As a secondary objective of the study, polymorphisms were analysed in relation to asthma severity, with significant differences observed for 2 polymorphisms, namely, NM_000492.3 (CFTR): c.2506G>T (p.Asp836Tyr) and NM_000492.4(CFTR): c.3140-92T>C (p = 0.024 and p = 0.049, respectively), more frequently present in majority alleles in patients with severe persistent asthma, and absent or present to a lesser extent in minority alleles (Table 3). This evidence concerns the gene CFTR and asthma.