CFTR and cystic fibrosis: Although it is well known that variables in genetic background (e.g. modifier genes) and environment factors also affect CF disease manifestations [18], our finding that G1208D-CFTR has residual CFTR function (33 % of normal CFTR) correlates well with the mild disease phenotype in this patient, with preserved pancreatic function and intermediate sweat chloride levels, when paired with a classical CFTR mutation like F508del.