CFTR and cystic fibrosis: Cystic Fibrosis Transmembrane Conductance Regulator (CFTR) mutation analysis in both twins had been performed after the first surgery, initially using the Cystic Fibrosis v3Genotyping Assay (Abbott Laboratories, Wiesbaden, Germany) and subsequently by Sanger sequencing of the entire coding region (27 exons) and 50 bp of flanking intronic sequences of the gene.