Self-reported racial/ethnic discrimination and bronchodilator response in African American youth with asthma

<div><p>Importance</p><p>Asthma is a multifactorial disease composed of endotypes with varying risk profiles and outcomes. African Americans experience a high burden of asthma and of psychosocial stress, including racial discrimination. It is unknown which endotypes of asthma are vulnerable to racial/ethnic discrimination.</p><p>Objective</p><p>We examined the association between self-reported racial/ethnic discrimination and bronchodilator response (BDR) among African American youth with asthma ages 8 to 21 years (n = 576) and whether this association varies with tumor necrosis factor alpha (TNF-α) level.</p><p>Materials and methods</p><p>Self-reported racial/ethnic discrimination was assessed by a modified Experiences of Discrimination questionnaire as none or any. Using spirometry, BDR was specified as the mean percentage change in forced expiratory volume in one second before and after albuterol administration. TNF-α was specified as high/low levels based on our study population mean. Linear regression was used to examine the association between self-reported racial/ethnic discrimination and BDR adjusted for selected characteristics. An interaction term between TNF-α levels and self-reported racial/ethnic discrimination was tested in the final model.</p><p>Results</p><p>Almost half of participants (48.8%) reported racial/ethnic discrimination. The mean percent BDR was higher among participants reporting racial/ethnic discrimination than among those who did not (10.8 versus 8.9, p = 0.006). After adjustment, participants reporting racial/ethnic discrimination had a 1.7 (95% CI: 0.36–3.03) higher BDR mean than those not reporting racial/ethnic discrimination. However, we found heterogeneity of this association according to TNF-α levels (p-interaction = 0.040): Among individuals with TNF-α high level only, we observed a 2.78 higher BDR mean among those reporting racial/ethnic discrimination compared with those not reporting racial/ethnic discrimination (95%CI: 0.79–4.77).</p><p>Conclusions</p><p>We found BDR to be increased in participants reporting racial/ethnic discrimination and this association was limited to African American youth with TNF-α high asthma, an endotype thought to be resistant to traditional asthma medications. These results support screening for racial/ethnic discrimination in those with asthma as it may reclassify disease pathogenesis.</p></div

Mean difference in bronchodilator response^a and 95% CI for reports of racial/ethnic discrimination and according to TNF-α status for SAGE II participants with asthma (2006–2014).

<p>Mean difference in bronchodilator response<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0179091#t002fn001" target="_blank">^a</a> and 95% CI for reports of racial/ethnic discrimination and according to TNF-α status for SAGE II participants with asthma (2006–2014).</p

Selected characteristics of participants with asthma according to self-reported racial/ethnic discrimination in SAGE II (2006–2014).

<p>Selected characteristics of participants with asthma according to self-reported racial/ethnic discrimination in SAGE II (2006–2014).</p

Comparison of CNV allele frequency between Hutterites and CEU.

<p>A histogram of the difference in allele frequency for the non-reference allele between Hutterites and the CEU individuals from the 1000 Genomes Project is shown. On the x-axis are bins for the absolute value of the non-reference allele frequency in the Hutterites minus the allele frequency in CEU. The y-axis represents the number of CNVs in each bin.</p

Overview of sequenced genomes.

<p>Ideograms of the autosomes and X chromosome are shown. Red bars represent segments of autozygosity observed in five individuals with asthma (parents of the sequenced trios) and yellow triangles represent asthma-specific gene-disruptive SNVs or indels. The regions of autozygosity in multiple cases on chromosomes 1q and 5q were also observed to be autozygous in at least one control individual.</p

Association results of 593 CNVs to asthma.

<p>CNVs for association testing in the full Hutterite pedigree were identified in the 16 sequenced genomes. The points for these CNVs are colored based on the results of the whole-genome sequencing to represent whether the variant was observed in cases only (red), control individuals only (blue), or in both case and control individuals (gray). The genomic position is represented on the x-axis and the −log₁₀(p-value) of the nominal association of each CNV to asthma in the full Hutterite pedigree is on the y-axis.</p

Identification of an intronic deletion in <i>NEDD4L</i> associated with asthma.

<p>(<b>A</b>) A representation of the location of the 6 kbp deletion. This deletion occurs in an intron shared by all reported transcripts of this gene (blue). The deletion was identified from paired-end sequence reads and validated by array CGH as shown for one of the sequenced trios. The log₂ ratios of the probes in this region are shown as vertical bars with a log₂ ratio of zero represented by the horizontal line. The red vertical bars in the child and mother indicate negative log₂ ratios and confirm the deletion. (<b>B</b>) The frequency of this deletion in multiple populations is shown in the bar graph with the deletion allele frequency on the y-axis. The error bars represent the standard error on the allele frequency based on the binomial distribution. The Hutterite case (black) and control (gray) frequencies were determined by array CGH; the frequencies for the other populations are as reported by the 1000 Genomes Project.</p

Whole-Genome Sequencing of Individuals from a Founder Population Identifies Candidate Genes for Asthma

<div><p>Asthma is a complex genetic disease caused by a combination of genetic and environmental risk factors. We sought to test classes of genetic variants largely missed by genome-wide association studies (GWAS), including copy number variants (CNVs) and low-frequency variants, by performing whole-genome sequencing (WGS) on 16 individuals from asthma-enriched and asthma-depleted families. The samples were obtained from an extended 13-generation Hutterite pedigree with reduced genetic heterogeneity due to a small founding gene pool and reduced environmental heterogeneity as a result of a communal lifestyle. We sequenced each individual to an average depth of 13-fold, generated a comprehensive catalog of genetic variants, and tested the most severe mutations for association with asthma. We identified and validated 1960 CNVs, 19 nonsense or splice-site single nucleotide variants (SNVs), and 18 insertions or deletions that were out of frame. As follow-up, we performed targeted sequencing of 16 genes in 837 cases and 540 controls of Puerto Rican ancestry and found that controls carry a significantly higher burden of mutations in <i>IL27RA</i> (2.0% of controls; 0.23% of cases; nominal p = 0.004; Bonferroni p = 0.21). We also genotyped 593 CNVs in 1199 Hutterite individuals. We identified a nominally significant association (p = 0.03; Odds ratio (OR) = 3.13) between a 6 kbp deletion in an intron of <i>NEDD4L</i> and increased risk of asthma. We genotyped this deletion in an additional 4787 non-Hutterite individuals (nominal p = 0.056; OR = 1.69). <i>NEDD4L</i> is expressed in bronchial epithelial cells, and conditional knockout of this gene in the lung in mice leads to severe inflammation and mucus accumulation. Our study represents one of the early instances of applying WGS to complex disease with a large environmental component and demonstrates how WGS can identify risk variants, including CNVs and low-frequency variants, largely untested in GWAS.</p></div

SNVs and indels nominally associated with asthma in the Hutterites.

<p>*Position in NCBI build 36.</p>#<p>Based on the 1000 Genomes Project Phase 1 <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0104396#pone.0104396-Consortium2" target="_blank">[50]</a>.</p>†<p>Corrected for relatedness as previously described <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0104396#pone.0104396-Bourgain1" target="_blank">[55]</a>.</p>‡<p>Odds ratio (OR).</p

Association of intronic deletion in <i>NEDD4L</i> with asthma in additional populations.

<p>*Odds ratio (OR).</p>#<p>Combined association statistics were obtained using the Cochran–Mantel–Haenszel test.</p