Intestinal Current Measurement Research Articles

Rectal organoid morphology analysis (ROMA) as a novel physiological assay for diagnostic classification in cystic fibrosis

BackgroundDiagnosing cystic fibrosis (CF) is not always straightforward, in particular when sweat chloride concentration (SCC) is intermediate and <2 CF-causing CFTR variants are identified. The physiological CFTR assays proposed in...

Contribution of the intestinal current measurement method to assessment of the efficacy of CFTR modulators in cystic fibrosis

Cystic fibrosis (CF) is a disease caused by pathogenic variants of the CFTR gene. In the last decade, the treatment algorithm has entered a new era as several drugs have become available that restore the function of the CFTR chloride channel and are called CFTR modulators. The efficacy and safety of targeted drugs in cystic fibrosis needs to be further investigated using additional assessment methods.The aim of this study was to investigate the role of intestinal current measurement (ICM) in assessing the efficacy of targeted therapy for cystic fibrosis.Methods. The efficacy of CFTR modulator therapy was evaluated in 15 patients, of which 10 were children and 5 were adults. In addition to the ICM method, patients’ clinical parameters, sweat test, and pulmonary function were also evaluated according to clinical guidelines.Results. Patients with genotypes 2143delT/7121G&gt;T and G542X/R785X had no restoration of chloride channel function with elexacaftor + tezacaftor + ivacaftor therapy, and patients with the L467F;F508del genotype with lumacaftor + ivacaftor therapy. In patients with the F508del/F508del, N1303K/G461E, N1303K/3321delG genotype, improvements were noted in terms of the restoration of CFTR channel function during therapy with elexacaftor + tezacaftor + ivacaftor therapy, and in patients with the F508del/F508del genotype during therapy with tezacaftor + ivacaftor therapy and lumacaftor + ivacaftor.Conclusion. Restoring the function of the epithelial chloride channel (CFTR) is the basis for increasing life expectancy in CF. The crucial role of the ICM method in determining the efficacy of CFTR modulators is shown.

The first described pathogenic variant c.2617G&gt;T of the CFTR gene

Cystic fibrosis (CF) is a disease caused by pathogenic variants in the CFTR gene. The greatest difficulty at the moment is assessing the contribution to the development of the disease of rare and previously unidentified genetic variants (mutations), mutations of uncertain clinical significance, as well as determining the genotype-phenotype relationship. Additional diagnostic methods are needed due to the large number of patients with borderline sweat test values. Purpose of the study: to study the pathogenicity of a newly identified variant of the nucleotide sequence of the CFTR gene based on assessing the functional activity of epithelial ion channels (ENaC, CFTR, CaCCs). Materials and methods: medical history data, method intestinal current measurement (ICM). Results: the patient had a severe course of the disease. Positive sweat test results, low fecal pancreatic elastase. The ICM method showed the absence of chlorine channel function. Conclusion: For the first time, the clinical features of a patient with the c.2617G&gt;T genetic variant in the genotype have been described. The results of the examination and the clinical course of the disease correspond to the severe course of the disease. Additional use of the ICM method confirmed the absence of CFTR channel function in a patient carrier of this variant of the CFTR gene.

CFTR function is impaired in a subset of patients with pancreatitis carrying rare CFTR variants

BackgroundMany affected by pancreatitis harbor rare variants of the cystic fibrosis (CF) gene, CFTR, which encodes an epithelial chloride/bicarbonate channel. We investigated CFTR function and the effect of CFTR modulator drugs in pancreatitis patients carrying CFTR variants. MethodsNext-generation sequencing was performed to identify CFTR variants. Sweat tests and nasal potential difference (NPD) assays were performed to assess CFTR function in vivo. Intestinal current measurement (ICM) was performed on rectal biopsies. Patient-derived intestinal epithelial monolayers were used to evaluate chloride and bicarbonate transport and the effects of a CFTR modulator combination: elexacaftor, tezacaftor and ivacaftor (ETI). ResultsOf 32 pancreatitis patients carrying CFTR variants, three had CF-causing mutations on both alleles and yielded CF-typical sweat test, NPD and ICM results. Fourteen subjects showed a more modest elevation in sweat chloride levels, including three that were provisionally diagnosed with CF. ICM indicated impaired CFTR function in nine out of 17 non-CF subjects tested. This group of nine included five carrying a wild type CFTR allele. In epithelial monolayers, a reduction in CFTR-dependent chloride transport was found in six out of 14 subjects tested, whereas bicarbonate secretion was reduced in only one individual. In epithelial monolayers of four of these six subjects, ETI improved CFTR function. ConclusionsCFTR function is impaired in a subset of pancreatitis patients carrying CFTR variants. Mutations outside the CFTR locus may contribute to the anion transport defect. Bioassays on patient-derived intestinal tissue and organoids can be used to detect such defects and to assess the effect of CFTR modulators.

Comprehensive Assessment of CFTR Modulators' Therapeutic Efficiency for N1303K Variant.

p.Asn1303Lys (N1303K) is a common missense variant of the CFTR gene, causing cystic fibrosis (CF). In this study, we initially evaluated the influence of CFTR modulators on the restoration of N1303K-CFTR function using intestinal organoids derived from four CF patients expressing the N1303K variant. The forskolin-induced swelling assay in organoids offered valuable insights about the beneficial effects of VX-770 + VX-661 + VX-445 (Elexacaftor + Tezacaftor + Ivacaftor, ETI) on N1303K-CFTR function restoration and about discouraging the prescription of VX-770 + VX-809 (Ivacaftor + Lumacaftor) or VX-770 + VX-661 (Ivacaftor + Tezacaftor) therapy for N1303K/class I patients. Then, a comprehensive assessment was conducted on an example of one patient with the N1303K/class I genotype to examine the ETI effect on the restoration of N1303K-CFTR function using in vitro the patient's intestinal organoids, ex vivo the intestinal current measurements (ICM) method and assessment of the clinical status before and after targeted therapy. All obtained results are consistent with each other and have proven the effectiveness of ETI for the N1303K variant. ETI produced a significant positive effect on forskolin-induced swelling in N1303K/class I organoids indicating functional improvement of the CFTR protein; ICM demonstrated that ETI therapy restored CFTR function in the intestinal epithelium after three months of treatment, and the patient improved his clinical status and lung function, increased his body mass index (BMI) and reduced the lung pathogenic flora diversity, surprisingly without improving the sweat test results.

Personalized CFTR Modulator Therapy for G85E and N1303K Homozygous Patients with Cystic Fibrosis.

CFTR modulator therapy with elexacaftor/tezacaftor/ivacaftor (ETI) has been approved for people with CF and at least one F508del allele in Europe. In the US, the ETI label has been expanded to 177 rare CFTR mutations responsive in Fischer rat thyroid cells, including G85E, but not N1303K. However, knowledge on the effect of ETI on G85E or N1303K CFTR function remains limited. In vitro effects of ETI were measured in primary human nasal epithelial cultures (pHNECs) of a G85E homozygous patient and an N1303K homozygous patient. Effects of ETI therapy in vivo in these patients were assessed using clinical outcomes, including multiple breath washout and lung MRI, and the CFTR biomarkers sweat chloride concentration (SCC), nasal potential difference (NPD) and intestinal current measurement (ICM), before and after initiation of ETI. ETI increased CFTR-mediated chloride transport in G85E/G85E and N1303K/N1303K pHNECs. In the G85E/G85E and the N1303K/N1303K patient, we observed an improvement in lung function, SCC, and CFTR function in the respiratory and rectal epithelium after initiation of ETI. The approach of combining preclinical in vitro testing with subsequent in vivo verification can facilitate access to CFTR modulator therapy and enhance precision medicine for patients carrying rare CFTR mutations.

WS04.06 Validation of rectal organoid morphology analysis (ROMA) as a novel physiological CFTR assay for diagnosis of cystic fibrosis

Objectives: When a diagnosis of CF remains inconclusive (intermediate sweat chloride concentration (SCC) and inconclusive genetics), physiological CFTR assays are the next step in the diagnostic algorithm. Nasal potential difference and intestinal current measurement are however not readily available and not feasible at all ages. We propose rectal organoid morphology analysis (ROMA) as a novel diagnostic assay. ROMA quantifies morphological differences between patient-derived rectal organoids (PDRO) from subjects with CF (no visible lumen, irregular shape) and without CF (visible lumen, round shape).

P007 Experience of using intestinal current measurement (ICM) in Russia

P007 Experience of using intestinal current measurement (ICM) in Russia

Effects of lumacaftor-ivacaftor therapy on cystic fibrosis transmembrane conductance regulator function in F508del homozygous patients with cystic fibrosis aged 2-11 years.

Rationale: Lumacaftor/ivacaftor was approved for the treatment of patients with cystic fibrosis who are homozygous for F508del aged 2years and older following positive results from phase three trials. However, the improvement in CFTR function associated with lumacaftor/ivacaftor has only been studied in patients over 12years of age, while the rescue potential in younger children is unknown. Methods: In a prospective study, we aimed to evaluate the effect of lumacaftor/ivacaftor on the CFTR biomarkers sweat chloride concentration and intestinal current measurement as well as clinical outcome parameters in F508del homozygous CF patients 2-11years before and 8-16weeks after treatment initiation. Results: A total of 13 children with CF homozygous for F508del aged 2-11years were enrolled and 12 patients were analyzed. Lumacaftor/ivacaftor treatment reduced sweat chloride concentration by 26.8mmol/L (p = 0.0006) and showed a mean improvement in CFTR activity, as assessed by intestinal current measurement in the rectal epithelium, of 30.5% compared to normal (p = 0.0015), exceeding previous findings of 17.7% of normal in CF patients homozygous for F508del aged 12years and older. Conclusion: Lumacaftor/ivacaftor partially restores F508del CFTR function in children with CF who are homozygous for F508del, aged 2-11years, to a level of CFTR activity seen in patients with CFTR variants with residual function. These results are consistent with the partial short-term improvement in clinical parameters.

Description of the clinical picture and assessment of functional activity of the CFTR channel in a patient with a complex allele [S466X; R1070Q

The presence of pathogenic variants in the CFTR gene causes cystic fibrosis (CF) through various molecular mechanisms that affect the formation and functional activity of the CFTR chloride channel. An important factor affecting the phenotypic manifestations of CF and the effectiveness of targeted therapy is the presence of complex alleles with &gt; 2 consecutive mutations per 1 allele, or in the cis position. The influence of complex alleles on the manifestations of CF has not been sufficiently studied globally due to the small number of studies.The aim of the study was to investigate the influence of the complex allele [S466X; R1070Q] on the phenotypic manifestations of CF and the effectiveness of targeted therapy in a model of intestinal organoids from a patient with [S466X; R1070Q]/CFTRdele2,3 genotype.Methods. We used medical history data, intestinal current measurement, intestinal organoid method, and forskolin test.Results. The progressive nature of the disease with a clear degradation of lung function was established. The ICM method showed absent chloride channel function. The tests on the culture of organoids obtained from the intestinal tissue indicated a complete loss of the chloride channel function. In addition, the complex allele [S466X; R1070Q] was insensitive to all targeted drugs tested.Conclusion. The complex allele [S466X; R1070Q] causes a complete loss of the functional CFTR protein and is not sensitive to any of the approved targeted drugs.

Clinical and Functional Characteristics of the E92K CFTR Gene Variant in the Russian and Turkish Population of People with Cystic Fibrosis

The pathogenic variant E92K (c.274G > A) of the CFTR gene is rare in America and Europe, but it is common for people with cystic fibrosis from Russia and Turkey. We studied the effect of the E92K genetic variant on the CFTR function. The function of the CFTR channel was studied using the intestinal current measurements (ICM) method. The effects of CFTR modulators on the restoration of the CFTR function were studied in the model of intestinal organoids. To assess the effect of E92K on pre-mRNA splicing, the RT-PCR products obtained from patients' intestinal organoid cultures were analyzed. Patients with the genetic variant E92K are characterized by an older age of diagnosis compared to homozygotes F508del and a high frequency of pancreatic sufficiency. The results of the sweat test and the ICM method showed partial preservation of the function of the CFTR channel. Functional analysis of CFTR gene expression revealed a weak effect of the E92K variant on mRNA-CFTR splicing. Lumacaftor (VX-809) has been shown to restore CFTR function in an intestinal organoid model, which allows us to consider the E92K variant as a promising target for therapy with CFTR correctors.

Differential effects of ELX/TEZ/IVA on organ-specific CFTR function in two patients with the rare CFTR splice mutations c.273+1G>A and c.165-2A>G.

Introduction: Evidence for the efficiency of highly-effective triple-CFTR-modulatory therapy with elexacaftor/tezacaftor/ivacaftor (ETI), either demonstrated in clinical trials or by in vitro testing, is lacking for about 10% of people with cystic fibrosis (pwCF) with rare mutations. Comprehensive assessment of CFTR function can provide critical information on the impact of ETI on CFTR function gains for such rare mutations, lending argument of the prescription of ETI. The mutation c.165-2A>G is a rare acceptor splice mutation that has not yet been functionally characterized. We here describe the functional changes induced by ETI in two brothers who are compound heterozygous for the splice mutations c.273+1G>C and c.165-2A>G. Methods: We assessed the effects of ETI on CFTR function by quantitative pilocarpine iontophoresis (QPIT), nasal potential difference measurements (nPD), intestinal current measurements (ICM), β-adrenergic sweat secretion tests (SST) and multiple breath washout (MBW) prior to and 4months after the initiation of ETI. Results: Functional CFTR analysis prior to ETI showed no CFTR function in the respiratory and intestinal epithelia and in the sweat gland reabsorptive duct in either brother. In contrast, β-adrenergic stimulated, CFTR-mediated sweat secretion was detectable in the CF range. Under ETI, both brothers continued to exhibit high sweat chloride concentration in QPIT, evidence of low residual CFTR function in the respiratory epithelia, but normalized β-adrenergically stimulated production of primary sweat. Discussion: Our results are the first to demonstrate that the c.165-2A>G/c.273+1G>C mutation genotype permits mutant CFTR protein expression. We showed organ-specific differences in the expression of CFTR and consecutive responses to ETI of the c.165-2A>G/c.273+1G>C CFTR mutants that are probably accomplished by non-canonical CFTR mRNA isoforms. This showcase tells us that the individual response of rare CFTR mutations to highly-effective CFTR modulation cannot be predicted from assays in standard cell cultures, but requires the personalized multi-organ assessment by CFTR biomarkers.

CFTR Modulators Rescue the Activity of CFTR in Colonoids Expressing the Complex Allele p.[R74W;V201M;D1270N]/dele22_24

An Italian, 46-year-old female patient carrying the complex allele p.[R74W;V201M;D1270N] in trans with CFTR dele22_24 was diagnosed at the Cystic Fibrosis (CF) Center of Verona as being affected by CF-pancreatic sufficient (CF-PS) in 2021. The variant V201M has unknown significance, while both of the other variants of this complex allele have variable clinical consequences, according to the CFTR2 database, with reported clinical benefits for treatment with ivacaftor + tezacaftor and ivacaftor + tezacaftor + elexacaftor in patients carrying the R74W-D1270N complex allele, which are currently approved (in USA, not yet in Italy). She was previously followed up by pneumologists in northern Italy because of frequent bronchitis, hemoptysis, recurrent rhinitis, Pseudomonas aeruginosa lung colonization, bronchiectasis/atelectasis, bronchial arterial embolization and moderately compromised lung function (FEV1: 62%). Following a sweat test with borderline results, she was referred to the Verona CF Center where she presented abnormal values in both optical beta-adrenergic sweat tests and intestinal current measurement (ICM). These results were consistent with a diagnosis of CF. CFTR function analyses were also performed in vitro by forskolin-induced swelling (FIS) assay and short-circuit currents (Isc) in the monolayers of the rectal organoids. Both of these assays showed significantly increased CFTR activity following treatment with the CFTR modulators. Western-blot analysis revealed increased fully glycosylated CFTR protein after treatment with correctors, in line with the functional analysis. Interestingly, tezacaftor, together with elexacaftor, rescued the total organoid area under steady-state conditions, even in the absence of the CFTR agonist forskolin. In conclusion, in ex vivo and in vitro assays, we measured a residual function that was significantly enhanced by in vitro incubation with CFTR modulators, especially by ivacaftor + tezacaftor + elexacaftor, suggesting this combination as a potentially optimal treatment for this case.

Personalized Selection of a CFTR Modulator for a Patient with a Complex Allele [L467F;F508del

The presence of complex alleles in the CFTR gene can lead to difficulties in diagnosing cystic fibrosis and cause resistance to therapy with CFTR modulators. Tezacaftor/ivacaftor therapy for 8 months in a patient with the initially established F508del/F508del genotype did not lead to an improvement in her condition—there was no change in spirometry and an increase in the patient’s weight, while there was only a slight decrease in NaCl values, measured by a sweat test. The intestinal current measurements of the patient’s rectal biopsy showed no positive dynamics in the rescue of CFTR function while taking tezacaftor/ivacaftor. The assumption that the patient had an additional mutation in the cis position was confirmed by sequencing the CFTR gene, and the complex allele [L467F;F508del] was identified. Based on the rescue of CFTR function by elexacaftor/tezacaftor/ivacaftor obtained using forskolin-induced swelling on intestinal organoids, the patient was prescribed therapy with this targeted drug. The use of elexacaftor/tezacaftor/ivacaftor for 7 months resulted in a significant improvement in the patient’s clinical condition.

ECFS standards of care on CFTR-related disorders: Diagnostic criteria of CFTR dysfunction

The spectrum of disorders involving CFTR (cystic fibrosis transmembrane conductance regulator) dysfunction correlates with a continuous gradient of CFTR function defined by the combination of two allelic CFTR variants. CFTR-related disorders are clinical entities with features of cystic fibrosis (CF) and evidence for presence of CFTR dysfunction but not meeting criteria for diagnosis of CF. Individuals with CFTR-RDs demonstrate a wide range of CFTR activity and are still under-recognized or misclassified. The level of CFTR dysfunction may be measured in vivo (sweat testing, nasal potential difference measurements) and/or by ex vivo tests (intestinal current measurement), or indirectly indicated by CFTR variants, as alteration in sequence of the CFTR gene translates into CFTR dysfunction. CFTR bioassays can aid in the diagnosis of individuals with CF, but we lack parameters to differentiate CF from CFTR-RD. In the era of the CFTR modulators and their potential clinical benefit, it is of utmost importance to diagnose CFTR-RD as unambiguously as possible. We therefore propose the following to define compatible CFTR dysfunction in a person with a suspected diagnosis of CFTR-RD :(1) evidence of CFTR dysfunction in vivo or ex vivo in at least two different CFTR functional test types, or(2) One CFTR variant known to reduce CFTR function and evidence of CFTR dysfunction in vivo or ex vivo in at least two different CFTR functional test types, or(3) Two CFTR variants shown to reduce CFTR function, with at most one CF-causing variant.

Evaluation of the Complex p.[Leu467Phe;Phe508del] CFTR Allele in the Intestinal Organoids Model: Implications for Therapy.

In the cohort of Russian patients with cystic fibrosis, the p.[Leu467Phe;Phe508del] complex allele (legacy name [L467F;F508del]) of the CFTR gene is understudied. In this research, we present the results of frequency evaluation of the [L467F;F508del] complex allele in the Russian Federation among patients with a F508del/F508del genotype, its effect on the clinical course of cystic fibrosis, the intestinal epithelium ionic channel function, and the effectiveness of target therapy. The frequency of the [L467F;F508del] complex allele among patients with homozygous F508del was determined with multiplex ligase-dependent probe amplification followed by polymerase chain reaction and fragment analysis. The function of ionic channels, including the residual CFTR function, and the effectiveness of CFTR modulators was analyzed using intestinal current measurements on rectal biopsy samples and the forskolin-induced swelling assay on organoids. The results showed that the F508del/[L467F;F508del] genotype is present in 8.2% of all Russian patients with F508del in a homozygous state. The clinical course of the disease in patients with the F508del/[L467F;F508del] genotype is severe and does not vary from the course in the cohort with homozygous F508del, although the CFTR channel function is significantly lower. For patients with the F508del/[L467F;F508del] genotype, we can recommend targeted therapy using a combined ivacaftor + tezacaftor + elexacaftor medication.

Assays of CFTR Function In Vitro, Ex Vivo and In Vivo.

Cystic fibrosis, a multi-organ genetic disease, is characterized by abnormal function of the cystic fibrosis transmembrane conductance regulator (CFTR) protein, a chloride channel at the apical membrane of several epithelia. In recent years, therapeutic strategies have been developed to correct the CFTR defect. To evaluate CFTR function at baseline for diagnosis, or the efficacy of CFTR-restoring therapy, reliable tests are needed to measure CFTR function, in vitro, ex vivo and in vivo. In vitro techniques either directly or indirectly measure ion fluxes; direct measurement of ion fluxes and quenching of fluorescence in cell-based assays, change in transmembrane voltage or current in patch clamp or Ussing chamber, swelling of CFTR-containing organoids by secondary water influx upon CFTR activation. Several cell or tissue types can be used. Ex vivo and in vivo assays similarly evaluate current (intestinal current measurement) and membrane potential differences (nasal potential difference), on tissues from individual patients. In the sweat test, the most frequently used in vivo evaluation of CFTR function, chloride concentration or stimulated sweat rate can be directly measured. Here, we will describe the currently available bio-assays for quantitative evaluation of CFTR function, their indications, advantages and disadvantages, and correlation with clinical outcome measures.

Состояние здоровья близнецов с генотипом F508del/R334W при муковисцидозе и возможности таргетной терапии

The CFTR gene contains 27 exons and is located at position 31.1 of the long arm of chromosome 7 (7q31.1). More than 2000 variants of the CFTR gene have been described so far. The R334W variant is associated with the mild disease course. Objective. To perform comprehensive assessment of the health status, functional CFTR activity, and efficacy of CFTR modulators in twins with the F508del/R334W genotype. Materials and methods. Data from medical records, intestinal current measurement (ICM), intestinal organoid culture. Results. We examined two twins with moderate cystic fibrosis who had similar clinical manifestations, including rhinosinusitis with nasal polyps and respiratory infections caused by gram-negative bacteria. Both patients also had polyvalent allergy. One child presented with a decrease of pancreatic elastase 1 in stool from 500 μg/g to 125 500 μg/g, which required administration of pancreatin and dosage increase later. Both children had reduced chloride channel function as demonstrated by ICM. The administration of a corrector (VX-809) and a potentiator (VX-770) effectively restored the channel function; their simultaneous use ensured an additive effect. The quantitative results obtained in both cultures of intestinal organoids were very similar. Key words: cystic fibrosis, CFTR gene, pathogenic variant R334W, intestinal current measurement, intestinal organoids, forskolin-induced swelling assay, correctors, potentiators, targeted therapy, ivacaftor, lumacaftor

Исследование функциональной активности CFTR-канала у пациента с муковисцидозом и генотипом E92K/4428insGA

Clinical manifestations of cystic fibrosis depend on the patient’s genotype since there are more than 2,000 variants of the CFTR gene. Main complications of the disease are expressed in a reduction or loss of pancreatic function and bacterial lung infection, leading to respiratory failure. The E92K (p.(Glu92Lys) and 4428insGA (p.(Ser1435Glyfs*14) mutations in the CFTR gene are accompanied by a high frequency of preserved pancreatic function. In a 3-year-old patient with recurrent pancreatitis and E92K/4428insGA genotype, the functional activity of the CFTR channel was studied using the intestinal current measurement method on rectal biopsy specimens and the forskolin-induced swelling assay in intestinal organoids. The personalized assessment of the action of CFTR modulators was also performed on organoid cultures obtained from the patient’s intestinal biopsies. In a 3-year-old child with cystic fibrosis and recurrent pancreatitis with frequent exacerbations, a high preservation of residual CFTR channel function was revealed. All the investigated targeted drugs were effective in increasing the functional activity of the CFTR chloride channel. Key words: cystic fibrosis, CFTR gene, targeted therapy, pancreatitis, intestinal organoids, intestinal current measurement, E92K, 4428insGA

Фенотипические проявления варианта гена CFTR c.3140-16T&gt;A (3272-16T&gt;A) в гомозиготном состоянии у ребенка с муковисцидозом

We report a case of cystic fibrosis (CF) in a 9-year-old child with the rare c.3140-16T&gt;A (3272-16T&gt;A) variant of the CFTR gene in homozygous state. CF was suspected at neonatal screening. The results of the sweat test (Nanoduct) were 88 and 84 mmol/L. Since the age of 1.5 months, the patient received inhalation of dornase alfa, kinesitherapy, pancreatic enzymes (only in case of abundant intake of fatty foods), and vitamin therapy. The boy early developed cough with sputum; at the age of 5 years, he also developed chronic sinusitis. At the age of 3 years, his level of fecal pancreatic elastase 1 was 597 μg/g, which indicated preserved exocrine function of the pancreas. At the age of 9 years, the boy demonstrated normal physical development and lung function (examined using spirometry). Computed tomography showed no bronchiectasis. X-ray revealed radiological signs of chronic sinusitis. The assessment of intestinal current measurement (ICM) demonstrated a reduced CFTR function typical of mild genetic variants. Thus, the patient with the c.3140-16T&gt;A (3272-16T&gt;A) variant in homozygous state has developed only chronic rhinosinusitis by the age of 9 years. Measurement of ICM confirmed the diagnosis of mild CF genotype. Key words: c.3140-16T&gt;A (3272-16T&gt;A) genetic variant, cystic fibrosis, mild phenotype