NASAL POTENTIAL DIFFERENCE IN CYSTIC-FIBROSIS PATIENTS PRESENTING BORDERLINE SWEAT TEST

The diagnosis of cystic fibrosis (CF) can be difficult if the sweat te st and routine deoxyribonucleic acid (DNA) analysis are inconclusive. Under these circumstances, measurement of nasal potential difference ( NPD) was proposed as a complementary diagnostic tool, as demonstrated in subjects bearing the G551S or 3849+10KbC-->T mutations. The purpose of the present study was to verify the diagnostic value of this techn ique in CF patients with a borderline sweat test. NPD was measured in 18 patients with a borderline sweat test, in whom CF diagnosis was bas ed on the presence of one CF gene mutation in each chromosome (CF bord erline), These patients were compared both to non-CF controls and CF p atients with an abnormal sweat test (CF controls). Basal NPD values of CF borderline patients (mean value -39+/-6 mV, range -29 to -52 mV; n =18) were in the pathological range of CF controls (-39+/-8 mV, range -28 to -57 mV; n=37), and both were statistically different from value s obtained in non-CF controls (-15+/-4 mV, range -6 to -23 mV; n=24; p <0.0001). Mutation analysis confirmed a high frequency of the 3849+10K bC-->T mutation in this group of CF borderline patients (positive in 1 4 out of 18 subjects), whereas other mutations, such as Delta F508, Q5 52X, N1303K and R1162X, were also found to be associated with this aty pical CF phenotype. These results confirm the presence of pathological values of basal NPD in CF patients with borderline sweat test, and al so extend this finding to subjects bearing genotypes other than the G5 51S and 3849+10KbC-->T mutations, The present findings, therefore, con firm the usefulness of measurement of basal nasal potential difference in all those patients in whom diagnosis of cystic fibrosis can be sus pected bat the sweat test remains inconclusive.