CFTR and cystic fibrosis: The evaluation of the phenotypic manifestations of CF showed that p.Leu997Phe alone can cause a “mild” phenotype of CF or CFTR-RD, while as part of the complex allele p.[Arg117Leu;Leu997Phe], it causes a characteristic clinical picture of the disease: four of the twelve compound heterozygotes with p.[Arg117Leu;Leu997Phe] were characterized by severe and mild courses of the disease [40].