Although nonsense mutation readthrough usually yields only a small percentage of the normal expression levels of the full-length protein, in some cases, such as in lysosomal storage disease, even 1% of normal protein function may restore a near-normal or clinically less severe phenotype [16,17], this threshold is disease and gene dependent as for cystic fibrosis (CF), it has been shown that 10% to 35% of CFTR activity might be needed to alleviate pulmonary morbidity significantly [18]; in Duchenne muscular dystrophy (DMD)—1% to 30% of the full-length dystrophin protein is needed [3]. The gene discussed is CFTR; the disease is cystic fibrosis.