Extensive sequence analysis of CFTR, SCNN1A, SCNN1B, SCNN1G and SERPINA1 suggests an oligogenic basis for cystic fibrosis-like phenotypes.

The term cystic fibrosis (CF)-like disease is used to describe patients with a borderline sweat test and suggestive CF clinical features but without two CFTR(cystic fibrosis transmembrane conductance regulator) mutations. We have performed the extensive molecular analysis of four candidate genes (SCNN1A, SCNN1B, SCNN1G and SERPINA1) in a cohort of 10 uncharacterized patients with CF and CF-like disease. We have used whole-exome sequencing to characterize mutations in the CFTR gene and these four candidate genes. CFTR molecular analysis allowed a complete characterization of three of four CF patients. Candidate variants in SCNN1A, SCNN1B, SCNN1G and SERPINA1 in six patients with CF-like phenotypes were confirmed by Sanger sequencing and were further supported by in silico predictive analysis, pedigree studies, sweat test in other family members, and analysis in CF patients and healthy subjects. Our results suggest that CF-like disease probably results from complex genotypes in several genes in an oligogenic form, with rare variants interacting with environmental factors.

Next generation diagnostics of cystic fibrosis and CFTR-related disorders by targeted multiplex high-coverage resequencing of CFTR.

BACKGROUND: Here we have developed a novel and much more efficient strategy for the complete molecular characterisation of the cystic fibrosis (CF) transmembrane regulator (CFTR) gene, based on multiplexed targeted resequencing. We have tested this approach in a cohort of 92 samples with previously characterised CFTR mutations and polymorphisms. METHODS: After enrichment of the pooled barcoded DNA libraries with a custom NimbleGen SeqCap EZ Choice array (Roche) and sequencing with a HiSeq2000 (Illumina) sequencer, we applied several bioinformatics tools to call mutations and polymorphisms in CFTR. RESULTS: The combination of several bioinformatics tools allowed us to detect all known pathogenic variants (point mutations, short insertions/deletions, and large genomic rearrangements) and polymorphisms (including the poly-T and poly-thymidine-guanine polymorphic tracts) in the 92 samples. In addition, we report the precise characterisation of the breakpoints of seven genomic rearrangements in CFTR, including those of a novel deletion of exon 22 and a complex 85 kb inversion which includes two large deletions affecting exons 4-8 and 12-21, respectively. CONCLUSIONS: This work is a proof-of-principle that targeted resequencing is an accurate and cost-effective approach for the genetic testing of CF and CFTR-related disorders (ie, male infertility) amenable to the routine clinical practice, and ready to substitute classical molecular methods in medical genetics.

The origin of the major cystic fibrosis mutation (delta F508) in European populations.

delta F508 is the most frequent cystic fibrosis (CF) mutation and accounts for approximately 70% of CF chromosomes worldwide. Three highly polymorphic microsatellite markers have been used to study the origin and evolution of delta F508 chromosomes in Europe. Haplotype data demonstrate that delta F508 occurred more than 52,000 years ago, in a population genetically distinct from any present European group, and spread throughout Europe in chronologically distinct expansions, which are responsible for the different frequencies of delta F508 in Europe.

N-terminal CFTR missense variants severely affect the behavior of the CFTR chloride channel.

Over 1,500 cystic fibrosis transmembrane conductance regulator (CFTR) gene sequence variations have been identified in patients with cystic fibrosis (CF) and related disorders involving an impaired function of the CFTR chloride channel. However, detailed structure-function analyses have only been established for a few of them. This study aimed evaluating the impact of eight N-terminus CFTR natural missense changes on channel behavior. By site-directed mutagenesis, we generated four CFTR variants in the N-terminal cytoplasmic tail (p.P5L, p.S50P, p.E60K, and p.R75Q) and four in the first transmembrane segment of membrane-spanning domain 1 (p.G85E/V, p.Y89C, and p.E92K). Immunoblot analysis revealed that p.S50P, p.E60K, p.G85E/V, and p.E92K produced only core-glycosylated proteins. Immunofluorescence and whole cell patch-clamp confirmed intracellular retention, thus reflecting a defect of CFTR folding and/or trafficking. In contrast, both p.R75Q and p.Y89C had a glycosylation pattern and a subcellular distribution comparable to the wild-type CFTR, while the percentage of mature p.P5L was considerably reduced, suggesting a major biogenesis flaw on this channel. Nevertheless, whole-cell chloride currents were recorded for all three variants. Single-channel patch-clamp analyses revealed that the channel activity of p.R75Q appeared similar to that of the wild-type CFTR, while both p.P5L and p.Y89C channels displayed abnormal gating. Overall, our results predict a major impact of the CFTR missense variants analyzed, except p.R75Q, on the CF phenotype and highlight the importance of the CFTR N-terminus on channel physiology.

Consensus on the use and interpretation of cystic fibrosis mutation analysis in clinical practice.

It is often challenging for the clinician interested in cystic fibrosis (CF) to interpret molecular genetic results, and to integrate them in the diagnostic process. The limitations of genotyping technology, the choice of mutations to be tested, and the clinical context in which the test is administered can all influence how genetic information is interpreted. This paper describes the conclusions of a consensus conference to address the use and interpretation of CF mutation analysis in clinical settings. Although the diagnosis of CF is usually straightforward, care needs to be exercised in the use and interpretation of genetic tests: genotype information is not the final arbiter of a clinical diagnosis of CF or CF transmembrane conductance regulator (CFTR) protein related disorders. The diagnosis of these conditions is primarily based on the clinical presentation, and is supported by evaluation of CFTR function (sweat testing, nasal potential difference) and genetic analysis. None of these features are sufficient on their own to make a diagnosis of CF or CFTR-related disorders. Broad genotype/phenotype associations are useful in epidemiological studies, but CFTR genotype does not accurately predict individual outcome. The use of CFTR genotype for prediction of prognosis in people with CF at the time of their diagnosis is not recommended. The importance of communication between clinicians and medical genetic laboratories is emphasized. The results of testing and their implications should be reported in a manner understandable to the clinicians caring for CF patients.

[Cystic fibrosis presenting as acute recurrent pancreatitis]. / Pancreatitis aguda recidivante como forma de presentación de fibrosis quística.

Cystic fibrosis is a multiorgan autosomal recessive disease resulting from mutations in a gene located on the long arm of chromosome 7. The disease is usually diagnosed in the first few years of life when it typically presents with severe pulmonary manifestations and pancreatic insufficiency; however, a small percentage of patients with less dramatic symptoms is not diagnosed until adolescence or even adulthood. The genotype of each patient seems to influence the various forms of clinical presentation. Although uncommon, acute recurrent pancreatitis can be one of the forms of delayed presentation of cystic fibrosis. We report the case of an 17-year-old man who was diagnosed with cystic fibrosis after presenting 2 episodes of acute pancreatitis without associated pancreatic insufficiency. Subsequent study also revealed nasal polyps.

ATB(0)/SLC1A5 gene. Fine localisation and exclusion of association with the intestinal phenotype of cystic fibrosis.

The Na+-dependent amino acid transporter named ATB(0) was previously found to be located in 19q13.3 by fluorescence in situ hybridisation. Genetic heterogeneity in the 19q13.2-13.4 region, syntenic to the Cystic Fibrosis Modulator Locus 1 (CFM1) in mouse, seemed to be associated to the intestinal phenotypic variation of cystic fibrosis (CF). We performed fine chromosomal mapping of ATB(0) on radiation hybrid (RH) panels G3 and TNG. Based on the most accurate location results from TNG-RH panel, mapping analysis evidenced that ATB(0) is localised between STS SHGC-13875 (D19S995) and STS SHGC-6138 in 19q13.3, that corresponds with the immediately telomeric/distal segment of the strongest linkage region within the human CFM1 (hCFM1) syntenic region. Regarding to the genomic structure and exon organisation, our results show that the ATB(0) gene is organised into eight exons. The knowledge of the genomic structure allowed us to perform an exhaustive mutational analysis of the gene. Evaluation of the possible implication of ATB(0) in the intestinal phenotype of CF was performed on the basis of the functional characteristics of the encoded protein, its apparent relevance to meconium ileus (MI) and position in relation to the hCFM1 syntenic region. We have analysed this gene in samples from CF patients with and without MI. Several sequence variations in the ATB(0) gene were identified, although none of them seemed to be related to the intestinal phenotype of CF. Even though no particular allele or haplotype in ATB(0) appears to be associated to CF-MI disease, new SNPs identified should be useful in segregation and linkage disequilibrium analyses in families affected by other disorders caused by the impairment of neutral amino acid transport.

[Detection of carriers and prenatal diagnosis of cystic fibrosis in Spanish families using DNA markers]. / Detección de portadores y diagnóstico prenatal de fibrosis quística en familias españolas utilizando marcadores del ADN.

A molecular study of 36 Spanish families with cystic fibrosis (CF) patients is reported. The analysis of seven DNA polymorphisms adjacent to the CF gene permitted the diagnosis of 95% of the probable carriers and the antenatal diagnosis in the seven cases in which it was requested. The application of recombinant DNA techniques to the study of CF by means of the analysis of DNA markers linked to the CF gene is useful, not only to identify the latter, but also as a reference to investigate its molecular pathology and for diagnostic purposes in high risk families (families with involved members).

[DNA polymorphisms as implant markers in allogeneic bone marrow transplantation. Preliminary evaluation]. / Los polimorfismos del DNA como marcadores de implante en el trasplante alogénico de medula ósea. Valoración preliminar.

After allogeneic bone marrow transplantation (BMT), patient hematopoietic and lymphoid cells are replaced by cells derived from the donor marrow. To document and characterize successful engraftment, host and donor cells must be distinguished from each other. We have used DNA sequence polymorphism analysis in 6 patients, at times varying, to determine reliably the host or donor origin of posttransplant cell populations and to compare these results with those obtained using red blood cell antigens and cytogenetics. Initially full engraftment was documented in all patients. In 1 patient a mixed lymphohematopoietic chimerism was documented 6 months after BMT and it reverted to donor hematopoiesis at 1 year post BMT. Posttransplant leukemic relapse was studied in two patients and shown to be of host origin in both cases. The DNA restriction fragment length polymorphisms (RFLP), are a powerful tool for the documentation of engraftment after BMT, to document mixed lymphohematopoietic chimerism and for the evaluation of leukemic relapse.

[Use of the polymerase chain reaction technic in the genetic analysis of cystic fibrosis]. / Aplicación del método de la reacción en cadena de la polimerasa al análisis genético de la fibrosis quística.

The development of polymerase chain reaction (PCR) which allows the specific amplification of DNA sequences has improved considerably the genetic analysis of hereditary diseases. We present here the application of this new technique to the genetic analysis of cystic fibrosis (CF), the most frequent severe genetic disease in caucasians. We have amplified four sequences containing polymorphisms linked to the CF gene (CS.7, KM.19, MP6d-9 and J3.11), and analysed the amplified products with restriction enzymes. Complete concordance was found with classical Southern methods, allowing the application of PCR to routine CF family studies.

Cystic fibrosis in a southern Brazilian population: characteristics of 90% of the alleles.

Cystic fibrosis (CF) is a genetic disease that frequently leads to death in infancy among Europeans and their descendants. The goals of the present study were to analyze the molecular aspects of CFTR gene characterizing mutations, their frequencies, and the haplotypes formed by four CFTR gene intragenic markers, IVS8-6(T)n, IVS8CA, IVS17bTA and IVS17bCA, in a southern Brazilian population of Caucasian origin. DNA samples from 56 non-related CF patients were analyzed using scanning techniques (single strand conformation polymorphism and denaturing gradient gel electrophoresis), restriction fragment length polymorphism and direct DNA sequencing to identify the mutations. Our results revealed a total of 25 different CF mutations representing nearly 90% of CF alleles, two being novel mutations. Microsatellite haplotypes were defined for CF and normal alleles. The mutational spectrum and the associated haplotypes described for the first time in this study should prove relevant for genetic counselling and CF population screening in Brazil. Moreover, our results suggest the presence of a major Mediterranean component in the contemporary Brazilian CF patient pool.

Spectrum of mutations in the CFTR gene in cystic fibrosis patients of Spanish ancestry.

We analyzed 1,954 Spanish cystic fibrosis (CF) alleles in order to define the molecular spectrum of mutations in the CFTR gene in Spanish CF patients. Commercial panels showed a limited detection power, leading to the identification of only 76% of alleles. Two scanning techniques, denaturing gradient gel electrophoresis (DGGE) and single strand conformation polymorphism/hetroduplex (SSCP/HD), were carried out to detect CFTR sequence changes. In addition, intragenic markers IVS8CA, IVS8-6(T)n and IVS17bTA were also analyzed. Twelve mutations showed frequencies above 1%, p.F508del being the most frequent mutation (51%). We found that eighteen mutations need to be studied to achieve a detection level of 80%. Fifty-one mutations (42%) were observed once. In total, 121 disease-causing mutations were identified, accounting for 96% (1,877 out of 1,954) of CF alleles. Specific geographic distributions for the most common mutations, p.F508del, p.G542X, c.1811 + 1.6kbA > G and c.1609delCA, were confirmed. Furthermore, two other relatively common mutations (p.V232D and c.2789 + 5G > A) showed uneven geographic distributions. This updated information on the spectrum of CF mutations in Spain will be useful for improving genetic testing, as well as to facilitate counselling in people of Spanish ancestry. In addition, this study contributes to defining the molecular spectrum of CF in Europe, and corroborates the high molecular mutation heterogeneity of Mediterranean populations.

Molecular evaluation of CFTR sequence variants in male infertility of testicular origin.

Although the involvement of the CFTR gene has been well established in congenital agenesia of vas deferens, its role in non-obstructive (NOb) infertility is still a matter of debate. In order to definitively define the involvement of the CFTR gene in spermatogenic impairment and a potential synergistic contribution to known genetic and clinical factors, genetic variants in the entire coding sequence and the immediately flanking regions of the CFTR gene, along with a thorough clinical evaluation, were analysed in 83 NOb infertile patients and 87 clinically well-defined fertile individuals as controls. The results of our study showed no statistical difference between CFTR carrier frequency in the infertile and fertile population. Specifically, the IVS8-6(5T) allele carrier frequency was similar in NOb infertile patients when compared with fertile men, but it is noteworthy that, when fertile men were classified into having optimal and suboptimal fertility, no 5T allele was found among the 35 men with optimal fertility parameters. In conclusion, extensive CFTR analysis in infertile individuals and fertile population as adequate control definitively excludes the involvement of the CFTR gene variants in sperm production and stresses the importance of carefully identifying those individuals with obstructive defects, in whom CFTR screening will be beneficial.

Genotype-phenotype correlation for pulmonary function in cystic fibrosis.

BACKGROUND: Since the CFTR gene was cloned, more than 1000 mutations have been identified. To date, a clear relationship has not been established between genotype and the progression of lung damage. A study was undertaken of the relationship between genotype, progression of lung disease, and survival in adult patients with cystic fibrosis (CF). METHODS: A prospective cohort of adult patients with CF and two CFTR mutations followed up in an adult cystic fibrosis unit was analysed. Patients were classified according to functional effects of classes of CFTR mutations and were grouped based on the CFTR molecular position on the epithelial cell surface (I-II/I-II, I-II/III-V). Spirometric values, progression of lung disease, probability of survival, and clinical characteristics were analysed between groups. RESULTS: Seventy four patients were included in the study. Patients with genotype I-II/I-II had significantly lower current spirometric values (p < 0.001), greater loss of pulmonary function (p < 0.04), a higher proportion of end-stage lung disease (p < 0.001), a higher risk of suffering from moderate to severe lung disease (odds ratio 7.12 (95% CI 1.3 to 40.5)) and a lower probability of survival than patients with genotype I-II/III, I-II/IV and I-II/V (p < 0.001). CONCLUSIONS: The presence of class I or II mutations on both chromosomes is associated with worse respiratory disease and a lower probability of survival.

CA/GT microsatellite alleles within the cystic fibrosis transmembrane conductance regulator (CFTR) gene are not generated by unequal crossingover.

The gene responsible for cystic fibrosis (CF) has recently been identified, and a three-nucleotide deletion (delta F508 mutation) that results in the loss of a phenylalanine residue in the first putative ATP-binding domain of the predicted protein (CF transmembrane conductance regulator, CFTR) has been found to be the major CF mutation. Although several other mutations have been identified in the CFTR gene, most of them are very rare, making their application to genetic diagnosis difficult. While characterizing the genomic region encompassing the CF locus, we have identified three CA/GT blocks that flank exon 9 of the CF gene. One of the CA/GT blocks exhibits a highly informative variable number of dinucleotide repeats (VNDR) polymorphism. This intragenic VNDR microsatellite should, by itself, provide full information for genetic analysis in approximately 80% of CF families and will help elucidate the associations between DNA polymorphism haplotypes and specific gene mutations. Haplotype analyses of CF chromosomes with and without the delta F508 mutation suggest that the different alleles are generated by slipped-strand mispairing within the dinucleotide repeat during DNA replication, rather than by unequal crossingover within a recombination hot spot.