In each of two out of 60 tested CF chromosomes [9], two genetic changes were found: one mutation plus one polymorphism.

Patient 1 had her genotype determined as DF508/ G542X+F508C. The allele with two genetic changes, G542X+F508C, was composed of one mutation, G542X in exon 11, and one polymorphism, F508C in exon 10 (Figs. 1 and 2). The patient was a 9-year-old girl whose clinical features were mostly in gastrointestinal form, with a severe pancreatic insufficiency. Sweat Cl^– concentration was between 90 and 100 mmol/L. She was born without meconium ileus (Table 1).

Patient 2 had the genotype DF508/G542X+P1290P. The allele with two genetic changes, G542X+P1290P, was composed of one mutation, G542X in exon 11, and one polymorphism, P1290P in exon 20 (Fig. 3). The same allele with two genetic changes was found in the patient’s healthy mother. The patient, a 5-year-old girl, suffers often from respiratory problems caused by a Pseudomonas aeruginosa infection, and also severe pancreatic insufficiency. Sweat Cl^– concentration was between 70 and 80 mmol/L (Table 1). She was born without meconium ileus.