Cystic Fibrosis Transmembrane Conductance Regulator Genotype Research Articles

Cystic Fibrosis in the Genomic Era: CFTR Genotyping as a Diagnostic Test

Our insight into cystic fibrosis (CF) disease and diseases associated with CF gene mutations has significantly increased in recent years, particularly after the discovery of the cystic fibrosis transmembrane conductance regulator (CFTR) gene over two decades ago. This has resulted in a widened spectrum of phenotypic manifestations of CF ranging from the classic multisystem disease in infancy and early childhood to adults with single-organ manifestations of CF such as chronic sinopulmonary disease, pancreatitis and obstructive azoospermia. As a consequence, the diagnosis of CF can be difficult to establish or exclude. Extensive CFTR genotyping has been limited by the inability to interpret the functional and clinical significance of a large number of identified CFTR mutations. As identified CFTR mutations can either be “disease-causing”, “of varying clinical consequences”, “benign” or have unknown consequences, the identification of mutations on both alleles may be insufficient alone to confirm the diagnosis of CF. More recently though, the number of mutations recognized to be disease-causing was greatly expanded by the Clinical and Functional Translation of CFTR (CFTR2) project. This review article discusses the role and yield of CFTR mutation analysis in the diagnosis of CF.

Unraveling the complex genetic model for cystic fibrosis: pleiotropic effects of modifier genes on early cystic fibrosis-related morbidities

The existence of pleiotropy in disorders with multi-organ involvement can suggest therapeutic targets that could ameliorate overall disease severity. Here we assessed pleiotropy of modifier genes in cystic fibrosis (CF). CF, caused by mutations in the cystic fibrosis transmembrane conductance regulator (CFTR) gene, affects the lungs, liver, pancreas and intestines. However, modifier genes contribute to variable disease severity across affected organs, even in individuals with the same CFTR genotype. We sought to determine whether SLC26A9, SLC9A3 and SLC6A14, that contribute to meconium ileus in CF, are pleiotropic for other early-affecting CF co-morbidities. In the Canadian CF population, we assessed evidence for pleiotropic effects on (1) pediatric lung disease severity (n = 815), (2) age at first acquisition of Pseudomonas aeruginosa (P. aeruginosa) (n = 730), and (3) prenatal pancreatic damage measured by immunoreactive trypsinogen (n = 126). A multiple-phenotype analytic strategy assessed evidence for pleiotropy in the presence of phenotypic correlation. We required the same alleles to be associated with detrimental effects. SLC26A9 was pleiotropic for meconium ileus and pancreatic damage (p = 0.002 at rs7512462), SLC9A3 for meconium ileus and lung disease (p = 1.5 × 10(-6) at rs17563161), and SLC6A14 for meconium ileus and both lung disease and age at first P. aeruginosa infection (p = 0.0002 and p = 0.006 at rs3788766, respectively). The meconium ileus risk alleles in SLC26A9, SLC9A3 and SLC6A14 are pleiotropic, increasing risk for other early CF co-morbidities. Furthermore, co-morbidities affecting the same organ tended to associate with the same genes. The existence of pleiotropy within this single disorder suggests that complementary therapeutic strategies to augment solute transport will benefit multiple CF-associated tissues.

The IFRD1 (57460C>T Polymorphism) Gene: A Negative Report in Cystic Fibrosis Clinical Severity

Cystic fibrosis (CF) is an autosomal recessive disease caused by more than 1,900 mutations in the Cystic Fibrosis Transmembrane Conductance Regulator (CFTR) gene. In CF, one intriguing aspect is that patients, with same CFTR mutation, can have high clinical variability. Thus, the CFTR genotype does not seem to be the only determining factor in the clinical severity modulation. Therefore, the modifier genes and the environment must be considered. The IFRD1 (Interferon-related developmental regulator 1) gene, acts on the immune system and in the recruitment of immune cells, and consequently could be a modulator. In our data we included 88 CF patients, diagnosed by CFTR mutation screening and positive sweat test. The 57460C>T polymorphism screening in the IFRD1 gene was made by polymerase chain reaction associated to enzymatic digestion. A genotypic comparison was performed with 23 CF clinical variables. The data was analyzed by the SPSS program considering α=0.05. The patients were analyzed considering the CFTR genotype characteristic by mutation class. In our data 64.77% of patients had mutations of classes I, II or III in the CFTR gene. The IFRD1 polymorphism frequency was 28 (12.99%), 35 (75.32%) and 25 (11.69%) to the CC, CT and TT genotypes, respectively. In our study, the 57460C>T polymorphism in the IFRD1 gene was not associated with the CF clinical variables. The analysis was performed with and without consideration of the CFTR genotype, and after correction for multiple testing (Bonferroni test), no positive association was observed in both cases. Taking into account our results, in the CF patients population analyzed, there were no associations of the 57460C>T polymorphism in the IFRD1 gene with the CF clinical variables.

Role of Cystic Fibrosis Transmembrane Conductance Regulator in Patients With Chronic Sinopulmonary Disease

Previous studies report a high frequency of mutations in the cystic fibrosis (CF) transmembrane conductance regulator gene (CFTR) in patients with idiopathic bronchiectasis. However, most studies have based their findings on preselected patient groups or have performed limited testing for CF transmembrane conductance regulator (CFTR) dysfunction. The objective of our study was to evaluate the prevalence of CFTR gene mutations and/or CFTR-related ion channel abnormalities among subjects with idiopathic chronic sinopulmonary disease and the prevalence of CF or a CFTR-related disorder in this population. We evaluated 72 prospectively enrolled patients from 1995 to 2005 at the Hospital for Sick Children and St. Michael’s Hospital with idiopathic chronic sinopulmonary disease for evidence of CFTR-mediated abnormalities. We performed CFTR genotyping and assessed CFTR function using sweat testing and nasal potential difference testing. The results were compared with data from healthy control subjects, CF heterozygotes, and patients with CF. The CFTR functional tests in idiopathic sinopulmonary patients showed a continuous spectrum, ranging from normal to values typically seen in individuals with CF. Forty-eight patients (66%) demonstrated CFTR mutations and/or abnormalities of CFTR function. Twenty-two (31%) fulfilled criteria for a diagnosis of CF and 26 (36%) for a CFTR-related disorder with a strong female preponderance. Functional tests, more than genotyping, were instrumental in establishing a CF diagnosis. Clinical features failed to distinguish subjects with CF from those with CFTR-related or idiopathic disease. The high prevalence of CF and CFTR dysfunction among patients with idiopathic chronic sinopulmonary disease underscores the need for extensive diagnostic evaluation for CF.

Personalized medicine for cystic fibrosis: the next generation.

The field of personalized medicine, based on genetic information, represents a tremendous but largely unfulfilled opportunity for a future generation of therapies [1]. While better clinical outcomes have been realized using predictive biomarkers in some forms of cancer [2], the influence of genetic information on the treatment of most other human diseases has been limited. However, in the case of the inherited genetic disease cystic fibrosis (CF), pre-emptive possibilities have recently been uncovered. In particular, an investigational drug known as VX-770, has demonstrated great promise in clinical trials in patients with a specific cystic fibrosis transmembrane conductance regulator (CFTR) allele selected for clinical investigation based on data from in vitro studies [3,4]. This article highlights some of the opportunities and challenges associated with developing novel genotype-directed therapies for CF.

Cystic fibrosis modifier genes related to Pseudomonas aeruginosa infection

Cystic fibrosis (CF) is one of the most common life-shortening genetic disorders, and the CF transmembrane conductance regulator (CFTR) is the major causal gene. However, a substantial clinical variability among patients with identical CFTR genotypes suggests the presence of modifier genes. We tested the effect of four genes involved in Pseudomonas aeruginosa infection. Analysis of a primary cohort detected eight candidate polymorphisms that were genotyped in the secondary cohort of 1579 patients; lung function and age at first infection with P. aeruginosa were considered as the phenotypes. Both additive and codominant models were considered, adjusting for confounding variables but not for multiple comparisons. In the secondary cohort, heme oxygenase-1 (HMOX1) rs2071749 had the most significant effect on lung function in the pediatric group (P=0.01; P(corrected)=0.03), and complement factor 3 (C3) rs11569393 and HMOX1 rs2071746 in the adult groups (P=0.03 for both variants; P(corrected)=0.16, 0.09). No polymorphism of complement factor B (CFB) or toll-like receptor 4 (TLR4) had a significant modifying effect on lung function in either group. We have identified two genes that showed nominal association with disease severity among CF patients. However, because of the multiple comparisons made, further studies are required to confirm the interaction between these modifying genes and CFTR.

Comprehensive description of CFTR genotypes and ultrasound patterns in 694 cases of fetal bowel anomalies: a revised strategy

Fetal bowel anomalies may reveal cystic fibrosis (CF) and the search for CF transmembrane conductance regulator (CFTR) gene mutations is part of the diagnostic investigations in such pregnancies, according to European recommendations. We report on our 18-year experience to document comprehensive CFTR genotypes and correlations with ultrasound patterns in a series of 694 cases of fetal bowel anomalies. CFTR gene analysis was performed in a multistep process, including search for frequent mutations in the parents and subsequent in-depth search for rare mutations, depending on the context. Ultrasound patterns were correlated with the genotypes. Cases were distinguished according to whether they had been referred directly to our laboratory or after an initial testing in another laboratory. A total of 30 CF fetuses and 8 cases compatible with CFTR-related disorders were identified. CFTR rearrangements were found in 5/30 CF fetuses. 21.2% of fetuses carrying a frequent mutation had a second rare mutation, indicative of CF. The frequency of CF among fetuses with no frequent mutation was 0.43%. Correlation with ultrasound patterns revealed a significant frequency of multiple bowel anomalies in CF fetuses. The results emphasize the need to search for rearrangements in the diagnosis strategy of fetal bowel anomalies. The diagnostic value of ultrasound patterns combining hyperechogenic bowel, loop dilatation and/or non-visualized gallbladder reveals a need to revise current strategies and to offer extensive CFTR gene testing when the triad is diagnosed, even when no frequent mutation is found in the first-step analysis.

Partitioning core and satellite taxa from within cystic fibrosis lung bacterial communities

Cystic fibrosis (CF) patients suffer from chronic bacterial lung infections that lead to death in the majority of cases. The need to maintain lung function in these patients means that characterising these infections is vital. Increasingly, culture-independent analyses are expanding the number of bacterial species associated with CF respiratory samples; however, the potential significance of these species is not known. Here, we applied ecological statistical tools to such culture-independent data, in a novel manner, to partition taxa within the metacommunity into core and satellite species. Sputa and clinical data were obtained from 14 clinically stable adult CF patients. Fourteen rRNA gene libraries were constructed with 35 genera and 82 taxa, identified in 2139 bacterial clones. Shannon–Wiener and taxa-richness analyses confirmed no undersampling of bacterial diversity. By decomposing the distribution using the ratio of variance to the mean taxon abundance, we partitioned objectively the species abundance distribution into core and satellite species. The satellite group comprised 67 bacterial taxa from 33 genera and the core group, 15 taxa from 7 genera (including Pseudomonas (1 taxon), Streptococcus (2), Neisseria (2), Catonella (1), Porphyromonas (1), Prevotella (5) and Veillonella (3)], the last four being anaerobes). The core group was dominated by Pseudomonas aeruginosa. Other recognised CF pathogens were rare. Mantel and partial Mantel tests assessed which clinical factors influenced the composition observed. CF transmembrane conductance regulator genotype and antibiotic treatment correlated with all core taxa. Lung function correlated with richness. The clinical significance of these core and satellite species findings in the CF lung is discussed.

Intestinal current measurement for diagnostic classification of patients with questionable cystic fibrosis: validation and reference data

BackgroundIn questionable cystic fibrosis (CF), mild or monosymptomatic phenotypes frequently cause diagnostic difficulties despite detailed algorithms. CF transmembrane conductance regulator (CFTR)-mediated ion transport can be studied ex vivo in rectal...

Cystic Fibrosis Transmembrane Conductance Regulator Channel Dysfunction in Non–Cystic Fibrosis Bronchiectasis

Although in patients with diffuse bronchiectasis (DB) and a normal sweat test the presence of one mutation in the cystic fibrosis transmembrane conductance regulator (CFTR) gene is frequently observed, its pathogenic role in the development of DB remains unclear. To evaluate the association between CFTR heterozygosity and CFTR protein dysfunction in the airways of patients with DB. Nasal potential difference was measured in 122 patients with DB of unknown origin and with a normal sweat test (Cl(-) < 60 mmol/L). They were classified according to the presence of CFTR mutations: zero (85 patients), one (22 patients), or two mutations (15 patients). Control groups comprised 26 healthy subjects, 38 obligate heterozygotes for CFTR, and 92 patients with classic cystic fibrosis (CF) with an abnormal sweat test (Cl(-) > or = 60 mmol/L). Patients classified as mild-CF were carrying at least one mild mutation and patients classified as severe-CF were homozygous for the F508del mutation. There was a continuum of airway CFTR dysfunction in the study population as shown by nasal potential difference measurements, ranging from normal values in healthy subjects, to intermediate values in subjects with DB, to highly abnormal values in subjects classified as severe-CF. This continuum of airway CFTR dysfunction was thus strongly associated with defects in the CFTR gene. Moreover, among patients with DB, a similar continuum in intermediate nasal potential difference was identified that was associated with the bearing of zero, one, or two CFTR mutations. These electrophysiological phenotypes and CFTR genotypes were also associated with the clinical phenotype, as shown by the frequency of Staphylococcus aureus and Pseudomonas aeruginosa bronchial colonization. Our study supports the hypothesis that a unique CFTR mutation may have pathogenic consequences in patients with DB.

Disease-causing Mutations in the Cystic Fibrosis Transmembrane Conductance Regulator Determine the Functional Responses of Alveolar Macrophages

Alveolar macrophages (AMs) play a major role in host defense against microbial infections in the lung. To perform this function, these cells must ingest and destroy pathogens, generally in phagosomes, as well as secrete a number of products that signal other immune cells to respond. Recently, we demonstrated that murine alveolar macrophages employ the cystic fibrosis transmembrane conductance regulator (CFTR) Cl(-) channel as a determinant in lysosomal acidification (Di, A., Brown, M. E., Deriy, L. V., Li, C., Szeto, F. L., Chen, Y., Huang, P., Tong, J., Naren, A. P., Bindokas, V., Palfrey, H. C., and Nelson, D. J. (2006) Nat. Cell Biol. 8, 933-944). Lysosomes and phagosomes in murine cftr(-/-) AMs failed to acidify, and the cells were deficient in bacterial killing compared with wild type controls. Cystic fibrosis is caused by mutations in CFTR and is characterized by chronic lung infections. The information about relationships between the CFTR genotype and the disease phenotype is scarce both on the organismal and cellular level. The most common disease-causing mutation, DeltaF508, is found in 70% of patients with cystic fibrosis. The mutant protein fails to fold properly and is targeted for proteosomal degradation. G551D, the second most common mutation, causes loss of function of the protein at the plasma membrane. In this study, we have investigated the impact of CFTR DeltaF508 and G551D on a set of core intracellular functions, including organellar acidification, granule secretion, and microbicidal activity in the AM. Utilizing primary AMs from wild type, cftr(-/-), as well as mutant mice, we show a tight correlation between CFTR genotype and levels of lysosomal acidification, bacterial killing, and agonist-induced secretory responses, all of which would be expected to contribute to a significant impact on microbial clearance in the lung.

Nasal polyposis in atypical cystic fibrosis: A case report

Abstract Cystic fibrosis (CF) is one of the most common inherited life-shortening diseases with an incidence of 1:2.500–3500 and a carrier frequency of 4–5% [1] . It is caused by mutations in the CF transmembrane conductance regulator (CFTR) gene, which encodes a protein expressed in the apical membrane of exocrine epithelial cells, resulting in changes to the fluid and electrolytes on cell surface. More than 1500 mutations have been described so far in the CFTR gene, grouped in 5 classes on the basis of the impact on protein synthesis or activity [2] . In the last years a mounting number of reports described patients that did not meet all diagnostic criteria for CF [4] ; in particular, atypical or nonclassic CF is characterized by normal or borderline sweat test, pancreatic sufficiency and a monosymptomatic phenotype; the most studied forms are: congenital bilateral absence of vasa deferentes, acute or chronic recurrent pancreatitis, idiopathic bronciectasis [5] . These patients typically bear a severe and a mild (classes 4–5) CFTR mutation, the latter being dominant [6] . The involvement of upper airways is observed in up to 100% of classic CF patients, including recurrent sinusitis and rhinitis. Nasal polyps are present in 6–48% of overall CF patients and in 5–15.2% of less than 10 years old CF patients. Surgery is required for syntomatic polyps. It is the second most common class of operations performed on CF patients. In spite of the best of operations CF patients will have recurrence, because of systemic disease. We describe a patient diagnosed as “atypical CF” on the basis of persisting chronic rhinosinusitis, that showed a very rare CFTR genotype.

Extended cystic fibrosis testing - does the end justify the means?

Introduction Mutation testing of the cystic fibrosis transmembrane conductance regulator (CFTR) gene is often required for a definitive diagnosis of cystic fibrosis, but >1000 mutations are known. Aims To compare the mutation detection rate of our in-house 11-mutation panel against a 33-mutation panel and direct gene sequencing in patient groups stratified by sweat test (SWT) status. Methods All clinically diagnosed cystic fibrosis (CF) patients presenting between 2003 and 2007 were reviewed to determine their SWT results and CFTR genotypes as identifiable by sequencing, the 11-plex screen or the Abbott-Celera 33-plex oligonucleotide ligation assay (OLA) kit. In total, 85 patients in total were analysed. Results 56% of SWT positive patients were fully characterised by the 11-plex screen, compared with 62% by 33-plex screen and 85% by sequencing. The detection rate was substantially lower in SWT equivocal/negative patients (16% by 11-plex, 21% by 33-plex, 58% by sequencing). Ten of 66 SWT positive patients remained incompletely genotyped even by sequencing, while 11 of 19 SWT equivocal/negative patients carried 2 mutant CFTR alleles. Discussion The 33-plex screen offers improved detection rate over the 11-plex screen but sequencing remains necessary for a substantial proportion of patients. Negative SWT or negative sequencing alone should not be taken to exclude CF.

TheCFTRM470V Gene Variant as a Potential Modifier of COPD Severity: Study of Serbian Population

Chronic obstructive pulmonary disease (COPD) is a complex disease influenced by genetic and environmental factors. Cystic fibrosis transmembrane conductance regulator (CFTR) protein is an important component of the lung tissue homeostasis, involved in the regulation of the rate of mucociliary clearance. As it is known that certain CFTR variants have consequences on the function of CFTR protein, the aim of this study was to examine the possible role of F508del, M470V, Tn locus, and R75Q variants in COPD development and modulation. Total number of 86 COPD patients and 102 control subjects were included in the study. Possible association between COPD susceptibility, severity, and onset of the disease and allele or genotype of four analyzed CFTR variants was examined. No associations were detected between COPD development, onset of the disease and tested CFTR alleles and genotypes. However, VV470 genotype was associated with mild/moderate COPD stages in comparison to severe/very severe ones (OR = 0.29, 95%CI = 0.11-0.80, p = 0.016). Our study showed that patients with VV470 genotype had a 3.4-fold decreased risk for the appearance of severe/very severe COPD symptoms, and the obtained results indicate that this genotype may have a protective role. These results also suggest the importance of studying CFTR gene as a modifier of this disease.

Primary Sclerosing Cholangitis in Childhood is Associated with Abnormalities in Cystic Fibrosis–Mediated Chloride Channel Function

To determine whether primary sclerosing cholangitis (PSC) in childhood is associated with abnormalities in cystic fibrosis transmembrane conductance regulator (CFTR). Subjects with PSC diagnosed in childhood (n = 20) were recruited from Children's Hospital. Subjects had testing with sweat chloride concentration, nasal transmembrane potential difference, and extensive genetic analysis of the CFTR gene. Disease control subjects consisted of 14 patients with inflammatory bowel disease alone and no liver disease. t tests were performed to determine statistical significance. In the PSC group, CFTR chloride channel function (deltaChloride free + isoproterenol) was markedly diminished at -8.6 +/- 8.2 mV (reference range: -24.6 +/- 10.4 mV). In contrast, disease control subjects had normal function, at -17.8 +/- 9.7 mV (P = .008). Sweat chloride concentration in subjects with PSC was greater than in disease control subjects (20.8 +/- 3.4 mmol/L vs 12.0 +/- 1.6 mmol/L, P = .045). Comprehensive CFTR genotyping revealed that 5 of 19 (26.3%) subjects with PSC had a CFTR mutation or variant, compared with 6 of 14 (42.9%) disease control subjects. There is a high prevalence of CFTR-mediated ion transport dysfunction in subjects with childhood PSC.

Association of Pancreas Divisum and Recurrent Acute Pancreatitis With the IVS8-5T-12TG Allele of the CFTR Gene and CFTR Dysfunction

Pancreas divisum (PD) occurs in approximately 10% of individuals. Although a minority of patients with PD develop acute pancreatitis (AP), PD is found in up to 25% of patients with unexplained AP. Mild mutations or variants of the cystic fibrosis transmembrane conductance regulator (CFTR) gene, including the IVS8-5T variant, are associated with idiopathic pancreatitis, but their relationship with PD is unknown. We hypothesized for such association. Case of 2 patients with PD, recurrent AP, and CFTR-related disease are reported. Both patients had similar clinical patterns (young female adults, nonsevere onsets of AP, mild upper airway manifestations, no major clinical criteria for cystic fibrosis). They had 2 mutations or variants of the CFTR gene (including the IVS8-5T-12TG allele) and mild abnormalities of the CFTR function (increased sweat chloride concentrations in one patient, normal basal but low responses to low-chloride and/or isoproterenol solutions on nasal potential difference). These observations suggest that impaired epithelial ion transport due to mild CFTR genotype (namely, IVS8-5T-TG12) might be involved as a triggering factor in acute onsets of pancreatitis in PD, possibly through abnormal pancreatic fluid secretion. Further studies on CFTR mutations and abnormal nasal airway ion transport in patients with PD, either with or without recurrent AP, should be conducted.

ENaCβ and γ genes as modifier genes in cystic fibrosis

Background Clinical phenotype varies among cystic fibrosis (CF) patients with identical CF transmembrane conductance regulator ( CFTR)genotype, suggesting that genetic modifiers exist. Transgenic mice that overexpress SCNN1β present CF-like lung disease symptoms. Mutations or variants in SCNN1β may therefore potentially modulate the clinical phenotype in CF patients. Methods We analysed by DHPLC SCNN1β and SCNN1γ genes in 56 patients with classical CF. Patients were classified into two groups according to their CFTR genotype and their severity: 38 patients with severe genotype and an unexpectedly mild lung phenotype, and 18 patients with mild genotype and a severe lung phenotype. Results We found 3 patients out of 56 carrying at least one missense mutation. Two were novel (p.Thr313Met in SCNN1β, p.Leu481Gln in SCNN1γ) and two were previously described (p.Gly589Ser in SCNN1β and p.Val546Ileu in SCNNγ). p.Thr313Met has been identified in a CF patient with mild genotype and severe lung phenotype suggesting that it could act in increasing ENaC activity. The three other variants have been identified in CF patients with severe genotype and mild lung phenotype suggesting that they might decrease ENaC activity. However, the function of ENaC in the nasal epithelia of these patients, evaluated by nasal potential difference measurements, did not support the fact that these variants were functional, at least in nasal epithelium. Conclusion Our results suggest that genetic variants in ENaCβ and γ genes do not modulate disease severity in the majority of CF patients.

Disease modifying genes in cystic fibrosis: therapeutic option or one-way road?

Cystic fibrosis (CF) is the most common genetic disease among Caucasians and is caused by mutations in the CF transmembrane conductance regulator (CFTR) gene. CF affects multiple organs but lung disease is the major determinant for morbidity and mortality. Many studies have focussed on the correlation between CFTR genotype and severity of disease. Since patients with identical CFTR mutations often show considerable variability in disease progression, genes other than CFTR are thought to have the potential to modify the course of lung disease in CF patients. Therefore, identification of CF-modifying genes has become the goal of several studies over the last 15 years. Pharmaceutical approaches for CF lung disease have been developed regardless of the underlying genetic defect and in general target symptoms such as airway obstruction and treatment of bacterial infection. Analysing the pathophysiological processes of modifiers may lead to the discovery of pathways involved in CF pathophysiology and possibly to the design of new therapeutics. The purpose of this review is not only to list potential CFTR modifier genes, but also to discuss new therapeutic strategies that could be derived from knowledge of these CF modifiers.

Relative Contribution of Genetic and Nongenetic Modifiers to Intestinal Obstruction in Cystic Fibrosis

Neonatal intestinal obstruction (meconium ileus [MI]) occurs in 15% of patients with cystic fibrosis (CF). Our aim was to determine the relative contribution of genetic and nongenetic modifiers to the development of this major complication of CF. A total of 65 monozygous twin pairs, 23 dizygous twin/triplet sets, and 349 sets of siblings with CF were analyzed for MI status, significant covariates, and genome-wide linkage. Specific mutations in the CF transmembrane conductance regulator (CFTR), the gene responsible for CF, correlated with MI, indicating a role for CFTR genotype. Monozygous twins showed substantially greater concordance for MI than dizygous twins and siblings (P = 1 x 10(-5)), showing that modifier genes independent of CFTR contribute substantially to this trait. Regression analysis revealed that MI was correlated with distal intestinal obstruction syndrome (P = 8 x 10(-4)). Unlike MI, concordance analysis indicated that the risk for development of distal intestinal obstruction syndrome in CF patients is caused primarily by nongenetic factors. Regions of suggestive linkage (logarithm of the odds of linkage >2.0) for modifier genes that cause MI (chromosomes 4q35.1, 8p23.1, and 11q25) or protect from MI (chromosomes 20p11.22 and 21q22.3) were identified by genome-wide analyses. These analyses did not support the existence of a major modifier gene on chromosome 19 in a region previously linked to MI. The CFTR gene along with 2 or more modifier genes are the major determinants of intestinal obstruction in newborn CF patients, whereas intestinal obstruction in older CF patients is caused primarily by nongenetic factors.

Variants in the glutamate-cysteine-ligase gene are associated with cystic fibrosis lung disease.

Chronic progressive lung disease is the most serious complication of cystic fibrosis (CF). Glutathione plays an important role in the protection of the CF lung against oxidant-induced lung injury. We hypothesized that a polymorphism in a novel candidate gene that regulates glutathione synthesis might influence CF lung disease. In a cross-sectional study, subjects were recruited from CF clinics in Seattle and multiple centers in Canada. We tested for an association between CF lung disease and a functional polymorphism in the glutamate-cysteine ligase catalytic subunit (GCLC) gene. Multiple linear regression was used to test for association between polymorphisms of GCLC and severity of CF lung disease while adjusting for age, Pseudomonas aeruginosa infection, and cystic fibrosis transmembrane conductance regulator (CFTR) genotype. Analysis was repeated for patients with CF stratified by CFTR genotype. A total of 440 subjects with CF participated in the study (51% male; mean [+/- SD] age, 26 +/- 11 yr; mean FEV(1), 62 +/- 28% predicted). In the total population, there was a trend toward an association between GCLC genotypes and CF lung disease (linear regression coefficient [SEM], 1.68 [1.0]; p = 0.097). In the stratified analysis, there was a highly significant association between GCLC genotype and CF lung function in subjects with a milder CFTR genotype (linear regression coefficient [SEM], 5.5 (1.7); p = 0.001). In patients with CF with a milder CFTR genotype, there is a strong association between functional polymorphisms of the GCLC gene and CF lung disease severity.