CFTR and asthma: Though these reports suggest that the absolute risk is low, 3–4% of the population are CF carriers in the USA, Canada, and Northern Europe [15], and the potential morbidity caused by CFTR heterozygosity in these populations is large. Most recently, the CFTR gene was sequenced in participants from the severe asthma research program (SARP), and potentially pathogenic CFTR variants were found in 9.5% of this severe asthma-enriched cohort [20].