STAT6 and asthma: Epistatic interactions between pairs of SNPs between all asthma subgroups were tested, revealing significant epistasis for loci IL4-590 and STAT6-21 in moderate-to-severe compared to intermittent asthma (p-value = 0.044) and IL13-c.144 and ADAM33-V4 between persistent asthma and the Madeira reference set (p-value = 0.035).