The c.3140-26A>G Variant of the CFTR Gene in Homozygous State Causes Mild Cystic Fibrosis - Overview of Longitudinal Clinical Data of the Patient Managed in our CF Center and Review of the Literature.

There are over 70.000 patients with cystic fibrosis (CF) in the world and numerous sequence variations in the CFTR gene have been reported but the clinical significance of all of them is still not known. There are currently 195 patients with the c.3140-26A>G (legacy name 3272-26A>G) variant in the CFTR gene listed in the European Cystic Fibrosis Society Patient Registry (ECFSPR) and only 4 are homozygous. We present longitudinal clinical data of one of these patients who is managed in our CF Center at the University Children's Hospital in Ljubljana and compare it with the patient data from the ECFSPR and the CFTR2 database in which additional 3 homozygous patients are described. Moreover, the effect of the detected variant in the described patient was evaluated on the RNA level in nasal epithelial cells. The variant was shown to result in aberrant splicing introducing a frameshift and a premature termination codon while normal transcript was not detected. Alternative spliced mutant transcripts in other tissues or the presence of spliceosome-mediated RNA trans-splicing could explain the mild clinical presentation of patients with this variant in homozygous state.