No abstract

The identification of small molecules that target specific CFTR variants has ushered in a new era of treatment for cystic fibrosis (CF), yet optimal, individualized treatment of CF will require identification and targeting of disease modifiers. Here we use genome-wide association analysis to identify genetic modifiers of CF lung disease, the primary cause of mortality. Meta-analysis of 6,365 CF patients identifies five loci that display significant association with variation in lung disease. Regions on chr3q29 (MUC4/MUC20; P=3.3 × 10−11), chr5p15.3 (SLC9A3; P=6.8 × 10−12), chr6p21.3 (HLA Class II; P=1.2 × 10−8) and chrXq22-q23 (AGTR2/SLC6A14; P=1.8 × 10−9) contain genes of high biological relevance to CF pathophysiology. The fifth locus, on chr11p12-p13 (EHF/APIP; P=1.9 × 10−10), was previously shown to be associated with lung disease. These results provide new insights into potential targets for modulating lung disease severity in CF.

Variants associated with meconium ileus in cystic fibrosis (CF) were identified in 3,763 patients by GWAS. Five SNPs at two loci near SLC6A14 (min P=1.28×10−12 at rs3788766), chr Xq23-24 and SLC26A9 (min P=9.88×10−9 at rs4077468), chr 1q32.1 accounted for ~5% of the phenotypic variability, and were replicated in an independent patient collection (n=2,372; P=0.001 and 0.0001 respectively). By incorporating that disease-causing mutations in CFTR alter electrolyte and fluid flux across epithelia into an hypothesis-driven genome-wide analysis (GWAS-HD), we identified the same SLC6A14 and SLC26A9 associated SNPs, while establishing evidence for the involvement of SNPs in a third solute carrier gene, SLC9A3. In addition, GWAS-HD provided evidence of association between meconium ileus and multiple constituents of the apical plasma membrane where CFTR resides (P=0.0002, testing 155 apical genes jointly and replicated, P=0.022). These findings suggest that modulating activities of apical membrane constituents could complement current therapeutic paradigms for cystic fibrosis.

A combined genome-wide association and linkage study was used to identify loci causing variation in CF lung disease severity. A significant association (P=3. 34 × 10-8) near EHF and APIP (chr11p13) was identified in F508del homozygotes (n=1,978). The association replicated in F508del homozygotes (P=0.006) from a separate family-based study (n=557), with P=1.49 × 10-9 for the three-study joint meta-analysis. Linkage analysis of 486 sibling pairs from the family-based study identified a significant QTL on chromosome 20q13.2 (LOD=5.03). Our findings provide insight into the causes of variation in lung disease severity in CF and suggest new therapeutic targets for this life-limiting disorder.