CFTR is a dynamically regulated anion channel. Intracellular WNK1-SPAK activation causes CFTR to change permeability and conductance characteristics from a chloride-preferring to bicarbonate-preferring channel through unknown mechanisms. Two severe CFTR mutations (CFTRsev) cause complete loss of CFTR function and result in cystic fibrosis (CF), a severe genetic disorder affecting sweat glands, nasal sinuses, lungs, pancreas, liver, intestines, and male reproductive system. We hypothesize that those CFTR mutations that disrupt the WNK1-SPAK activation mechanisms cause a selective, bicarbonate defect in channel function (CFTRBD) affecting organs that utilize CFTR for bicarbonate secretion (e.g. the pancreas, nasal sinus, vas deferens) but do not cause typical CF. To understand the structural and functional requirements of the CFTR bicarbonate-preferring channel, we (a) screened 984 well-phenotyped pancreatitis cases for candidate CFTRBD mutations from among 81 previously described CFTR variants; (b) conducted electrophysiology studies on clones of variants found in pancreatitis but not CF; (c) computationally constructed a new, complete structural model of CFTR for molecular dynamics simulation of wild-type and mutant variants; and (d) tested the newly defined CFTRBD variants for disease in non-pancreas organs utilizing CFTR for bicarbonate secretion. Nine variants (CFTR R74Q, R75Q, R117H, R170H, L967S, L997F, D1152H, S1235R, and D1270N) not associated with typical CF were associated with pancreatitis (OR 1.5, p = 0.002). Clones expressed in HEK 293T cells had normal chloride but not bicarbonate permeability and conductance with WNK1-SPAK activation. Molecular dynamics simulations suggest physical restriction of the CFTR channel and altered dynamic channel regulation. Comparing pancreatitis patients and controls, CFTRBD increased risk for rhinosinusitis (OR 2.3, p<0.005) and male infertility (OR 395, p<<0.0001). WNK1-SPAK pathway-activated increases in CFTR bicarbonate permeability are altered by CFTRBD variants through multiple mechanisms. CFTRBD variants are associated with clinically significant disorders of the pancreas, sinuses, and male reproductive system.
Genetic disorders of ion channels can affect the body's ability to function properly in many ways. CFTR, an ion channel regulating movement of chloride and bicarbonate across cell membranes, is important for absorbing and secreting fluids. If the gene responsible for the CFTR channel is mutated severely, the result is cystic fibrosis, a hereditary disorder in which the patient develops thick mucus, especially in the lungs, as well as scarring (fibrosis) in the pancreas. Cystic fibrosis also affects the sweat glands, nasal sinuses, intestines, liver, and male reproductive system. Mutations to the CFTR gene that do not cause cystic fibrosis have been considered benign. However, we discovered 9 CFTR mutations that do not cause cystic fibrosis but do cause inflammation and scarring of the pancreas (chronic pancreatitis). These mutant CFTR channels secrete chloride, which is important in the sweat glands, lungs, and intestines, but not bicarbonate, which is important in the pancreas, sinuses, and male reproductive tract. We found patients with any of these 9 mutations had chronic pancreatitis, and often sinus infections, and male infertility, but not other symptoms of cystic fibrosis. Our computer models and data will help researchers develop better drugs and help physicians treating patients with chronic pancreatitis.
Cystic fibrosis (CF) is caused by mutations in the cystic fibrosis transmembrane regulator gene (CFTR). In light of the strong allelic heterogeneity and regional specificity of the mutation spectrum, the strategy of molecular diagnostics and counseling in CF requires genetic tests to reflect the frequency profile characteristic for a given population. The goal of the study was to provide an updated comprehensive estimation of the distribution of CFTR mutations in Polish CF patients and to assess the effectiveness of INNOLiPA_CFTR tests in Polish population. The analyzed cohort consisted of 738 patients with the clinically confirmed CF diagnosis, prescreened for molecular defects using INNOLiPA_CFTR panels from Innogenetics. A combined efficiency of INNOLiPA CFTR_19 and CFTR_17_TnUpdate tests was 75.5%; both mutations were detected in 68.2%, and one mutation in 14.8% of the affected individuals. The group composed of all the patients with only one or with no mutation detected (109 and 126 individuals, respectively) was analyzed further using a mutation screening approach, i.e. SSCP/HD (single strand conformational polymorphism/heteroduplex) analysis of PCR products followed by sequencing of the coding sequence. As a result, 53 more mutations were found in 97 patients. The overall efficiency of the CF allele detection was 82.5% (7.0% increase compared to INNOLiPA tests alone). The distribution of the most frequent mutations in Poland was assessed. Most of the mutations repetitively found in Polish patients had been previously described in other European populations. The most frequent mutated allele, F508del, represented 54.5% of Polish CF chromosomes. Another eight mutations had frequencies over 1%, 24 had frequencies between 1 and 0.1%; c.2052-2053insA and c.3468+2_3468+3insT were the most frequent non-INNOLiPA mutations. Mutation distribution described herein is also relevant to the Polish diaspora. Our study also demonstrates that the reported efficiency of mutation detection strongly depends on the diagnostic experience of referring health centers.
Cystic fibrosis (CF) is one of the most common genetic diseases in the Caucasian population and is characterized by chronic obstructive pulmonary disease, exocrine pancreatic insufficiency, and elevation of sodium and chloride concentrations in the sweat and infertility in men. The disease is caused by mutations in the CF transmembrane conductance regulator (CFTR) gene, which encodes a protein that functions as chloride channel at the apical membrane of different epithelia. Owing to the high genotypic and phenotypic disease heterogeneity, effects and consequences of the majority of the CFTR mutations have not yet been studied. Recently, the frameshift mutation 3905insT was identified as the second most frequent mutation in the Swiss population and found to be associated with a severe phenotype. The frameshift mutation produces a premature termination codon (PTC) in exon 20, and transcripts bearing this PTC are potential targets for degradation through nonsense-mediated mRNA decay (NMD) and/or for exon skipping through nonsense-associated alternative splicing (NAS). Using RT–PCR analysis in lymphocytes and different tissue types from patients carrying the mutation, we showed that the PTC introduced by the mutation does neither elicit a degradation of the mRNA through NMD nor an alternative splicing through NAS. Moreover, immunocytochemical analysis in nasal epithelial cells revealed a significantly reduced amount of CFTR at the apical membrane providing a possible molecular explanation for the more severe phenotype observed in F508del/3905insT compound heterozygotes compared with F508del homozygotes. However, further experiments are needed to elucidate the fate of the 3905insT CFTR in the cell after its biosynthesis.
cystic fibrosis; CFTR; nonsense-mediated mRNA decay (NMD); nonsense-associated alternative splicing (NAS); genotype/phenotype correlation
Cystic fibrosis (CF) is the most frequent lethal genetic disorder among Caucasians. It depends on alterations of a chloride channel expressed by most epithelial cells and encoded by CFTR gene. Also using scanning techniques to analyze the whole coding regions of CFTR gene, mutations are not identified in up to 10% of CF alleles, and such figure increases in CFTR-related disorders (CFTR-RD). Other gene regions may be the site of causing-disease mutations. We searched for genetic variants in the 1500 bp of CFTR 3′ untranslated region, typical target of microRNA (miRNA) posttranscriptional gene regulation, in either CF patients with the F508del homozygous genotype and different clinical expression (n = 20), CF (n = 32) and CFTR-RD (n = 43) patients with one or none mutation after CFTR scanning and in controls (n = 50). We identified three SNPs, one of which, the c.*1043A>C, was located in a region predicted to bind miR-433 and miR-509-3p. Such mutation was peculiar of a CFTR-RD patient that had Congenital Bilateral Absence of Vas Deferens (CBAVD), diffuse bronchiectasis, a borderline sweat chloride test and the heterozygous severe F508del mutation on the other allele. The expression analysis demonstrated that the c.*1043A>C increases the affinity for miR-509-3p and slightly decreases that for the miR-433. Both miRNAs cause in vitro a reduced expression of CFTR protein. Thus, the c.*1043A>C may act as a mild CFTR mutation enhancing the affinity for inhibitory miRNAs as a novel pathogenetic mechanism in CF.
The Cystic Fibrosis Transmembrane conductance Regulator (CFTR) gene encodes a cAMP-regulated chloride channel that is important in controlling the exchange of fluid and electrolytes across epithelial cells. Mutation of CFTR can lead to Cystic Fibrosis (CF), the most common lethal genetic disease in Caucasians. CF is a systemic illness with multiple organ systems affected including pulmonary, gastrointestinal, pancreatic, immune, endocrine and reproductive systems. To understand the role of CFTR in the various tissues in which it is expressed, we generated a murine conditional null allele of Cftr (Cftrfl10) in which loxP sites were inserted around exon 10 of the Cftr gene. The Cftr conditional null allele was validated by generating constitutive Cftr null (CftrΔ10) mice using the protamine-cre system. The CftrΔ10/Δ10 mice displayed almost identical phenotypes to previously published CF mouse models, including poor growth, decreased survival, intestinal obstruction and loss of Cftr function as assessed by electrophysiology measurements on gut and nasal epithelium. Mice containing the conditional null Cftr allele will be useful in future studies to understand the role of Cftr in specific tissues and developmental time points and lead to a better understanding of CF disease.
Background: Cystic fibrosis is a monogenic recessive disorder found predominantly in Caucasian population. This disease arises from mutations in the cystic fibrosis transmembrane conductance regulator (CFTR) gene. In this study we consider poly T polymorphism c.1210-12T, c.1210-12T, c.1210-12T (T5, T7, T9) in the intron 8 of CFTR gene in normal individuals and cystic fibrosis patients in the north of Iran.
Material and methods: 40 CF patients and 40 normal individuals were screened for poly T polymorphism in intron 8 of CFTR gene using Reverse Dot Blot method which was also used to detect p.Phe508del among CF patients.
Results: T7 allele is the most prevalent in both normal and CF patients. Its abundance is approximately 75%. T9 and T5 represent approximately 20% and 5% of alleles respectively. T7/ T7 genotype is the most present in both normal and CF patients with 72.5% and 60% prevalence respectively. p.Phe508del was present in 13 CFTR alleles belonging to 7 patients with either homozygote T9/ T9, T7/ T7 or compound heterozygote T7/ T9 genotypes.
Conclusion: Contrary to the Caucasians, T7 allele is more frequent in Northern Iranian CF patients. The presence of p.Phe508del and T7 allele in the same framework is reported for the first time in this part of the world. Further investigations of other populations will help to understand whether p.Phe508del arose by selection pressure in this part of the world or was imported from European countries. The abundance of T5, T7, T9 alleles indicates that this polymorphism can be used as one of the informative markers for detection of normal and mutant alleles in prenatal diagnosis or carrier assessment in families with previous history of the disease in regions with high degree of CFTR mutation heterogeneity.
Cystic fibrosis; IVS8 polyT; polymorphism; p.Phe508del; Iran
F508del-CFTR, the most frequent disease-causing mutation among Caucasian cystic fibrosis (CF) patients, has been characterised as a mutant defective in protein folding, processing and trafficking. We have investigated the two neighbouring cytokeratin genes KRT8 and KRT18 in a candidate gene approach to ask whether variants in KRT8 and/or KRT18 modify the impaired ion conductance known as the CF basic defect, and whether they are associated with correct trafficking of mutant CFTR and disease severity of CF.
We have selected contrasting F508del-CFTR homozygous patient subpopulations stratified for disease severity, comparing 13 concordant mildly affected sib pairs vs. 12 concordant severely affected sib pairs, or manifestation of the CF basic defect in intestinal epithelium, comparing 22 individuals who exhibit CFTR-mediated residual chloride secretion vs. 14 individuals who do not express any chloride secretion, for an association. The KRT8/KRT18 locus was initially interrogated with one informative microsatellite marker. Subsequently, a low density SNP map with four SNPs in KRT8 and two SNPs in KRT18, each selected for high polymorphism content, was used to localize the association signal.
KRT8, but not KRT18, showed an association with CF disease severity (Pbest = 0.00131; Pcorr = 0.0185) and CFTR mediated residual chloride secretion (Pbest = 0.0004; Pcorr = 0.0069). Two major four-marker-haplotypes spanning 13 kb including the entire KRT8 gene accounted for 90% of chromosomes, demonstrating strong linkage disequilibrium at that locus. Absence of chloride secretion was associated with the recessive haplotype 1122 at rs1907671, rs4300473, rs2035878 and rs2035875. The contrasting haplotype 2211 was dominant for the presence of CFTR mediated residual chloride secretion. In consistency, the KRT8 haplotype 2211 was associated with mild CF disease while 1122 was observed as risk haplotype. Analysis of microsatellite allele distributions on the SNP background suggests that the mild KRT8 haplotype 2211 is phylogenetically older than its severe counterpart.
The two opposing KRT8 alleles which have been identified as a benign and as a risk allele in this work are likely effective in the context of epithelial cell differentiation. As the mild KRT8 allele is associated with CFTR mediated residual chloride secretion among F508del-CFTR homozygotes, the KRT8/KRT18 heterodimeric intermediary filaments of the cytoskeleton apparently are an essential component for the proper targeting of CFTR to the apical membrane in epithelial cells.
Cystic fibrosis transmembrane conductance regulator-related disorders encompass a disease spectrum from focal male reproductive tract involvement in congenital absence of the vas deferens to multiorgan involvement in classic cystic fibrosis. The reproductive, gastrointestinal, and exocrine manifestations of cystic fibrosis transmembrane conductance regulator deficiency are correlated with CFTR genotype, whereas the respiratory manifestations that are the main cause of morbidity and mortality in cystic fibrosis are less predictable. Molecular genetic testing of CFTR has led to new diagnostic strategies and will enable targeting of molecular therapies now in development. Older diagnostic methods that measure sweat chloride and nasal potential difference nonetheless remain important because of their sensitivity and specificity. In addition, the measurement of immunoreactive trypsinogen and the genotyping of CFTR alleles are key to newborn screening programs because of low cost. The multiorgan nature of cystic fibrosis leads to a heavy burden of care, thus therapeutic regimens are tailored to the specific manifestations present in each patient. The variability of cystic fibrosis lung disease and the variable expressivity of mild CFTR alleles complicate genetic counseling for this autosomal recessive disorder. Widespread implementation of newborn screening programs among populations with significant cystic fibrosis mutation carrier frequencies is expected to result in increasing demands on genetic counseling resources.
cystic fibrosis; congenital absence of vas deferens; CFTR; diagnostic testing; genetic counseling
Cystic fibrosis (CF) is caused by mutations in the gene encoding the cystic fibrosis transmembrane conductance regulator (CFTR) protein, which acts as a chloride channel activated by cyclic AMP (cAMP). The most frequent mutation found in 70% of CF patients is F508del, while premature stop mutations are found in about 10% of patients. In vitro aminoglycoside antibiotics (e.g. gentamicin) suppress nonsense mutations located in CFTR permitting translation to continue to the natural termination codon. Pharmacologic suppression of stop mutations within the CFTR may be of benefit to a significant number of patients. Our pilot study was conducted to determine whether intravenous gentamicin suppresses stop codons in CF patients and whether it has clinical benefits.
A dual gene reporter system was used to determine the gentamicin-induced readthrough level of the most frequent stop mutations within the CFTR in the French population. We investigated readthrough efficiency in response to 10 mg/kg once-daily intravenous gentamicin perfusions in patients with and without stop mutations. Respiratory function, sweat chloride concentration, nasal potential difference (NPD) and CFTR expression in nasal epithelial cells were measured at baseline and after 15 days of treatment.
After in vitro gentamicin incubation, the readthrough efficiency for the Y122X mutation was at least five times higher than that for G542X, R1162X, and W1282X. In six of the nine patients with the Y122X mutation, CFTR immunodetection showed protein at the membrane of the nasal epithelial cells and the CFTR-dependent Cl- secretion in NPD measurements increased significantly. Respiratory status also improved in these patients, irrespective of the gentamicin sensitivity of the bacteria present in the sputum. Mean sweat chloride concentration decreased significantly and normalised in two patients. Clinical status, NPD and sweat Cl- values did not change in the Y122X patients with no protein expression, in patients with the other stop mutations investigated in vitro and those without stop mutations.
Suppression of stop mutations in the CFTR gene with parenteral gentamicin can be predicted in vitro and is associated with clinical benefit and significant modification of the CFTR-mediated Cl- transport in nasal and sweat gland epithelium.
Background: Mutations in the cystic fibrosis transmembrane conductance regulator (CFTR) gene—many of which cause cystic fibrosis—have also been reported in patients with chronic pancreatitis. The authors examine whether mild or severe CFTR mutations, homozygous or compound heterozygous CFTR mutations, or even simple cystic fibrosis carrier status alone increases the risk of developing pancreatitis.
Methods: After exclusion of patients with trypsinogen (PRSS1) mutations, cystic fibrosis, or pulmonary disease, and with known risk factors for pancreatitis 67 patients with idiopathic chronic pancreatitis (ICP) from northwest Germany and 60 geographically and ethnically matched controls were recruited. The entire coding region of the CFTR gene was sequenced in all patients and controls. ICP patients were also analysed for serine protease inhibitor Kazal type 1 (SPINK1) gene mutations.
Results: Abnormal CFTR alleles were found to be twice as frequent in ICP patients as in controls (25/134 v 11/120; p<0.05). Three of four severe CFTR mutations detected in patients were compound heterozygous with another abnormal CFTR allele, whereas among controls three severe CFTR mutations were found in heterozygous cystic fibrosis carriers. In ICP patients 19 uncommon/mild mutations, including combinations of the 5T allele with 12TG repeats, were identified compared with only five in controls (p = 0.012). Heterozygous SPINK1 mutations were detected in eight ICP patients (15% v 1% in controls) but only one also carried an additional mild CFTR mutation.
Conclusions: These data show that not only compound heterozygosity, but also cystic fibrosis carrier status for different types of CFTR mutations, including uncommon/mild mutations, significantly increase the risk of developing pancreatitis. Although 45% of the study’s ICP patients carried predisposing genetic risk factors (for example, mutations in CFTR or SPINK1), the authors found no evidence that the risk conveyed by CFTR mutations depends on co-inherited SPINK1 mutations.
CFTR; gene mutation; idiopathic chronic pancreatitis
There is great heterogeneity in the clinical manifestations of cystic fibrosis (CF). Some patients may have all the classical manifestations of CF from infancy and have a relatively poor prognosis, while others have much milder or even atypical disease manifestations and still carry mutations on each of the CFTR genes. It is important to distinguish between these categories of patients. The European Diagnostic Working Group proposes the following terminology. Patients are diagnosed with classic or typical CF if they have one or more phenotypic characteristics and a sweat chloride concentration of >60 mmol/l. The vast majority of CF patients fall into this category. Usually one established mutation causing CF can be identified on each CFTR gene. Patients with classic CF can have exocrine pancreatic insufficiency or pancreatic sufficiency. The disease can have a severe course with rapid progression of symptoms or a milder course with very little deterioration over time. Patients with non‐classic or atypical CF have a CF phenotype in at least one organ system and a normal (<30 mmol/l) or borderline (30–60 mmol/l) sweat chloride level. In these patients confirmation of the diagnosis of CF requires detection of one disease causing mutation on each CFTR gene or direct quantification of CFTR dysfunction by nasal potential difference measurement. Non‐classic CF includes patients with multiorgan or single organ involvement. Most of these patients have exocrine pancreatic sufficiency and milder lung disease. Algorithms for a structured diagnostic process are proposed.
cystic fibrosis; lung disease; diagnostic algorithms; CFTR gene; sweat test
Cystic fibrosis (CF) is the most common inherited disorder of childhood. The diagnosis of CF has traditionally been based on clinical features with confirmatory evidence by sweat electrolyte analysis. Since 1989 it has been possible to also use gene mutation analysis to aid the diagnosis. Cloning of the cystic fibrosis transmembrane conductance regulator (CFTR) gene has advanced our understanding of CF, in particular the molecular basis of an expanded CF phenotype. However, because there are over 1000 mutations and 200 polymorphisms, many without recognised effects on CFTR, the molecular diagnosis can be troublesome. This has necessitated measurement of CFTR function with renewed interest in the sweat test. This review provides an overview of the clinical features of CF, the diagnosis and complex genetics. We provide a detailed discussion of the structure and function of CFTR and the classification of CFTR mutations. Sweat electrolyte analysis is discussed, from the physiology of sweating to the rigours of a properly performed sweat test and its interpretation. With this information it is possible to understand the relevance of the sweat test in the genomic era.
Patients with cystic fibrosis (CF) manifest a multisystem disease due to deleterious mutations in each gene encoding the cystic fibrosis transmembrane conductance regulator (CFTR). However, the role of dysfunctional CFTR is uncertain in individuals with mild forms of CF (ie, pancreatic sufficiency) and mutation in only one CFTR gene.
Eleven pancreatic sufficient (PS) CF patients with only one CFTR mutation identified after mutation screening (three patients), mutation scanning (four patients) or DNA sequencing (four patients) were studied. Bi-directional sequencing of the coding region of CFTR was performed in patients who had mutation screening or scanning. If a second CFTR mutation was not identified, CFTR mRNA transcripts from nasal epithelial cells were analysed to determine if any PS-CF patients harboured a second CFTR mutation that altered RNA expression.
Sequencing of the coding regions of CFTR identified a second deleterious mutation in five of the seven patients who previously had mutation screening or mutation scanning. Five of the remaining six patients with only one deleterious mutation identified in the coding region of one CFTR gene had a pathologic reduction in the amount of RNA transcribed from their other CFTR gene (8.4–16% of wild type).
These results show that sequencing of the coding region of CFTR followed by analysis of CFTR transcription could be a useful diagnostic approach to confirm that patients with mild forms of CF harbour deleterious alterations in both CFTR genes.
This report describe for the first time a clinical case with a CFTR allelic variant 186-8T/C (c.54-8 T/C) in intron 1 of CFTR and underline the importance of applying a combination of genetic and functional tests to establish or exclude a diagnosis of Cystic Fibrosis. In this case the diagnostic algorithm proposed for CF has been successfully applied at our Center and previous CF diagnosis assigned in a different Center was not confirmed.
A 38 year-old Italian woman had been treated as affected by CF since 2010, following diagnosis based on sweat tests (reported values of 73 and 57 mEq/L) and a clinical history consistent with CF. No mutations were identified by first level of genetic analysis. Afterwards the patient referred to our center for assessing the relevance of these findings. The genetic variant 186-8T/C (c.54-8 T/C) in intron 1 of the CFTR gene was detected by sequencing. Low-level interstitial-alveolar infiltration was recorded by high-resolution computerized tomography. Lung function was normal and sputum and Broncho Alveolar Lavage cultures resulted bacteriologically negative. Sweat chloride levels was re-assessed and resulted with values of 57 and 35 mEq/L, with a borderline range between 40 and 60 mEq/L. Nasal Potential Difference measurements resulted in three reliable measurements consistent with a non-CF phenotype. Differential diagnosis with ciliary dyskinesia was excluded, as was exon 2 skipping of CFTR gene that might have caused a CFTR functional defect. Furthermore, single cell fluorescence analysis in response to cAMP agonists performed in patient’s monocytes overlapped those obtained in healthy donors.
We concluded that this patient was not affected by CF. This case highlights the need for referrals to highly specialized centers and the importance of combined functional and genetic tests in making a correct diagnosis. Moreover, we confirmed a correlation between NPD tracings and cell depolarization in monocytes providing a rationale for proposing the use of leukocytes as a potential support for CF diagnosis.
Cystic Fibrosis; Cystic Fibrosis Conductance Transmembrane Regulator; Mutation analysis; Nasal potential difference measurements; Cystic fibrosis conductance transmembrane regulator function
Cystic fibrosis (CF) is an autosomal recessive disorder usually found in populations of white Caucasian descent. CF is caused by mutations in the Cystic Fibrosis Transmembrane conductance Regulator (CFTR) gene. A 5-yr-old Korean girl was admitted complaining of coughing and greenish sputum. Chest radiographs and computed tomographic (CT) scan revealed diffuse bronchiectasis in both lungs. The patient had chronic diarrhea and poor weight gain, and the abdominal pancreaticobiliary CT scan revealed atrophy of the pancreas. Finally, CF was confirmed by the repeated analysis of the quantitative pilocarpine iontophoresis test. The chloride concentration of sweat samples taken from both forearms of the pateint was an average of 88.7 mM/L (normal value <40 mM/L). After a comprehensive search for mutations in the CFTR gene, the patient was found to carry the non-synonymous L441P mutation in one allele. Molecular physiologic analysis of the L441P mutation of CFTR revealed that the L441P mutation completely abolished the CFTR Cl- channel activity by disrupting proper protein folding and membrane trafficking of CFTR protein. These results confirmed the pathogenicity of the L441P mutation of CFTR circulating in the Korean population. The possibility of CF should be suspected in patients with chronic bronchiectasis, although the frequency of CF is relatively rare in East Asia.
Bronchiectasis; Cl- channel; Cystic Fibrosis; Cystic Fibrosis Transmembrane Conductance Regulator; Korea
Cystic fibrosis is a genetic disease that is associated with abnormal sweat electrolytes, sino-pulmonary disease, exocrine pancreatic insufficiency, and male infertility. Insights into genotype/phenotype relations have recently been gained in this disorder. The strongest relationship exists between 'severe' mutations in the gene that encodes the cystic fibrosis transmembrane regulator (CFTR) and pancreatic insufficiency. The relationship between 'mild' mutations, associated with residual CFTR function, and expression of disease is less precise. Atypical 'mild' mutations in the CFTR gene have been linked to late-onset pulmonary disease, congenital bilateral absence of the vas deferens, and idiopathic pancreatitis. Less commonly, sinusitis, allergic bronchopulmonary aspergillosis, and possibly even asthma may also be associated with mutations in the CFTR gene, but those syndromes predominantly reflect non-CFTR gene modifiers and environmental influences.
asthma; cystic fibrosis (CF); cystic fibrosis transmembrane regulator (CFTR); mutations; pancreatitis; phenotype
Mutations in the CFTR gene cause Cystic Fibrosis (CF) the most common life-threatening autosomal recessive disease affecting Caucasians. We identified a CFTR mutation (c.120del23) abolishing the normal translation initiation codon, which occurs in two Portuguese CF patients. This study aims at functionally characterizing the effect of this novel mutation.
RNA and protein techniques were applied to both native tissues from CF patients and recombinant cells expressing CFTR constructs to determine whether c.120del23 allows CFTR protein production through usage of alternative internal codons, and to characterize the putative truncated CFTR form(s).
Our data show that two shorter forms of CFTR protein are produced when the initiation translation codon is deleted indicating usage of internal initiation codons. The N-truncated CFTR generated by this mutation has decreased stability, very low processing efficiency, and drastically reduced function. Analysis of mutants of four methionine codons downstream to M1 (M82, M150, M152, M156) revealed that each of the codons M150/M152/M156 (exon 4) can mediate CFTR alternative translation.
The CFTR N-terminus has an important role in avoiding CFTR turnover and in rendering effective its plasma membrane traffic. These data correlate well with the severe clinical phenotype of CF patients bearing the c.120del23 mutation.
CFTR; Cystic Fibrosis; Mutation; Truncated proteins; Alternative translation; N-terminus
Background/Aims: Mutations in the CFTR gene cause Cystic Fibrosis (CF) the most common life-threatening autosomal recessive disease affecting Caucasians. We identified a CFTR mutation (c.120del23) abolishing the normal translation initiation codon, which occurs in two Portuguese CF patients. This study aims at functionally characterizing the effect of this novel mutation. Methods: RNA and protein techniques were applied to both native tissues from CF patients and recombinant cells expressing CFTR constructs to determine whether c.120del23 allows CFTR protein production through usage of alternative internal codons, and to characterize the putative truncated CFTR form(s). Results: Our data show that two shorter forms of CFTR protein are produced when the initiation translation codon is deleted indicating usage of internal initiation codons. The N-truncated CFTR generated by this mutation has decreased stability, very low processing efficiency, and drastically reduced function. Analysis of mutants of four methionine codons downstream to M1 (M82, M150, M152, M156) revealed that each of the codons M150/M152/M156 (exon 4) can mediate CFTR alternative translation. Conclusions: The CFTR N-terminus has an important role in avoiding CFTR turnover and in rendering effective its plasma membrane traffic. These data correlate well with the severe clinical phenotype of CF patients bearing the c.120del23 mutation.
CFTR; Cystic Fibrosis; Mutation; Truncated proteins; Alternative translation; N-terminus
Objective: The aim of the study is to evaluate the role of Denaturing High Performance Liquid Chromatography (DHPLC) in the second level screening of the Cystic Fibrosis Transmembrane Conductance Regulator (CFTR) gene.
Methods: A 9-month prospective study, between June 2008 and March 2009 at Artemisia Fetal Medical Centre, included 3829 samples of amniotic fluid collected from women undergoing mid-trimester amniocentesis.
The genetic diagnosis of CF was based on research of the main mutations of the CFTR gene on fetal DNA extracted from the amniocytes, (first level screening) using different commercial diagnostic systems. A second level screening using DHPLC, on the amniotic fluid and on a blood sample from the couple, was offered in case of fetuses heterozygous at first level screening.
Results: Of 3829 fetuses, 134 were found to be positive, 129 heterozygous and 5 affected. Of the 129 couples, following appropriate genetic counselling, 53 requested a second level screening. Through the use of DHPLC, 44 couples were found to be negative, and in nine couples, nine rare mutations were identified.
Conclusions: The first level screening can be useful to evidence up to 75% of the CF mutations. The second level screening can identify a further 10% of mutant alleles. DHPLC was found to be a reliable and specific method for the rapid identification of the rare CFTR mutations which were not revealed in initial first level screening.
CFTR; gene; cystic fibrosis; chromatography
The p.Leu1077Pro CFTR mutation was firstly described in 1992 as a mild allele that confers a pancreatic sufficiency phenotype but the information collected in database CFTR2 lead to consider p.Leu1077Pro as a severe CF mutation. Although it is typical of Southern Italy, p.Leu1077Pro is not included in the mutation panel firstly tested in individuals originated from this area. The aim of our study was to describe prevalence and clinical features in patients bearing this mutation followed in our Cystic Fibrosis Centre to demonstrate that this mutation should be included in the mutation panel firstly tested in patients originated from Southern Italy.
We reviewed data from a cohort of 111 cystic fibrosis patients. 4 patients who were heterozygous for the p.Leu1077Pro mutation were included in the study.
In our Cystic Fibrosis Centre, the prevalence of p.Leu1077Pro is 3.6% among all mutations. All patients had positive sweat test values, pancreatic insufficiency and pulmonary exacerbations. One out of four patients even showed both FEV1 and FVC values significantly below the normal range, the presence of bronchiectasis and chronic Pseudomonas aeruginosa colonization.
We found that the p.Leu1077Pro CFTR mutation is associated with a classic CF phenotype confirming what is reported in CFTR2 database. The relatively high prevalence of p.Leu1077Pro associated with the severe clinical course of the disease in patients bearing this mutation is of interest for genetic counselling purposes, as it should be part of mutation panel to be tested in individuals originated from Southern Italy.
Cystic fibrosis; CFTR; pLeu1077Pro; L1077P; Genotype-phenotype; Sicilian patients
Purpose of review
Recent progress in understanding the production, processing, and function of the cystic fibrosis gene product, the cystic fibrosis transmembrane conductance regulator (CFTR), has revealed new therapeutic targets to repair the mutant protein. Classification of CFTR mutations and new treatment strategies to address each will be described here.
High-throughput screening and other drug discovery efforts have identified small molecules that restore activity to mutant CFTR. Compounds such as VX-770 that potentiate CFTR have demonstrated exciting results in recent clinical trials and demonstrate robust effects across several CFTR mutation classes in the laboratory. A number of novel F508del CFTR processing correctors restore protein to the cell surface and improve ion channel function in vitro and are augmented by coadministration of CFTR potentiators. Ongoing discovery efforts that target protein folding, CFTR trafficking, and cell stress have also indicated promising results. Aminoglycosides and the novel small molecule ataluren induce translational readthrough of nonsense mutations in CFTR and other genetic diseases in vitro and in vivo and have shown activity in proof of concept trials, and ataluren is now being studied in confirmatory trials.
An improved understanding of the molecular mechanisms underlying the basic genetic defect in cystic fibrosis have led to new treatment strategies to repair the mutant protein.
cystic fibrosis; cystic fibrosis transmembrane conductance regulator; new therapies
Cystic fibrosis (CF) is one of the most common hereditary disorders among Caucasians. The most common mutations of the cystic fibrosis transmembrane conductance regulator (CFTR) gene have been well established among Caucasian populations. In Koreans, however, there are very few cases of genetically confirmed CF thus far, and the spectrum of mutations seems quite different from that observed in Caucasians.
In the present study, we describe the cases of 2 Korean CF patients, present sequencing results identifying mutations in their CFTR gene, and summarize the results of CFTR mutational spectrum from previously reported Korean CF patients. The mutations described were identified by performing direct sequencing analysis of the complete coding regions and flanking intronic sequences of the CFTR gene, followed by multiplex ligation-dependent probe amplification (MLPA) analysis in order to detect gene deletions or duplications that could not be identified by a direct sequencing method.
Three CFTR mutations were identified in the 2 patients, including p.Q98R, c.2052delA, and c.579+5G>A. In an analysis of 9 Korean CF patients that included the 2 patients presented in this study, p.Q98R mutation was the only recurrently observed mutation with a frequency of 18.8% (3/16 alleles). Furthermore, only one of the mutations (c.3272-26A>G) was found among the 32 common mutations in the screening panel for Caucasians from the Cystic Fibrosis Mutation Database.
Sequencing of the entire CFTR gene followed by MLPA analysis, rather than using the targeted sequencing-based screening panel for mutations commonly found in Caucasian populations, is recommended for genetic analysis of Korean CF patients.
CFTR; Cystic fibrosis transmembrane conductance regulator; Cystic fibrosis; Mutations; Koreans; Sequencing; MLPA
In this study we investigated the effects of the Cystic Fibrosis Transmembrane conductance Regulator (CFTR) gene variants on the composition of faecal microbiota, in patients affected by Cystic Fibrosis (CF). CFTR mutations (F508del is the most common) lead to a decreased secretion of chloride/water, and to mucus sticky secretions, in pancreas, respiratory and gastrointestinal tracts. Intestinal manifestations are underestimated in CF, leading to ileum meconium at birth, or small bowel bacterial overgrowth in adult age.
Thirty-six CF patients, fasting and under no-antibiotic treatment, were CFTR genotyped on both alleles. Faecal samples were subjected to molecular microbial profiling through Temporal Temperature Gradient Electrophoresis and species-specific PCR. Ecological parameters and multivariate algorithms were employed to find out if CFTR variants could be related to the microbiota structure.
Patients were classified by two different criteria: 1) presence/absence of F508del mutation; 2) disease severity in heterozygous and homozygous F508del patients. We found that homozygous-F508del and severe CF patients exhibited an enhanced dysbiotic faecal microbiota composition, even within the CF cohort itself, with higher biodiversity and evenness. We also found, by species-specific PCR, that potentially harmful species (Escherichia coli and Eubacterium biforme) were abundant in homozygous-F508del and severe CF patients, while beneficial species (Faecalibacterium prausnitzii, Bifidobacterium spp., and Eubacterium limosum) were reduced.
This is the first report that establishes a link among CFTR variants and shifts in faecal microbiota, opening the way to studies that perceive CF as a ‘systemic disease’, linking the lung and the gut in a joined axis.
Misfolding of cystic fibrosis transmembrane conductance regulator protein (CFTR) causes the fatal lung disease cystic fibrosis. VX-809 was developed to suppress disease-related folding defects in CFTR. VX-809 suppresses folding defects in CFTR by modulating the conformation of membrane-spanning domain 1. VX-808 is thereby able to partially restore function to F508del-CFTR and other disease-related mutants.
Cystic fibrosis (CF) is a fatal genetic disorder associated with defective hydration of lung airways due to the loss of chloride transport through the CF transmembrane conductance regulator protein (CFTR). CFTR contains two membrane-spanning domains (MSDs), two nucleotide-binding domains (NBDs), and a regulatory domain, and its channel assembly requires multiple interdomain contacts. The most common CF-causing mutation, F508del, occurs in NBD1 and results in misfolding and premature degradation of F508del-CFTR. VX-809 is an investigational CFTR corrector that partially restores CFTR function in people who are homozygous for F508del-CFTR. To identify the folding defect(s) in F508del-CFTR that must be repaired to treat CF, we explored the mechanism of VX-809 action. VX-809 stabilized an N-terminal domain in CFTR that contains only MSD1 and efficaciously restored function to CFTR forms that have missense mutations in MSD1. The action of VX-809 on MSD1 appears to suppress folding defects in F508del-CFTR by enhancing interactions among the NBD1, MSD1, and MSD2 domains. The ability of VX-809 to correct F508del-CFTR is enhanced when combined with mutations that improve F508del-NBD1 interaction with MSD2. These data suggest that the use of VX-809 in combination with an additional CFTR corrector that suppresses folding defects downstream of MSD1 may further enhance CFTR function in people with F508del-CFTR.
Over 1900 mutations have been reported in the cystic fibrosis transmembrane conductance regulator (CFTR), the gene defective in patients with cystic fibrosis. These mutations have been discovered primarily in individuals who have features consistent with the diagnosis of CF. In some cases, it has been recognized that the mutations are not causative of cystic fibrosis but are responsible for disorders with features similar to CF, and these conditions have been termed CFTR-related disorders or CFTR-RD. There are also mutations in CFTR that do not contribute to any known disease state. Distinguishing CFTR mutations according to their penetrance for an abnormal phenotype is important for clinical management, structure/function analysis of CFTR, and understanding the molecular and cellular mechanisms underlying CF.
More than 1900 mutations in the CFTR gene are known. Functionally characterizing these mutations is important for diagnosing and treating patients with cystic fibrosis and related disorders.