Susceptibility to chronic mucus hypersecretion, a genome wide association study

Background: Chronic mucus hypersecretion (CMH) is associated with an increased frequency of respiratory infections, excess lung function decline, and increased hospitalisation and mortality rates in the general population. It is associated with smoking, but it is unknown why only a minority of smokers develops CMH. A plausible explanation for this phenomenon is a predisposing genetic constitution. Therefore, we performed a genome wide association (GWA) study of CMH in Caucasian populations. Methods: GWA analysis was performed in the NELSON-study using the Illumina 610 array, followed by replication and meta-analysis in 11 additional cohorts. In total 2,704 subjects with, and 7,624 subjects without CMH were included, all current or former heavy smokers (≥20 pack-years). Additional studies were performed to test the functional relevance of the most significant single nucleotide polymorphism (SNP). Results: A strong association with CMH, consistent across all cohorts, was observed with rs6577641 (p = 4.25x10-6, OR = 1.17), located in intron 9 of the special AT-rich sequence-binding protein 1 locus (SATB1) on chromosome 3. The risk allele (G) was associated with higher mRNA expression of SATB1 (4.3x10 -9) in lung tissue. Presence of CMH was associated with increased SATB1 mRNA expression in bronchial biopsies from COPD patients. SATB1 expression was induced during differentiation of primary human bronchial epithelial cells in culture. Conclusions: Our findings, that SNP rs6577641 is associated with CMH in multiple cohorts and is a cis-eQTL for SATB1, together with our additional observation that SATB1 expression increases during epithelial differentiation provide suggestive evidence that SATB1 is a gene that affects CMH

Susceptibility to chronic mucus hypersecretion, a genome wide association study

Background: Chronic mucus hypersecretion (CMH) is associated with an increased frequency of respiratory infections, excess lung function decline, and increased hospitalisation and mortality rates in the general population. It is associated with smoking, but it is unknown why only a minority of smokers develops CMH. A plausible explanation for this phenomenon is a predisposing genetic constitution. Therefore, we performed a genome wide association (GWA) study of CMH in Caucasian populations.Methods: GWA analysis was performed in the NELSON-study using the Illumina 610 array, followed by replication and metaanalysis in 11 additional cohorts. In total 2,704 subjects with, and 7,624 subjects without CMH were included, all current or former heavy smokers (&gt;= 20 pack-years). Additional studies were performed to test the functional relevance of the most significant single nucleotide polymorphism (SNP).Results: A strong association with CMH, consistent across all cohorts, was observed with rs6577641 (p = 4.25610(-6), OR = 1.17), located in intron 9 of the special AT-rich sequence-binding protein 1 locus (SATB1) on chromosome 3. The risk allele (G) was associated with higher mRNA expression of SATB1 (4.3610 29) in lung tissue. Presence of CMH was associated with increased SATB1 mRNA expression in bronchial biopsies from COPD patients. SATB1 expression was induced during differentiation of primary human bronchial epithelial cells in culture.Conclusions: Our findings, that SNP rs6577641 is associated with CMH in multiple cohorts and is a cis-eQTL for SATB1, together with our additional observation that SATB1 expression increases during epithelial differentiation provide suggestive evidence that SATB1 is a gene that affects CMH.</p

Overview of populations.

<p>Populations and corresponding period of data collection, type of population, genotyping platform and soft-ware used for imputation.</p><p>NA = not applicable.</p

Meta-analysis of the effect of rs6577641 on mRNA expression levels of <i>SATB1</i> in the lung^*.

<p>*To assess the effect of the SNP rs6577641 on gene expression, a Kruskal-Wallis test was performed. This test generates a p-value, but does not give a direction of the effect. To assess the direction of the effect, a Spearman's correlation test was performed. Next, a Z-score was calculated for each center and a meta-analysis performed for each of the three <i>SATB1</i> probes across all centers. Finally, a meta-analysis for all three <i>SATB1</i> probes was performed across all centers. This generated a Z-score of −5.87 and a corresponding p-value of 4.3*10⁻⁹, indicating that the susceptibility G allele of the SNP rs6577641 increases <i>SATB1</i> expression.</p

Percentage of subjects with chronic mucus hypersecretion (CMH) within genotypes (AA, AG and GG) of rs6577641 in the identification cohort (NELSON), and distributed among ex- and current smokers.

<p>Percentage of subjects with chronic mucus hypersecretion (CMH) within genotypes (AA, AG and GG) of rs6577641 in the identification cohort (NELSON), and distributed among ex- and current smokers.</p

<i>SATB1</i>, <i>MUC5AC</i> and <i>FOXJ1</i> mRNA expression levels during mucociliary human airway epithelial cell differentiation (n = 2 donors).

<p>Expression of <i>SATB1</i>, the identified gene in our study, <i>MUC5AC</i> a marker of mucus, and <i>FOXJ1</i>, representing ciliated cells in epithelial cell culture on air liquid interface.</p

Meta-analysis of top SNPs associated with CMH in replication cohorts, in identification and replication cohorts and corresponding direction of effect in all cohorts and associated feature and gene(s).

<p>MAF = minor allele frequency in NELSON;</p><p>*Direction of effect per cohort: each sign reflects one cohort, direction of effect is presented by: + = (OR>1.05), − = (OR<0.95), 0 = (0.95Table 2; OR is odds ratio; Q is p-value for heterogeneity;</p>#<p>means corresponding SNP is located in an intron in this gene.</p

Questions used to define chronic mucus hypersecretion in the corresponding cohorts.

<p>Questions used to define chronic mucus hypersecretion in the corresponding cohorts.</p