Nasal potential difference outcomes support diagnostic decisions in cystic fibrosis

BACKGROUND

When cystic fibrosis (CF) is suspected Nasal Potential Difference (NPD) measurements are proposed to support controversial diagnosis: we investigated appropriate outcomes at the CF Centre of Verona.

SUBJECTS/METHODS

NPD were measured in 196 subjects: 50 non-CF, 65 classical CF (the reference group) and 81 with uncertain CF (case group). Discriminating power was determined by comparison between several outcomes from the CF reference group versus non-CF: basal, amiloride, 0Cl, isoproterenol, ATP, Delta-amiloride, Delta-0Cl, Delta-isoproterenol, Delta-ATP, Delta-isoproterenol+Delta-0Cl, Wilschanski Index (WI) and Sermet score (SS). The most appropriate cut-off values for variables with the best discriminating power were then applied to the case group. Descriptive statistics, logistic regression models and ROC curve analysis were applied.

RESULTS

WI and SS were the most powerful in discriminating CF from non-CF subjects. In the reference group sensitivity of the 0.82 WI cut-off was 98%, specificity 96%; both sensitivity and specificity of the -0.44 SS cut-off value were 100%. For the case group, WI and SS were, respectively, consistent with CF diagnosis in 94% and 92% of the cases.

CONCLUSIONS

Formulae have the highest discriminating power and can support the diagnosis in uncertain cases; they should be utilized for standardized interpretation of NPD for diagnosis and possibly for clinical research.

Impaired CFTR function in mild cystic fibrosis associated with the S977F/T5TG12complex allele in trans with F508del mutation

BACKGROUND

The S977F mutation (c.2930C>T) in the CFTR gene (CFTR/ABCC7) is extremely rare. We describe the case of an adult patient carrying the complex allele S977F/T5TG12 in trans with the F508del mutation. Mild respiratory manifestations arose in adulthood associated with azoospermia, acute pancreatitis, minor hemoptysis and Cl(-) levels ranging from 40 to 42 mEq/L.

METHOD

Diagnosis was confirmed by repeated NPD measurements, genetic DHPLC analysis and a recently described functional assay measuring cAMP-dependent cell depolarization in peripheral blood monocytes.

RESULTS

NPD measurements, DHPLC and monocyte functional assay (CF index=-18). Results were consistent with a CF phenotype.

CONCLUSIONS

The combined application of DHPLC and NPD analysis in the algorithm for CF diagnosis appears useful for the management of similar cases. In addition, the novel monocyte functional assay might contribute to improve our diagnostic capability, counseling and better treatment of these challenging clinical cases.