The purpose of this research study is to provide a novel method for the diagnosis of Cystic
Fibrosis (CF). This protocol is designed to test the ability of the cells to regulate the
movement of salt and water in people with features of CF in whom the diagnosis is not
entirely clear. We will be studying these cells in the nose, by a technique called nasal
transepithelial potential difference (NPD).
Cystic Fibrosis (CF) is an autosomal recessive systemic disorder of exocrine glands and
secretory epithelia. The disease results from mutations in the cystic fibrosis transmembrane
conductance regulator (CFTR) gene which cause a variety of abnormalities. CFTR is absent or
dysfunctional in cystic fibrosis. Most of the defects in CFTR result in abnormal chloride ion
transport and abnormally viscous mucus. Nasal epithelial CFTR function will be assessed by
the NPD procedure.
NPD measurements are useful as a diagnostic tool in individuals with borderline or normal
sweat chlorides, one or no identified CFTR mutations, and a clinical history suggestive of
CF. The NPD has become the gold standard for detection and quantification of CFTR function in
the airways. The assay has also served as an important endpoint since 1981. It has been used
extensively and is standardized to assess the ability of new therapeutics in studies designed
to replace, repair or restore defective ion transport in CF patients.
The assay basically involves dripping small amounts of the test solutions into the anterior
nostril in order to measure uptake or secretion of sodium and chloride. There are five
solutions required for the NPD measurement:
- Solution #1: Buffered Ringers
- Solution #2: Solution #1+Amiloride
- Solution #3: Buffered Zero Chloride Solution + Amiloride
- Solution #4: Solution #3 + Isoproterenol
- Solution #5: Solution #4 + Adenosine 5'-Triphosphate-Disodium salt (ATP)
The Cystic Fibrosis Therapeutics Development Network (TDN) is a formal affiliation of CF
Research Centers in the US. Two Standard Operating Procedures have been developed by the TDN
for the NPD procedure and qualification of those performing the measurement.
Briefly, a series of stopcocks is configured to allow perfusion of the above solutions
through the port at the tip of an exploring catheter (PE50 tubing. All test solutions are
perfused at a rate of 5.0 cc per minute. In each nostril, the PD readings in Ringer's at 0.5,
1.0, 1.5, 2, and 3 cm (lumen negative) are averaged and taken as the average 'baseline' PD.
The catheter tip is then placed at the most negative PD site and maintained for
superperfusion measurements with a small piece of tape applied to the nasal tip (to hold the
catheter for the duration of the protocol). All solutions are warmed to 37˚C prior to contact
with the nasal mucosa.
For each perfusion condition, a steady-state recording is obtained. The recording lasts at
least one minute (for Solution #1) and for three minutes (for Solutions #2, 3, and 4) prior
to proceeding to the next solution within the sequence. Solution #5 is perfused for a minimum
of one minute, and confirms retention of ATP-activated Clˉ secretion in both CF and non-CF
individuals. Several readings are obtained for data analysis, and then all nasal P.D.
tracings are scored by investigators.
- All ethnic groups accepted
- Individuals with borderline or normal sweat chloride, one or no identified CFTR
mutations and a clinical history suggestive of CF.
- Children less than 6-8 years of age may be unable to cooperate (hold still) for the
procedure, or be frightened by the procedure. Sedation may be necessary for
performance of the procedure on a young child
Ronald Rubenstein, M.D., PhD.
Children's Hospital of Philadelphia
Christina Kubrak, RRT, CCRC