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, TNF a , CD95, STAT3 and TNFR). The intragenic background of F508del-CFTR chromosomes determined disease severity and manifestation of the basic defect (Praw ¼ 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. whereby extreme basic defect phenotypes were selected for in pairs for whom discordance ICM or NPD was observed. As NPD measurements were obtained for two siblings of a pair in most cases, two subsets for each case e control test were evaluated to provide an internal control depending on which sibling was assigned at random to be the index case. Candidate genes were interrogated for their association with disease severity using the phenotypic contrast between concordant/mildly affected patient concordant/severely affected patient and discordant patient pairs. For this purpose, 37 d representing the most patient pairs were selected based on a algorithm as NPD to for an association with sodium transport via the amiloride sensitive proportion of the potential, extreme phenotypes, secondly to evaluate an association with residual chloride secretion activated by chloride-free gluconate solution and isoproterenol, and thirdly to analyse a contribution of the selected candidate genes on ATP stimulated chloride response. The basic defect assessed by ICM was evaluated using a set of patients devoid of residual chloride secretion as controls. The pleiotropic chloride channel inhibitor DIDS, to which CFTR is not sensitive at the chosen concentration, was used to discriminate CFTR mediated residual chloride secretion from chloride secretion mediated by alternative channels which are DIDS sensitive.