High allelic heterogeneity between Afro-Brazilians and Euro-Brazilians impacts cystic fibrosis genetic testing

Cystic fibrosis (CF) is an autosomal recessive disease caused by at least 1,000 different mutations in the cystic fibrosis transmembrane conductance regulator gene (CFTR). To determine the frequency of 70 common worldwide CFTR mutations in 155 Euro-Brazilian CF patients and in 38 Afro-Brazilian CF patients, we used direct PCR amplification of DNA from a total of 386 chromosomes from CF patients born in three different states of Brazil. The results show that screening for seventy mutations accounts for 81% of the CF alleles in Euro-Brazilians, but only 21% in the Afro-Brazilian group. We found 21 different mutations in Euro-Brazilians and only 7 mutations in Afro-Brazilians. The frequency of mutations and the number of different mutations detected in Euro-Brazilians are different from Northern European and North American populations, but similar to Southern European populations; in Afro-Brazilians, the mix of CF-mutations is different from those reported in Afro-American CF patients. We also found significant differences in detection rates between Euro-Brazilian (75%) and Afro-Brazilian CF patients (21%) living in the same state, Minas Gerais. These results, therefore, have implications for the use of DNA-based tests for risk assessment in heterogeneous populations like the Brazilians. Further studies are needed to identify the remaining CF mutations in the different populations and regions of Brazil.     

Cystic fibrosis as a cause of infertility

Cystic fibrosis (CF) is one of the autosomal recessive diseases, caused by mutations in a gene known as cystic fibrosis transmembrane regulator (CFTR). The majority of adult males with CF (99%) is characterized by congenital bilateral absence of vas deferens (CBAVD). CBAVD is encountered in 1-2% of infertile males without CF. Females with CF are found to be less fertile than normal healthy women. In females with CF, delayed puberty and amenorrhoea are common due to malnutrition. CFTR mutations are also associated with congenital absence of the uterus and vagina (CAUV). The National Institutes of Health recommend genetic counseling for any couple seeking assisted reproductive techniques with a CF male or obstructive azoospermia which is positive for a CF mutation.     

Genotype-phenotype correlation in cystic fibrosis patients bearing [H939R;H949L] allele

Cystic fibrosis (CF) is caused by CFTR (cystic fibrosis transmembrane conductance regulator) gene mutations. We ascertained five patients with a novel complex CFTR allele, with two mutations, H939R and H949L, inherited in cis in the same exon of CFTR gene, and one different mutation per patient inherited in trans in a wide population of 289 Caucasian CF subjects from South Italy. The genotype-phenotype relationship in patients bearing this complex allele was investigated. The two associated mutations were related to classical severe CF phenotypes.     

Identification of common cystic fibrosis mutations in African-Americans with cystic fibrosis increases the detection rate to 75%.

Cystic fibrosis (CF)--an autosomal recessive disorder caused by mutations in CF transmembrane conductance regulator (CFTR) and characterized by abnormal chloride conduction across epithelial membranes, leading to chronic lung and exocrine pancreatic disease--is less common in African-Americans than in Caucasians. No large-scale studies of mutation identification and screening in African-American CF patients have been reported, to date. In this study, the entire coding and flanking intronic sequence of the CFTR gene was analyzed by denaturing gradient-gel electrophoresis and sequencing in an index group of 82 African-American CF chromosomes to identify mutations. One novel mutation, 3120+1G-->A, occurred with a frequency of 12.3% and was also detected in a native African patient. To establish frequencies, an additional group of 66 African-American CF chromosomes were screened for mutations identified in two or more African-American patients. Screening for 16 "common Caucasian" mutations identified 52% of CF alleles in African-Americans, while screening for 8 "common African" mutations accounted for an additional 23%. The combined detection rate of 75% was comparable to the sensitivity of mutation analysis in Caucasian CF patients. These results indicate that African-Americans have their own set of "common" CF mutations that originate from the native African population. Inclusion of these "common" mutations substantially improves CF mutation detection rates in African-Americans.     

Characterization of the metal binding environment of catalytic site 1 of chloroplast F1-ATPase from Chlamydomonas

Metal ligands of the VO(2+)-adenosine diphosphate (ADP) complex bound to high-affinity catalytic site 1 of chloroplast F(1) adenosine triphosphatase (CF(1) ATPase) were characterized by electron paramagnetic resonance (EPR) spectroscopy. This EPR spectrum contains two EPR species designated E and F not observed when VO(2+)-nucleotide is bound to site 3 of CF(1). Site-directed mutations betaE197C, betaE197D, and betaE197S in Chlamydomonas CF(1) impair ATP synthase and ATPase activity catalyzed by CF(1)F(o) and soluble CF(1), respectively, indicating that this residue is important for enzyme function. These mutations caused large changes in the (51)V hyperfine tensors of VO(2+)-nucleotide bound to site 1 but not to site 3. Mutations to the Walker homology B aspartate betaD262C, betaD262H, and betaD262T of Chlamydomonas CF(1) caused similar effects on the EPR spectrum of VO(2+)-ADP bound to site 1. These results indicate that the conversion of the low-affinity site 3 conformation to high-affinity site 1 involves the incorporation betaE197 and betaD262 as metal ligands.     

Effect of genotype on selected clinical features of Polish cystic fibrosis adults

Cystic fibrosis (CF), the most common autosomal recessive disorder of Caucasians, is caused by the mutations in the gene encoding CFTR (Cystic Fibrosis Transmembrane Conductance Regulator) protein. Until now, approximately 1000 mutations of the CFTR gene have been described. The genotype-phenotype relationships in CF are still not completely understood. This study was undertaken in an attempt to characterise the distribution of CFTR mutations and their effect on selected clinical parameters in a group of Polish CF adults. A total number of 38 adult CF patients (mean age 21.6 +/- 6.8); 18 females & 20 males were enrolled in the study. The CFTR gene identification was conducted with the use of PCR & InnoLipa-CF set. The assessed clinical parameters included: age at diagnosis, age, lung function test, X-ray scored in Brasfield score, weight & height. We found that: (1) the genotypes of the studied population were unevenly distributed (65.8%- genotype deltaF508/M), (2) a high percentage of 3849+10kbC-->T was noted, (3) patients homozygous for the deltaF508 mutation were diagnosed significantly earlier and had a lower body mass index, (4) no differences were observed in the patients' length of life or the progression of lung disease. Conclusions: 1. In comparison to other populations, Polish adult CF patients display a relatively higher frequency of mild mutations. 2. Late diagnosis of CF in the studied group may be partially caused by a high percentage of CFTR mutations connected with the mild course of the disease that are difficult to identify. 3. Cystic fibrosis should be more commonly taken into consideration in the differential diagnosis in adult patients with milder symptoms.     

CFTR Haplotype Analysis Reveals Genetic Heterogeneity in the Etiology of Congenital Bilateral Aplasia of the Vas Deferens

Congenital bilateral aplasia of the vas deferens (CBAVD) was suggested to be a mild form of cystic fibrosis (CF). Mutation analysis of the cystic fibrosis transmembrane conductance regulator (CFTR) gene in males with CBAVD revealed that in some males CBAVD is caused by two defective CFTR alleles. The genetic basis of CBAVD in the other males and its association with CF remained unclear. We undertook this study to test the hypothesis of commonality of CBAVD and CF by haplotype analysis, in the CFTR locus, of males suffering from CBAVD and of their families. According to the hypothesis of commonality of CBAVD and CF, two brothers with CBAVD are expected to carry the same two CFTR alleles, while their fertile brothers are expected to carry at least one different allele. Eleven families were studied, of which two families, with unidentified CFTR mutations, did not support this hypothesis. In these families two brothers with CBAVD inherited different CFTR alleles. Their fertile brothers inherited the same CFTR alleles as their brothers with CBAVD. These results provide evidence for genetic heterogeneity in CBAVD. Though in some families CBAVD is associated with two CFTR mutations, we suggest that in others it is caused by other mechanisms, such as mutations at other loci or homozygosity or heterozygosity for partially penetrant CFTR mutations.     

Implication of the Cystic Fibrosis Transmembrane Conductance Regulator Gene in Infertile Family Members of Indian CF Patients

Cystic fibrosis (CF) is an autosomal recessive disease caused by mutations in the CFTR gene. Among males with CF, 95% are infertile due to congenital absence of the vas deferens. We investigated the role of family history of infertility among CF subjects and characterized mutations in them. Among 50 CF subjects, four had a family history of infertility. A homozygous c.1521_1523delCTT mutation was detected in one, two had a compound heterozygous genotype (c.1521_1523delCTT/c.3717 + 10 kbC>T), and c.1521_1523delCTT mutation was identified on one allele of fourth CF subject. Genetic analysis of each infertile family members of CF subjects revealed the c.1521_1523delCTT mutation on one allele; however, no mutation could be identified on other allele. Haplotype analysis of the infertile family members showed that at least one of the alleles shared the same haplotype as that of the index case. It is suggested that the CFTR gene is implicated in the infertile members of the CF families. Failure to detect mutations on the other allele by SSCP analysis demands direct gene sequencing to detect mutations in the intronic or promoter region.     

Applications of proteomic technologies for understanding the premature proteolysis of CFTR

Cystic fibrosis (CF) is caused by mutations in the CF transmembrane conductance regulator (CFTR) gene, which encodes an ATP-dependent anion channel. Disease-causing mutations can affect channel biogenesis, trafficking or function, and result in reduced ion transport at the apical surface of many tissues. The most common CFTR mutation is a deletion of phenylalanine at position 508 (ΔF508), which results in a misfolded protein that is prematurely targeted for degradation. This article focuses on how proteomic approaches have been utilized to explore the mechanisms of premature proteolysis in CF. Additionally, we emphasize the potential for proteomic-based technologies in expanding our understanding of CF pathophysiology and therapeutic approaches.     

Consanguinity sans reproche

Summary In a family with two cystic fibrosis (CF) patients and consanguineous parents, DNA analysis showed that the CF in the children was not caused by homozygosity by descent, since two different mutations were involved. A formula is given for calculating the probability that parental consanguinity, if it exists, is causally related to the existence of an autosomal recessive disease in affected children.     

DNA marker haplotype association with pancreatic sufficiency in cystic fibrosis.

Patients with cystic fibrosis (CF) generally suffer from chronic obstructive lung disease, pancreatic insufficiency (PI), and a number of other exocrine malfunctions. Approximately 15% of CF patients are, however, pancreatic sufficient. To investigate whether the two clinical subgroups, PI and pancreatic sufficiency (PS), are caused by different CF mutant alleles, we have performed linkage disequilibrium and haplotype association analysis with three DNA markers that are tightly linked to the CF locus. The study showed that the allelic and haplotype distributions for these RFLPs are significantly different between the two groups. The data suggest that most of the CF-PI patients are probably descendants of a single mutational event at the CF locus and that the CF-PS patients resulted from multiple, different mutations. While final interpretation of these data awaits molecular cloning of the CF gene, the information on haplotype association in CF may be useful in genetic counseling and disease prognosis, in identifying the gene itself, and in defining the mutations.     

Role of inflammation and oxidative stress in tissue damage associated with cystic fibrosis: CAPE as a future therapeutic strategy

Molecular and Cellular Biochemistry - Cystic fibrosis (CF) is an autosomal recessive disease caused by mutations in the cystic fibrosis transmembrane conductance regulator (CFTR) gene, responsible...     

Genetic comparisons of patients with cystic fibrosis with or without meconium ileus. Clinical Centers of the French CF Registry.

Cystic fibrosis (CF) is an autosomal disorder caused by mutations in the cystic fibrosis transmembrane conductance regulator gene (CFTR). Neonatal meconium ileus (MI) occurs in 10-20 percent of newborns with CF. The purpose of this study was to determine the allelic frequencies of the CF mutation in French patients with and without MI and the incidence of MI in 7 homozygotes or compound heterozygotes for mutation of the CFTR gene. Our study confirms the positive association between delta F508, the most frequent CF mutation, G542X mutation and MI and a negative association with G551D.     

Cystic fibrosis: a disease of vulnerability to airway surface dehydration

Cystic fibrosis (CF) lung disease involves chronic bacterial infection of retained airway secretions (mucus). Recent data suggest that CF lung disease pathogenesis reflects the vulnerability of airway surfaces to dehydration and collapse of mucus clearance. This predisposition is caused by mutations in the CF transmembrane conductance regulator (CFTR) gene, resulting in (i) the absence of CFTR-mediated Cl- secretion and regulation of epithelial Na+ channel (ENaC) function; and (ii) the sole dependence on extracellular ATP to rebalance these ion transport processes through P2 purinoceptor signaling. Recent clinical studies indicate that inhalation of hypertonic saline osmotically draws sufficient water onto CF airway surfaces to provide clinical benefit.     

Current concepts of immune dysregulation in cystic fibrosis

Cystic fibrosis (CF) lung disease is caused by mutations in the Cystic Fibrosis Transmembrane Conductance Regulator (CFTR) gene and is characterized by a perpetuated feedback loop of bacterial infection and inflammation. Both intrinsic (CFTR-dependent) and extrinsic (CFTR-independent) mechanisms contribute to the inflammatory phenotype of CF lung disease. Innate immune cells, initially recruited to combat bacterial pathogens, are acting in a dysregulated and non-resolving fashion in CF airways and cause harm to the host by releasing proteases and oxidants. Targeting harmful immune pathways, while preserving protective ones, remains the challenge for the future. This review highlights current concepts of innate immune dysregulation in CF lung disease.This article is part of a Directed Issue entitled: Cystic Fibrosis: From o-mics to cell biology, physiology, and therapeutic advances.     

Absent secretion to vasoactive intestinal peptide in cystic fibrosis airway glands

We are testing the hypothesis that the malfunctioning of airway gland serous cells is a component of cystic fibrosis (CF) airway disease. CF is caused by mutations that disrupt CF transmembrane conductance regulator, an anion channel essential for proper fluid secretion in some epithelia. Submucosal glands supply most of the mucus in upper airways, and gland serous cells are the primary site of CF transmembrane conductance regulator expression in airways. We have discovered a major defect in CF glands by in situ optical monitoring of secretions from single human airway glands. CF glands did not secrete to agents that elevated [cAMP](i) (0 responses/450 glands, 8 subjects), whereas glands were responsive in all donor tracheas (605/827 glands, 15 subjects) and in bronchi from subjects who were transplanted because of other lung diseases (148/166 glands, n = 10). CF glands secreted to cholinergic stimulation, and serous cells were abundant in glands from all CF subjects. The complete absence of secretion to agents that elevate [cAMP](i) suggests that altered secretion of gland mucus could contribute to CF lung disease.     

Analysis of the whole CFTR coding regions and splice junctions in azoospermic men with congenital bilateral aplasia of epididymis or vas deferens

Several recent studies have demonstrated the presence of mutations in the cystic fibrosis transmembrane conductance regulator (CFTR) gene in healthy males with infertility caused by congenital absence of the vas deferens (CBAVD), previously recognized as an idiopathic genetic condition distinct from CF. In order to document further the genetic commonality of these two disorders, we undertook a double screening of the entire coding and flanking sequences of the CFTR gene, by using single-strand conformational polymorphism analysis and denaturing gradient gel electrophoresis in 12 unrelated infertile men with abnormalities of the vas deferens and/or epididymis. This strategy allowed us to identify 11 DNA sequence alterations considered as CF-causing mutations and several variations. Despite this double analysis, only two patients out of eight with CBAVD could be demonstrated as compound heterozygotes for CF mutations.     

C-terminal truncations destabilize the cystic fibrosis transmembrane conductance regulator without impairing its biogenesis. A novel class of mutation.

Defective cAMP-stimulated chloride conductance of the plasma membrane of epithelial cell is the hallmark of cystic fibrosis (CF) and results from mutations in the cystic fibrosis transmembrane conductance regulator, CFTR. In the majority of CF patients, mutations in the CFTR lead to its misfolding and premature degradation at the endoplasmic reticulum (ER). Other mutations impair the cAMP-dependent activation or the ion conductance of CFTR chloride channel. In the present work we identify a novel mechanism leading to reduced expression of CFTR at the cell surface, caused by C-terminal truncations. The phenotype of C-terminally truncated CFTR, representing naturally occurring premature termination and frameshift mutations, were examined in transient and stable heterologous expression systems. Whereas the biosynthesis, processing, and macroscopic chloride channel function of truncated CFTRs are essentially normal, the degradation rate of the mature, complex-glycosylated form is 5- to 6-fold faster than the wild type CFTR. These experiments suggest that the C terminus has a central role in maintaining the metabolic stability of the complex-glycosylated CFTR following its exit from the ER and provide a plausible explanation for the severe phenotype of CF patients harboring C-terminal truncations.     

Role of airway surface liquid and submucosal glands in cystic fibrosis lung disease

Cysticfibrosis (CF) is caused by mutations in the CF transmembraneconductance regulator (CFTR) protein, an epithelial chloride channelexpressed in the airways, pancreas, testis, and other tissues. Acentral question is how defective CFTR function in CF leads to chroniclung infection and deterioration of lung function. Several mechanismshave been proposed to explain lung disease in CF, including abnormalairway surface liquid (ASL) properties, defective airway submucosalgland function, altered inflammatory response, defective organellaracidification, loss of CFTR regulation of plasma membrane iontransporters, and others. This review focuses on the physiology of theASL and submucosal glands with regard to their proposed role in CF lungdisease. Experimental evidence for defective ASL properties and glandfunction in CF is reviewed, and deficiencies in understanding ASL/glandphysiology are identified as areas for further investigation. New modelsystems and measurement technologies are being developed to makeprogress in establishing lung disease mechanisms in CF, which shouldfacilitate mechanism-based design of therapies for CF.