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BackgroundNasal potential difference (NPD) and intestinal current measurements (ICM) are cystic fibrosis transmembrane conductance regulator (CFTR) biomarkers recommended to make a diagnosis in individuals with inconclusive sweat test and CFTR genetics and a clinical suspicion for cystic fibrosis (CF) or CFTR-related disorder (CFTR-RD).MethodsNPD and ICM were measured according to standard operating procedures of the European Cystic Fibrosis Society Diagnostic Network Working Group.ResultsWe assessed 219 individuals by NPD or ICM who had been referred to our laboratory due to clinical symptoms suggestive of CF, but inconclusive sweat test and CFTR genetics (median age: 16.3 years, range 0.4 to 76 years). CF or CFTR-related disorder was diagnosed in 22 of 29 patients (76%) with a CFTR genotype of unknown or variable clinical significance and in 51 of 190 carriers (27%) of one (35/42) or no (16/148) identified CFTR mutation. If two CFTR sequence variants had been identified, the outcome of NPD and ICM was consistent with the classification of the CFTR2 database. Moreover, a suspected false-positive diagnosis of CF was confirmed in seven and withdrawn in eight patients. Of 26 individuals assessed by both NPD and ICM, eleven individuals exhibited discordant tracings of ICM and NPD, with one measurement being in the CF range and the other in the normal range.ConclusionThe majority of patients whom we diagnosed with CF or CFTR-RD by extended electrophysiology are carriers of the wild-type CFTR coding sequence on at least one of their CF alleles. The disease-causing genetic lesions should reside in the non-coding region of CFTR or elsewhere in the genome, affecting the regulation of CFTR expression in a tissue-depending fashion which may explain the large within-group variability of CFTR activity in the respiratory and intestinal epithelium seen in this group.

BackgroundMultiple-breath washout (MBW)-derived lung clearance index (LCI) detects early cystic fibrosis (CF) lung disease. LCI was used as an end-point in single- and multicentre settings at highly experienced MBW centres in preschool children. However, multicentre feasibility of MBW in children aged 2–6 years, including centres naïve to this technique, has not been determined systematically.MethodsFollowing central training, 91 standardised nitrogen MBW investigations were performed in 74 awake preschool children (15 controls, 46 with CF, and 13 with other lung diseases), mean age 4.6±0.9 years at investigation, using a commercially available device across five centres in Germany (three experienced, two naïve to the performance in awake preschool children) with central data analysis. Each MBW investigation consisted of several measurements.ResultsOverall success rate of MBW investigations was 82.4% ranging from 70.6% to 94.1% across study sites. The number of measurements per investigation was significantly different between sites ranging from 3.7 to 6.2 (p<0.01), while the mean number of successful measurements per investigation was comparable with 2.1 (range, 1.9 to 2.5; p=0.46). In children with CF, the LCI was increased (median 8.2, range, 6.7–15.5) compared to controls (median 7.3, range 6.5–8.3; p<0.01), and comparable to children with other lung diseases (median 7.9, range, 6.6–13.9; p=0.95).ConclusionThis study demonstrates that multicentre MBW in awake preschool children is feasible, even in centres previously naïve, with central coordination to assure standardised training, quality control and supervision. Our results support the use of LCI as multicentre end-point in clinical trials in awake preschoolers with CF.

Cystic fibrosis (CF) is the most common life-limiting monogenetic disease in European populations and is caused by mutations in the CFTR gene. Chronic airway infections with opportunistic pathogens are the major morbidity that determines prognosis and quality of life in most people with CF.

Background: Defects in expression, maturation or function of the epithelial membrane glycoprotein CFTR are causative for the progressive disease cystic fibrosis. Recently, molecular therapeutics that improve CFTR maturation and functional defects have been approved. We aimed to verify whether we could detect an improvement of CFTR protein expression and maturation by triple therapy with elexacaftor-tezacaftor-ivacaftor (ELX/TEZ/IVA).Methods: Rectal suction biopsies of 21 p.Phe508del homozygous or compound heterozygous CF patients obtained pre- and during treatment with ELX/TEZ/IVA were analyzed by CFTR Western blot that was optimized to distinguish CFTR glycoisoforms.Findings: CFTR western immunoblot analysis revealed that—compared to baseline—the levels of CFTR protein increased by at least twofold in eight out of 12 patients upon treatment with ELX/TEZ/IVA compared to baseline (p &lt; 0.02). However, polydispersity of the mutant CFTR protein was lower than that of the fully glycosylated wild type CFTR Golgi isoform, indicating an incompletely glycosylated p.Phe508el CFTR protein isoform C* in patients with CF which persists after ELX/TEZ/IVA treatment.Interpretation: Treatment with ELX/TEZ/IVA increased protein expression by facilitating the posttranslational processing of mutant CFTR but apparently did not succeed in generating the polydisperse spectrum of N-linked oligosaccharides that is characteristic for the wild type CFTR band C glycoisoform. Our results caution that the lower amounts or immature glycosylation of the C* glycoisoform observed in patients’ biomaterial might not translate to fully restored function of mutant CFTR necessary for long-term provision of clinical benefit.