Fibrosis Transmembrane Conductance Regulator Mutations Research Articles

Effect of Elexacaftor/Tezacaftor/Ivacaftor on Pseudomonas aeruginosa Acquisition and Chronic Infection at a Single Pediatric Cystic Fibrosis Care Center

OBJECTIVES As cystic fibrosis (CF) lung disease progresses, the airways become infected with opportunistic pathogens, such as Pseudomonas aeruginosa (PA). In October 2019, the US Food and Drug Administration approved elexacaftor/tezacaftor/ivacaftor (ETI), a highly effective modulator therapy (HEMT), for individuals 12 years and older with 1 copy of the F508del cystic fibrosis transmembrane conductance regulator (CFTR) mutation. ETI increases the amount of and function of CFTR in the respiratory epithelium, improving mucociliary clearance and reducing static airway mucus, a major trigger for chronic infection and inflammation. METHODS A retrospective analysis of inhaled tobramycin (iTOB) prescriptions between January 1, 2016, and December 31, 2021, was performed. This captured data before and after ETI approval at Children’s Mercy Kansas City (CMKC). The number of individuals with new PA acquisition and individuals considered ­chronically infected was analyzed. RESULTS The number of eradication prescriptions declined in 2020 and 2021, with 15 (7%) and 12 (5%) ­individuals prescribed therapy for those years, respectively. A similar pattern was observed for ­prescriptions for chronic infection. A reduction was seen in 2020 and 2021, with 28 (13%) and 20 (9%) individuals ­prescribed therapy for the respective years. CONCLUSIONS The CMKC experienced a decrease in the number of courses of iTOB prescribed during the last 6 years. The reasons for this are likely multifactorial and may include the implementation of standardized PA surveillance and eradication protocols, the effect of HEMT on mucociliary clearance and airway microbiology, and the poorly understood effects of the SARS-CoV-2 pandemic on the epidemiology of respiratory infections.

Predicting Mutational Effects on Ca2+-Activated Chloride Conduction of TMEM16A Based on a Simulation Study.

The dysfunction and defects of ion channels are associated with many human diseases, especially for loss-of-function mutations in ion channels such as cystic fibrosis transmembrane conductance regulator mutations in cystic fibrosis. Understanding ion channels is of great current importance for both medical and fundamental purposes. Such an understanding should include the ability to predict mutational effects and describe functional and mechanistic effects. In this work, we introduce an approach to predict mutational effects based on kinetic information (including reaction barriers and transition state locations) obtained by studying the working mechanism of target proteins. Specifically, we take the Ca2+-activated chloride channel TMEM16A as an example and utilize the computational biology model to predict the mutational effects of key residues. Encouragingly, we verified our predictions through electrophysiological experiments, demonstrating a 94% prediction accuracy regarding mutational directions. The mutational strength assessed by Pearson's correlation coefficient is -0.80 between our calculations and the experimental results. These findings suggest that the proposed methodology is reliable and can provide valuable guidance for revealing functional mechanisms and identifying key residues of the TMEM16A channel. The proposed approach can be extended to a broad scope of biophysical systems.

The Anion Channel TMEM16a/Ano1 Modulates CFTR Activity, but Does Not Function as an Apical Anion Channel in Colonic Epithelium from Cystic Fibrosis Patients and Healthy Individuals.

Studies in human colonic cell lines and murine intestine suggest the presence of a Ca2+-activated anion channel, presumably TMEM16a. Is there a potential for fluid secretion in patients with severe cystic fibrosis transmembrane conductance regulator (CFTR) mutations by activating this alternative pathway? Two-dimensional nondifferentiated colonoid-myofibroblast cocultures resembling transit amplifying/progenitor (TA/PE) cells, as well as differentiated monolayer (DM) cultures resembling near-surface cells, were established from both healthy controls (HLs) and patients with severe functional defects in the CFTR gene (PwCF). F508del mutant and CFTR knockout (null) mice ileal and colonic mucosa was also studied. HL TA/PE monolayers displayed a robust short-circuit current response (ΔIeq) to UTP (100 µM), forskolin (Fsk, 10 µM) and carbachol (CCH, 100 µM), while ΔIeq was much smaller in differentiated monolayers. The selective TMEM16a inhibitor Ani9 (up to 30 µM) did not alter the response to luminal UTP, significantly decreased Fsk-induced ΔIeq, and significantly increased CCH-induced ΔIeq in HL TA/PE colonoid monolayers. The PwCF TA/PE and the PwCF differentiated monolayers displayed negligible agonist-induced ΔIeq, without a significant effect of Ani9. When TMEM16a was localized in intracellular structures, a staining in the apical membrane was not detected. TMEM16a is highly expressed in human colonoid monolayers resembling transit amplifying cells of the colonic cryptal neck zone, from both HL and PwCF. While it may play a role in modulating agonist-induced CFTR-mediated anion currents, it is not localized in the apical membrane, and it has no function as an apical anion channel in cystic fibrosis (CF) and healthy human colonic epithelium.

Infection Dynamics of Aspergillus fumigatus in Adults with Cystic Fibrosis (CF).

Aspergillus fumigatus (A. fumigatus) has emerged as a significant pathogen in patients with cystic fibrosis (CF) and currently is within the top five isolated organisms reported in several international CF patient registries. A. fumigatus has been attributed to disease progression, although its role remains controversial. There is a paucity of reports on its infection dynamics, it was the aim of this study to examine time to first laboratory reports of A. fumigatus acquisition and to correlate this with patient gender and cystic fibrosis transmembrane conductance regulator (CFTR) mutation type. One hundred adult (≥ 18years) CF patients were examined (50 females, 50 males; mean age 24.6years ± 6.25 (SD), median age 24years; maximum age 76years). CFTR mutation groups consisted (i) F508del/F508del homozygous (n = 45), (ii) F508del/other heterozygous (n = 45) and (iii) others (n = 10). CFTR mutation type, patient gender, presence/absence of A. fumigatus and time (months) to first isolation of A. fumigatus were examined. Microbiological data was examined from 100 patients from birth to present (31/12/2021), equating to 2455 patient years. A. fumigatus was isolated from 66/100 (66%) adult CF patients; (i) F508del/F508del homozygous (82%; 37/45), (ii) F508del/other heterozygous (56%; 25/45) and (iii) others (40%; 4/10). Within the F508del/other heterozygous group, 14 mutations were noted on the second allele, with R560T and R117H collectively accounting for 36% of the second mutations. Four unique allele/allele mutations were noted in the Other Mutations category. There was a trend to a higher A. fumigatus acquisition in F508del/F508del homozygous patients than with F508del/other patients (p = 0.0529). Of the 66 patients who were positive for A. fumigatus, 35(53%) were male and 31(47%) were female. The median and mean time to first isolation of A. fumigatus in all A. fumigatus-positive patients was 119.5months and 128months, respectively, shortest time was 12months, longest time 288months. There was a statistical significance in time-to-first isolation in relation to CFTR mutation group (p = 0.0272), whereby F508del homozygous individuals had their first isolation of A. fumigatus at 116.8 ± 7.9months (mean ± standard error of the mean (SEM)) and F508del heterozygous patients had their first isolate of A. fumigatus at 150.4months ± 13.7months (mean ± SEM), approximately 2.75years after their F508del homozygous peers. There was no significant difference (p = 0.12) in time to first acquisiton between males and females, whereby males had their first A. fumigatus isolate at 118 ± 9.4months, whereas females had their first A. fumigatus isolate at 140 ± 10.8months. The highest rate of first A. fumigatus isolation was from 4years until 16years and by the age of 16years, approximately 85% of A. fumigatus-positive patients had recorded their first A. fumigatus isolate. To minimise the risk of first acquisition of A. fumigatus, it is important that infection prevention educational messaging is delivered in the paediatric clinic, to enhance health literacy around A. fumigatus acquisition.

Outcomes of children with cystic fibrosis screen positive, inconclusive diagnosis/CFTR related metabolic syndrome.

Some infants undergoing newborn screening (NBS) tests have inconclusive sweat chloride test (SCT) results that lead to the designation of Cystic Fibrosis Screen Positive, Inconclusive Diagnosis/CFTR-related metabolic syndrome (CFSPID/CRMS). Some proportion of them transition to a CF diagnosis, but no predictive markers can stratify which are at risk for this transition. We report single-center outcomes of children with CRMS. We retrospectively identified all infants born in Alabama from 2008 through 2020 referred to our CF Center with an elevated immunoreactive trypsinogen level (IRT) associated with a cystic fibrosis transmembrane conductance regulator (CFTR) mutation (IRT+/DNA+) who had at least one SCT result documented. Infants were classified per established guidelines as Carrier, CRMS, or CF based on the IRT+/DNA+ and SCT results. The electronic health record was reviewed for follow-up visits until the children received a definitive diagnosis (to carrier or CF) according to current diagnostic guidelines for CF, or through the end of the 2020 year. Of the 1,346 infants with IRT+ and at least 1 CFTR mutation identified (IRT+/DNA+), 63 (4.7%) were designated as CRMS. Of these infants, 12 (19.1%) transitioned to Carrier status (CRMS-Carrier), 40 (63.5%) of them remained CRMS status (CRMS-Persistent) and 11 (17.5%) of them transitioned to a diagnosis of CF (CRMS-CF). Of the 11 children in the CRMS-CF group, 4 (36%) had an initial SCT 30-39 mmol/L, 4 (36%) had an initial SCT 40-49 mmol/L and 3 (27%) had an initial SCT 50-59 mmol/L. These children also had higher initial sweat tests and greater yearly increases in sweat chloride values than others with CRMS. We found that in comparison to children in the CRMS-P group, a greater proportion of children in the CRMS-CF group cultured bacteria like methicillin-resistant Staphylococcus aureus, Stenotrophomonas maltophilia, and Pseudomonas aeruginosa, had smaller weight-for-height percentiles and remained smaller over time despite slightly greater growth. Infants with an inconclusive diagnosis of CF should continue to receive annual care and management given their potential risk of transition to CF. Further research is needed to assess whether certain phenotypic patterns, clinical symptoms, diagnostic tests or biomarkers could better stratify these children.

Risk factors for forced expiratory volume in 1 s decline in European patients with cystic fibrosis: data from the European Cystic Fibrosis Society Patient Registry.

To examine the trajectory of forced expiratory volume in 1 s (FEV1) using data from the European Cystic Fibrosis Society patient registry (ECFPR) collected from 2008 to 2016, i.e. the era before highly effective modulator therapy (HEMT). We evaluated risk factors for FEV1 decline. The study population included patients with a confirmed diagnosis of cystic fibrosis recorded in the ECFPR (2008-2016). The evolution of FEV1 % predicted (%FEV1) with age, and the yearly change in %FEV1 were evaluated. Risk factors considered were cystic fibrosis transmembrane conductance regulator (-CFTR) mutation class, gender, age at diagnosis, neonatal screening, meconium ileus, sweat chloride concentration at diagnosis and country's income level. We used 199 604 FEV1 recordings from 38 734 patients. The fastest decline was seen during puberty and in patients diagnosed before the age of 10 years. Males had a higher %FEV1, but a higher yearly %FEV1 loss between the ages of 15 and 25 years. We showed stabilisation and even improvement in %FEV1 over age in adults with a class III CFTR mutation, but a steady decline in patients homozygous for F508del or with both mutations of classes I/II. A faster decline in %FEV1 was found in patients from low-income countries compared to a similar %FEV1 evolution in patients from middle- and high-income countries. These longitudinal FEV1 data reflect the reality of cystic fibrosis across Europe in the era pre-HEMT, and can serve as baseline for comparison with the post-HEMT era. The similar evolution in middle- and high-income countries underlines opportunities for low-income countries.

Loss-of-function CFTR p.G970D missense mutation might cause congenital bilateral absence of the vas deferens and be associated with impaired spermatogenesis.

Congenital bilateral absence of the vas deferens (CBAVD) is observed in 1%-2% of males presenting with infertility and is clearly associated with cystic fibrosis transmembrane conductance regulator (CFTR) mutations. CFTR is one of the most well-known genes related to male fertility. The frequency of CFTR mutations or impaired CFTR expression is increased in men with nonobstructive azoospermia (NOA). CFTR mutations are highly polymorphic and have established ethnic specificity. Compared with F508Del in Caucasians, the p.G970D mutation is reported to be the most frequent CFTR mutation in Chinese patients with cystic fibrosis. However, whether p.G970D participates in male infertility remains unknown. Herein, a loss-of-function CFTR p.G970D missense mutation was identified in a patient with CBAVD and NOA. Subsequent retrospective analysis of 122 Chinese patients with CBAVD showed that the mutation is a common pathogenic mutation (4.1%, 5/122), excluding polymorphic sites. Furthermore, we generated model cell lines derived from mouse testes harboring the homozygous Cftr p.G965D mutation equivalent to the CFTR variant in patients. The Cftr p.G965D mutation may be lethal in spermatogonial stem cells and spermatogonia and affect the proliferation of spermatocytes and Sertoli cells. In spermatocyte GC-2(spd)ts (GC2) Cftr p.G965D cells, RNA splicing variants were detected and CFTR expression decreased, which may contribute to the phenotypes associated with impaired spermatogenesis. Thus, this study indicated that the CFTR p.G970D missense mutation might be a pathogenic mutation for CBAVD in Chinese males and associated with impaired spermatogenesis by affecting the proliferation of germ cells.

The risk of colorectal cancer in individuals with mutations of the cystic fibrosis transmembrane conductance regulator (CFTR) gene: An English population-based study

BackgroundStudies have demonstrated a higher risk of developing colorectal cancer (CRC) in individuals with Cystic Fibrosis (CF), and also a potentially increased risk in carriers of cystic fibrosis transmembrane conductance regulator (CFTR) mutations. Life expectancy for those with CF is rising, increasing the number at risk of developing CRC. MethodsThe incidence of CRC amongst individuals with CF was calculated using data from CORECT-R and linked UK CF Registry and Secondary User Services (SUS) data. Crude, age-specific and age-standardised rates were compared to those without CF. The presence of CFTR mutations in individuals with CRC was assessed using 100,000 Genomes Project data. FindingsThe crude incidence rate of CRC in the CF population was 0.29 per 1,000 person-years (28 cases). The CF population were significantly younger than those without (median age at CRC diagnosis 52 years versus 73 years; p<0·01). When age-adjusted, there was a 5-fold increased CRC incidence amongst individuals with CF compared to those without (SIR 5.0 95%CI 3.2–6.9). When compared to other population studies the overall prevalence of CFTR mutations in the CRC population was significantly higher than expected (p<0·01). InterpretationCF is linked to an increased risk of CRC. The incidence of CFTR mutations in the CRC population is higher than would be expected, suggesting an association between CFTR function and CRC risk. Further research is needed to develop effective screening strategies for these populations. FundingCancer Research UK (grants C23434/A23706 & C10674/A27140)

659 Inflammation augments elexacaftor/tezacaftor/ivacaftor-induced cystic fibrosis transmembrane conductance regulator rescue in primary airway epithelia carrying F508del and rare cystic fibrosis transmembrane conductance regulator mutations

659 Inflammation augments elexacaftor/tezacaftor/ivacaftor-induced cystic fibrosis transmembrane conductance regulator rescue in primary airway epithelia carrying F508del and rare cystic fibrosis transmembrane conductance regulator mutations

586 ΔF508–cystic fibrosis transmembrane conductance regulator mutation in C57BL/6 and Collaborative Cross mice to unravel the contribution of genetic background in the cystic fibrosis disease phenotype

586 ΔF508–cystic fibrosis transmembrane conductance regulator mutation in C57BL/6 and Collaborative Cross mice to unravel the contribution of genetic background in the cystic fibrosis disease phenotype

638 Splice-switching antisense oligonucleotides for the treatment of class I cystic fibrosis transmembrane conductance regulator mutations

638 Splice-switching antisense oligonucleotides for the treatment of class I cystic fibrosis transmembrane conductance regulator mutations

660 Triple potentiator-mediated activation of cystic fibrosis transmembrane conductance regulator mutants with gating defects is independent of channel phosphorylation and nucleotide binding domain dimerization

660 Triple potentiator-mediated activation of cystic fibrosis transmembrane conductance regulator mutants with gating defects is independent of channel phosphorylation and nucleotide binding domain dimerization

648 Distinct proteostasis and structural states drive VX-809 susceptibility of cystic fibrosis transmembrane conductance regulator mutants

648 Distinct proteostasis and structural states drive VX-809 susceptibility of cystic fibrosis transmembrane conductance regulator mutants

Recombinant Adeno-Associated Virus-Mediated Editing of the G551D Cystic Fibrosis Transmembrane Conductance Regulator Mutation in Ferret Airway Basal Cells.

Mutations in the cystic fibrosis transmembrane conductance regulator (CFTR) gene cause cystic fibrosis (CF), a chronic disease that affects multiple organs, including the lung. We developed a CF ferret model of a scarless G551→D substitution in CFTR (CFTRG551D-KI), enabling approaches to correct this gating mutation in CF airways via gene editing. Homology-directed repair (HDR) was tested in Cas9-expressing CF airway basal cells (Cas9-GKI) from this model, as well as reporter basal cells (Y66S-Cas9-GKI) that express an integrated nonfluorescent Y66S-EGFP (enhanced green fluorescent protein) mutant gene to facilitate rapid assessment of HDR by the restoration of fluorescence. Recombinant adeno-associated virus (rAAV) vectors were used to deliver two DNA templates and sgRNAs for dual-gene editing at the EGFP and CFTR genes, followed by fluorescence-activated cell sorting of EGFPY66S-corrected cells. When gene-edited airway basal cells were polarized at an air-liquid interface, unsorted and EGFPY66S-corrected sorted populations gave rise to 26.0% and 70.4% CFTR-mediated Cl- transport of that observed in non-CF cultures, respectively. The consequences of gene editing at the CFTRG551D locus by HDR and nonhomologous end joining (NHEJ) were assessed by targeted gene next-generation sequencing (NGS) against a specific amplicon. NGS revealed HDR corrections of 3.1% of G551 sequences in the unsorted population of rAAV-infected cells, and 18.4% in the EGFPY66S-corrected cells. However, the largest proportion of sequences had indels surrounding the CRISPR (clustered regularly interspaced short palindromic repeats) cut site, demonstrating that NHEJ was the dominant repair pathway. This approach to simultaneously coedit at two genomic loci using rAAV may have utility as a model system for optimizing gene-editing efficiencies in proliferating airway basal cells through the modulation of DNA repair pathways in favor of HDR.

Integrative pan cancer analysis reveals the importance of CFTR in lung adenocarcinoma prognosis.

Cystic fibrosis (CF) and cystic fibrosis transmembrane conductance regulator (CFTR) mutations have been shown to be associated with the risk of a variety of cancers. However, the clinical significance of aberrant CFTR gene expression in human tumors remains unknown. The expression profiles and prognostic landscapes of CFTR in human cancers were identified from the PubMed, OVID, CNKI, TCGA, ONCOMINE, PrognoScan, and GEPIA databases. Over 11, 000 cancer samples from the literature, GEPIA database, and PrognoScan database were included in this study. In general, CFTR has various expression and prognostic profiles in cancers, but the results from cross-database and meta-analyses revealed that CFTR is a robust biomarker for LUAD prognosis. Collectively, this study suggests that CFTR is an important prognostic biomarker for LUAD survival, implying that it could be used as a prognostic biomarker and therapeutic target for LUAD.

Association Between Cystic Fibrosis Severity Markers and CFTR Genotypes in Turkish Children.

To compare class I/II cystic fibrosis transmembrane conductance regulator (CFTR) mutations to class III-V mutations with regards to cystic fibrosis disease severity markers in children. This study was designed as a cross-sectional study in Antalya province, located on the south coast of Turkey. The study included 38 cystic fibrosis patients aged between 0.6 and 18 years. The CFTR genotype of the patients was categorized into 2 groups based on the presence or absence of class I or class II mutations in any of the alleles. Group I comprised 8 homozygous, 8 with unknown alleles, and 8 compound heterozygous patients, and group II comprised 11 homozygous and 3 compound heterozygous patients. The groups were analyzed in respect of cystic fibrosis disease severity markers, such as spirometry, ShwachmanKulczycki score, body mass index (BMI), sweat chloride concentration, chronic Pseudomonas aeruginosa infection, annual exacerbation frequency, and severe exacerbations requiring hospitalization during the previous year. In the comparison of group I and group II patients, a significant difference was observed in pancreas insufficiency (83.3% vs. 35.7%; P = .005), chronic P. aeruginosa infection (58.3% vs. 7.1%; P = .002), cough severity score (1.7 ± 1.1 vs. 0.9 ± 1.5; P = .029), number of severe exacerbations requiring hospitalization during the previous year (0.9 ± 1 vs. 0.3 ± 0.8; P = .03), and sweat chloride levels (76.7 ± 15.2 vs. 61 ± 22.3; P = .02). All these values were higher in group I patients. The mean BMI values (15.8 ± 2.2 vs. 17.6 ± 2.8; P = .03) were lower in group I patients. There seems to be a difference between class I/II CFTR mutations and class III-V mutations on the severity of the disease in cystic fibrosis patients.

Development of a multivariable prediction model for congenital unilateral absence of the vas deferens in male partners of infertile couples.

Congenital unilateral absence of vas deferens has been diagnosed in fertile and normozoospermic males and is associated with the risk of unilateral renal absence or cystic fibrosis transmembrane conductance regulator mutations; but no prediction model currently exists to diagnose this condition. The study aims to identify clinical and biological variables that may have a predictive value for the diagnosis of congenital unilateral absence of vas deferens in male partners of infertile couples MATERIALS AND METHODS: We designed a retrospective, cross-sectional, case-control study on electronic health records of a single tertiary-care andrological centre collected between 1998 and 2018. We included all subjects diagnosed with congenital unilateral absence of vas deferens using combined scrotal and transrectal ultrasounds. Controls were confirmed free of congenital unilateral absence of vas deferens by the same way. Both groups received standardised exploration procedures. Multivariable logistic regression model was built in a backward stepwise manner. Model performance and calibration were assessed. The study is reported according to TRIPOD statement. We included 69 congenital unilateral absence of vas deferens cases and 78 controls. Cases had a lower semen volume than controls. The congenital unilateral absence of vas deferens risk was associated with history of cryptorchidism and both levels of semen fructose and α-glucosidase. These predictors were confirmed by a random forest algorithm. The area under the curve was 0.886 (95% interval: 0.81-0.92). Calibration was performed with the Hosmer-Lemeshow test (p=0.88). History of cryptorchidism, semen fructose and α-glucosidase were identified as relevant and independent predictors for the diagnosis of congenital unilateral absence of vas deferens. The model enables to identify male patients with a high risk of congenital unilateral absence of vas deferens to whom a transrectal ultrasounds would be proposed to confirm the diagnosis, whatever their semen parameters. It will also help to address the risks of unilateral renal absence and of cystic fibrosis transmembrane conductance regulator mutations carrying during the management of infertile couples.

Recent advances in the early treatment of cystic fibrosis: Bridging the gap to highly effective modulator therapy.

Highly effective modulator therapy (HEMT) for cystic fibrosis (CF) has been touted as one of the greatest advances to date in CF care. As these therapies are now available for many older children and adults with CF, marked improvement of their nutritional status, pulmonary and gastrointestinal symptoms has been observed. However, most infants and younger children are not current candidates for HEMT due to age and/or cystic fibrosis transmembrane conductance regulator (CFTR) mutation. For these young children, it is essential to provide rigorous monitoring and care to avoid potential disease sequelae while awaiting HEMT availability. The following article highlights recent advances in the care of infants and young children with CF with regard to surveillance and treatment of nutritional, pulmonary, and gastrointestinal disorders. Recent clinical trials in this population are also reviewed.

The Intestinal Microbiome and Cystic Fibrosis Transmembrane Conductance Regulator Modulators: Emerging Themes in the Management of Gastrointestinal Manifestations of Cystic Fibrosis.

While commonly associated with pulmonary manifestations, cystic fibrosis (CF) is a systemic disease with wide-ranging effects on the gastrointestinal (GI) tract. This article reviews major recent updates in gastroenterological CF care and research. The high burden of GI symptoms in CF has led to recent studies assessing GI-specific symptom questionnaires and scoring systems. Intestinal dysbiosis potentially contributes to gastrointestinal symptoms in patients with CF and an increased risk of gastrointestinal cancers in CF. An increased incidence of colorectal cancer (CRC) has led to CF-specific CRC screening and surveillance recommendations. Pharmacologic therapies targeting specific cystic fibrosis transmembrane conductance regulator (CFTR) mutations have shown promise in treating GI manifestations of CF. New research has highlighted the importance of intestinal dysbiosis in CF. Future studies should assess whether CFTR modulators affect the gut microbiome and whether altering the gut microbiome will impact GI symptoms and GI cancer risk.

First report of the cystic fibrosis transmembrane conductance regulator mutation c.1521_1523delCTT (p. Phe508del) in two Qatari patients with cystic fibrosis

We report two cases of Qatari children with cystic fibrosis (CF) from different families presenting the homozygous CFTR 1521_1523delCTT (p. Phe508del) mutation with classic CF phenotypes. This gene mutation is considered the second CF mutation identified in Qatar. Herein, we review the frequency and distribution of this mutation in Arab countries.