Rationale: Vitamin D insufficiency (a serum 25(OH)D <30 ng/ml) has been associated with severe asthma exacerbations, but this could be explained by underlying racial ancestry or disease severity. Little is known about vitamin D and asthma in Puerto Ricans.
Objectives: To examine whether vitamin D insufficiency is associated with severe asthma exacerbations in Puerto Rican children, independently of racial ancestry, atopy, and time outdoors.
Methods: A cross-sectional study was conducted of 560 children ages 6–14 years with (n = 287) and without (n = 273) asthma in San Juan, Puerto Rico. We measured plasma vitamin D and estimated the percentage of African racial ancestry among participants using genome-wide genotypic data. We tested whether vitamin D insufficiency is associated with severe asthma exacerbations, lung function, or atopy (greater than or equal to one positive IgE to allergens) using logistic or linear regression. Multivariate models were adjusted for African ancestry, time outdoors, atopy, and other covariates.
Measurements and Main Results: Vitamin D insufficiency was common in children with (44%) and without (47%) asthma. In multivariate analyses, vitamin D insufficiency was associated with higher odds of greater than or equal to one severe asthma exacerbation in the prior year (odds ratio [OR], 2.6; 95% confidence interval [CI], 1.5–4.9; P = 0.001) and atopy, and a lower FEV1/FVC in cases. After stratification by atopy, the magnitude of the association between vitamin D insufficiency and severe exacerbations was greater in nonatopic (OR, 6.2; 95% CI, 2–21.6; P = 0.002) than in atopic (OR, 2; 95% CI, 1–4.1; P = 0.04) cases.
Conclusions: Vitamin D insufficiency is associated with severe asthma exacerbations in Puerto Rican children, independently of racial ancestry, atopy, or markers of disease severity or control.
vitamin D; asthma exacerbations; Puerto Ricans; childhood
Vitamin D deficiency and asthma are common conditions that share risk factors such as African American ethnicity, inner-city residence, and obesity. This review provides a critical examination of current experimental and epidemiologic evidence of a causal association between vitamin D status and asthma or asthma morbidity, including potential protective mechanisms such as antiviral effects and enhanced steroid responsiveness. Because most published epidemiologic studies of vitamin D and asthma or asthma morbidity are observational, a recommendation for or against vitamin D supplementation as preventive or secondary treatment for asthma is not advisable and must await results of ongoing clinical trials. Should these trials confirm a beneficial effect of vitamin D, others will be needed to assess the role of vitamin D supplementation to prevent or treat asthma in different groups such as infants, children of school age, and ethnic minorities.
vitamin D; asthma; asthma morbidity
Rationale: The epidemiology of cigarette smoking–related chronic obstructive pulmonary disease (COPD) is not well characterized in Hispanics in the United States. Understanding how ethnicity influences COPD is important for a number of reasons, from informing public health policies to dissecting the genetic and environmental effects that contribute to disease.
Objectives: The present study assessed differences in risk between Hispanics and non-Hispanic whites for longitudinal and cross-sectional COPD phenotypes. Genetic ancestry was used to verify findings based on self-reported ethnicity. Hispanics in New Mexico are primarily differentiated from non-Hispanic whites by their proportion of Native American ancestry.
Methods: The study was performed in a New Mexican cohort of current and former smokers. Self-reported Hispanic and non-Hispanic white ethnicity was validated by defining genetic ancestry proportions at the individual level using 48 single-nucleotide polymorphism markers. Self-reported ethnicity and genetic ancestry were independently used to assess associations with cross-sectional and longitudinal measures of lung function. Multivariable models were adjusted for indicators of smoking behavior.
Measurements and Main Results: Self-reported Hispanic ethnicity was significantly associated with lower odds of COPD (odds ratio, 0.49; 95% confidence interval, 0.35–0.71; P = 0.007), and this protection was validated by the observation that Hispanic smokers have reduced risk of rapid decline in lung function (odds ratio, 0.48; 95% confidence interval, 0.30–0.78; P = 0.003). Similar findings were noted when Native American genetic ancestry proportions were used as predictors instead of self-report of Hispanic ethnicity.
Conclusions: Hispanic ethnicity is inversely associated with cross-sectional and longitudinal spirometric COPD phenotypes even after adjustment for smoking. Native American genetic ancestry may account for this “Hispanic protection.”
Rationale: Animal models demonstrate that aberrant gene expression in utero can result in abnormal pulmonary phenotypes.
Objectives: We sought to identify genes that are differentially expressed during in utero airway development and test the hypothesis that variants in these genes influence lung function in patients with asthma.
Methods: Stage 1 (Gene Expression): Differential gene expression analysis across the pseudoglandular (n = 27) and canalicular (n = 9) stages of human lung development was performed using regularized t tests with multiple comparison adjustments. Stage 2 (Genetic Association): Genetic association analyses of lung function (FEV1, FVC, and FEV1/FVC) for variants in five differentially expressed genes were conducted in 403 parent-child trios from the Childhood Asthma Management Program (CAMP). Associations were replicated in 583 parent-child trios from the Genetics of Asthma in Costa Rica study.
Measurements and Main Results: Of the 1,776 differentially expressed genes between the pseudoglandular (gestational age: 7–16 wk) and the canalicular (gestational age: 17–26 wk) stages, we selected 5 genes in the Wnt pathway for association testing. Thirteen single nucleotide polymorphisms in three genes demonstrated association with lung function in CAMP (P < 0.05), and associations for two of these genes were replicated in the Costa Ricans: Wnt1-inducible signaling pathway protein 1 with FEV1 (combined P = 0.0005) and FVC (combined P = 0.0004), and Wnt inhibitory factor 1 with FVC (combined P = 0.003) and FEV1/FVC (combined P = 0.003).
Conclusions: Wnt signaling genes are associated with impaired lung function in two childhood asthma cohorts. Furthermore, gene expression profiling of human fetal lung development can be used to identify genes implicated in the pathogenesis of lung function impairment in individuals with asthma.
asthma; lung development; lung function; genetic variation; gene expression
Rationale: Association studies have implicated many genes in asthma pathogenesis, with replicated associations between single-nucleotide polymorphisms (SNPs) and asthma reported for more than 30 genes. Genome-wide genotyping enables simultaneous evaluation of most of this variation, and facilitates more comprehensive analysis of other common genetic variation around these candidate genes for association with asthma.
Objectives: To use available genome-wide genotypic data to assess the reproducibility of previously reported associations with asthma and to evaluate the contribution of additional common genetic variation surrounding these loci to asthma susceptibility.
Methods: Illumina Human Hap 550Kv3 BeadChip (Illumina, San Diego, CA) SNP arrays were genotyped in 422 nuclear families participating in the Childhood Asthma Management Program. Genes with at least one SNP demonstrating prior association with asthma in two or more populations were tested for evidence of association with asthma, using family-based association testing.
Measurements and Main Results: We identified 39 candidate genes from the literature, using prespecified criteria. Of the 160 SNPs previously genotyped in these 39 genes, 10 SNPs in 6 genes were significantly associated with asthma (including the first independent replication for asthma-associated integrin β3 [ITGB3]). Evaluation of 619 additional common variants included in the Illumina 550K array revealed additional evidence of asthma association for 15 genes, although none were significant after adjustment for multiple comparisons.
Conclusions: We replicated asthma associations for a minority of candidate genes. Pooling genome-wide association study results from multiple studies will increase the power to appreciate marginal effects of genes and further clarify which candidates are true “asthma genes.”
asthma; replication; single-nucleotide polymorphism; integrin β3; association
Rationale: Maternal vitamin D intake during pregnancy has been inversely associated with asthma symptoms in early childhood. However, no study has examined the relationship between measured vitamin D levels and markers of asthma severity in childhood.
Objectives: To determine the relationship between measured vitamin D levels and both markers of asthma severity and allergy in childhood.
Methods: We examined the relation between 25-hydroxyvitamin D levels (the major circulating form of vitamin D) and markers of allergy and asthma severity in a cross-sectional study of 616 Costa Rican children between the ages of 6 and 14 years. Linear, logistic, and negative binomial regressions were used for the univariate and multivariate analyses.
Measurements and Main Results: Of the 616 children with asthma, 175 (28%) had insufficient levels of vitamin D (<30 ng/ml). In multivariate linear regression models, vitamin D levels were significantly and inversely associated with total IgE and eosinophil count. In multivariate logistic regression models, a log10 unit increase in vitamin D levels was associated with reduced odds of any hospitalization in the previous year (odds ratio [OR], 0.05; 95% confidence interval [CI], 0.004–0.71; P = 0.03), any use of antiinflammatory medications in the previous year (OR, 0.18; 95% CI, 0.05–0.67; P = 0.01), and increased airway responsiveness (a ≤8.58-μmol provocative dose of methacholine producing a 20% fall in baseline FEV1 [OR, 0.15; 95% CI, 0.024–0.97; P = 0.05]).
Conclusions: Our results suggest that vitamin D insufficiency is relatively frequent in an equatorial population of children with asthma. In these children, lower vitamin D levels are associated with increased markers of allergy and asthma severity.
Rationale: Polymorphisms in the gene for transforming growth factor-β1 (TGFB1) have been associated with asthma, but not with airway responsiveness or disease exacerbations in subjects with asthma.
Objectives: To test for association between single nucleotide polymorphisms (SNPs) in TGFB1 and markers of asthma severity in childhood.
Methods: We tested for the association between nine SNPs in TGFB1 and indicators of asthma severity (lung function, airway responsiveness, and disease exacerbations) in two cohorts: 416 Costa Rican parent-child trios and 465 families of non-Hispanic white children in the Childhood Asthma Management Program (CAMP). We also tested for the interaction between these polymorphisms and exposure to dust mite allergen on asthma severity.
Measurements and Main Results: The A allele of promoter SNP rs2241712 was associated with increased airway responsiveness in Costa Rica (P = 0.0006) and CAMP (P = 0.005), and the C allele of an SNP in the promoter region (rs1800469) was associated with increased airway responsiveness in both cohorts (P ≤ 0.01). Dust mite exposure modified the effect of the C allele of exonic SNP rs1800471 on airway responsiveness (P = 0.03 for interactions in both cohorts). The T allele of a coding SNP (rs1982073) was associated with a reduced risk of asthma exacerbations in Costa Rica (P = 0.009) and CAMP (P = 0.005). Dust mite exposure also significantly modified the effect of the A allele of the promoter SNP rs2241712 on asthma exacerbations in both cohorts.
Conclusions: SNPs in TGFB1 are associated with airway responsiveness and disease exacerbations in children with asthma. Moreover, dust mite exposure may modify the effect of TGFB1 SNPs on airway responsiveness and asthma exacerbations.
airway responsiveness; asthma; dust mite allergen; single nucleotide polymorphisms; transforming growth factor-β1
Rationale: Puerto Ricans have the highest prevalence of and morbidity from asthma of all ethnic groups in the United States. One potential contributor to the high burden of asthma in Puerto Rican children is exposure to stress and violence.
Objectives: To examine whether exposure to stress and violence is associated with an increased risk of asthma among Puerto Rican children.
Methods: This study was a population-based probability sample of children in the San Juan and Caguas metropolitan areas in Puerto Rico. Information was collected in a household survey of 1,213 children and their primary caretakers.
Measurements and Main Results: The prevalence of lifetime physician-diagnosed asthma was 39.6%. In the year before the survey, 14% of children had witnessed an act of violence, 7% had been victims of violence, and 6% had been victims of physical or sexual abuse. Although stressful life events and exposure to neighborhood violence were not associated with asthma, a history of physical or sexual abuse was associated with approximately twice the odds of current asthma (odd ratio [OR], 2.52; 95% confidence interval [CI], 1.27–5.00), health care use for asthma (OR, 1.95; 95% CI, 0.96–3.96), and medication use for asthma (OR, 2.35; 95% CI, 1.05–5.26).
Conclusions: Physical or sexual abuse is associated with high asthma morbidity among Puerto Rican children. To our knowledge, this is the first report of an association between childhood abuse and asthma. Our findings highlight the importance of screening for asthma among victims of childhood abuse, and to be aware of the possibility of physical or sexual abuse among children with asthma.
asthma; children; stress; violence; abuse
Rationale: The basis for gender influences on allergen-specific IgEs is unclear.
Objectives: To perform regular and sex-stratified genomewide linkage analyses of IgE to each of three allergens (Ascaris lumbricoides, Blatella germanica [German cockroach]), and Dermatophagoides pteronyssinus [dust mite]) and to conduct an association study of a candidate gene in a linked genomic region.
Methods: Genomewide linkage analyses of allergen-specific IgEs were conducted in 653 members of eight large families of Costa Rican children with asthma. An analysis of the association between single-nucleotide polymorphisms in thymic stromal lymphopoietin (TSLP) and IgE measurements was conducted in 417 parent–child trios in Costa Rica. Significant results were replicated in 470 families of white children in the Childhood Asthma Management Program (CAMP).
Measurements and Main Results: Among all subjects, there was suggestive evidence of linkage (LOD ⩾ 2.72) to IgE to Ascaris (on chromosome 7q) and IgE to dust mite (on chromosomes 7p and 12q). In a sex-stratified analysis, there was significant evidence of linkage to IgE to cockroach on chromosome 5q23 (peak LOD, 4.14 at 127 cM) in female subjects. TSLP is located within the 1.5 LOD-unit support interval for this linkage peak and has female-specific effects on lung disease in mice. In a sex-stratified analysis, the T allele of single-nucleotide polymorphism rs2289276 in TSLP was associated with reductions in IgE to cockroach (in Costa Rican girls) and total IgE (in girls in Costa Rica and in CAMP; P value for sex-by-genotype interaction, <0.01 in both studies).
Conclusions: Consistent with findings in murine models, a variant in TSLP may have female-specific effects on allergic phenotypes.
immunoglobulin E; linkage; thymic stromal lymphopoietin; single-nucleotide polymorphisms
Hispanics are individuals whose ancestry can be traced to Spain and/or areas previously under Spanish control (e.g., Mexico, Puerto Rico). They are a rapidly growing subset of the population of the United States and are quite diverse in their racial ancestry, country of origin, area of residence, socioeconomic status, tobacco use, and access to health care. Current evidence suggests that the prevalence and morbidity of chronic obstructive pulmonary disease (COPD) vary widely among Hispanic-American nations, with similar but limited findings among Hispanic subgroups in the United States. Potential reasons for such variation include differences in racial ancestry and genetic susceptibility, exposure to tobacco smoke and/or biomass smoke, access to health care, and disease management. Future studies of COPD in Hispanics should include large samples of subgroups that are well defined with regard to self-reported ethnicity, country of origin, area of residence, tobacco use, and socioeconomic status. Areas that need to be carefully examined include validation of COPD diagnoses for epidemiologic studies (e.g., by radiologic assessment), COPD in high-risk groups (e.g., Puerto Ricans), impact of biomass smoke (in rural areas) and air pollution (in urban areas) on COPD morbidity, effects of migration and acculturation on COPD prevalence and morbidity among Hispanic subgroups in the United States, development of reference values for spirometry, smoking cessation, and overcoming barriers to management. Public health measures, such as effective smoking prevention and cessation programs, reduction of air pollution and exposure to biomass smoke, and improved access to health care, would help reduce the burden of COPD among Hispanics in the United States and Latin America.
chronic obstructive pulmonary disease; genetics; Hispanics; risk factors
Rationale: Replication of gene-disease associations has become a requirement in complex trait genetics.
Objectives: In studies of childhood asthma from two different ethnic groups, we attempted to replicate associations with five potential asthma susceptibility genes previously identified by positional cloning.
Methods: We analyzed two family-based samples ascertained through an asthmatic proband: 497 European-American children from the Childhood Asthma Management Program and 439 Hispanic children from the Central Valley of Costa Rica. We genotyped 98 linkage disequilibrium–tagging single-nucleotide polymorphisms (SNPs) in five genes: ADAM33, DPP10, GPR154 (HUGO name: NPSR1), HLA-G, and the PHF11 locus (includes genes SETDB2 and RCBTB1). SNPs were tested for association with asthma and two intermediate phenotypes: airway hyperresponsiveness and total serum immunoglobulin E levels.
Measurements and Main Results: Despite differing ancestries, linkage disequilibrium patterns were similar in both cohorts. Of the five evaluated genes, SNP-level replication was found only for GPR154 (NPSR1). In this gene, three SNPs were associated with asthma in both cohorts, although the opposite alleles were associated in either study. Weak evidence for locus-level replication with asthma was found in the PHF11 locus, although there was no overlap in the associated SNP across the two cohorts. No consistent associations were observed for the three other genes.
Conclusions: These results provide some further support for the role of genetic variation in GPR154 (NPSR1) and PHF11 in asthma susceptibility and also highlight the challenges of replicating genetic associations in complex traits such as asthma, even for genes identified by linkage analysis.
bronchial hyperreactivity; immunoglobulin E; linkage disequilibrium; NPSR1; single-nucleotide polymorphism
Rationale: Patients with severe chronic obstructive pulmonary disease (COPD) may have varying levels of disability despite similar levels of lung function. This variation may reflect different COPD subtypes, which may have different genetic predispositions.
Objectives: To identify genetic associations for COPD-related phenotypes, including measures of exercise capacity, pulmonary function, and respiratory symptoms.
Methods: In 304 subjects from the National Emphysema Treatment Trial, we genotyped 80 markers in 22 positional and/or biologically plausible candidate genes. Regression models were used to test for association, using a test–replication approach to guard against false-positive results. For significant associations, effect estimates were recalculated using the entire cohort. Positive associations with dyspnea were confirmed in families from the Boston Early-Onset COPD Study.
Results: The test–replication approach identified four genes—microsomal epoxide hydrolase (EPHX1), latent transforming growth factor-β binding protein-4 (LTBP4), surfactant protein B (SFTPB), and transforming growth factor-β1 (TGFB1)—that were associated with COPD-related phenotypes. In all subjects, single-nucleotide polymorphisms (SNPs) in EPHX1 (p ⩽ 0.03) and in LTBP4 (p ⩽ 0.03) were associated with maximal output on cardiopulmonary exercise testing. Markers in LTBP4 (p ⩽ 0.05) and SFTPB (p = 0.005) were associated with 6-min walk test distance. SNPs in EPHX1 were associated with carbon monoxide diffusing capacity (p ⩽ 0.04). Three SNPs in TGFB1 were associated with dyspnea (p ⩽ 0.002), one of which replicated in the family study (p = 0.02).
Conclusions: Polymorphisms in several genes seem to be associated with COPD-related traits other than FEV1. These associations may identify genes in pathways important for COPD pathogenesis.
dyspnea; emphysema; exercise tolerance; genetic association; pulmonary function tests
Hispanic individuals trace their ancestry to countries that were previously under Spanish rule, including Mexico, large parts of Central and South America, and some Caribbean islands. Most—but not all—Hispanics have variable proportions of European, Amerindian, and African ancestry. Hispanics are diverse with regard to many factors, including racial ancestry, country of origin, area of residence, socioeconomic status, education, and access to health care. Recent findings suggest that there is marked variation in the prevalence, morbidity, and mortality of asthma in Hispanics in the United States and in Hispanic America. The reasons for differences in asthma and asthma morbidity among and within Hispanic subgroups are poorly understood but are likely due to the interaction between yet-unidentified genetic variants and other factors, including environmental tobacco smoke exposure, obesity, allergen exposure, and availability of health care. Barriers to optimal management of asthma in Hispanics in the United States and in Hispanic America include inadequate access to health care, suboptimal use of antiinflammatory medications, and lack of reference values for spirometric measures of lung function in many subgroups (e.g., Puerto Ricans). Future studies of asthma in Hispanics should include large samples of subgroups that are well characterized with regard to self-reported ethnicity, country of origin, place of birth, area of residence, and indicators of socioeconomic status. Because Hispanics are disproportionately represented among the poor in the United States, implementation of adequate access to health care and social reforms (e.g., improving housing conditions) would likely have a major impact on reducing asthma morbidity in this population.
asthma; genetics; Hispanics; risk factors
Rationale: Little is known regarding the relationship between parental history of asthma and subsequent airway hyperresponsiveness (AHR) in children with asthma. Objectives: We evaluated this relationship in 1,041 children with asthma participating in a randomized trial of antiinflammatory medications (the Childhood Asthma Management Program [CAMP]). Methods: Methacholine challenge testing was performed before treatment randomization and once per year over an average of 4.5 years postrandomization. Cross-sectional and longitudinal repeated measures analyses were performed to model the relationship between PC20 (the methacholine concentration causing a 20% fall in FEV1) with maternal, paternal, and joint parental histories of asthma. Models were adjusted for potential confounders. Measurements and Main Results: At baseline, AHR was strongly associated with a paternal history of asthma. Children with a paternal history of asthma demonstrated significantly greater AHR than those without such history (median logePC20, 0.84 vs. 1.13; p = 0.006). Although maternal history of asthma was not associated with AHR, children with two parents with asthma had greater AHR than those with no parents with asthma (median logePC20, 0.52 vs. 1.17; p = 0.0008). Longitudinal multivariate analysis of the relation between paternal history of asthma and AHR using repeated PC20 measurements over 44 months postrandomization confirmed a significant association between paternal history of asthma and AHR among children in CAMP. Conclusions: Our findings suggest that the genetic contribution of the father is associated with AHR, an important determinant of disease severity among children with asthma.
airway responsiveness; asthma; genetics; longitudinal analysis; parent of origin