Reproducibility of Nasal Potential Difference Measurements in Cystic Fibrosis

doi:10.1378/chest.06-2975

Chest

Volume 132, Issue 4, October 2007, Pages 1219-1226

https://doi.org/10.1378/chest.06-2975 Get rights and content

Background

Nasal potential difference (NPD) measurement has been advocated as a diagnostic tool for cystic fibrosis (CF) patients and as a method for assessing the response to new therapies. The purpose of this study was to examine the reproducibility of NPD measurements performed in a single center.

Methods

A total of 68 CF patients with a mean (± SD) age of 16 ± 8 years (age range, 6 to 52 years) underwent NPD measurements on at least two occasions.

Results

A total of 25 patients with classic CF (mean age, 21 ± 8 years) and 43 patients with nonclassic CF (mean age, 14 ± 8 years) underwent sweat tests and NPD measurements. The mean sweat chloride values were 102 ± 18 and 54 ± 14 mEq/L, respectively, for classic CF and nonclassic CF groups. All patients underwent repeat NPD measurements. The basal NPD and the response to amiloride (ΔAmil) and response to Cl⁻ free and isoproterenol (ΔCl⁻ free + iso) were very similar in both measurements. In the classic CF group, the basal potential difference values were −40 ± 12 vs −39 ± 11 mV (p = 0.57), respectively, for the first and second measurements; 27 ± 9 vs 26 ± 10 mV (p = 0.55), respectively, for ΔAmil; and 2.1 ± 3.8 vs 0.4 ± 2.9 mV (p = 0.07), respectively, for ΔCl⁻ free + iso. In the nonclassic CF group, the values were −32 ± 13 vs −28 ± 10 mV (p = 0.008), respectively; 19 ± 10 vs 17 ± 8 mV (p = 0.388), respectively; and −3.2 ± 4.6 vs −3.3 ± 4.4 mV (p = 0.876), respectively.

Conclusion

When performed in a single center, NPD is a reproducible test for CF patients and thus may be a useful outcome measurement for assessment of the efficacy of new treatments.

Section snippets

Patients

We analyzed retrospectively repeated NPD measurements in 68 CF patients (mean [± SD] age, 16 ± 8 years; age range, 6 to 52 years) who had at least two NPD measurements. The patients were divided into the following two groups:

1
A group of 25 CF patients (mean age, 21 ± 8 years; 12 men) with classic disease. CF was diagnosed by typical respiratory and GI presentation together with elevated sweat chloride levels. All patients had genetic analysis for all known CFTR mutations in Israel

Results

Table 1 shows the clinical characteristics of CF patients with classic and nonclassic disease. All patients underwent standard sweat testing, the results of which were borderline (54 ± 14 mEq/L) for the nonclassic CF group and pathologic (102 ± 19 mEq/L) for the classic CF group. The time period between the measurements was within 1 year for 80% of the patients. NPD in the control group was significantly different in all parameters (basal NPD, −16 ± 5 mV; ΔAmil, 10 ± 4 mV; and ΔCl⁻ free + iso,

Discussion

In this study, we have shown for the first time in a heterogeneous group of patients with CF that NPD is reproducible with variability in the acceptable range. For most parameters, there was no significant change between the two measurements (p > 0.05) except for the basal PD values in the nonclassic CF group (p = 0.008). These results were confirmed by all the different statistical approaches we applied to the data.

NPD is made up of the following three important parameters: basal PD; ΔAmil;

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Cited by (39)

ECFS standards of care on CFTR-related disorders: Diagnostic criteria of CFTR dysfunction
2022, Journal of Cystic Fibrosis
Citation Excerpt :
On the other hand, single center studies provide provisional confidence in reproducibility. Yaakov et al. repeated NPD measurements in 68 CF patients divided in a classical and non-classical CF group and showed acceptable variability between measurements [97]. All differences were within the +/−1 standard deviation which was defined as a clinically significant difference.
The spectrum of disorders involving CFTR (cystic fibrosis transmembrane conductance regulator) dysfunction correlates with a continuous gradient of CFTR function defined by the combination of two allelic CFTR variants. CFTR-related disorders are clinical entities with features of cystic fibrosis (CF) and evidence for presence of CFTR dysfunction but not meeting criteria for diagnosis of CF. Individuals with CFTR-RDs demonstrate a wide range of CFTR activity and are still under-recognized or misclassified. The level of CFTR dysfunction may be measured in vivo (sweat testing, nasal potential difference measurements) and/or by ex vivo tests (intestinal current measurement), or indirectly indicated by CFTR variants, as alteration in sequence of the CFTR gene translates into CFTR dysfunction. CFTR bioassays can aid in the diagnosis of individuals with CF, but we lack parameters to differentiate CF from CFTR-RD. In the era of the CFTR modulators and their potential clinical benefit, it is of utmost importance to diagnose CFTR-RD as unambiguously as possible. We therefore propose the following to define compatible CFTR dysfunction in a person with a suspected diagnosis of CFTR-RD :
(1) evidence of CFTR dysfunction in vivo or ex vivo in at least two different CFTR functional test types, or
(2) One CFTR variant known to reduce CFTR function and evidence of CFTR dysfunction in vivo or ex vivo in at least two different CFTR functional test types, or
(3) Two CFTR variants shown to reduce CFTR function, with at most one CF-causing variant.
Insights into the variability of nasal potential difference, a biomarker of CFTR activity
2020, Journal of Cystic Fibrosis
Citation Excerpt :
The same goes for the Na+ conductance parameters, but with larger measurement errors, (±21.4 mV for the basal PD and ±17.4 mV for Δ Amiloride). Our cut-offs are higher than those for the Δ Low Cl−-Isoproterenol of 5 mV usually used in clinical trials and that reported in the study of Leonard at 5.7 mV, but similar to that of Yaakov and when applying similar calculations to the reported SD measurements [19,20,30]. Importantly, these cut-offs are clearly higher than the values reported for VX-770 in CF patients with G551D mutation which demonstrated a difference of 3.7 mV in the Δ Low Cl−-Isoproterenol between the placebo and VX-770/150 mg group and a 5.1 mV difference between the placebo and the VX-770/250 mg group [10].
Nasal potential difference (NPD) is used to evaluate CFTR function in vivo. We aimed to evaluate the intrasubject and intersubject variability of NPD measurements.
We reviewed NPD tracings of 116 patients with CF enrolled in the placebo arm of a multicenter study. Patients carried at least one nonsense mutation and underwent repeated NPD tests every 16 weeks. NPD parameters included basal potential difference (basal PD), inhibition of sodium absorption by amiloride (Δ Amiloride), chloride (Cl⁻) transport in response to a Cl⁻-free solution (Δ Low Cl⁻), isoproterenol (Δ Isoproterenol), the sum of Δ Low Cl⁻ and Δ Isoproterenol (Δ Low Cl⁻-Isoproterenol) and ATP (Δ ATP).
Basal PD and Δ Amiloride displayed the highest variabilities, mainly stemming from intercenter and intrasubject effect. Δ Low Cl⁻, Δ Isoproterenol and Δ Low Cl⁻-Isoproterenol demonstrated a large intrasubject variability but a smaller intersubject variability. The intrasubject measurement variability for Δ Low Cl⁻-Isoproterenol, was within ± 7.2 mV with 95% probability. It was greater in patients reporting ongoing pulmonary exacerbations.
The large intercenter variability of basal PD and Δ Amiloride highlights the operator-dependent aspect of these measurements. A difference greater than 7.2 mV in Δ Low Cl⁻-Isoproterenol in a given patient on CFTR modulator can be attributed, with 95% probability, to a treatment effect rather than to the variability inherent in the measurement.
Nanomedicine for Cystic Fibrosis
2019, SLAS Technology
Cystic fibrosis is a genetic disease affecting more than 70,000 people worldwide. Caused by a mutation in the CFTR gene, cystic fibrosis can result in difficulty breathing, widespread bacterial infections, edema, malnutrition, pancreatitis, and death. Current drug-based treatments struggle to reach the site of action due to the thick mucus, and only manage symptoms such as blocked airways, lung infections, and limited ability to digest food. Nanotechnology opens up possibilities for improved treatment strategies by focusing on drug penetration through the mucus lining, eliminating resulting bacterial infections, and targeting the underlying genetic cause of the disease. In this review, we present recent nanoparticle developments for cystic fibrosis, challenges in nanomedicine therapeutics, and future research directions in gene editing and nonviral vectors for gene delivery.
Primary sclerosing cholangitis is associated with abnormalities in CFTR
2018, Journal of Cystic Fibrosis
The etiology of primary sclerosing cholangitis (PSC) is unknown. PSC and Cystic Fibrosis related liver disease have common features: chronic inflammation, biliary damage and similar cholangiographic findings. It is unknown whether or not PSC is related to cystic fibrosis transmembrane conductance regulator (CFTR) dysfunction. We hypothesize that a sub-group of PSC patients may be a “single-organ” presentation of CF.
Patients with PSC underwent nasal potential difference (NPD) measurement, sweat chloride measurement and complete CFTR sequencing by new generation sequencing.
6/32 patients aged 46 ± 13 yrs. had CFTR causing mutations on one allele and 19 had CFTR polymorphisms; 6/23 tested had abnormal and 21 had intermediate sweat tests; 4/32 patients had abnormal NPD. One patient had chronic pancreatitis and was infertile.
19% of PSC patients had features of CFTR related disorder, 19% carry CFTR mutations and 50% had CFTR polymorphisms. In some patients, PSC may be a single organ presentation of CF or a CFTR-related disorder.
The diagnosis of cystic fibrosis
2017, Presse Medicale
Establishing the diagnosis of cystic fibrosis (CF) is straight forward in the majority of patients: they present with a clear clinical picture (most frequently chronic respiratory symptoms plus malabsorption), the sweat chloride value is > 60 mmol/L and two known disease causing CFTR mutations are identified. In less than 5% of subjects, mainly those with a milder or limited phenotype, the diagnostic process is more complex, because initial diagnostic test results are inconclusive: sweat chloride concentration in the intermediate range, less than 2 CF causing mutations identified or both. These patients should be referred to expert centers where bioassays of CFTR function like nasal potential difference measurement or intestinal current measurement can be done. Still, in some patients, despite symptoms compatible with CF and some indication of CFTR dysfunction (e.g. only intermediate sweat chloride value), diagnostic criteria are not met (e.g. only 1 CFTR mutation identified). For these subjects, the term CFTR related disorder (CFTR-RD) is used. Patients with disseminated bronchiectasis, congenital bilateral absence of the vas deferens and acute or recurrent pancreatitis may fall in this category. CF has a very wide disease spectrum and increasingly the diagnosis is being made during adult life, mainly in subjects with milder phenotypes. In many countries, nationwide CF newborn screening (NBS) has been introduced. In screen positive babies, the diagnosis of CF must be confirmed by a sweat test demonstrating a sweat chloride concentration above 60 mmol/L. To achieve the benefit of NBS, every baby in whom the diagnosis of CF is confirmed must receive immediate follow-up and treatment in a CF reference center. CF NBS is not full proof: some diagnoses will be missed and in some babies the diagnosis cannot be confirmed nor ruled out with certainty. Screening algorithms that include gene sequencing will detect a high number of such babies that are screen positive with an inconclusive diagnosis (CFSPID). Even in 2016, the most reliable and widely available diagnostic test for CF is the measurement of chloride concentration in sweat. The method of choice is sweat induction by pilocarpine iontophoresis, followed by sweat collection on a gauze or filter paper or in a Macroduct coil. Since mutation specific therapies have become available, it is important to identify the mutations responsible for CF in each individual patient.
Diagnostic Testing in Cystic Fibrosis
2016, Clinics in Chest Medicine

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: The authors have reported to the ACCP that no significant conflicts of interest exist with any companies/organizations whose products or services may be discussed in this article.

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Chest

ORIGINAL RESEARCHCYSTIC FIBROSISReproducibility of Nasal Potential Difference Measurements in Cystic Fibrosis

Background

Methods

Results

Conclusion

Section snippets

Patients

Results

Discussion

J Pediatr

J Biol Chem

J Biol Chem

FEBS Lett

J Biol Chem

Mol Ther

Chest

Nasal potential difference measurements in patients with atypical cystic fibrosis

Eur Respir J

Nasal potential difference in congenital bilateral absence of the vas deference

Am J Respir Crit Care Med

The cystic fibrosis transmembrane conductance regulator gene and ion channel function in patients with idiopathic pancreatitis

Hum Genet

Increased prevalence of CFTR mutations and variants and decreased chloride secretion in primary sclerosing cholangitis

Hum Genet

Genotype and phenotype in cystis fibrosis

Respiration

Nonclassic cystic fibrosis and CFTR-related diseases

Curr Opin Pulm Med

Cystic fibrosis: terminology and diagnostic algorithms

Thorax

ORIGINAL RESEARCH
CYSTIC FIBROSIS
Reproducibility of Nasal Potential Difference Measurements in Cystic Fibrosis