Mutations of the cystic fibrosis gene and intermediate sweat chloride levels in children

Diagnosing Cystic Fibrosis in the 21st Century-A Complex and Challenging Task

Cystic fibrosis (CF) is a chronic and potentially life-threatening condition, wherein timely diagnosis assumes paramount significance for the prompt initiation of therapeutic interventions, thereby ameliorating pulmonary function, addressing nutritional deficits, averting complications, mitigating morbidity, and ultimately enhancing the quality of life and extending longevity. This review aims to amalgamate existing knowledge to provide a comprehensive appraisal of contemporary diagnostic modalities pertinent to CF in the 21st century. Deliberations encompass discrete delineations of each diagnostic modality and the elucidation of potential diagnostic quandaries encountered in select instances, as well as the delineation of genotype-phenotype correlations germane to genetic counseling endeavors. The synthesis underscores that, notwithstanding the availability and strides in diagnostic methodologies, including genetic assays, the sweat test (ST) retains its position as the preeminent diagnostic standard for CF, serving as a robust surrogate for CFTR functionality. Prospective clinical investigations in the realm of CF should be orchestrated with the objective of discerning novel diagnostic modalities endowed with heightened specificity and sensitivity.

Efficacy and safety profile of elexacaftor-tezacaftor-ivacaftor triple therapy on cystic fibrosis: a systematic review and single arm meta-analysis

Background: Elexacaftor-Tezacaftor-Ivacaftor (ELE/TEZ/IVA) is believed to be an effective and well-tolerated treatment for cystic fibrosis (CF), but the exact efficacy and safety profile are still unknown. Objective: This study aimed to clarify the extent of functional restoration when patients are given with triple combination treatment and demonstrate the prevalence of adverse events, to evaluate the overall profile of ELE/TEZ/IVA on CF. Methods: A literature search was conducted in PubMed, Web of Science and Cochrane Library. Random effects single-arm meta-analysis was performed to decipher the basal characteristics of CF, the improvement and safety profile after ELE/TEZ/IVA treatment. Results: A total 53 studies were included in this analysis. For all the patients in included studies. 4 weeks after ELE/TEZ/IVA treatment, the increasement of percentage of predicted Forced Expiratory Volume in the first second (ppFEV1) was 9.23% (95%CI, 7.77%-10.70%), the change of percentage of predicted Forced Vital Capacity (ppFVC) was 7.67% (95%CI, 2.15%-13.20%), and the absolute change of Cystic Fibrosis Questionnaire-Revised (CFQ-R) score was 21.46 points (95%CI, 18.26-24.67 points). The Sweat chloride (SwCl) was significantly decreased with the absolute change of -41.82 mmol/L (95%CI, -44.38 to -39.25 mmol/L). 24 weeks after treatment, the increasement of ppFEV1 was 12.57% (95%CI, 11.24%-13.90%), the increasement of ppFVC was 10.44% (95%CI, 7.26%-13.63%), and the absolute change of CFQ-R score was 19.29 points (95%CI, 17.19-21.39 points). The SwCl was significantly decreased with the absolute change of -51.53 mmol/L (95%CI, -56.12 to -46.94 mmol/L). The lung clearance index2.5 (LCI2.5) was also decreased by 1.74 units (95%CI, -2.42 to -1.07 units). The body mass index increased by 1.23 kg/m2 (95%CI, 0.89-1.57 kg/m2). As for adverse events, 0.824 (95%CI, 0.769-0.879) occurred during ELE/TEZ/IVA period, while the incidence of severe adverse events was 0.066 (95%CI, 0.028-0.104). Conclusion: ELE/TEZ/IVA is a highly effective strategy and relatively safe for CF patients and needs to be sustained to achieve better efficacy. Systematic Review Registration: Identifier: CRD42023441840.

Proof of concept for identifying cystic fibrosis from perspiration samples

The gold standard for cystic fibrosis (CF) diagnosis is the determination of chloride concentration in sweat. Current testing methodology takes up to 3 h to complete and has recognized shortcomings on its diagnostic accuracy. We present an alternative method for the identification of CF by combining desorption electrospray ionization mass spectrometry and a machine-learning algorithm based on gradient boosted decision trees to analyze perspiration samples. This process takes as little as 2 min, and we determined its accuracy to be 98 ± 2% by cross-validation on analyzing 277 perspiration samples. With the introduction of statistical bootstrap, our method can provide a confidence estimate of our prediction, which helps diagnosis decision-making. We also identified important peaks by the feature selection algorithm and assigned the chemical structure of the metabolites by high-resolution and/or tandem mass spectrometry. We inspected the correlation between mild and severe CFTR gene mutation types and lipid profiles, suggesting a possible way to realize personalized medicine with this noninvasive, fast, and accurate method.

Initial Evaluation of Prospective and Parallel Assessments of Cystic Fibrosis Newborn Screening Protocols in Eastern Andalusia: IRT/IRT versus IRT/PAP/IRT

Identifying newborns at risk for cystic fibrosis (CF) by newborn screening (NBS) using dried blood spot (DBS) specimens provides an opportunity for presymptomatic detection. All NBS strategies for CF begin with measuring immunoreactive trypsinogen (IRT). Pancreatitis-associated protein (PAP) has been suggested as second-tier testing. The main objective of this study was to evaluate the analytical performance of an IRT/PAP/IRT strategy versus the current IRT/IRT strategy over a two-year pilot study including 68,502 newborns. The design of the study, carried out in a prospective and parallel manner, allowed us to compare four different CF-NBS protocols after performing a post hoc analysis. The best PAP cutoff point and the potential sources of PAP false positive results in our non-CF newborn population were also studied. 14 CF newborns were detected, resulting in an overall CF prevalence of 1/4, 893 newborns. The IRT/IRT algorithm detected all CF cases, but the IRT/PAP/IRT algorithm failed to detect one case of CF. The IRT/PAP/IRT with an IRT-dependent safety net protocol was a good alternative to improve sensitivity to 100%. The IRT × PAP/IRT strategy clearly performed better, with a sensitivity of 100% and a positive predictive value (PPV) of 39%. Our calculated optimal cutoffs were 2.31 µg/L for PAP and 167.4 µg2/L2 for IRT × PAP. PAP levels were higher in females and newborns with low birth weight. PAP false positive results were found mainly in newborns with conditions such as prematurity, sepsis, and hypoxic-ischemic encephalopathy.

Guidelines for the clinical management and follow-up of infants with inconclusive cystic fibrosis diagnosis through newborn screening

Neonatal screening for cystic fibrosis (CF) can detect infants with elevated immunoreactive trypsinogen (IRT) levels and inconclusive sweat tests and/or CFTR DNA results. These cases of uncertain diagnosis are defined by (1) either the presence of at most one CF-associated cystic fibrosis transmembrane conductance regulator (CFTR) mutation with sweat chloride values between 30 and 59mmol/L or (2) two CFTR mutations with at least one of unknown pathogenic potential and a sweat chloride concentration below 60mmol/L. This encompasses various clinical situations whose progression cannot be predicted. In these cases, a sweat chloride test has to be repeated at 12 months, and if possible at 6 and 24 months of life along with extended CFTR sequencing to detect rare mutations. When the diagnosis is not definite, CFTR functional explorations may provide a better understanding of CFTR dysfunction. The initial evaluation of these infants must be conducted in dedicated CF reference centers and should include bacteriological sputum analysis, chest radiology, and fecal elastase assay. The primary care physicians in charge of these patients should be familiar with the current management of CF and should work in collaboration with CF centers. A follow-up should be performed in a CF reference center at 3, 6, and 12 months of life and every year thereafter. Any symptom indicative of CF requires immediate reevaluation of the diagnosis. These guidelines were established by the "neonatal screening and difficult diagnoses" working group of the French CF society. Their objective is to standardize the management of infants with unclear diagnosis.

[Management of infants whose diagnosis is inconclusive at neonatal screening for cystic fibrosis]

Neonatal screening for cystic fibrosis (CF) may detect infants with elevated immunoreactive trypsinogen (IRT) levels but with inconclusive sweat tests and/or DNA results. This includes cases associating (1) either the presence of at most one CF-causing mutation and sweat chloride values between 30 and 59mmol/L or (2) two CFTR mutations with at least one of unknown pathogenicity and a sweat chloride below 60mmol/L. This encompasses different clinical situations whose progression cannot be predicted. These cases require redoing the sweat test at 12 months and if possible at 6 and 24 months of life. This must be associated with extended genotyping. CFTR functional explorations can also help by investigating CFTR dysfunction. These infants must be initially evaluated in dedicated CF centers including bacteriological sputum analysis, chest radiology and fecal elastase dosage. A home practitioner must be informed of the specificity of follow-up. These infants will be reviewed in the CF center at 3, 6 and 12 months and every year. Any CF-related symptom requires reevaluation of the diagnosis. These guidelines were established by the "neonatal screening and difficult diagnoses" working group of the French CF Society. They aim to standardize management of infants with unclear diagnosis in French CF centers.

Diagnosis of Cystic Fibrosis in Screened Populations

OBJECTIVE

Cystic fibrosis (CF) can be difficult to diagnose, even when newborn screening (NBS) tests yield positive results. This challenge is exacerbated by the multitude of NBS protocols, misunderstandings about screening vs diagnostic tests, and the lack of guidelines for presumptive diagnoses. There is also confusion regarding the designation of age at diagnosis.

STUDY DESIGN

To improve diagnosis and achieve standardization in definitions worldwide, the CF Foundation convened a committee of 32 experts with a mission to develop clear and actionable consensus guidelines on diagnosis of CF with an emphasis on screened populations, especially the newborn population. A comprehensive literature review was performed with emphasis on relevant articles published during the past decade.

RESULTS

After reviewing the common screening protocols and outcome scenarios, 14 of 27 consensus statements were drafted that apply to screened populations. These were approved by 80% or more of the participants.

CONCLUSIONS

It is recommended that all diagnoses be established by demonstrating dysfunction of the CF transmembrane conductance regulator (CFTR) channel, initially with a sweat chloride test and, when needed, potentially with newer methods assessing membrane transport directly, such as intestinal current measurements. Even in babies with 2 CF-causing mutations detected via NBS, diagnosis must be confirmed by demonstrating CFTR dysfunction. The committee also recommends that the latest classifications identified in the Clinical and Functional Translation of CFTR project [http://www.cftr2.org/index.php] should be used to aid with CF diagnosis. Finally, to avoid delays in treatment, we provide guidelines for presumptive diagnoses and recommend how to determine the age of diagnosis.

Cystic fibrosis

Cystic fibrosis is an autosomal recessive, monogenetic disorder caused by mutations in the cystic fibrosis transmembrane conductance regulator (CFTR) gene. The gene defect was first described 25 years ago and much progress has been made since then in our understanding of how CFTR mutations cause disease and how this can be addressed therapeutically. CFTR is a transmembrane protein that transports ions across the surface of epithelial cells. CFTR dysfunction affects many organs; however, lung disease is responsible for the vast majority of morbidity and mortality in patients with cystic fibrosis. Prenatal diagnostics, newborn screening and new treatment algorithms are changing the incidence and the prevalence of the disease. Until recently, the standard of care in cystic fibrosis treatment focused on preventing and treating complications of the disease; now, novel treatment strategies directly targeting the ion channel abnormality are becoming available and it will be important to evaluate how these treatments affect disease progression and the quality of life of patients. In this Primer, we summarize the current knowledge, and provide an outlook on how cystic fibrosis clinical care and research will be affected by new knowledge and therapeutic options in the near future. For an illustrated summary of this Primer, visit: http://go.nature.com/4VrefN.

Sweat chloride as a biomarker of CFTR activity: proof of concept and ivacaftor clinical trial data

BACKGROUND

We examined data from a Phase 2 trial {NCT00457821} of ivacaftor, a CFTR potentiator, in cystic fibrosis (CF) patients with aG551D mutation to evaluate standardized approaches to sweat chloride measurement and to explore the use of sweat chloride and nasal potential difference (NPD) to estimate CFTR activity.

METHODS

Sweat chloride and NPD were secondary endpoints in this placebo-controlled, multicenter trial. Standardization of sweat collection, processing,and analysis was employed for the first time. Sweat chloride and chloride ion transport (NPD) were integrated into a model of CFTR activity.

RESULTS

Within-patient sweat chloride determinations showed sufficient precision to detect differences between dose-groups and assess ivacaftor treatment effects. Analysis of changes in sweat chloride and NPD demonstrated that patients treated with ivacaftor achieved CFTR activity equivalent to approximately 35%–40% of normal.

CONCLUSIONS

Sweat chloride is useful in multicenter trials as a biomarker of CFTR activity and to test the effect of CFTR potentiators.

Cystic fibrosis: insight into CFTR pathophysiology and pharmacotherapy

Cystic fibrosis is the most common life-threatening recessively inherited disease in Caucasians. Due to early provision of care in specialized reference centers and more comprehensive care, survival has improved over time. Despite great advances in supportive care and in our understanding of its pathophysiology, there is still no cure for the disease. Therapeutic strategies aimed at rescuing the abnormal protein are either being sought after or under investigation. This review highlights salient insights into pathophysiology and candidate molecules suitable for CFTR pharmacotherapy. Clinical trials using Ataluren, VX-809 and ivacaftor have provided encouraging data. Preclinical data with inhibitors of phosphodiesterase type 5, such as sildenafil and analogs, have highlighted their potential for CFTR pharmacotherapy. Because sildenafil and analogs are in clinical use for other clinical applications, research on this class of drugs might speed up the development of new therapies for CF.

A randomized placebo-controlled trial of miglustat in cystic fibrosis based on nasal potential difference

BACKGROUND

Preclinical data suggest that miglustat could restore the function of the cystic fibrosis transmembrane conductance regulator gene in cystic fibrosis cells.

METHODS

Single-center, randomized, double-blind, placebo-controlled, crossover Phase II study in 11 patients (mean±SD age, 26.3±7.7 years) homozygous for the F508del mutation received oral miglustat 200 mgt.i.d. or placebo for two 8-day cycles separated by a 14-day washout period. The primary endpoint was the change in total chloride secretion (TCS) assessed by nasal potential difference.

RESULTS

No statistically significant changes in TCS, sweat chloride values or FEV(1) were detected. Pharmacokinetic and safety were similar to those observed in patients with other diseases exposed to miglustat.

CONCLUSIONS

There was no evidence of a treatment effect on any nasal potential difference variable. Further studies with miglustat need to adequately address criteria for assessment of nasal potential difference.

Factors accounting for a missed diagnosis of cystic fibrosis after newborn screening

Newborn screening is a public health policy program involving the centralized testing laboratory, infant and their family, primary care provider, and subspecialist for confirmatory testing and follow-up of abnormal results. Cystic fibrosis (CF) newborn screening has now been enacted in all 50 states and the District of Columbia and throughout many countries in the world. Although CF neonatal screening will identify the vast majority of infants with CF, there are many factors in the newborn screening system that can lead to a missed diagnosis of CF. To inform clinicians, this article summarizes the CF newborn screening system and highlights 14 factors that can account for a missed diagnosis of CF. Care providers should maintain a high suspicion for CF if there are compatible symptoms, regardless of the results of the newborn screening test. These factors in newborn screening programs leading to a missed diagnosis of CF present opportunities for quality improvement in specimen collection, laboratory analysis of immunoreactive tryspinogen (IRT) and CF mutation testing, communication, and sweat testing.

Introduction to Section I: the relevance of CF diagnostic tools for measuring restoration of CFTR function after therapeutic interventions in human clinical trials

The pilocarpine sweat test, and in vivo assessment of CFTR function via nasal potential difference or intestinal current measurement are important tools to confirm the diagnosis of CF in subjects with suggestive symptoms. Since these tests reflect CFTR function and thus relate to the basic disease process in CF, changes in these parameters are also being used to assess the pharmacologic effect of compounds aimed at restoring CFTR function. However, longitudinal data proving that changes in these measurements are associated with meaningful clinical improvements in the course of disease in CF patients are needed. Consequently, many CF clinical investigators need to be facile with these existing methods to measure CFTR-related outcomes. This introduction sets the stage for more in-depth discussion of existing strategies to measure changes in CFTR function generated by gene therapy or small molecule modulators of CFTR function such as correctors and potentiators. It is hoped that lessons learned through the use of these measures will inform the future development of other robust methods to assess novel therapeutic strategies uncovered by basic scientists.

Physiological measurements confirming the diagnosis of cystic fibrosis: the sweat test and measurements of transepithelial potential difference

Post-natal screening allied with genetic mutation testing has altered our perception of cystic fibrosis (CF) as a clinical entity. Increasingly, infants identified through screening programmes have few or no symptoms or present with atypical forms of the disease. We review how the sweat test has evolved to be the gold standard for confirming the diagnosis of CF and examine its limitations. Other physiological measurements, including nasal potential difference and intestinal current measurement, which might aid in establishing the diagnosis, particularly in patients exhibiting a mild phenotype, are also considered.

Cystic fibrosis: defining a disease under-diagnosed in Pakistan

OBJECTIVE

Cystic fibrosis is frequently missed in the Pakistani population due to lack of appropriate diagnostic tools. Thus our aim was to define unknown disease-causing mutations to help create suitable diagnostic tests and improve understanding of what appears to be an aggressive and under-diagnosed disease in this population.

METHODS

Patients with elevated sweat chloride values and clinically suspected CF were recruited from Aga Khan University, Pakistan. Mutations DF508, S549R, S549N, Y569D, 296 + 12(T>C), G553X, G551D and G551X were screened for by allele specific polymerase chain reactions. CFTR exons 10, 11 and 12 were sequenced by direct DNA sequencing.

RESULTS

Of 150 patients tested by PCR, 26 (17.3%) were positive for DeltaF508. One patient was a F508/S549N compound heterozygote. Eighty-three of 87 patients sequenced for mutations in exon 10 were normal; 42/43 for exon 11 and 29 for exon 12 were normal.

CONCLUSION

This first step in defining mutations involved in Pakistani CF suggests that DeltaF508 is uncommon and S549 was the only additional mutation identified in CFTR exons 10, 11 and 12. Identification of the remaining mutations and their frequency is required to design appropriate tests and improve understanding and management of the disease.

Recurrent respiratory infections

The child who has recurrent infections poses one of the most difficult diagnostic challenges in pediatrics. The clinician faces a two-fold challenge in determining first whether the child is normal or has a serious disease, and then, in the latter case, how to confirm or exclude the diagnosis with the minimum number of the least invasive tests. It is hoped that, in the absence of good-quality evidence for most clinical scenarios, the experience-based approach described in this article may prove a useful guide to the clinician.

Diagnosis of cystic fibrosis by sweat testing: age-specific reference intervals

OBJECTIVE

To develop reference intervals (RIs) for sweat chloride and sodium in healthy children, adolescents, and adults.

STUDY DESIGN

Healthy, unrelated subjects aged from 5 to >50 years and subjects who were pancreatic insufficient with cystic fibrosis (CF) were recruited. Sweat collection was performed on all subjects with the Wescor Macroduct system. Sweat electrolytes were analyzed with direct ion selective electrodes. DeltaF508 mutation analysis was performed on the healthy subjects >/=15 years old.

RESULTS

A total of 282 healthy and 40 subjects with CF were included for analysis. There was no overlap of sweat chloride between the group with CF and the group without CF, but there was some overlap of sweat sodium. Sweat chloride increased with age, with the rate of increase slowing progressively to zero after the age of 19 years. The estimated median (95% RI) for sweat chloride were: 5 to 9 years, 13 mmol/L (1-39 mmol/L); 10 to 14 years, 18mmol/L (3-47 mmol/L); 15 to 19 years, 20 mmol/L (3-51mmol/L); and 20+ years 23 mmol/L (5-56mmol/L).

CONCLUSIONS

We have successfully developed the age-related RI for sweat electrolytes, which will be useful for clinicians interpreting sweat test results from children, adolescents, and adults.

Guidelines for diagnosis of cystic fibrosis in newborns through older adults: Cystic Fibrosis Foundation consensus report

Newborn screening (NBS) for cystic fibrosis (CF) is increasingly being implemented and is soon likely to be in use throughout the United States, because early detection permits access to specialized medical care and improves outcomes. The diagnosis of CF is not always straightforward, however. The sweat chloride test remains the gold standard for CF diagnosis but does not always give a clear answer. Genotype analysis also does not always provide clarity; more than 1500 mutations have been identified in the CF transmembrane conductance regulator (CFTR) gene, not all of which result in CF. Harmful mutations in the gene can present as a spectrum of pathology ranging from sinusitis in adulthood to severe lung, pancreatic, or liver disease in infancy. Thus, CF identified postnatally must remain a clinical diagnosis. To provide guidance for the diagnosis of both infants with positive NBS results and older patients presenting with an indistinct clinical picture, the Cystic Fibrosis Foundation convened a meeting of experts in the field of CF diagnosis. Their recommendations, presented herein, involve a combination of clinical presentation, laboratory testing, and genetics to confirm a diagnosis of CF.

Nasal potential difference in non-classic cystic fibrosis-long term follow up

BACKGROUND

Nasal potential difference (NPD) measurement is an electrophysiological test that assesses cystic fibrosis transmembrane conductance regulator (CFTR) activity and is a recognized diagnostic tool in CF. The aim of this study is to assess in the long term the role of NPD in patients whose diagnosis is questionable.

METHODS

We performed follow up study on 70 patients with questionable CF (QCF) who were divided previously into two groups according to their NPD results: patients who likely have CF (QCF-CF) (n = 24), and those who likely do not have CF (QCF-non-CF) (n = 46).

RESULTS

Sixty out of 70 patients were available for study. Sixteen patients in the QCF-CF group were being followed up at CF Centers as opposed to 1 in the QCF-non-CF group (P < 0.01). Seven patients from the QCF-CF group developed sinusitis during the follow up years compared to none from the QCF-non-CF group. During the years of the follow up, 17 QCF-non-CF patients were diagnosed with other medical conditions that could explain their previous symptoms. On repeated NPD measurement in the QCF-CF group, the results were similar to the original test.

CONCLUSIONS

This study supports the diagnostic role of NPD measurement. Larger cohort studies are required for confirmation.

New York State cystic fibrosis consortium: the first 2.5 years of experience with cystic fibrosis newborn screening in an ethnically diverse population

OBJECTIVE

The purpose of this work was to report on the first 2.5 years of newborn screening for cystic fibrosis in New York.

METHODS

Directors of the 11 New York cystic fibrosis centers were asked to provide mutation data, demographic data, and selected laboratory results for each patient diagnosed by newborn screening and followed at their center. Summary data were also submitted from the New York newborn screening laboratory on the total number of patients screened, the number of positive screens, and the number of patients that were lost to follow-up. A second survey was submitted by each center regarding the availability of genetic counseling services at the center.

RESULTS

A total of 106 patients with cystic fibrosis were diagnosed through newborn screening in the first 2.5 years and followed at the 11 Cystic Fibrosis Foundation-sponsored cystic fibrosis care centers in New York. Two screen-negative infants were subsequently diagnosed with cystic fibrosis when symptoms developed. The allele frequency of deltaF508 was 57.4%, which is somewhat lower than the allele frequency of deltaF508 in the US cystic fibrosis population of 70%. There were 90 non-Hispanic white (84%), 12 Hispanic, 2 Asian, and 1 black infants diagnosed with cystic fibrosis during this period. Five patients were diagnosed secondary to a positive screen based on a high immunoreactive trypsinogen and no mutations.

CONCLUSIONS

Newborn screening for cystic fibrosis has been effectively conducted in New York using a unique screening algorithm that was designed to be inclusive of the diverse racial makeup of the state. However, this algorithm results in a high false-positive rate, and a large number of healthy newborns are referred for confirmatory sweat tests and genetic counseling. This experience indicates that it would be helpful to convene a working group of cystic fibrosis newborn screening specialists to evaluate which mutations should be included in a newborn screening panel.

Towards zero prevalence of chronic Pseudomonas aeruginosa infection in children with cystic fibrosis

BACKGROUND

Data from the Belgian Cystic Fibrosis Registry consistently show that in one of the seven reference centres, the prevalence of Pseudomonas aeruginosa is half that observed at the national level.

OBJECTIVES

To report the characteristics of non-transplanted patients in this clinic at the end of 2003, with special focus on paediatric patients. To describe and discuss our policy of inhaled antibiotic therapy.

FINDINGS

The prevalence of P. aeruginosa among 116 patients is 20.7%. The chronic colonization rate is 19.8% but only 2.8% in patients aged under 18 (n=72). Serologic data strongly support these results. Most paediatric patients (95%) are prescribed inhaled antibiotics, at least on an intermittent basis but the mean number of days of intravenous antibiotic treatment is four times lower than in other CF children in Belgium. 70% of children have an FEV1> or =90% predicted.

DISCUSSION

We have reported a distinctly low rate of chronic colonization by P. aeruginosa in a cohort of CF children and suspect that a strategy of early, often <<prophylactic>> use of inhaled antibiotics, progressively implemented for over 15 years has substantially contributed to these results. Given the major impact of chronic P. aeruginosa colonization on prognosis in CF, it is suggested that a large prospective study of this approach is warranted.

Prospective analysis of cystic fibrosis transmembrane regulator mutations in adults with bronchiectasis or pulmonary nontuberculous mycobacterial infection

BACKGROUND

Bronchiectasis and pulmonary infection with nontuberculous mycobacteria (NTM) may be associated with disease-causing mutations in the cystic fibrosis transmembrane regulator (CFTR).

METHODS

Fifty adult patients at Stanford University Medical Center with a diagnosis of bronchiectasis and/or pulmonary NTM infection were prospectively characterized by sweat chloride measurement, comprehensive mutational analysis of CFTR, and sputum culture results.

RESULTS

A de novo diagnosis of cystic fibrosis (CF) was established in 10 patients (20%). Patients with CF were more likely than those without CF to have mucus plugging seen on chest high-resolution CT, and women with a CF diagnosis were thinner, with a significantly lower mean body mass index than the non-CF subjects. Thirty CFTR mutations were identified in 24 patients (50% prevalence). Sweat chloride concentration was elevated > 60 mEq/dL (diagnostic of CF) in seven patients (14%), and from 40 to 60 mEq/dL in eight patients (16%). The frequency of CFTR mutations was elevated above that expected in the general population: heterozygous DeltaF508 (12% vs 3%), R75Q (14% vs 1%), and intron 8 5T (17% vs 5 to 10%). Other known CFTR mutations identified were V456A, G542X, R668C, I1027T, D1152, R1162L, W1282X, and L183I. Three novel CFTR mutations were identified: A394V, F650L, and C1344S.

CONCLUSIONS

Mutations in CFTR that alter RNA splicing and/or functional chloride conductance are common in this population, and are likely to contribute to the susceptibility and pathogenesis of adult bronchiectasis and pulmonary NTM infection. Careful clinical evaluation for disease cause should be undertaken in this clinical context.

Cystic fibrosis: terminology and diagnostic algorithms

There is great heterogeneity in the clinical manifestations of cystic fibrosis (CF). Some patients may have all the classical manifestations of CF from infancy and have a relatively poor prognosis, while others have much milder or even atypical disease manifestations and still carry mutations on each of the CFTR genes. It is important to distinguish between these categories of patients. The European Diagnostic Working Group proposes the following terminology. Patients are diagnosed with classic or typical CF if they have one or more phenotypic characteristics and a sweat chloride concentration of >60 mmol/l. The vast majority of CF patients fall into this category. Usually one established mutation causing CF can be identified on each CFTR gene. Patients with classic CF can have exocrine pancreatic insufficiency or pancreatic sufficiency. The disease can have a severe course with rapid progression of symptoms or a milder course with very little deterioration over time. Patients with non-classic or atypical CF have a CF phenotype in at least one organ system and a normal (<30 mmol/l) or borderline (30-60 mmol/l) sweat chloride level. In these patients confirmation of the diagnosis of CF requires detection of one disease causing mutation on each CFTR gene or direct quantification of CFTR dysfunction by nasal potential difference measurement. Non-classic CF includes patients with multiorgan or single organ involvement. Most of these patients have exocrine pancreatic sufficiency and milder lung disease. Algorithms for a structured diagnostic process are proposed.

Sweat testing infants detected by cystic fibrosis newborn screening

OBJECTIVE

Describe and define limitations of early pilocarpine iontophoresis (sweat testing) for cystic fibrosis (CF) newborn screening (NBS).

STUDY DESIGN

Population-based results from follow-up of CF NBS-positive newborns.

RESULTS

Insufficient quantity of sweat is more likely if the sweat test is done too early, but testing is generally successful after 2 weeks of age. Sweat chloride levels drop over the first weeks of life. CF carriers have higher sweat chloride concentrations than non-carriers.

CONCLUSIONS

Sweat testing can be performed effectively after 2 weeks of age for CF NBS-positive newborns. Earlier testing has a higher risk of insufficient sweat for completing testing.

Premarital and prenatal screening for cystic fibrosis: experience in the Ashkenazi Jewish population

PURPOSE

Since the early 1990s, Dor Yeshorim (DY) and the Mount Sinai School of Medicine (MSSM) have conducted premarital and prenatal carrier screening for cystic fibrosis (CF) in the Ashkenazi Jewish (AJ) population as part of their genetic testing programs, respectively. Together, over 170,000 screenees have been tested. In this study, we report the CF mutation frequencies in over 110,000 screenees who reportedly were of 100% AJ descent from the DY program and MSSM. In addition, the CF mutation frequencies in a group of > 7,000 screenees for AJ diseases who were of < 100% AJ descent are reported.

METHODS

Testing for CF mutations was performed by either PCR and restriction digestion or ASO hybridization analyses at MSSM or sent to various academic and commercial laboratories by DY.

RESULTS

The overall (and individual) carrier frequency for the five common AJ mutations, W1282X (0.020), DeltaF508 (0.012), G542X (0.0024), 3849+10kb C>T (0.0020), and N1303K (0.0016), among screenees who were 100% AJ was 1 in 26; when D1152H and the rare 1717-1G>A were included, the overall carrier frequency increased to approximately 1 in 23. In four families with D1152H, five compound heterozygotes for D1152H and W1282X (n = 2), DeltaF508 (1) or 3849+10kb C>T (1) were identified. In contrast, the carrier frequency for screenees reporting < 100% AJ descent was approximately 1 in 30 for the seven mutations.

CONCLUSIONS

The carrier frequency for five common CF mutations in a large 100% AJ sample increased from 1 in 26 to 1 in 23 when D1152H was included in the panel. Addition of D1152H to mutation panels when screening the AJ population should be considered because compound heterozygosity is associated with a variable disease phenotype. Further studies to delineate the phenotype of CF patients with this mutation are needed.

Nasal airway ion transport and lung function in young people with cystic fibrosis

There is strong evidence that abnormal airway ion transport is the primary defect that initiates the pathophysiology of lung disease in cystic fibrosis (CF). To examine the relationship between airway ion transport abnormality and severity of lung disease, we measured nasal potential difference in 51 young people with CF using a validated modified technique. There was no correlation between any component of the ion transport measurement and clinical condition (respiratory function, chest radiograph score, or Shwachman clinical score). Thirty subjects, homozygous for the DeltaF508 mutation, were divided into those above and those below average respiratory function for their age. There was no significant difference in any of the ion transport parameters between those with above and below average pulmonary function. Of the 51 subjects, 10 had significant hyperpolarization after perfusion with a zero Cl- solution (> 5 mV). This Cl- secretory capacity did not correlate with above average lung function. These data do not support the assertion that the extent of lung disease in CF reflects the degree of ion transport abnormality. We suggest that although an ion transport abnormality initiates lung disease, other factors (e.g., environmental and genetic modifiers) are more influential in determining disease severity.

Modified method to measure nasal potential difference

Nasal potential difference (NPD) measurements have been proposed to assess defective ion transport in cystic fibrosis (CF). Implementing it routinely is, however, difficult. Therefore, a modified method based on nasal instillation in supine position at reduced flow rate was tested to evaluate its ability to discriminate CF from non-CF subjects. Classical and modified methods were compared in nine healthy subjects and there were no statistical differences. Following the new method, 97 tests were performed on 74 subjects divided in three cohorts: 21 CF patients and two control groups consisting of 19 patients with other pulmonary diseases and 34 healthy subjects. Twenty five children were enrolled in this study. Maximal NPD in CF patients (-44.9 +/- 2.5 mV) was significantly different from that obtained in control groups (-18.1 +/- 1.6 and -17.2 +/- 1.1 mV). Depolarization after amiloride also discriminated CF patients (25.9 +/- 1.4 mV) from control groups (10.5 +/- 0.9 and 8.1 +/- 0.7 mV). Marked repolarization following isoprenaline plus amiloride in low chloride solution was seen in control groups (-15.7 +/- 1.1 and -15.3 +/- 1.1 mV). We conclude that the modified method represents a simplified and equally effective approach to discriminate CF patients from non-CF subjects. Moreover, this method presents practical advantages for the patients related to hygiene and convenience, favoring its application in small children.