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

Abstract

BackgroundThe 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.MethodsPatients 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.ResultsVariants 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.ConclusionsThe 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.

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

“…The study population and the selection criteria for cases and references of the association study has been described in detail elsewhere. 26 Briefly, genotyping data from 101 CF families, 85 of which are a subgroup of the twin and sibling study panel of 466 twin and sibling pairs, were used for the association study. All patients have been enrolled into the association study based on their extreme clinical and/or their electrophysiological phenotype as characterized by intestinal current measurement or nasal potential difference measurement of the CF basic defect of the intestinal and respiratory epithelium, respectively.…”

“…We have compared cases and reference patient populations to detect an association with CF disease severity, CF intrapair discordance and the CFTR-mediated basic defect using as a first-step informative microsatellite markers to interrogate the candidate genes. 26 Here, we describe previously unreported details of: (1) STAT3 where functional data indicate that the intragenic microsatellite used for initial genotyping determines STAT3 expression levels; (2) IL1B where follow-up analysis with intragenic SNPs confirmed the microsatellite signal; and (3) IFNGR1 where haplotype-guided hierarchical fine mapping 33 allowed us to describe the major modifying variants by the base.…”

“…The disease is characterized by a proinflammatory state, 10 which has been described in-vitro in cell systems, [11][12][13][14][15][16] using a murine model 17 and was confirmed mostly, [18][19][20][21] albeit not exclusively, 22,23 in ex-vivo material studied from CF patients. Consequently, several studied candidate genes were derived from the field of immunity, immunology and host defense such as the cytokines IL8, [24][25][26] IL1B 25,26 and TGFB1. [28][29][30] We report our data on three candidate genes as modifiers of CF investigated in the framework of the European CF Twin and Sibling Study, 26 based on which we have described previously the immunorelevant receptors for TNFa 31 and FAS 32 as CF modifiers.…”

“…Consequently, several studied candidate genes were derived from the field of immunity, immunology and host defense such as the cytokines IL8, [24][25][26] IL1B 25,26 and TGFB1. [28][29][30] We report our data on three candidate genes as modifiers of CF investigated in the framework of the European CF Twin and Sibling Study, 26 based on which we have described previously the immunorelevant receptors for TNFa 31 and FAS 32 as CF modifiers. For this work, the signal transducer and activator of translation 3 (STAT3), the cytokine interleukin 1b (IL1B) and the receptor for interferon g (IFNGR1) have been selected based on transcriptome data comparing F508del-CFTR homozygous CF patients stratified for low, medium or high residual chloride secretion and non-CF controls.…”

Clinical and molecular characterization of the potential CF disease modifier syntaxin 1A

“…14 Evaluation of STX1A/C genotype data was based on transmitted chromosomes of the entire patient population of 101 CF families (171 p.Phe508del-CFTR homozygotes) and the following subpopulations selected for extreme clinical phenotypes: concordant mildly affected patient pair (CON þ ; 13 families), concordant severely affected patient pair (CON À; 12 families) and discordant sib pairs (DIS; 14 families). 14 Informed consent was obtained from all subjects, and the local ethics committees approved the study.…”