Reduced CFTR activity measured by NPD was also associated with the severity of bronchitic symptoms (r = 0.30, P<0.05), as assessed by BCSS [27], even when controlled for cigarette smoking (r = 0.31, P<0.05), indicating an association with a phenotype reminiscent of CF (i.e. chronic bronchitis). The gene discussed is CFTR; the disease is cystic fibrosis.