In contrast, inducible nitric oxide synthase (NOS2) is reduced in CF airway epithelial cells most likely in direct response to the CFTR deficiency,58 and there is no significant difference in the natural NOS inhibitor asymmetric dimethylarginine (ADMA) in the breath condensate from children with CF,59 suggesting much of the oxidative stress is driven by ROS rather than RNS. This evidence concerns the gene CFTR and cystic fibrosis.