Since CTCF has a major role in long-range interactions of cis-regulatory elements to cognate promoter regions36, 37, 38, 39, we hypothesized that the switching of CTCF-binding sites may affect the 3D architecture (organization) of the 17q21 locus to favour enhanced transcription of ORMDL3 in the asthma-risk alleles. This evidence concerns the gene ORMDL3 and asthma.