Heterogeneity of CFTR modulator-induced sweat chloride concentrations in people with cystic fibrosis

BACKGROUND

Sweat chloride (SC) concentrations in people with cystic fibrosis (PwCF) reflect relative CF transmembrane conductance regulator (CFTR) protein function, the primary CF defect. Populations with greater SC concentrations tend to have lesser CFTR function and more severe disease courses. CFTR modulator treatment can improve CFTR function within specific CF genotypes and is commonly associated with reduced SC concentration. However, SC concentrations do not necessarily fall to concentrations seen in the unaffected population, suggesting potential for better CFTR treatment outcomes. We characterized post-modulator SC concentration variability among CHEC-SC study participants by genotype and modulator.

METHODS

PwCF receiving commercially approved modulators for ≥90 days were enrolled for a single SC measurement. Clinical data were obtained from chart review and the CF Foundation Patient Registry (CFFPR). Variability of post-modulator SC concentrations was assessed by cumulative SC concentration frequencies.

RESULTS

Post-modulator SC concentrations (n = 3787) were collected from 3131 PwCF; most (n = 1769, 47 %) were collected after elexacaftor/tezacaftor/ivacaftor (ETI) treatment. Modulator use was associated with lower SC distributions, with post-ETI concentrations the lowest on average. Most post-ETI SC concentrations were <60 mmol/L (79 %); 26 % were <30 mmol/L. Post-ETI distributions varied by genotype. All genotypes containing at least one F508del allele had individuals with post-ETI SC ≥60 mmol/L, with the largest proportion being F508del/minimal function (31 %).

CONCLUSIONS

Post-modulator SC concentration heterogeneity was observed among all genotypes and modulators, including ETI. The presence of PwCF with post-modulator SC concentrations within the CF diagnostic range suggests room for additional treatment-associated CFTR restoration in this population.

Human epididymis protein 4 (HE4) plasma concentration inversely correlates with the improvement of cystic fibrosis lung disease in p.Phe508del-CFTR homozygous cases treated with the CFTR modulator lumacaftor/ivacaftor combination

BACKGROUND

We previously documented that elevated HE4 plasma concentration decreased in people with CF (pwCF) bearing the p.Gly551Asp-CFTR variant in response to CFTR modulator (CFTRm) ivacaftor (IVA), and this level was inversely correlated with the FEV1% predicted values (ppFEV1). Although the effectiveness of lumacaftor (LUM)/IVA in pwCF homozygous for the p.Phe508del-CFTR variant has been evaluated, plasma biomarkers were not used to monitor treatment efficacy thus far.

METHODS

Plasma HE4 concentration was examined in 68 pwCF drawn from the PROSPECT study who were homozygous for the p.Phe508del-CFTR variant before treatment and at 1, 3, 6 and 12 months after administration of LUM/IVA therapy. Plasma HE4 was correlated with ppFEV1 using their absolute and delta values. The discriminatory power of delta HE4 was evaluated for the detection of lung function improvements based on ROC-AUC analysis and multiple regression test.

RESULTS

HE4 plasma concentration was significantly reduced below baseline following LUM/IVA administration during the entire study period. The mean change of ppFEV1 was 2.6% (95% CI, 0.6 to 4.5) by 6 months of therapy in this sub-cohort. A significant inverse correlation between delta values of HE4 and ppFEV1 was observed especially in children with CF (r=-0.7053; p<0.0001). Delta HE4 predicted a 2.6% mean change in ppFEV1 (AUC: 0.7898 [95% CI 0.6823-0.8972]; P < 0.0001) at a cut-off value of -10.7 pmol/L. Moreover, delta HE4 independently represented the likelihood of being a responder with ≥ 5% delta ppFEV1 at 6 months (OR: 0.89, 95% CI: 0.82-0.95; P = 0.001).

CONCLUSIONS

Plasma HE4 level negatively correlates with lung function improvement assessed by ppFEV1 in pwCF undergoing LUM/IVA CFTRm treatment.

Impact of elexacaftor/tezacaftor/ivacaftor on lung function, nutritional status, pulmonary exacerbation frequency and sweat chloride in people with cystic fibrosis: real-world evidence from the German CF Registry

BACKGROUND

Treatment with elexacaftor/tezacaftor/ivacaftor (ETI) improves multiple clinical outcomes in people with cystic fibrosis (pwCF) with at least one F508del allele. This study evaluated the real-world impact of ETI on lung function, nutritional status, pulmonary exacerbation frequency, and sweat chloride concentrations in a large group of pwCF.

METHODS

This observational cohort study used data from the German CF Registry for pwCF who received ETI therapy and were followed up for a period of 12 months.

FINDINGS

The study included 2645 pwCF from 67 centres in Germany (mean age 28.0 ± 11.5 years). Over the first year after ETI was initiated, percent predicted forced expiratory volume in 1 s (ppFEV1) increased by 11.3% (95% confidence interval [CI] 10.8-11.8, p < 0.0001), body mass index (BMI) z-score increased by 0.3 (95% CI 0.3-0.4, p < 0.0001) in individuals aged 12 to <18 years and BMI in adults increased by 1.4 kg/m2 (95% CI 1.3-1.4, p < 0.0001), pulmonary exacerbations decreased by 75.9% (p < 0.0001) and mean sweat chloride concentration decreased by 50.9 mmol/L (95% CI -52.6, -49.3, p < 0.0001). Improvements in ppFEV1 over the first year of therapy were greater in pwCF who had not previously received cystic fibrosis transmembrane conductance regulator (CFTR) modulator therapy (12.6% [95% CI 11.9-13.4] vs. 9.7% [95% CI 9.0-10.5] in those with prior CFTR modulator treatment.

INTERPRETATION

These real-world data are consistent with the findings of randomised clinical trials, and support the use of ETI as a highly effective treatment option for pwCF who have at least one F508del allele.

FUNDING

None.

Variability of the sweat test in children with Cystic Fibrosis previously CRMS/CFSPID: A retrospective monocenter experience

Some studies have evaluated the sweat test (ST) intra individual variability in CRMS/CFSPID. Here, we retrospectively evaluated this in a cohort followed at the CF center in Florence, Italy. We enrolled 37 CRMS/CFSPID and 37 CF children, born between 2011 and 2019. A total of 327 ST were retrospectively recovered, of which 17 (5.2%) were quantity not sufficient. After a median follow-up of 33.8 months (range 1.7-88.2), 11 (24.3%) became CF with at least two pathological sweat chloride (SC) values at a median age of 46.9 months (range 1.4-49). The coefficient of variation was 6.2% in CF patients and 32.5% in the CRMS/CFSPID that transitioned to CF (P<.001). Our data highlight a more variability of SC values in CRMS/CFSPID, especially in those that transitioned to a diagnosis of CF. Further studies are needed to understand whether it is correct to define an asymptomatic CRMS/CFSPID with pathological SC as CF.

Characterizing CFTR modulated sweat chloride response across the cf population: Initial results from the CHEC-SC study

BACKGROUND

CHEC-SC is an ongoing epidemiologic study characterizing modulator-induced sweat chloride (SC) responses across the CF population, with interim results available prior to the availability of triple combination modulator therapy.

METHODS

Eligible participants had been prescribed a modulator for ≥90 days with re-enrollment allowed upon establishment of a new modulator. Pre-modulator SC values were obtained from chart review; post-modulator sweat was collected and analyzed locally. SC changes were descriptively summarized with biologic sex effects adjusted for age, weight, and CFTR genotype. Heterogeneity in ivacaftor SC response was characterized in relation to published CFTR functional responses.

RESULTS

1848 participants provided 2004 SC measurements, 26.2% on ivacaftor, 39.1% on lumacaftor/ivacaftor, and 34.7% on tezacaftor/ivacaftor. Average SC changes for all modulators were consistent with those reported in previous clinical studies, with greater variation in SC response observed among rarer mutations and notable shifts in the proportion with SC <60mmol/L independent of the magnitude of SC change. Ivacaftor induced in vitro CFTR functional change was significantly correlated with ivacaftor-modulated SC response (Pearson correlation= ‒0.52, 95% CI: ‒0.773, ‒0.129). Average SC change from ivacaftor to tezacaftor/ivacaftor was ‒4.9 mmol/L (n=17,95% CI:‒9.3, ‒0.5) and differed from those switching from lumacaftor/ivacaftor (10.0 mmol/L, n=139, 95% CI:7.8,12.3). Sex at birth was not associated with SC response.

CONCLUSIONS

CHEC-SC is the largest study characterizing modulator-induced SC changes across the CF population. There was a strong association between ivacaftor induced in vitro CFTR function and SC response across a genotypically heterogenous cohort. Biological sex was not associated with SC response.

Genotype-phenotype correlations of cystic fibrosis in siblings compound heterozygotes for rare variant combinations: Review of literature and case report

Here, we describe a cystic fibrosis (CF) family with affected siblings, two of whom have a combination of I1234V and 1677delTA variants with classic CF features, the third child with a combination of I1234V and L997F variants with atypical CF, and the apparently healthy mother with a combination of 1677delTA and L997F alleles. Interestingly, the sibling with I1234V and L997F variants had normal sweat test results and had a much milder phenotype than the other two siblings with I1234V and 1677delTA variants, suggesting that this combination is causative for atypical CF. The fact that their mother with the combination of 1677delTA and L997F appears to be healthy suggests that the L997F variant causes different phenotypes in different allele combinations. The current cases show that there is a genotype-phenotype correlation in this disease and underline the importance of genotyping individuals with suspected CF to allow prediction of disease severity and effective treatment.

Silver-manganese nanocomposite modified screen-printed carbon electrode in the fabrication of an electrochemical, disposable biosensor strip for cystic fibrosis

A silver-manganese nanocomposite was successfully prepared by the urea hydrolysis method and used to detect chloride ions in sweat electrochemically. The synthesis involves the reaction of manganese sulphate, silver nitrate, and urea at 100 °C for 24 h. The crystalline nature of the particle was studied by diffraction analysis and found to be mixed-phase oxides of manganese alongside the oxides of silver. Morphological studies revealed the presence of quasi-prism-like structures, which is characteristic of β-MnO₂. A disposable sensor was fabricated by screen-printing the catalyst and used for the electrochemical detection of chloride ions in sweat. The sensor exhibited good selectivity, a sensitivity of 22.93 ± 0.64 µA mM^-1 cm^-2 in solution and 3010 ± 60 µA (log mM) ^-1 cm^-2 for the fabricated sensor strip with a detection range from 5 mM up to 200 mM. The detection limit is 207 ± 7 µM (S/N = 3) in solution and 17 ± 6 µM for the fabricated sensor strip. The relative standard deviation (RSD) of sensor response is 2.38%. A prototype of the biosensor strip was fabricated and validated using real samples. This brings the possibility of developing a real-time biosensor strip for cystic fibrosis in point-of-care testing applications.

Measuring the impact of CFTR modulation on sweat chloride in cystic fibrosis: Rationale and design of the CHEC-SC study

BACKGROUND

The Characterizing CFTR Modulated Changes in Sweat Chloride and their Association with Clinical Outcomes (CHEC-SC) study is a large epidemiologic study designed to determine the relationship between sweat chloride response and clinical outcomes in people with cystic fibrosis (CF) on commercially approved CFTR modulators. A challenge to study feasibility was capturing sweat chloride measurements before modulator initiation. We tested the hypothesis that historic sweat chloride approximated contemporary pre-modulator values to estimate CFTR modulator-induced changes, allowing a single-visit study design.

METHODS

GOAL and PROSPECT were multi-center prospective studies of individuals initiating ivacaftor or lumacaftor-ivacaftor. At enrollment, pre-modulator sweat chloride was measured and historic results recorded. Post-modulator sweat chloride was measured at 1, 3 and 6 months. For this analysis, differences between historic and pre-modulator sweat chloride were estimated. CFTR modulator-induced sweat chloride mean changes were compared using historic and pre-modulator sweat chloride.

RESULTS

Paired historic and pre-modulator sweat chloride (n=406 participants) revealed a non-significant mean change of -1.0 mmol/L (95% CI: -2.71, 0.66) over an average of 17.2 years. Calculating sweat response to ivacaftor or lumacaftor-ivacaftor using historic or pre-modulator values resulted in similar estimates of modulator response. Based on these results, the CHEC-SC study was designed with a single, post-modulator sweat chloride measurement.

CONCLUSIONS

Historic sweat chloride values provide a reliable estimate of pre-modulator sweat chloride for people starting on modulator therapy. The CHEC-SC study anticipates capturing approximately 5,000 sweat chloride values, providing an unprecedented understanding of sweat chloride across the CF population in the era of CFTR modulators.

Long term clinical effectiveness of ivacaftor in people with the G551D CFTR mutation

BACKGROUND

The cystic fibrosis transmembrane conductance regulator (CFTR) potentiator, ivacaftor, was first approved for people with CF and the G551D CFTR mutation. This study describes the long-term clinical effectiveness of ivacaftor in this population.

METHODS

We conducted a multicenter, prospective, longitudinal, observational study of people with CF ages ≥6 years with at least one copy of the G551D CFTR mutation. Measurements of lung function, growth, quality of life, and sweat chloride were performed after ivacaftor initiation (baseline, 1 month, 3 months, 6 months, and annually thereafter until 5.5 years).

RESULTS

Ninety-six participants were enrolled, with 81% completing all study measures through 5.5 years. This cohort experienced significant improvements in percent predicted forced expiratory volume in 1 second (ppFEV1) of 4.8 [2.6, 7.1] (p < 0.001) at 1.5 years, that diminished to 0.8 [-2.0, 3.6] (p = 0.57) at 5.5 years. Adults experienced larger improvements in ppFEV1 (7.4 [3.6, 11.3], p < 0.001 at 1.5 years and 4.3 [0.6, 8.1], p = 0.02 at 5.5 years) than children (2.8 [0.1, 5.6], p = 0.04 at 1.5 years and -2.0 [-5.9, 2.0], p = 0.32 at 5.5 years). Rate of lung function decline for the overall study cohort from 1 month after ivacaftor initiation through 5.5 years was estimated to be -1.22 pp/year [-1.70, -0.73]. Significant improvements in growth, quality of life measures, sweat chloride, Pseudomonas aeruginosa detection, and pulmonary exacerbation rates requiring antimicrobial therapy persisted through five years of therapy.

CONCLUSIONS

These findings demonstrate the long-term benefits and disease modifying effects of ivacaftor in children and adults with CF and the G551D mutation.

Extensive CFTR sequencing through NGS in Brazilian individuals with cystic fibrosis: unravelling regional discrepancies in the country

BACKGROUND

The Brazilian population has a tri-hybrid composition with a high degree of ethnic admixture. We hypothesized that Brazilian individuals with CF from different Brazilian regions have a specific distribution of CFTR variants.

METHODS

Individuals with CF with data available in the Patient Registry and without an established genotype were submitted to CFTR sequencing by Next Generation Sequencing (NGS) methodology, and results were anonymously incorporated to the Registry Database. Genotyping results were expressed as 'positive', 'inconclusive' or 'negative'. Logistic regression models were performed to investigate the association between demographic/clinical variables and genotyping results. Mediation analysis was conducted to estimate direct and indirect effects of Brazilian region on a binary positive genotyping response.

RESULTS

In October 2017, data from 4,654 individuals with CF were available, and 3,104(66.7%) of them had a genotyping result. A total of 236 variants (114 new variants) were identified, with F508del identified in 46% of the alleles tested. Genotyping revealed 2,002(64.5%) individuals positive, 757(24.4%) inconclusive and 345(11.1%) negative. Distribution of genotype categories was markedly different across Brazilian Regions, with greater proportions of negative individuals in the North (45%) and Northeast (26%) regions. Newborn screening (CF-NBS) and age at diagnosis were identified as mediators of the effect of Brazilian region on a positive genotyping result.

CONCLUSIONS

This large initiative of CFTR genotyping showed significant regional discrepancies in Brazil, probably related to socio-economic conditions, lack of adequate CF-NBS and poor access to reliable sweat testing. These results may be useful to indicate Regions where CF care demands more attention.

Females with cystic fibrosis have a larger decrease in sweat chloride in response to lumacaftor/ivacaftor compared to males

AIM

To explore which patient-related factors influence sweat test response to CFTR modulators, as well as examining the correlation between the sweat chloride response and ppFEV₁ or BMI response, using systematically collected real-life clinical data.

METHODS

160 CF patients were identified who had used lumacaftor/ivacaftor for at least six months. Of these patients, age, sweat chloride levels, ppFEV₁ weight and BMI at the start of treatment and after 6 months were collected retrospectively. Pearson and Spearman tests were performed to assess correlations.

RESULTS

Females compared to males in this group showed a larger response in sweat chloride (mean difference 10.6 mmol/l, 95% CI: 5.7-15.4) and BMI (mean difference 0.27 kg/m², 95% CI: 0.01-0.54). A modest but significant correlation was found between patient weight and sweat chloride response (Pearson R = 0.244, p = 0.001), which diminished upon correction for the other factors. The correlation between sex and sweat chloride response remained; R = 0.253, p = 0.001. Sweat chloride response did not correlate with ppFEV₁ change or BMI change at 6 months after start of therapy.

CONCLUSION

Sweat chloride response is larger in females compared to males, which also explains the negative correlation of weight with the response in sweat chloride concentration after start of lumacaftor/ivacaftor. Sweat chloride response does not correlate with the responses in ppFEV₁ and BMI. This information may help the interpretation of sweat test results acquired for the follow up and evaluation of CFTR modulating treatments, and warrants further investigation into the underlying mechanisms of sex differences in response to CFTR modulators.

Is it cystic fibrosis? The challenges of diagnosing cystic fibrosis

The spectrum of conditions caused by abnormal CFTR function is broad - from 'classic' cystic fibrosis (CF) to single organ conditions termed CFTR-related disorders. Defining and securing the diagnosis in an important minority of patients can be a challenge as the sweat test is equivocal or normal; the impact this has on the patient (at different stages of their life) can be very significant as it has the potential to lead to misdiagnosis and over (or under) treatment with associated psychological burden. The nasal potential difference test and intestinal current measurements are physiological measurements of CFTR function and thus can provide important diagnostic information. This article provides an overview of the latest developments in CF diagnostics, outlining the approach to be taken when the diagnosis is unclear and some of the areas of uncertainty.

Nasal potential difference in suspected cystic fibrosis patients with 5T polymorphism

BACKGROUND

5T polymorphism is a CFTR mutation with unclear clinical consequences: the phenotype varies from healthy individuals to Cystic Fibrosis (CF). The aim of this study was to evaluate if nasal potential difference (NPD) and sweat testing correlate with symptoms and CF diagnosis in 5T patients.

METHODS

86 patients with 5T who had undergone NPD measurement, were included (6 homozygous (5T/5T), 41 with a PI-CF causing mutation in trans (5T/PI-CF), 11 with a PS-CF causing mutation in trans (5T/PS-CF) and 28 without a known mutation in trans (5T/?). Data including age, phenotype, sweat chloride and follow up were collected.

RESULTS

33% of the 5T/5T patients had abnormal NPD results, compared to 70% in 5T/PI-CF; 33% in 5T/PS-CF and 29% in 5T/?. The percentage of high or borderline sweat chloride was highest in 5T/PI-CF, and 5T/?, compared to 5T/5T and 5T/PS-CF (91, 96, 80, and 63%, respectively). TGm (number of TG repeats in intron 8) analysis was performed in 21 5T/PI-CF patients. TG11 was associated with lower sweat chloride, lower percentage of abnormal NPD and less progression of symptoms compared to TG12 and TG13.

CONCLUSION

There is much variation in clinical status among 5T patients. All patients in this study with 5T/PS CF, all patients with both normal NPD and sweat test, and most patients with TG11 were stable or improving over time. Therefore, NPD measurement and TGm status aid to assess if a patient is at high risk for developing CF or CFTR-related disease and if specific follow up in a CF center is required.

Human epididymis protein 4 (HE4) levels inversely correlate with lung function improvement (delta FEV1) in cystic fibrosis patients receiving ivacaftor treatment

BACKGROUND

We have recently shown that human epididymis protein 4 (HE4) levels correlate with the severity of cystic fibrosis (CF) lung disease. However, there are no data on how HE4 levels alter in patients receiving CFTR modulating therapy.

METHODS

In this retrospective clinical study, 3 independent CF patient cohorts (US-American: 29, Australian: 12 and Irish: 19 cases) were enrolled carrying at least one Class III CFTR CF-causing mutation (p.Gly551Asp) and being treated with CFTR potentiator ivacaftor. Plasma HE4 was measured by immunoassay before treatment (baseline) and 1-6 months after commencement of ivacaftor, and were correlated with FEV₁ (% predicted), sweat chloride, C-reactive protein (CRP) and body mass index (BMI).

RESULTS

After 1 month of therapy, HE4 levels were significantly lower than at baseline and remained decreased up to 6 months. A significant inverse correlation between absolute and delta values of HE4 and FEV₁ (r = -0.5376; P < .001 and r = -0.3285; P < .001), was retrospectively observed in pooled groups, including an independent association of HE4 with FEV₁ by multiple regression analysis (β = -0.57, P = .019). Substantial area under the receiver operating characteristic curve (ROC-AUC) value was determined for HE4 when 7% mean change of FEV₁ (0.722 [95% CI 0.581-0.863]; P = .029) were used as classifier, especially in the first 2 months of treatment (0.806 [95% CI 0.665-0.947]; P < .001).

CONCLUSIONS

This study shows that plasma HE4 levels inversely correlate with lung function improvement in CF patients receiving ivacaftor. Overall, this potential biomarker may be of value for routine clinical and laboratory follow-up of CFTR modulating therapy.

A multicenter evaluation of sweat chloride concentration and variation in infants with cystic fibrosis

Fifty-nineCF infants' sweat chloride concentrations were analyzed to answer the questions: What is the biological and analytical variation in sweat chloride concentrations collected from the 32 infants homozygous for the F508 deletion? Do sweat chloride concentrations change in the first year of life beyond the variance previously established for adults with similar CFTR mutations? The biological and analytical variation of the infants' sweat chloride concentration was similar to that seen in adult CF patients. While there was a statistically significant difference between sweat chloride concentration in early (89.8 mmol/L) and late (95.0 mmol/L) infancy, this change is not likely clinically significant. This suggests that sweat chloride concentrations in CF patients do not change in a meaningful way during the first year of life. Determining variability in infants with CF is the necessary first step for future design of clinical trials of CFTR modulators in younger patients.

Revisiting sweat chloride test results based on recent guidelines for diagnosis of cystic fibrosis

Objectives

Recent sweat chloride guidelines published by the Cystic Fibrosis Foundation changed the intermediate sweat chloride concentration range from 40-59 mmol/L to 30-59 mmol/L for age > 6 months. We wanted to know how this new guideline would impact detection of cystic fibrosis among patients who previously had sweat tests done at Texas Children's Hospital.

Methods

We revisited sweat chloride test results (n = 3012) in the last 5 years at Texas Children's Hospital based on the new guidelines on diagnosis of cystic fibrosis from the Cystic Fibrosis Foundation.

Results

We identified 125 patients that would be reclassified in the intermediate sweat chloride value with the new guidelines that were classified as "unlikely to have CF" in the previous guidelines. 8 (32%) patients with CFTR gene testing were positive for CFTR gene mutation(s). 4 (50%) of these patients were identified to have 2 CFTR mutations. One had variant combination that was reported to cause CF but all were diagnosed with CFTR-related metabolic syndrome.

Conclusion

Our findings concur with the new CF diagnosis guidelines that changing the intermediate cut-off to 30-59 mmol/L sweat chloride concentration in combination with CFTR genetic analysis enhances the probability of identifying individuals that have risk of developing CF or have CF and enables for earlier therapeutic intervention.

Analytical and biological variation in repeated sweat chloride concentrations in clinical trials for CFTR modulator therapy

BACKGROUND

Using sweat chloride as a biomarker for CFTR modifying drugs requires knowledge of analytical and biological variation.

METHODS

979 sweat chloride concentrations from 128 subjects enrolled in the placebo arm of 2 multicenter, investigational drug trials were analyzed to determine coefficients of variation (CV) as well as reference change value (RCV) and index of individuality (II).

RESULTS

For these populations, calculated values for the two studies were: analytical variation (3.9, 4.1%); within-subject variation (4.4, 6.0%); between-subject variation (8.9, 7.0%); RCV (13.7, 17.0%) and II (0.7, 1.0). Sweat chloride variation was not affected by sex, collection site or sample weight; but was slightly affected by age in one of the two studies.

CONCLUSION

Through determination of analytical as well as between- and within-subject variation, and with a larger sample size, our data allows improved estimates of the RCV and II, and can contribute to future trials of CFTR modulators and inform the design and interpretation of n of 1 trials in both research and clinical settings.

The relationship between sweat chloride levels and mortality in cystic fibrosis varies by individual genotype

RATIONALE

The association between CFTR genotype, sweat chloride and mortality has been inconsistent, but no previous analyses have examined the association stratified by individual genotypes.

OBJECTIVES

To evaluate the genotype-specific association between sweat chloride and mortality.

METHODS

The CFF Patient Registry was assessed and included all patients in the registry between 1996 and 2012 with at least one F508del allele. We excluded patients without a documented genotype or plausible sweat chloride level. The primary outcome was time to mortality during the observation period. We examined 15 genotypes using the three most prevalent alleles in each of 5 classes. We compared subgroups of sweat chloride using Kaplan-Meier curves, log-rank tests, and multivariable Cox PH models. The overall predictive value of sweat chloride on mortality was assessed using area under the receiver operating characteristic curves.

MEASUREMENTS AND MAIN RESULTS

18,893 subjects met inclusion criteria. Sweat chloride distribution was similar across genotypes in patients with class 1 mutations, but was significantly different across genotypes in mutation classes 2-5. The R117H/F508del genotype patients demonstrated an association between sweat chloride and mortality (HR: 1.32 for every 10mmol/L increase in sweat chloride [95% CI 1.12-1.54]. There were also significant associations in patients with F508del/F508del, I507del/F508del, G551D/F508del and 2789+5G→A/F508del genotypes, though the clinical relevance for these genotypes is unclear.

CONCLUSIONS

There is significant variability in sweat chloride distribution across CFTR class 2-5 genotypes. The relationship between sweat chloride and mortality varies by genotype with a relatively strong relationship in R117H/F508del patients.

Cystic Fibrosis Diagnosis and Newborn Screening

The diagnosis of cystic fibrosis (CF) has evolved over the past decade as newborn screening has become universal in the United States and elsewhere. The heterogeneity of phenotypes associated with CF transmembrane conductance regulator (CFTR) dysfunction and mutations in the CFTR gene has become clearer, ranging from classic pancreatic-insufficient CF to manifestations in only 1 organ system to indeterminate diagnoses identified by newborn screening. The tools available for diagnosis have also expanded. This article reviews the newest diagnostic criteria for CF, newborn screening, prenatal screening and diagnosis, and indeterminate diagnoses in newborn-screened infants and symptomatic adults.

Variability of sweat chloride concentration in subjects with cystic fibrosis and G551D mutations

INTRODUCTION

Sweat chloride concentration, a biomarker of CFTR function, is an appropriate outcome parameter in clinical trials aimed at correcting the basic CF defect. Although there is consensus on a cut-off value to diagnose CF, we have only limited information on the within subject variability of sweat chloride over time. Such information would be useful for sample size calculations in clinical trials. Therefore, we retrospectively analyzed repeated sweat chloride values obtained in patients with G551D mutation(s) assigned to placebo in an ivacaftor interventional trial.

METHODS

In subjects with G551D at least 12years of age, a pilocarpine sweat test using Macroduct collector was taken on both arms at 8 time points over 48weeks. We explored 1062 pilocarpine sweat test values obtained in 78 placebo patients of the VX08-770-102 trial.

RESULTS

Mean overall sweat chloride value (all patients, all tests, n=1062) was 100.8mmol/L (SD 12.7mmol/L). Using a multilevel mixed model, the between-subject standard deviation (SD) for sweat chloride was 8.9mmol/L (95% CI 7.4-10.6) and within-subject SD was 8.1mmol/L (95% CI 7.5-8.7). Limits of repeatability for repeat measurements were -19.7 to +21.6mmol/L using values from one arm, and -13.3 to 11.8mmol/L using mean of values obtained at 4 test occasions. Sample size calculations showed that the minimal treatment effect on sweat chloride concentration that can be demonstrated for a group of 5 patients is around 15mmol/L, using a cross-over design and combinations of 4 tests for each phase of the trial.

CONCLUSION

Although the sweat test is considered a robust measure, sweat chloride measurements in patients with CF and a G551D mutation had an inherent biological variability that is higher than commonly considered. Further analyses of placebo group data are crucial to learn more about the natural variability of this outcome parameter.

Diagnostic Testing in Cystic Fibrosis

Cystic Fibrosis (CF) is a rare, multisystem disease leading to significant morbidity and mortality. CF is caused by defects in the cystic fibrosis transmembrane conductance regulator protein (CFTR), a chloride and bicarbonate transporter. Early diagnosis and access to therapies provides benefits in nutrition, pulmonary health, and cognitive ability. Several screening and diagnostic tests are available to support a diagnosis. We discuss the characteristics of screening and diagnostic tests for CF and guideline-based algorithms using these tools to establish a diagnosis. We discuss classification and management of common "diagnostic dilemmas," including the CFTR-related metabolic syndrome and other CFTR-associated diseases.

Sweating the small stuff: adequacy and accuracy in sweat chloride determination

OBJECTIVES

Sweat chloride testing is the gold standard for diagnosis of cystic fibrosis (CF). Our objectives were to: 1) describe variables that determine sweat rate; 2) determine the analytic and diagnostic capacity of sweat chloride analysis across the range of observed sweat rates; and 3) determine the biologic variability of sweat chloride concentration.

METHODS

A retrospective analysis was performed using data from all sweat chloride tests performed at St. Louis Children's Hospital over a 21-month period.

RESULTS

A total of 1397 sweat chloride tests (1155 sufficient [≥75 mg], 242 insufficient [<75 mg]), were performed on 904 individuals. The sweat weight collected from forearms was statistically greater than that collected from legs. There was a negligible correlation between sweat weight and chloride concentration (r=-0.06). The mean individual biologic CV calculated from individuals with two or more sweat collections ≥75 mg was 13.1% (95% CI: 11.3-14.9%; range 0-88%) yielding a reference change value of 36%. Using 60 mmol/L as the diagnostic chloride cutoff, 100% of CF cases were detected whether a minimum sweat weight of 75, 40, or 20 mg was required.

CONCLUSIONS

1) Collection of sweat from forearms is preferable to upper legs, particularly in very young infants; 2) sweat chloride concentrations are not highly dependent upon sweat rate; 3) a change in sweat chloride concentration exceeding 36% may be considered a clinically significant response to cystic fibrosis transmembrane receptor targeted therapy, and 4) sweat collections of less than 75 mg provide clinically accurate information.

Profile of cystic fibrosis in a single referral center in Egypt

It was generally believed that Cystic fibrosis (CF) is rare among Arabs; however, the few studies available from Egypt and other Arabic countries suggested the presence of many undiagnosed patients. The aim of the present study was to determine the frequency of CF patients out of the referred cases in a single referral hospital in Egypt. A total of 100 patients clinically suspected of having CF were recruited from the CF clinic of the Allergy and Pulmonology Unit, Children's Hospital, Cairo University, Egypt, throughout a 2 year period. Sweat chloride testing was done for all patients using the Wescor macroduct system for collection of sweat. Quantitative analysis for chloride was then done by the thiocyanate colorimetric method. Patients positive for sweat chloride (⩾60 mmol/L) were tested for the ΔF508 mutation using primer specific PCR for cystic fibrosis transmembrane conductance regulator (CFTR) gene. Thirty-six patients (36%) had a positive sweat chloride test. The main clinical presentations in patients were chronic cough in 32 (88.9%), failure to thrive in 27 (75%), steatorrhea in 24 (66.7%), and hepatobiliary involvement in 5 (13.9%). Positive consanguinity was reported in 50% of CF patients. Thirty-two patients were screened for ΔF508 mutation. Positive ΔF508 mutation was detected in 22 (68.8%) patients, 8 (25%) were homozygous, 14 (43.8%) were heterozygous, and 10 (31.3%) tested were negative. CF was diagnosed in more than third of patients suspected of having the disease on clinical grounds. This high frequency of CF among referred patients indicates that a high index of suspicion and an increasing availability of diagnostic tests lead to the identification of a higher number of affected individuals.

Comparison of classic sweat test and crystallization test in diagnosis of cystic fibrosis

OBJECTIVE

Sweat chloride measurement is considered a standard diagnostic tool for cystic fibrosis (CF). This study was performed to compare sweat chloride values obtained by quantitative pilocarpine iontophoresis (classic test) with sweat crystallization detected by direct observation of a drop of perspiration under light microscopy in patients with and without CF.

METHODS

The tests using both techniques were performed simultaneously in patients with and without CF. Cutoff values of ≥60 mmol/L of chloride concentration for the classic sweat test was considered for diagnosis of CF. In crystallization method, observation of typical dendritic forms of salt crystals under light microscopy was interpreted positive.

FINDINGS

Sixty patients suspected to CF (31 males and 29 females) with age range of 9 months to 2 years underwent the sweat test using both techniques. Median sweat chloride values was 26.13+10.85 in group with negative and 72.76+12.78 mmol/L in group with positive sweat test, respectively. All the patients who had positive sweat test in classic method showed typical dendritic forms of salt crystal in sweat crystallization test, which provided the test with 100% sensitivity (95%CI: 93.1-100). Only one of the 31 subjects with negative results for classic sweat test had positive result for crystallization sweat test, which provided the test with 96.7% specificity (95%CI: 92.9-100). Time spent to perform the crystallization test was significantly shorter than the classic method whereas its cost was also lower than the second method.

CONCLUSION

There was a good correspondence between two studied methods of sweat test. These results suggested the sweat crystallization test as an alternative test for detecting CF disease with high sensitivity and specificity.