Reduction of alveolar epithelial ion and fluid transport by inflammatory mediators

Initial interrogation, confirmation and fine mapping of modifying genes: STAT3, IL1B and IFNGR1 determine cystic fibrosis disease manifestation

We have used a stepwise approach consisting of initial interrogation, confirmation and fine mapping to analyze STAT3, IL1B and IFNGR1 as modifiers of cystic fibrosis disease building upon the data and sample collection of the European Cystic Fibrosis Twin and Sibling Study. We have observed direct correlation between the length of the intronic microsatellite STAT3Sat to STAT3 expression levels among F508del-CFTR homozygous patients (P=0.0075), and an association of longer STAT3Sat-alleles with the presence of CFTR-mediated residual chloride secretion (P=0.0031), measured as the manifestation of the CF basic defect in intestinal tissue. Both, family-based analysis by TDT and case-reference comparison identified consistently the same intragenic IL1B haplotype as a risk variant (P(raw)=0.055 for TDT, P(raw)<0.3 for case-reference comparison). Using haplotype-guided hierarchical fine mapping, we have identified two single nucleotide exchanges for which concordant and discordant sibling pairs differ at a 7 kb-spanning core haplotype in IFNGR1 (P(raw)=0.0113). Taken together, our findings imply that immunorelevant pathways and ion secretion, dominated by CFTR in intestinal and respiratory epithelium, merge at the level of the epithelial cell to integrate the signaling of cytokines due to innate and acquired immune defense.

Genes that determine immunology and inflammation modify the basic defect of impaired ion conductance in cystic fibrosis epithelia

Background

The cystic fibrosis (CF) basic defect, caused by dysfunction of the apical chloride channel CFTR in the gastrointestinal and respiratory tract epithelia, has not been employed so far to support the role of CF modifier genes.

Methods

Patients were selected from 101 families with a total of 171 F508del-CFTR homozygous CF patients to identify CF modifying genes. A candidate gene based association study of 52 genes on 16 different chromosomes with a total of 182 genetic markers was performed. Differences in haplotype and/or diplotype distribution between case and reference CF subpopulations were analysed.

Results

Variants at immunologically relevant genes were associated with the manifestation of the CF basic defect (0.01<Praw<0.0001 at IL1B, TLR9, TNFα, CD95, STAT3 and TNFR). The intragenic background of F508del-CFTR chromosomes determined disease severity and manifestation of the basic defect (Praw=0.0009). Allele distributions comparing transmitted and non-transmitted alleles were distorted at several loci unlinked to CFTR.

Conclusions

The inherited capabilities of the innate and adaptive immune system determine the manifestation of the CF basic defect. Variants on F508del-CFTR chromosomes contribute to the observed patient-to-patient variability among F508del-CFTR homozygotes. A survivor effect, manifesting as a transmission disequilibrium at many loci, is consistent with the improvement of clinical care over the last decades, resulting in a depletion of risk alleles at modifier genes. Awareness of non-genetic factors such as improvement of patient care over time is crucial for the interpretation of CF modifier studies.