Mutations In Cystic Fibrosis Transmembrane Conductance Regulator Gene Research Articles

The changing face of the exocrine pancreas in cystic fibrosis: pancreatic sufficiency, pancreatitis and genotype

(Table is included in full-text article.)Cystic fibrosis (CF) is the most frequent cause of exocrine pancreatic insufficiency in childhood. The cystic fibrosis transmembrane conductance regulator (CFTR) gene encodes CFTR protein that functions as cyclic AMP-dependent chloride channel allowing the passage of anions and secondarily water into the lumen of pancreatic ducts. Luminal chlorides are exchanged for bicarbonates. The lack of CFTR channel or its disrupted function (being the consequence of CFTR gene mutations) results in reduced volume of more acidic secretion. It has been suggested that such a situation leads to the precipitation of highly concentrated protein-containing secretion with obstruction and organ damage. The intensity of this process determines the progression of the disease. Steatorrhea is the significant symptom of classical form of CF. Residual pancreatic secretion in a subset of patients, however, allows for normal lipid digestion and absorption. Previous cross-sectional clinical studies estimated that about 85-90% of CF patients in preschool, school and older age are pancreatic insufficient. More frequent detection of mild and nonclassic forms of CF leads to higher frequency of pancreatic sufficiency (PS). The potential decline of exocrine pancreatic function, however, should be always considered. All PS patients with at least one severe or unknown CFTR mutation should be longitudinally assessed for the progression of pancreatic dysfunction. Recurrent acute and chronic pancreatitis is not a rare clinical condition in PS patients with PS: it might be the presenting symptom, even preceding CF diagnosis by several years. Potential appearance of this complication in individuals with pancreatic insufficiency demands elucidation.

Cystic fibrosis transmembrane conductance regulator (CFTR) gene mutation associated with a congenital bilateral absence of vas deferens

Cystic fibrosis transmembrane conductance regulator (CFTR) gene mutations associated with cystic fibrosis have been reported to be rare in Japanese patients with congenital bilateral absence of vas deferens (CBAVD). A 28-year-old Japanese male was referred for infertility. Vas deferens and epididymis were not palpable bilaterally. Semen analyses showed azoospermia with volumes below 2.0 ml. Serum follicle-stimulating hormone value was slightly elevated. Seminal fructose concentration was also very low. Scrotal ultrasonography showed absence of the bodies and tails of the right and left epididymides. Imaging studies showed cystic dysplasia of the right seminal vesicle and agenesis of the left seminal vesicle. A CFTR gene mutation of I556V was found. Recent studies show that prevalence of CFTR gene mutation in Japanese CBAVD patients may be approximately equal to that of the Caucasian population. Genetic counselling may be recommended for any couple attempting assisted reproduction technology when the man has CBAVD.

Identification of a Novel Mutation of CFTR Gene in a Korean Patient with Cystic Fibrosis

Cystic fibrosis (CF) is the most common lethal autosomal recessive disease in Caucasians, but rare in Asians. The mutations of cystic fibrosis transmembrane conductance regulator (CFTR) gene are responsible for CF. To date, less than 5 cases of CF have been reported and a few of them diagnosed based on the genotype of the CFTR gene in Korea. We encountered a 4-month-old Korean infant with CF and the diagnosis was confirmed by CFTR gene mutation analysis. The patient underwent surgical operation, due to meconium ileus at birth. He suffered by recurrent respiratory infections, failure to thrive, fatty liver with hepatomegaly, and cholestasis. The mutations of the CFTR gene were identified in the patient and his parents. The patient was a compound heterozygote with a nonsense mutation of c.263T>G, resulting in an amino acid change of p.Leu88X in exon 3. It was previously described in a Korean patient with CF. The other is a novel mutation; c.2089-2090insA mutation (p.Arg697LysfsX33) in exon 13. The mutation c.263T>G was inherited from his father, and the c.2089-2090insA mutation from his mother. Respiratory infection was recovered by supportive care, and cholestasis was improved slowly with sufficient feeding and supplementation of pancreatic exocrine enzymes. He is 19-month old now and shows catch-up growth. We report a novel CFTR mutation in a Korean infant with CF.

Activation of CFTR-specific T Cells in Cystic Fibrosis Mice Following Gene Transfer

Gene therapy for cystic fibrosis (CF) airway disease has emerged as a potentially successful therapy, because expression of the CF gene would be expected to restore the electrophysiological function of the airway epithelium to normalcy. Although, cellular and humoral immune responses to viral gene transfer vectors have been studied extensively, there has been no evaluation of T cell-mediated responses to the therapeutic human CF gene product. Using an adenovirus vector we demonstrated that T cells against human CF gene protein are elicited in CF gene knockout (KO), heterozygote (Het), and wild-type (wt) mice. A dominant CD8 T cell epitope found in CF gene KO, Het, and wt mice was mapped to NTYLRYITV. In CF gene KO mice we also identified (to a conserved region of the CF gene CSQFSWIMPGTIKEN), a minor T cell epitope that did not show any activity in the Het or wt mice.

Molecular Study of (TG)m(T)n Polymorphisms in Iranian Males With Congenital Bilateral Absence of the Vas Deferens

Congenital bilateral absence of the vas deferens (CBAVD) is a frequent cause of obstructive azoospermia. Nearly 75% of men with CBAVD have at least 1 detectable common mutation in the cystic fibrosis transmembrane conductance regulator (CFTR) gene. The different alleles at the (TG)(m)(T)(n) polymorphic locus at the 3' end of human CFTR intron 8 determine the efficiency of exon 9 splicing. To study the CFTR gene mutations and (TG)(m)(T)(n) polymorphisms in Iranian CBAVD patients with presumed low CF frequency and to better understand the complex regulation of exon 9 splicing among our study population, we analyzed CFTR mutations and (TG)(m)(T)(n) polymorphisms in 112 Iranian CBAVD, 7 congenital unilateral absence of the vas deferens males from Iran, and 84 fertile males as controls. Moreover, we compared the rate of CFTR transcripts with exon 9 (9+) with reduction of the (T)(n) repeat in our study population. Our study showed that the 5T mutation was present with high frequency in our patients. Longer (TG)(m) polymorphic tracts increase the proportion of exon 9 deletion transcripts but only when activated by the 5T allele. The combination of the 5T allele in 1 copy of the CFTR gene with a CF mutation in the other copy is the most common cause of CBAVD in the Iranian population. We also observed the highest level of exon 9+ splicing efficiency among the tested samples with the (TG)(12)(T)(7) allele, which represents the most common intron 8 splice variant allele in the general population. Our results support the idea that a putative role of the (T)(n) repeat is to distance the (TG)(m) repeat from the 3' splice site and that the different alleles at the (T)(n) locus affect the efficiency by which the splice acceptor consensus sequence is recognized.

Targeted Therapy for Cystic Fibrosis

Cystic fibrosis (CF) results from the absence or dysfunction of a single protein, the CF transmembrane conductance regulator (CFTR). CFTR plays a critical role in the regulation of ion transport in a number of exocrine epithelia. Improvement or restoration of CFTR function, where it is deficient, should improve the CF phenotype. There are >1000 reported disease-causing mutations of the CFTR gene. Recent investigations have afforded a better understanding of the mechanism of dysfunction of many of these mutant CFTRs, and have allowed them to be classified according to their mechanism of dysfunction. These data, as well as an enhanced understanding of the role of CFTR in regulating epithelial ion transport, have led to the development of therapeutic strategies based on pharmacologic enhancement or repair of mutant CFTR dysfunction. The strategy, termed 'protein repair therapy', is aimed at improving the regulation of epithelial ion transport by mutant CFTRs in a mutation-specific fashion. The grouping of CFTR gene mutations, according to mechanism of dysfunction, yields some guidance as to which pharmacologic repair agents may be useful for specific CFTR mutations. Recent data has suggested that combinations of pharmacologic repair agents may be necessary to obtain clinically meaningful CFTR repair. Nevertheless, such strategies to improve mutant CFTR function hold great promise for the development of novel therapies aimed at correcting the underlying pathophysiology of CF.

CFTR gene mutations and asthma in the Norwegian Environment and Childhood Asthma study

Several candidate genes have been implicated in the etiology of asthma, including the gene coding for the cystic fibrosis transmembrane conductance regulator (CFTR). Mutations in the CFTR gene result in derangements of mucociliary clearance. Homozygotes for CFTR mutations develop cystic fibrosis (CF), a disorder characterized mainly by lung and pancreas disease. To investigate whether there was an increased frequency of CFTR mutations in asthma patients. Seven hundred and three subjects aged 10-11 years from the environment and childhood asthma (ECA) study were included in the present study. Possible associations between asthma, reduced lung function, bronchial hyperresponsiveness (BHR), and increased or decreased nitrogen oxide (NO) levels (based on structural parental interview, spirometry, PD20 methacholine challenge test and exhaled NO measurements), and the five most common CFTR mutations in Norway (DeltaF508, R117H, R117C, 4005+2T-->C, 394delTT), the modulating polymorphisms IVS8(TG)mTn and the IVS8-5T were investigated. No association were found between asthma, reduced lung function, BHR or exhaled NO levels and CF heterozygosity. However, the IVS8(TG)11T7 haplotype was associated with normal lung function. Our results do not support the hypothesis that CFTR mutations or polymorphisms play a role in the pathogenesis of asthma in children. However, the distribution of Tn(TG)m haplotypes differed between individuals with reduced lung function and individuals with normal lung function.

Mutation analysis of CFTR gene in 70 Iranian cystic fibrosis patients.

Cystic fibrosis (CF) is the most common inherited disorder in Caucasian populations, with over 1400 cystic fibrosis transmembrane conductance regulator (CFTR) mutations. The type of mutations and their distributions varies widely between different countries and/or ethnic groups. Seventy Iranian cystic fibrosis patients were screened for the CFTR gene mutation using ARMS/PCR (amplification refractory mutation system) for the following mutations: deltaF508, N1303K, G542X, 1717-1G>A, R553X, W1282X, G551D, 621+1G>T, deltaI507 and R560T. Single strand conformation polymorphism (SSCP) analysis of exons 3, 7, 10, 11 and 17b, including both the exon/intron junctions, of the CFTR gene was performed in patients in whom no mutation could be identified on one or both CFTR genes. As a result of this screening, only three mutations were found: deltaF508 mutation was found in 25 (17.8%) alleles, N1303K in six (4.3%) alleles and G542X in five (3.6%) alleles. Thus, a total of 3 mutations cover 25.7% of CF alleles. These finding will be used for planning future screening and appropriate genetic counseling programs in Iranian CF patients.

Cystic Fibrosis Transmembrane Conductance Regulator Function Is Suppressed in Cigarette Smokers

Cigarette smoke extract inhibits chloride secretion in human bronchial epithelial cells. Oxidants decrease gene expression, protein expression, and function of the cystic fibrosis transmembrane conductance regulator (CFTR). Because cigarette smoke is a rich source of oxidants, we verified the hypothesis that CFTR may be suppressed by exposure to cigarette smoke in vitro and in vivo. The effects of cigarette smoke exposure on Calu-3 and T84 cell CFTR expression and function were observed. Also studied were the nasal potential differences (PDs) in 26 men (9 smokers, 17 nonsmokers) who had no detectable CFTR gene mutations as determined during investigations for infertility. CFTR expression and function were determined by Northern blotting, Western blotting, and cAMP-dependent 125I efflux assays. Extensive CFTR genotyping was performed in each subject. Nasal PD measurements were made at baseline and during amiloride, chloride-free buffer, and isoproterenol perfusions. Cigarette smoke decreased CFTR expression and function in Calu-3 and T84 cell lines. Furthermore, the nasal PDs of cigarette smokers showed a pattern typical of CFTR deficiency with a blunted response to chloride-free buffer and isoproterenol compared with nonsmokers (-9.6 +/- 4.0 vs. -22.3 +/- 10.1 mV; p < 0.001). We conclude that cigarette smoke decreases the expression of CFTR gene, protein, and function in vitro and that acquired CFTR deficiency occurs in the nasal respiratory epithelium of cigarette smokers. We suggest that acquired CFTR deficiency may contribute to the physiopathology of cigarette-induced diseases such as chronic bronchitis.

CLINICAL, ANDROLOGICAL AND GENETIC CHARACTERISTICS OF PATIENTS WITH CONGENITAL BILATERAL ABSENCE OF VAS DEFERENS (CBAVD)

Congenital bilateral absence of the vas deferens (CBAVD) is a form of infertility with an autosomal recessive genetic background in otherwise healthy males. In this study, we examined the clinical and cystic fibrosis transmembrane-conductance regulator (CFTR) gene mutations in sixty patients with bilateral absence of vas deferens that applied to andrology clinic due to male factor infertility. Urogenital anomalies of vas deferens, seminal vesicle and epididymis were detected in our patient group. CFTR gene mutations, which are known to be frequent among cystic fibrosis patients, could not be detected in our patient group with that high frequency. Delta F508 mutations were detected in only 6% of patients. IVS8 polyT alleles were positive in 68% of patients. No 1677delTA mutations and M470V variants were detected in our patient group. However, sperm retrieval is almost always possible from CBAVD patients; secondary pathologies may also result defective spermatogenesis.

Mutations of the CFTR Gene in Idiopathic Pancreatic Hyperenzymemia

Idiopathic pancreatic hyperenzymemia is a new syndrome that is characterized by a chronic increase of serum pancreatic enzymes in the absence of pancreatic disease. The aim of this study was to assess whether mutations of the cystic fibrosis transmembrane conductance regulator (CFTR) gene may have a role in the etiology of this hyperenzymemia. Seventy subjects with idiopathic pancreatic hyperenzymemia, 44 men and 26 women (mean age, 48 years; range, 8-74 years), were studied. Thirteen of these 70 subjects had the familial form of the syndrome. The mutation analysis of the CFTR gene was carried out using diagnostic commercial kits for the simultaneous detection of 29 mutations and Tn polymorphism. Among the 70 subjects studied, 7 (10.0%) had CFTR gene mutations. None of these 7 subjects had the familial form of pancreatic hyperenzymemia. These mutations were DeltaF 508 in 1 subject, 2789 + 5 G > A in another subject, and T5 allele in the remaining 5. All these mutations were heterozygous, with the exception of 1 T5 allele that was homozygous in 1 subject. The frequencies of the mutations of the CFTR gene found in these subjects are similar to the carrier frequencies in the general Italian population. This finding does not support a role for CFTR gene mutations in the etiology of idiopathic pancreatic hyperenzymemia.

The cystic fibrosis transmembrane conductance regulator gene and ion channel function in patients with idiopathic pancreatitis

Cystic fibrosis transmembrane conductance regulator (CFTR) gene mutations are associated with cystic fibrosis (CF)-related monosymptomatic conditions, including idiopathic pancreatitis. We evaluated prospectively enrolled patients who had idiopathic recurrent acute pancreatitis or idiopathic chronic pancreatitis, healthy controls, CF heterozygotes, and CF patients (pancreatic insufficient or sufficient) for evidence of CFTR gene mutations and abnormalities of ion transport by sweat chloride and nasal potential difference testing. DNA samples from anonymous blood donors were controls for genotyping. At least one CFTR mutation or variant was carried in 18 of 40 patients (45%) with idiopathic chronic pancreatitis and in 6 of 16 patients (38%) with idiopathic recurrent acute pancreatitis but in only 11 of the 50 controls (22%, P=0.005). Most identified mutations were rare and would not be identified in routine genetic screening. CFTR mutations were identified on both alleles in six patient (11%). Ion transport measurements in patients with pancreatitis showed a wide range of results, from the values in patients with classically diagnosed CF to those in the obligate heterozygotes and healthy controls. In general, ion channel measurements correlated with the number and severity of CFTR mutations. Twelve of 56 patients with pancreatitis (21%) fulfilled current clinical criteria for the diagnosis of CF, but CFTR genotyping alone confirmed the diagnosis in only two of these patients. We concluded that extensive genotyping and ion channel testing are useful to confirm or exclude the diagnosis of CF in the majority of patients with idiopathic pancreatitis.

Modifizierende Gene bei der zystischen Fibrose

Cystic fibrosis is a common autosomal recessive disease that is caused by mutations in the cystic fibrosis transmembrane conductance regulator (CFTR) gene. The CFTR gene encodes a membrane-bound chloride ion channel. CFTR gene mutations cause alterations in fluid and salt secretion of various tissues. The CF phenotype is highly variable even in siblings and twins carrying the same CFTR mutations. The course of CF pulmonary disease is modulated by both environmental and genetic factors independent of CFTR. This review summarises association studies that focused on disease modifier genes in CF. Understanding the molecular and cellular basis of the genotype-phenotype associations will help to better understand the disease and to identify new targets for therapeutic interventions in CF.

Cystic Fibrosis Transmembrane Conductance Regulator Gene Mutations in Infertile Males with Congenital Bilateral Absence of the Vas Deferens

Congenital bilateral absence of the vas deferens (CBAVD) is characterized by azoospermia and male infertility. Mutations in the cystic fibrosis transmembrane conductance regulator (CFTR) gene are associated with cystic fibrosis (CF), the most common autosomal recessive disorder in Caucasians. Recent publications on CBAVD raised the question whether CFTR gene mutations are responsible for CBAVD occurrence or not. This study was conducted to explore the role of CFTR gene mutations in the occurrence of CBAVD-dependent male infertility. Forty-four chromosomes of 22 CBAVD patients from Austrian ancestry were studied. For detection of the most common mutation DeltaF508, a deletion of phenylalanine at the 508th position of mature CFTR chloride channel protein, the 10th exon of the gene was screened by heteroduplex analysis. In order to identify non-DeltaF508 mutations, we also analyzed the entire coding regions, exon/intron boundaries of 27 exons and the 5'- and 3'-untranslated regions of the gene by denaturing gradient gel electrophoresis (DGGE) after polymerase chain reaction. All exons showing different banding patterns on the DGGE gels were sequenced to define existing DNA sequence variations. Among the analyzed 44 chromosomes of 22 patients, disease producing mutations were found in 31.8% (14/44). The most common mutation was DeltaF508 with a frequency of 43% (6/14), followed by R117H with 29% (4/14). Our results indicate that CFTR gene mutations are common but not the only reason for the occurrence of CBAVD-dependent male infertility. We recommend screening of the CFTR gene in these patients.

Mid-trimester hyperechogenic bowel in a fetus of Japanese origin carrying a new mutation of CFTR gene (L548Q)

We present a case of a fetus with hyperechogenic bowel, in which the L548Q mutation was detected in the mother of Japanese origin and the deltaF508 mutation in the father of Caucasian origin. The fetus proved to be compound heterozygous. Research into cystic fibrosis transmembrane conductance regulator (CFTR) mutations in this case was triggered by the fact that the fetus had a characteristic hyperechogenic bowel image with normal karyotype and no indications of intrauterine infections. Hyperechogenic bowel is highly indicative of a CFTR gene mutation. The incidence of cystic fibrosis (CF) in fetuses with mid-trimester hyperechogenic bowel is 5%, but once the most frequent mutations have been accounted for, rarer mutations must be investigated.

Expression of cystic fibrosis transmembrane conductance regulator in human endometrium.

As a cAMP-regulated Cl- channel, cystic fibrosis transmembrane conductance regulator (CFTR) plays a critical role in the active secretion of electrolytes and fluid in epithelial cells. Women with CFTR gene mutations are less fertile, generally assumed to be due to cervical factors. However, there is little known about CFTR protein expression in human endometrium and its possible roles in reproduction. CFTR protein and mRNA levels in human endometrium were analysed using immunohistochemical and in situ hybridization methods, respectively. Significant expression of CFTR protein was only seen in the glandular cells from late proliferative to all secretory phases, consistent with western blot analysis. High levels of CFTR mRNA were present only around the ovulatory period. In cultured glandular cells, the production of CFTR protein and mRNA was stimulated by estradiol and inhibited by progesterone. A forskolin-activated Cl- current in endometrial epithelial cells with a linear I-V relationship was detected by the whole-cell patch-clamp technique. (i) CFTR mRNA and protein were localized in human endometrial epithelial cells and the amounts varied in a cyclic manner; (ii) CFTR expression in cultured glandular cells was up- and downregulated by estradiol and progesterone, respectively; and (iii) CFTR in human endometrium functions as a cAMP-activated Cl- channel.

Atypical sinusitis in adults must lead to looking for cystic fibrosis and primary ciliary dyskinesia.

HYPOTHESES/OBJECTIVES:: In adults, purulent pansinusitis or nasal polyposis starting early in life or that is permanently infected or associated either with chronic bronchial infection, infertility, or situs inversus are uncommon. In these atypical cases of chronic sinusitis (ACS), a primary dysfunction of the mucociliary clearance can be suspected. Adult patients with ACS were therefore investigated to detect primary ciliary dyskinesia (PCD) or cystic fibrosis (CF). Open, prospective study. Forty-two patients with ACS were investigated with ciliary beat frequency and ultrastructure analysis in nasal cells and cystic fibrosis transmembrane conductance regulator (CFTR) gene mutation analysis in blood leukocytes. The diagnosis of PCD was confirmed in seven (17%) patients. At least one CFTR gene mutation was detected in 16 (38%) patients. The diagnosis of CF was suggested in three (7%) compound heterozygous patients. Another 13 (31%) patients were heterozygous for a CFTR gene mutation or a complex allele. Comparison of clinical features of ACS showed that only a family history of chronic sinusitis (P <.01) or chronic bronchitis (P <.02) and the presence of diffuse bronchiectasis (P <.0001) or serous otitis media (P <.0001) were significantly more frequent in PCD patients than in patients carrying CFTR gene mutations or those without PCD or CFTR gene mutations. ACS should be considered a remarkable entity in which congenital abnormalities of epithelial cells are frequently detected (55% of patients). The higher frequency of mutations in ACS patients compared with the general population suggests that heterozygoty for CFTR gene mutation could be a sinusitis-causing status.

Mutations of the CFTR gene in Turkish patients with congenital bilateral absence of the vas deferens.

Mutations of the Cystic Fibrosis Transmembrane Conductance Regulator (CFTR) can cause congenital bilateral absence of the vas deferens (CBAVD) as a primarily genital form of cystic fibrosis. The spectrum and frequency of CFTR mutations in Turkish males with CBAVD is largely unknown. We investigated 51 Turkish males who had been diagnosed with CBAVD at the Hacettepe University, Ankara, for the presence of CFTR gene mutations by direct sequencing of the coding region and exon/intron boundaries. We identified 27 different mutations on 72.5% of the investigated alleles. Two-thirds of the patients harboured CFTR gene mutations on both chromosomes. Two predominant mutations, IVS8-5T and D1152H, accounted for more than one-third of the alleles. Five mutations are described for the first time. With one exception, all identified patients harboured at least one mutation of the missense or splicing type. Presently available mutation panels would have uncovered only 7-12% of CFTR alleles in this population cohort. Although cystic fibrosis is relatively rare in Turkey, CFTR mutations are responsible for the majority of CBAVD in Turkish males. Because of a specific mutation profile, a population-specific panel should be recommended for targeted populations such as CBAVD in Turkey or elsewhere.

The role of common single-nucleotide polymorphisms on exon 9 and exon 12 skipping in nonmutated CFTR alleles.

Classic cystic fibrosis (CF) is caused by two loss-of-function mutations in the cystic fibrosis transmembrane conductance regulator (CFTR) gene, whereas patients with nonclassic CF have at least one copy of a mutant gene that retains partial function of the CFTR protein. In addition, there are several other phenotypes associated with CFTR gene mutations, such as idiopathic chronic pancreatitis. In CFTR-associated disorders and in nonclassic CF, often only one CFTR mutation or no CFTR mutations can be detected. In this study, we screened 23 patients with CFTR-associated disorders for CFTR mutations by complete gene testing and quantitative transcript analysis. Mutations were found in 10 patients. In cells from respiratory epithelium, we detected aberrant splicing of CFTR mRNA in all investigated individuals. We observed a highly significant association between the presence of coding single-nucleotide polymorphisms (coding SNPs, or cSNPs) and increased skipping of exon 9 and 12. This association was found both in patients and in normal individuals carrying the same cSNPs. The cSNPs c.1540A>G, c.2694T>G, and c.4521G>A may have affected pre-mRNA splicing by changing regulatory sequence motifs of exonic splice enhancers, leading to lower amounts of normal transcripts. The analysis of CFTR exons indicated that less frequent and weak exonic splicing enhancer (ESE) motifs make exon 12 vulnerable to skipping. The number of splice variants in individuals with cSNPs was similar to previously reported values for the T5 allele, suggesting that cSNPs may enhance susceptibility to CFTR related diseases. In addition, cSNPs may be responsible for variation in the phenotypic expression of CFTR mutations. Quantitative approaches rather than conventional genomic analysis are required to interpret the role of cSNPs.

Genes and male infertility: what can go wrong?

Genes and male infertility: what can go wrong?