In fact, the three patients with severe CF and compound heterozygous for two CFTR severe mutations (cases 1 to 3) show a very low residual CFTR activity (i.e., < 10%); the two heterozygous subjects show an activity between 40 and 80%, and the patient with mild CF, compound heterozygous for the W1282X and the mild D1152H mutation [43] had an activity in the range 10 to 20%. Here, CFTR is linked to cystic fibrosis.