, there are also plausible biological mechanisms whereby obesity could be expected to either cause or worsen asthma. These include co-morbidities such as gastro-oesophageal reflux, complications from sleep-disordered breathing, breathing at low lung volumes, chronic systemic inflammation, and endocrine factors, including adipokines and reproductive hormones. Obesity related asthma is in general not associated with eosinophilic airway inflammation, and adipokines are likely to play important roles in the inflammatory pathogenesis of asthma in obese individuals.

CONCLUSION

The association between obesity and asthma is not straightforward, and further knowledge is clearly needed, as understanding the underlying mechanisms may lead to new therapeutic options for this high-risk part of the asthma population.

Weight loss interventions in asthma: EAACI evidence-based clinical practice guideline (part I)

BACKGROUND

Asthma and obesity are chronic multifactorial conditions that are associated with gene-environment interaction and immune function. Although the data are not fully consistent, it seems that obesity increases the risk of asthma and compromises asthma control.

OBJECTIVE

To investigate the impact that weight changes have on asthma.

METHODS

We carried out a systematic review of three large biomedical databases. Studies were scrutinized and critically appraised according to agreed exclusion and inclusion criteria. Quality assessment of eligible papers was conducted using the GRADE method. Meta-analyses of comparable studies were carried out.

RESULTS

Thirty studies met the eligibility criteria of the review. Interventions were limited to dietary manipulation in three studies, one of which also used anti-obesity drugs, and bariatric surgery in four. All the other studies reported observational data. Becoming obese increased the odds for incident asthma by 1.82 (95% CI 1.47, 2.25) in adults and 1.98 (95% CI 0.71, 5.52) in children. Weight loss was associated with significant improvement in mean scores for symptoms, rescue medication score, and asthma exacerbations in the only randomized controlled trial. Similarly, evidence gathered from observational studies, with follow-up ranging between 8 weeks to 1 year, and from changes 1 year after bariatric surgery showed improvements in all asthma control-related outcomes. Changes in lung function were reported in one randomized controlled and eight observational studies of asthmatic subjects, with conflicting results. Either improvement after weight loss, decline with weight gain, or no effects at all were reported. Changes in airway inflammation and responsiveness were reported only by observational studies.

CONCLUSION

Weight increases above the obesity threshold significantly increase the risk of asthma. The available studies show weak evidence of benefits from weight reduction on asthma outcomes.

The association of a variant in the cell cycle control gene CCND1 and obesity on the development of asthma in the Swiss SAPALDIA study

OBJECTIVE

The molecular mechanisms underlying the association between obesity (BMI ≥ 30 kg/m(2)) and asthma are poorly understood. Since shifts in the fate of bronchial cells due to low-grade systemic inflammation may provide a possible explanation, we investigated whether two of the best documented functional variants in cell cycle control genes modify the obesity-asthma association.

METHODS

We genotyped 5930 SAPALDIA cohort participants for the single-nucleotide polymorphisms (SNPs) rs9344 in the cyclin D1 gene (CCND1) and rs1042522 in the gene encoding tumor protein 53 (TP53). We assessed the independent association of these SNPs and obesity with asthma prevalence and incidence.

RESULTS

The CCND1 SNP modified the association between obesity and asthma prevalence (p(interaction )= 0.03). The odds ratios (ORs) and 95% confidence intervals (CIs) for reporting a physician diagnosis of asthma at baseline, comparing obese with non-obese participants, were 1.09 (0.51-2.33), 1.64 (0.94-2.88), and 3.51 (1.63-7.53) for GG, GA, and AA genotypes, respectively. We found comparable genotype differences for incident asthma within the 11 years of follow-up. As for the TP53 SNP, the interactions with obesity status with respect to asthma were not statistically significant.

CONCLUSIONS

Our results suggest that obesity may contribute to asthma and associated tissue remodeling by modifying the processes related to the CCND1 gene activity.

Sex Differences in the Effects of Inhaled Corticosteroids on Weight Gain among Patients with Asthma

Background. Studies have shown that asthma and asthma exacerbations are related to body weight and that this relationship might be sex-specific. While oral corticosteroids have been associated with weight gain, little is known about the effect of inhaled corticosteroid (ICS) use on short-term weight gain. The purpose of the present study was to examine whether ICSs would be associated with weight gain among asthmatic patients. Methods. A total of 180 adult patients with physician-diagnosed asthma provided details of their medical history and demographic information, along with height and weight at baseline and at one year. Weight change was defined as follow-up minus baseline weight. General linear models were used to assess the relationship between ICS dose (fluticasone propionate equivalent) and sex. Results. Significant main effects of sex (P=.005) and ICS dose (P=.036) and an interaction effect of sex and ICS dose (P=.003) on weight change were observed. Further analysis of the interaction indicated that women had greater weight gain, while men had decreased weight with increased ICS dose. Conclusions. Findings suggest that ICSs may trigger weight gain in females and highlight the need for studies to confirm this relationship and examine the potential underlying mechanisms.

Obesity and pulmonary disease: unanswered questions

Obesity is associated with risk of pulmonary disease, and adversely affects lung function. The parallel increase in obesity and asthma suggests the two conditions are linked; indeed, they can worsen each other. Obesity and inadequate asthma control are associated with poor quality of life, and place a high economic burden on public health. Although the obesity-lung interaction is a major issue for basic research and clinical studies, various questions remain unanswered. Do intrauterine and early life factors impact on the development of obesity and lung disease? If so, can this be prevented? Asthma is generally more severe in obese subjects, but is adiposity a driver of a new asthma phenotype that features greater morbidity and mortality, worse control and decreased response to medications? Obese individuals have small lung volumes, hence their airway calibre is reduced and airway resistance is increased. What puzzles physicians is whether peripheral airways undergo remodelling, which would increase bronchoconstriction. Obese asthmatics respond suboptimally to anti-inflammatory treatment, which raises the question: 'what drug for what patient?' Life expectancy is decreased in obesity and in chronic pulmonary disorders, but does obesity protect against or trigger chronic obstructive pulmonary disease? The time has come to find answers to these questions.

University of Washington Twin Registry: Construction and Characteristics of a Community-Based Twin Registry

The University of Washington Twin Registry is a community-based registry of twins identified from the Washington State Department of Licensing. A fortuitous quirk in the Washington State drivers' license and identification number assignment, and collaborative Washington State laws, permitted us to build a statewide registry. Since obtaining approval from the Washington State Attorney General, the Washington State Department of Licensing has provided us with information on over 26,000 newly licensed twins, and we continue to receive computerized records on approximately 80 new twins per week. The University of Washington Twin Registry is assembled by mailing each twin a recruitment packet that includes an information sheet, brochure, brief survey, and nominal gift. Once both members of a twin pair have completed the packet, the pair is enrolled in the registry. As of June 2006, 2287 adult twin pairs have enrolled in the registry; about one half of these are female–female pairs. Among all twins, the average age is 32 years. Based on self-report, 52% of twins are monozygotic, 42% are dizygotic, and zygosity on 6% cannot yet be determined. We also have instituted a clinical protocol for collecting additional data and DNA from all twins participating in research studies requiring an in-person visit. The registry has established policies and procedures to protect the confidentiality of twin data and guidelines for the use of the registry by investigators. Plans for the further growth of the University of Washington Twin Registry and its use are discussed.

Do Puerto Rican youth with asthma and obesity have higher odds for mental health disorders?

BACKGROUND

Island Puerto Rican (PR) youth experience disproportionately high asthma and obesity rates compared with other racial/ethnic groups on the U.S. mainland. Previous research has demonstrated associations of chronic disease with psychiatric disorders.

OBJECTIVE

We examined the relationship among anxiety/depressive disorders, asthma, and obesity in an epidemiologic community sample of youth.

METHODS

The sample (n = 656) was derived from the second wave of an island-wide probabilistic representative household sample of PR youth stratified and based on whether or not they had a diagnosis of asthma and/or depressive/anxiety disorder. For this study, we used the subpopulation ages 10-19 years.

RESULTS

Asthma and obesity were significantly related to higher odds of depressive/anxiety disorders in youth. Obesity moderated the relationship between asthma attacks and depressive/anxiety disorders. The relationship between asthma attack and higher odds for depressive/anxiety disorders was only present in the non-obese group. Among the obese, females show a significant increase from 11% to 36% in the prevalence of anxiety/depressive disorders. Asthma and obesity were highly prevalent and a significant association was found between asthma attack and depressive/anxiety disorders. The effects of asthma and obesity were not additive; the prevalence for psychiatric disorder for those having both conditions did not increase above the prevalence associated having only one of the conditions.

CONCLUSIONS

Future studies should consider including longitudinal designs and examine the extent to which important variables not included in this study, such as body image dissatisfaction (particularly among females), teasing, and discrimination may moderate the relationship among obesity and depressive and anxiety disorders in youth.

Association between body mass index and asthma among Japanese adults: risk within the normal weight range

BACKGROUND

Increasing amounts of data have shown that some Asian populations are more susceptible to increased weight and development of noncommunicable disease than Western populations. However, little is known about the association between increased weight, particularly within the normal range, and the development of asthma among Asian populations.

METHODS

To examine the association between increased body mass index (BMI) and asthma among Japanese adults, data from a nationwide population-based cross-sectional survey of asthma prevalence in Japan were analyzed (n = 22,962; age range 20-79 years). BMIs were classified into 7 categories considering WHO recommendations (cutoff points: 17.00, 18.50, 23.00, 25.00, 27.50 and 30.00), and the association between BMI and the prevalences of asthma as well as asthma symptoms were assessed by multivariate logistic regression.

RESULTS

The prevalences of obesity (BMI ≥ 30.00) in this population were relatively low (males 3.0%, females 2.3%). BMI categories of 25.00 or higher in both genders were significantly associated with an increased risk of asthma compared with the reference category (BMI 18.50-22.99). Even in females with a BMI of 23.00-24.99, the prevalence of asthma significantly increased (adjusted odds ratio 1.49, 95% confidence interval 1.16-1.92) compared with that in the reference category.

CONCLUSIONS

An increase in the prevalence of asthma among Japanese females starts at a BMI of 23.00, which was relatively lower than those reported from Western countries. This finding suggests that the Japanese population is likely to have asthma with a lesser degree of obesity than Western populations.

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.

Risk of asthma in adult twins with type 2 diabetes and increased body mass index

AIM

To examine the relationship between asthma, type 2 diabetes and increased body mass index (BMI) in adult twins.

METHODS

We performed record linkage between questionnaire-defined asthma and BMI, and hospital discharge diagnoses of type 2 diabetes in 34,782 Danish twins, 20-71 years of age.

RESULTS

The risk of asthma was increased in subjects with type 2 diabetes relative to nondiabetic subjects both in men (13.5%vs 7.5%), P = 0.001 and in women (16.6%vs 9.6%), P = 0.001. The result remained significant after adjustment for age, BMI, smoking, symptoms of chronic bronchitis, marital status and zygosity, men: OR = 1.70 (1.07-2.70), P = 0.026; women: OR = 1.88 (1.24-2.85), P = 0.003. In this analysis, BMI remained a highly significant predictor for asthma independently of diabetes status in women, P < 0.000 but not in men, P = 0.336. Significant positive genetic correlations were found between asthma and type 2 diabetes, 0.20 (0.01-0.40), P = 0.047; between asthma and BMI in women, 0.15 (0.07-0.22), P < 0.000; and between BMI and type 2 diabetes, 0.40 (0.29-0.43), P < 0.000.

CONCLUSIONS

Asthma, type 2 diabetes and increased BMI are strongly associated in adults, particularly in women. These results suggest a common aetiology for asthma and metabolic syndrome.

Gut microbiota, probiotics, and vitamin D: interrelated exposures influencing allergy, asthma, and obesity?

Current evidence supports a role for gut colonization in promoting and maintaining a balanced immune response in early life. An altered or less diverse gut microbiota composition has been associated with atopic diseases, obesity, or both. Moreover, certain gut microbial strains have been shown to inhibit or attenuate immune responses associated with chronic inflammation in experimental models. However, there has been no fully adequate longitudinal study of the relation between the neonatal gut microbiota and the development of allergic diseases (eg, atopic asthma) and obesity. The emergence of promising experimental studies has led to several clinical trials of probiotics (live bacteria given orally that allow for intestinal colonization) in human subjects. Probiotic trials thus far have failed to show a consistent preventive or therapeutic effect on asthma or obesity. Previous trials of probiotics have been limited by small sample size, short duration of follow-up, or lack of state-of-the art analyses of the gut microbiota. Finally, there is emerging evidence that the vitamin D pathway might be important in gut homeostasis and in signaling between the microbiota and the host. Given the complexity of the gut micriobiota, additional research is needed before we can confidently establish whether its manipulation in early life can prevent or treat asthma, obesity, or both.

Asthma and endocrine disorders: shared mechanisms and genetic pleiotropy

Asthma is a common inflammatory disease for which the cause is not yet known. Studies of the epidemiology and natural history of childhood asthma into adulthood demonstrate a change in gender prevalence with age. Hormones and inflammation may interact in asthma pathogenesis and determine its course. The same may be true for some endocrine disorders, including diabetes and obesity. Obesity plays a major role in the development of the metabolic syndrome and has been identified as an important risk factor for chronic diseases such as type 2 diabetes mellitus. The prevalence of asthma has paralleled the rise in obesity, suggesting that shared environmental factors could affect both conditions. In addition, endocrine diseases and asthma may share common genetic determinants. In the first part of this review we assess endocrine influences on asthma and overlaps between endocrine disorders and asthma while in the second part we explore the potential benefit of comparative genetic analyses between asthma and endocrine diseases.

Patterns of fetal and infant growth are related to atopy and wheezing disorders at age 3 years

BACKGROUND

Little is known about whether patterns of early growth are associated with altered respiratory and immune development. This study relates prenatal and infant growth patterns to wheeze and atopy at age 3&emsp14;years.

METHODS

Birth weight and length were measured in 1548 children born at term. Conditional fetal head and abdominal circumference growth velocities were calculated from antenatal ultrasound measurements. Conditional postnatal growth velocities were calculated from infant weight, length and adiposity data. Measures of size and conditional growth were related to parentally-reported infant and early childhood wheeze and to atopic status at age 3 years.

RESULTS

The risk of atopy increased by 46% per SD increase in abdominal circumference growth velocity from 11 to 19 weeks gestation but by 20% per SD decrease in abdominal growth velocity from 19 to 34 weeks (p=0.007 and p=0.011, respectively). The risk of atopic wheeze increased by 20% per SD decrease in 19-34-week abdominal growth (p=0.046). The risk of non-atopic wheeze increased by 10% per SD decrease in 11-19-week head circumference growth. Greater relative infant weight and adiposity gains were associated with both atopic and non-atopic wheeze.

CONCLUSIONS

A rapid growth trajectory during 11-19 weeks gestation followed by late gestation growth faltering is associated with atopy, suggesting that influences affecting fetal growth may also alter immune development. A lower early fetal growth trajectory is associated with non-atopic wheeze, possibly reflecting an association with smaller airways. An association between postnatal adiposity gain and wheeze may partly reflect prenatal influences that cause fetal growth to falter but are then followed by postnatal adiposity gain.

Analyses of shared genetic factors between asthma and obesity in children

BACKGROUND

Epidemiologic studies consistently show associations between asthma and obesity. Shared genetics might account for this association.

OBJECTIVE

We sought to identify genetic variants associated with both asthma and obesity.

METHODS

On the basis of a literature search, we identified genes from (1) genome-wide association studies (GWASs) of body mass index (BMI; n = 17 genes), (2) GWASs of asthma (n = 14), and (3) candidate gene studies of BMI and asthma (n = 7). We used GWAS data from the Childhood Asthma Management Program to analyze associations between single nucleotide polymorphisms (SNPs) in these genes and asthma (n = 359 subjects) and BMI (n = 537).

RESULTS

One top BMI GWAS SNP from the literature, rs10938397 near glucosamine-6-phosphate deaminase 2 (GNPDA2), was associated with both BMI (P = 4 x 10(-4)) and asthma (P = .03). Of the top asthma GWAS SNPs and the candidate gene SNPs, none was found to be associated with both BMI and asthma. Gene-based analyses that included all available SNPs in each gene found associations (P < .05) with both phenotypes for several genes: neuronal growth regulator 1 (NEGR1); roundabout, axon guidance receptor, homolog 1 (ROBO1); diacylglycerol kinase, gamma (DGKG); Fas apoptotic inhibitory molecule 2 (FAIM2); fat mass and obesity associated (FTO); and carbohydrate (N-acetylgalactosamine 4-0) sulfotransferase 8 (CHST8) among the BMI GWAS genes; interleukin 1 receptor-like 1 / interleukin 18 receptor 1 (IL1RL1/IL18R1), dipeptidyl-peptidase 10 (DPP10), phosphodiesterase 4D (PDE4D), V-myb myeloblastosis viral oncogene homolog (MYB), PDE10A, IL33, and especially protein tyrosine phosphatase, receptor type D (PTPRD) among the asthma GWAS genes; and protein kinase C, alpha (PRKCA) among the BMI and asthma candidate genes.

CONCLUSIONS

SNPs within several genes showed associations to BMI and asthma at a genetic level, but none of these associations were significant after correction for multiple testing. Our analysis of known candidate genes reveals some evidence for shared genetics between asthma and obesity, but other shared genetic determinants are likely to be identified in novel loci.

Impact of comorbidities on asthma

Asthma is a common and serious illness with suboptimal outcomes of care. Epidemiological studies show certain comorbidities occurring more frequently than expected with asthma, with some being associated with poor control and a differential response to therapy options. This review summarizes the evidence of clinically important comorbidities, focusing on the best-explored conditions, including rhinitis and rhinosinusitis, anxiety and depression, obesity, gastroesophageal reflux, smoking and dysfunctional breathing. The evidence of epidemiological and pathophysiological associations for these comorbidities is explored, and the practical therapeutic implications are considered. Comorbidities are important for clinicians treating asthma as they may be markers of patients at risk of poor outcomes, they may point to specific effective treatment options and they are important to researchers as possible confounding factors in clinical trials.

Obesity and asthma

Population-based studies have defined a significant, bidirectional, dose-dependent association between obesity and asthma. Obesity does not cause airflow obstruction, but can result in pulmonary restriction and a reduction in airway diameter, and that could contribute to airway hyper-responsiveness. Mouse models of asthma have demonstrated that obesity and adipokines can enhance airway hyper-responsiveness, airway inflammation, and allergic responses, but it is unclear whether obesity-associated inflammatory mechanisms are relevant in human asthma. Shared environmental and genetic factors are incompletely understood, but very likely to be relevant. Obese asthma appears to be a distinct and novel phenotype of asthma, associated with a reduction in lung volumes, lack of eosinophilic inflammation, altered response to asthma controller therapy, glucocorticoid resistance, and poor asthma control.

PRKCA: a positional candidate gene for body mass index and asthma

Asthma incidence and prevalence are higher in obese individuals. A potential mechanistic basis for this relationship is pleiotropy. We hypothesized that significant linkage and candidate-gene association would be found for body mass index (BMI) in a population ascertained on asthma affection status. Linkage analysis for BMI was performed on 657 subjects in eight Costa Rican families enrolled in a study of asthma. Family-based association studies were conducted for BMI with SNPs within a positional candidate gene, PRKCA. SNPs within PRKCA were also tested for association with asthma. Association studies were conducted in 415 Costa Rican parent-child trios and 493 trios participating in the Childhood Asthma Management Program (CAMP). Although only modest evidence of linkage for BMI was obtained for the whole cohort, significant linkage was noted for BMI in females on chromosome 17q (peak LOD = 3.39). Four SNPs in a candidate gene in this region (PRKCA) had unadjusted association p values < 0.05 for BMI in both cohorts, with the joint p value for two SNPs remaining significant after adjustment for multiple comparisons (rs228883 and rs1005651, joint p values = 9.5 x 10(-)(5) and 5.6 x 10(-)(5)). Similarly, eight SNPs had unadjusted association p values < 0.05 for asthma in both populations, with one SNP remaining significant after adjustment for multiple comparisons (rs11079657, joint p value = 2.6 x 10(-)(5)). PRKCA is a pleiotropic locus that is associated with both BMI and asthma and that has been identified via linkage analysis of BMI in a population ascertained on asthma.

Does leptin play a role in obesity-asthma relationship?

The increase of asthma has paralleled the rising obesity during the past decades. Obesity is characterized by the increase of leptin in the circulation. Leptin is an obesity gene product, and it can stimulate the production of pro-inflammatory mediators, such as tumor necrosis factor (TNF)-alpha, interleukin (IL)-6 and interferon (IFN)-gamma. There is a link between leptin and asthma, especially in children. It remains unclear however, if leptin is in the pathway of obesity-asthma relationship and if it plays a distinctive role in asthma in obese vs. non-obese subjects. Since leptin is in a positive feedback loop with the pro-inflammatory cytokines such as TNF-alpha, there is a possibility that leptin is involved as a regulatory rather than an etiologic mechanism of asthma development. Weight loss is associated with decreased circulating leptin concentration in children. Weight control program may need to be considered in the treatment of asthma in obese children.

A twin study of depression and migraine: evidence for a shared genetic vulnerability

OBJECTIVE

To determine if shared genetic or environmental vulnerabilities could underlie depression and migraine.

BACKGROUND

Depression and migraine headaches frequently coexist and their comorbidity may be due to shared etiologies.

METHODS

Female twins in the University of Washington Twin Registry responded to a mailed survey regarding their health history. Depression and migraine were determined by self-report of a physician's diagnosis. We used bivariate structural equation modeling to test for shared genetic, common environmental, and unique environmental components, and to estimate the magnitude of any shared component.

RESULTS

Among 758 monozygotic and 306 dizygotic female pairs, 23% reported depression and 20% reported migraine headaches. Heritability was estimated to be 58% (95% confidence interval: 48-67%) for depression and 44% (95% confidence interval: 32-56%) for migraine. Bivariate structural equation modeling estimated that 20% of the variability in depression and migraine headaches was due to shared genes and 4% was due to shared unique environmental factors.

CONCLUSIONS

The comorbidity of depression and migraine headache may be due in part to shared genetic risk factors. Research should focus attention on shared pathways, thereby making progress on 2 disease fronts simultaneously and perhaps providing clinicians with unified treatment strategies.

An interdisciplinary analysis of sex and gender in relation to the pathogenesis of bronchial asthma

BACKGROUND

An increasing number of studies confirm that pathogenesis and prevalence of bronchial asthma are age and sex dependent. Detailed physiological mechanisms of the changing sex ratios with age are not fully known, however, the gender (socio-cultural) factors are also imperative. Although multiple factors definitely influence the pathogenesis of asthma, only individual or few combinations of these have been investigated.

METHODS

The terms 'sex', 'gender' and plausible combinations of both were systematically researched in selected databases (Medline, Scopus) or other sources, including publications from January 2000 to June 2007. Generated articles were categorized, either as endogenous or exogenous factors influencing the pathogenesis of asthma, and divided into the following subgroups: genetic, immunological, hormonal, gynaecological, nutritional, and environmental parameters.

RESULTS

An increasing number of studies investigate the influence of sex and gender in the aetiology, therapy and prevention of asthma. While their results are still debatable, others regarding its initiation, perpetuation and cessation have been clarified. Recent insights into interactions at biomolecular and immunological levels greatly contribute to clarifying sex-specific influences. Despite occasional oversimplifications, a trend for explanations considering the complex interplay of different factors can be observed. This work is in line with this trend and offers explanation models from our point of view.

CONCLUSIONS

Some disagreements regarding the patho-physiology, diagnosis, treatment and prevention of asthma still prevail. Nevertheless, in order to better appreciate its complexity, openness to and persistent consideration for interdisciplinary as well as sex- and gender-related factors is required of the medical-research community in future investigations.

Adiposity, serum lipid levels, and allergic sensitization in Chinese men and women

BACKGROUND

Obesity and allergic diseases have increased dramatically in recent decades. Although adiposity has been associated with asthma, associations with allergic sensitization have been inconsistent.

OBJECTIVE

To examine the association of adiposity and lipid profiles with allergic sensitization.

METHODS

This study included 1187 rural Chinese twins (653 men) age 18 to 39 years, with skin prick tests, anthropometric and dual-energy x-ray absorptiometry-assessed adiposity measures, and lipid assessments. Allergic sensitization was defined as positive SPT to >/=1 allergen (9 foods and 5 aeroallergens tested). We applied sex-stratified generalized estimating equations to assess the association of adiposity and serum lipids with allergic sensitization, and structural equation models to estimate the genetic/environmental influences on any observed associations.

RESULTS

Men had lower percent body fat (% BF) (13.9% vs. 28.8%) but higher rates of allergic sensitization (56.2% vs 36.7%) than women. Men in the highest %BF quartile were 2.1 times more likely to be sensitized than the lowest quartile (95% CI, 1.3-3.5; P trend = .003). In men, the risk of allergic sensitization increased with high-density lipoprotein (HDL) <40 mg/dL (odds ratio = 4.0; 95% CI, 1.8-9.2) and higher low-density lipoprotein quartiles (P trend = .007). This appeared to be partially explained by shared genetic factors between serum lipid levels and allergic sensitization. In females, lower HDL was associated with increased risk of allergic sensitization.

CONCLUSION

In this relatively lean Chinese population, higher %BF, lower HDL and higher LDL were associated with greater risk of allergic sensitization, most notable in men. The observed associations among adiposity, serum lipids, and allergic sensitization in men appear to be partially explained by common genetic influences on these traits.

Etiological relationships in atopy: a review of twin studies

The genetics of asthma and atopy has been studied frequently in twin populations from various parts of the world. However, emphasis has been put on univariate analysis of questionnaire data, whereas clinical and intermediate traits only sporadically have been studied, especially in multivariate settings. This review focuses on multivariate twin studies of atopy and related traits. We conclude that the genetic liability to most atopic traits is significantly correlated but that trait-specific genes also play a role. Previous studies have estimated the genetic correlation between upper and lower respiratory allergic symptoms, that is, asthma and hay fever, to be between .47 and .95. Furthermore, atopic traits share a portion of their genetic determinants with other complex disorders like obesity and behavioral traits. A correlation of about .3 and .34 has been reported between genes associated with asthma and obesity, and between genes associated with asthma and depression, respectively. We emphasize that multivariate methods applied to twin studies, especially when genetic marker information is available, provide a valuable framework within which complex etiological mechanisms underlying atopy can be disentangled.

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.

Does the relationship between asthma and obesity differ by neighborhood?

BACKGROUND

Prior studies suggest that obesity may cause asthma. Obesity and asthma are prevalent in low-income urban neighborhoods, but the impact of obesity on asthma in such neighborhoods has not been examined.

METHODS

The New York City Department of Health and Mental Hygiene surveyed 6119 adults age 18-54 years in 2002. Obesity was defined as body mass index > or = 30 kg/m(2) and current asthma as physician diagnosed asthma plus recent symptoms. We calculated prevalence (risk) differences (RD) and population attributable risk percents (PAR%).

RESULTS

Obese individuals had a 2.0% (95% CI: 0.5%, 3.6%; p=0.01) higher risk of current asthma than normal weight individuals overall. Obesity was more common in low-income neighborhoods compared with middle-to-upper-income neighborhoods (23% vs. 14%, p<0.001), as was current asthma (6% vs. 4%, respectively, p=0.02). The risk of current asthma associated with obesity was similar in low-income (RD: 1.3%, 95% CI: -1.5%, 4.0%; p=0.36) and middle-to-upper-income neighborhoods (RD: 2.0%, 95% CI: 0.1%, 3.9%; p=0.04). The PAR% for asthma due to obesity was not greater in low-income (7.3%) than in middle-to-upper-income neighborhoods (7.7%).

CONCLUSIONS

It is unlikely that the excess asthma prevalence in urban low-income neighborhoods is disproportionately attributable to obesity. Instead, alternative causes of excess asthma should be sought.

Higher adiposity in infancy associated with recurrent wheeze in a prospective cohort of children

BACKGROUND

Few prospective data link early childhood adiposity with asthma-related symptoms.

OBJECTIVE

We sought to examine the associations of weight-for-length (WFL) at age 6 months with incidence of wheezing by age 3 years.

METHODS

We studied 932 children in a prospective cohort of children. The main outcome was recurrent wheezing, which was defined as parents' report of wheezing between 2 and 3 years of age plus wheezing in either year 1 or 2 of life. Secondary outcomes included any wheezing from 6 months to 3 years and current asthma. We used multiple logistic regression to examine associations of 6-month WFL z scores with these outcomes.

RESULTS

At 6 months, the infants' mean WFL z score was 0.68 (SD, 0.94; range -2.96 to 3.24). By age 3 years, 14% of children had recurrent wheezing. After adjustment for a variety of potential confounders, we found that each 1-unit increment in 6-month WFL z score was associated with greater odds of recurrent wheezing (odds ratio [OR], 1.46; 95% CI, 1.11-1.91) and any wheezing (OR, 1.23; 95% CI, 1.03-1.48). We observed a weaker association between 6-month WFL z score and current asthma (OR, 1.22; 95% CI, 0.94-1.59).

CONCLUSION

Infants with higher WFL z scores at 6 months of age had a greater risk of recurrent wheezing by age 3 years. It is unclear whether the relationship of infant adiposity and early-life wheeze extends to allergic asthma or wheeze that can persist into later childhood. Our findings suggest that early interventions to prevent excess infant adiposity might help reduce children's risk of asthma-related symptoms.

Asthma and obesity: common early-life influences in the inception of disease

The respective prevalences of both asthma and obesity have seen a significant rise in the past few decades. Although the association between these 2 conditions has been found in many studies from different areas around the world, the exact mechanisms for how this association arises remains unresolved. Because both asthma and obesity appear to have their beginnings in early childhood, common exposures that predispose individuals to both these conditions may explain how they are associated. These exposures include common genetic predictors, prenatal exposure to specific nutrients and overall maternal nutrition, patterns of colonization of the neonatal and infant gut, birth weight and infant weight gain, sedentary behaviors, and levels of adipokines in early life.

Genome-wide linkage analysis for circulating levels of adipokines and C-reactive protein in the Quebec family study (QFS)

Adipose tissue synthesizes and secretes a wide range of biologically active molecules considered as inflammatory markers whose dysregulation in obesity plays a role in the development of insulin resistance and vascular disorders. Thus, finding genes that influence circulating levels of inflammatory biomarkers may provide insights into the genetic determinants of obesity-related metabolic diseases. We performed linkage analyses for fasting plasma levels of adiponectin, C-reactive protein (CRP), interleukin-6 (IL-6) and tumor-necrosis factor-alpha (TNF-alpha) in 764 subjects enrolled in the Quebec family study (QFS). A maximum of 393 pairs of siblings from 211 nuclear families were available for analyses. A total of 443 markers spanning the 22 autosomal chromosomes with an average inter-marker distance of 6.24 Mb were genotyped. Linkage was tested using both allele-sharing (SIBPAL) and variance component linkage methods (MERLIN). We showed suggestive evidence of linkage for plasma adiponectin levels on chromosome 15q21.1 [D15S659; logarithm of the odds (LOD) score = 2.23], 3q13.33 (D3S3023; LOD = 2.09), 20q13.2 (D20S197; LOD = 1.96) and 14q32.2 (D14S1426; LOD = 1.79). Evidence of linkage (SIBPAL) was also found for CRP on 12p11.23 (P = 0.001) and 12q15 (P = 0.0005) and for IL-6 on 14q12 (P = 0.002). None of these linkages remained significant after adjustment for body mass index. No evidence of linkage was found for TNF-alpha plasma levels. These results suggest that several QTLs can influence plasma levels of adiponectin and CRP, partly via their effects on adiposity.

The link between the epidemics of obesity and allergic diseases: does obesity induce decreased immune tolerance?

There is increasing epidemiological evidence that obesity increases the risk of asthma, atopic, and autoimmune diseases. We hypothesize that the increase in these diseases is caused, at least in part, by decreased immunological tolerance as a consequence of immunological changes induced by adipokines (e.g. leptin and adiponectin) and cytokines [e.g. interleukin 6 (IL6) and tumor necrosis factor alpha (TNFalpha)] secreted by white adipose tissue. The increasing body weight increases the levels of circulating IL6, leptin, and TNFalpha. IL6 and leptin down-regulate the activity of regulatory T-lymphocytes (Tregs). Additionally, adiponectin, which decreases with increasing obesity, down-regulates the secretion of IL10 from macrophages and adipocytes. These changes in IL6, leptin, and IL10 decrease the regulatory effect of Tregs resulting in decreased immunological tolerance to antigens. In pregnant women, these obesity-induced immunological changes might be transmitted to the fetus by epigenetic inheritance thereby increasing the risk of atopic disease. We propose that obesity results in immunological changes resulting in decreased immunological tolerance to antigens and skewing of the immune system towards a Th2 cytokine profile increasing the risk of allergy and other immune-mediated diseases. Furthermore, this hypothesis offers a unifying explanation for the observation that older siblings appear to confer protection against atopic diseases, preeclampsia, and certain autoimmune diseases. More studies are definitely needed to explore further the immunological effects of obesity and its possible effects on allergic disease.

Association between obesity and asthma in a twin cohort

BACKGROUND

Obesity is linked to asthma in a yet poorly understood manner. We examined the relationship between obesity and asthma in a population-based sample of twins.

METHODS

From the cohorts born between 1953 and 1982, who were enrolled in The Danish Twin Registry, a total of 29 183 twin individuals participated in a nationwide questionnaire study, where data on height, weight and asthma were collected. Latent factor models of genetic and environmental effects were fitted using maximum likelihood methods.

RESULTS

The age-adjusted risk of asthma was increased both in obese females, OR = 1.96 (1.45-2.64), P < or = 0.001 and in obese males, OR = 1.59 (1.08-2.33), P = 0.02. According to best-fitting models, the heritability for obesity was 81% in males and 92% in females, whereas the heritability for asthma was 78% and 68% in males and females respectively. The age-adjusted genetic liabilities to obesity and asthma were significantly correlated only in females, r = 0.28 (0.16-0.38).

CONCLUSIONS

Obese subjects have an increased risk for asthma, which in females seems partly because of common genes.

The asthma-obesity link in childhood: open questions, complex evidence, a few answers only

Obesity and asthma are public health priorities in developed countries. Genes which may contribute to the control of both conditions include those encoding for the beta2-adrenergic receptor, tumour necrosis factor-alpha (TNF-alpha) and the insulin-like growth factor 1 (IGF-1). Prospective studies consistently supported a link between obesity and reported wheezing or asthma diagnosis in children. However, there are still no clear explanations for such a link. On one hand, overweight asthmatic children may perceive their asthma as worse. On the other hand, atopic sensitization and bronchial hyper-reactivity do not explain the observed associations. After puberty, the association between asthma and obesity tends to be stronger in girls than in boys. It is conceivable that severe obesity in adolescent females may aggravate asthma through mechanisms different from those linking prepubertal obesity to unremitting asthma in males. Future studies should therefore address multiple age- and gender-specific hypotheses about the mechanisms that link obesity to asthma throughout childhood.

Efeito do índice de massa corpórea na gravidade da asma e na reatividade brônquica induzida pelo exercício em crianças asmáticas com sobrepeso e obesas

OBJETIVO: Analisar a relação entre o grau de obesidade ou sobrepeso medido pelo índice de massa corpórea (IMC) de crianças e adolescentes asmáticos com a gravidade clínica e funcional da doença e com a intensidade do broncoespasmo induzido pelo exercício (BIE). MÉTODOS: 20 pacientes com idade entre seis e 18 anos, asma persistente e sobrepeso ou obesidade foram submetidos ao teste padronizado com exercício em bicicleta ergométrica e avaliação seriada dos parâmetros espirométricos, realizada aos 3, 6, 10, 15, 20 e 30 minutos após o exercício. BIE foi definido como a queda do volume expiratório forçado no primeiro segundo (VEF1) >10% e/ou do fluxo médio expiratório forçado medido entre 25 e 75% da capacidade vital forçada (FEF25-75%) >26% em relação aos valores pré-teste. Foram avaliadas as freqüências de positividade do teste e as maiores quedas de VEF1 e FEF25-75% após o término do exercício. RESULTADOS: A gravidade clínica da asma foi considerada leve, moderada e grave em dez, cinco e cinco pacientes, respectivamente. Houve BIE em 50% dos pacientes testados. Não houve correlação significativa entre os seguintes parâmetros confrontados: valores de IMC e valores basais do VEF1 e FEF25-75% percentuais em relação ao previsto; valores do IMC e as maiores quedas do VEF1 e do FEF25-75% em relação aos valores basais; valores do IMC e gravidade da asma. A melhor correlação ocorreu entre o IMC e as maiores quedas do FEF25-75% em relação ao basal. CONCLUSÕES: O IMC não teve influência no grau de hiperresponsividade brônquica induzida pelo exercício em crianças asmáticas com sobrepeso e obesas e na gravidade da obstrução basal medida pelo VEF1 e FEF25-75%.

Age and gender specific lung function predictive equations provide similar predictions for both a twin population and a general population from age 6 through adolescence

BACKGROUND

There have been numerous studies of asthma in twins, but no study has evaluated whether lung function predictive models yield similar results between twin and general populations. We sought to evaluate this in late childhood and adolescent subjects.

METHODS

We generated cross-sectional, sex- and age-specific regression models of FEV(1), and FVC, in a community-based cohort of 3140 healthy, non-smoking Chinese twins using generalized estimating equations to adjust for correlations within twin pairs. We applied the model to a healthy non-smoking general population cohort of 2187 subjects from the same region, and compared %predicted FEV(1) and FVC values between the two populations.

RESULTS

Stratified by age and sex, the associations of height with FEV(1) or FVC varied by age group. During the adolescent growth spurt (age 13 for girls and ages 14-16 for boys), the associations of height with FEV(1) or FVC were nonlinear and greater than that seen at other ages. During adolescence, FEV(1) and FVC for a given height increased with age. The percent predicted values of FEV(1) and FVC in the twin population were similar to that of the general population.

CONCLUSIONS

Twin and general populations have similar patterns of lung function change over middle childhood and adolescence. Similar equations may be used to estimate percent predicted values. Finally, a single prediction equation cannot completely describe patterns of lung function from childhood through adolescence due to puberty related changes.

University of Washington Twin Registry: construction and characteristics of a community-based twin registry

The University of Washington Twin Registry is a community-based registry of twins identified from the Washington State Department of Licensing. A fortuitous quirk in the Washington State drivers' license and identification number assignment, and collaborative Washington State laws, permitted us to build a statewide registry. Since obtaining approval from the Washington State Attorney General, the Washington State Department of Licensing has provided us with information on over 26,000 newly licensed twins, and we continue to receive computerized records on approximately 80 new twins per week. The University of Washington Twin Registry is assembled by mailing each twin a recruitment packet that includes an information sheet, brochure, brief survey, and nominal gift. Once both members of a twin pair have completed the packet, the pair is enrolled in the registry. As of June 2006, 2287 adult twin pairs have enrolled in the registry; about one half of these are female-female pairs. Among all twins, the average age is 32 years. Based on self-report, 52% of twins are monozygotic, 42% are dizygotic, and zygosity on 6% cannot yet be determined. We also have instituted a clinical protocol for collecting additional data and DNA from all twins participating in research studies requiring an in-person visit. The registry has established policies and procedures to protect the confidentiality of twin data and guidelines for the use of the registry by investigators. Plans for the further growth of the University of Washington Twin Registry and its use are discussed.

Obesity and asthma: implications for treatment

PURPOSE OF REVIEW

Epidemiological data as well as data from mouse models of asthma indicate a relationship between obesity and asthma. The purpose of this review is to evaluate recent data addressing this relationship and its biological basis, and to evaluate the implications of these data for treatment.

RECENT FINDINGS

Obesity increases the prevalence, incidence, and possibly severity of asthma, while weight loss in the obese improves asthma outcomes. Obesity also influences asthma control and the response to standard asthma therapeutics. Moreover, obese mice exhibit innate airway hyperresponsiveness and increased responses to common asthma triggers. The biological basis for the relationship between obesity and asthma may be the result of common etiologies, comorbidities, effects of obesity on lung volume, or adipokines such as tumor necrosis factor alpha, leptin, and adiponectin.

SUMMARY

Understanding the mechanistic basis for the relationship between obesity and asthma may lead to new therapeutic strategies for treatment of this susceptible population.

Advances in adult asthma 2006: its risk factors, course, and management

This Advances article updates our understanding of risk factors for asthma and its course and management. Studies relevant to clinical practice are discussed, with special attention to their clinical research methods.

Excessive body weight is associated with additional loss of quality of life in children with asthma

BACKGROUND

Asthma and excessive body weight frequently coexist, whereas the exact relationship between the 2 diseases is unknown.

OBJECTIVE

To study whether asthma combined with excessive body weight has a greater effect on quality of life in children than the separate effects of asthma or excessive body weight alone.

METHODS

In a cross-sectional design, 1758 school children (age 7-10 years) participated: 4 study groups were composed of children with asthma and with/without excessive body weight, and healthy controls with/without excessive body weight. Diagnosis of asthma was defined by either a doctor's diagnosis or by core questions of the International Study of Asthma and Allergies in Childhood questionnaire in combination with either reversible airway obstruction or bronchial hyperresponsiveness. Excessive body weight was defined by using international cutoff points for body mass index. Quality of life was evaluated by the Pediatric Asthma Quality of Life Questionnaire.

RESULTS

For all domains of quality of life, children with both asthma and excessive body weight had lower scores than children with either asthma alone or excessive body weight alone. Compared with healthy controls, the score was 25% lower in children with asthma and excessive body weight, 14% lower in children with asthma and normal weight, and only 1% lower in overweight controls.

CONCLUSION

Excessive body weight is associated with an additional decrease in quality of life in children with asthma.

CLINICAL IMPLICATIONS

Clinicians should be aware of the interaction between asthma and excessive body weight and the effect on quality of life and should give extra attention to children with both conditions.

Obesity and asthma

Asthma and obesity are prevalent disorders, each with a significant public health impact, and a large and growing body of literature suggests an association between the two. The systemic inflammatory milieu in obesity leads to metabolic and cardiovascular complications, but whether this environment alters asthma risk or phenotype is not yet known. Animal experiments have evaluated the effects of leptin and obesity on airway inflammation in response to both allergic and nonallergic exposures and suggest that airway inflammatory response is enhanced by both endogenous and exogenous leptin. Cross-sectional and prospective cohort studies of humans have shown a modest overall increase in asthma incidence and prevalence in the obese, although body mass index does not appear be a significant modifier of asthma severity. Studying the obesity-asthma relationship in large cohorts, in which self-reports are frequently used to ascertain the diagnosis of asthma, has been complicated by alterations in pulmonary physiology caused by obesity, which may lead to dyspnea or other respiratory symptoms but do not fulfill accepted physiologic criteria for asthma. Recent investigations toward elucidating a shared genetic basis for these two disorders have identified polymorphisms in specific regions of chromosomes 5q, 6p, 11q13, and 12q, each of which contains one or more genes encoding receptors relevant to asthma, inflammation, and metabolic disorders, including the beta(2)-adrenergic receptor gene ADRB2 and the glucocorticoid receptor gene NR3C1. Further research is warranted to synthesize these disparate observations into a cohesive understanding of the relationship between obesity and asthma.