Epigenetic differences may also contribute to incomplete penetrance in other conditions such as asthma, where DNA methylation has been reported to modulate the risk of disease conferred by genetic variants at the zona pellucida binding protein 2 (ZPBP2; Berlivet et al. 2012), forkhead box P3 (FOXP3; Runyon et al. 2012), interferon-γ (IFNG; Runyon et al. 2012) and interleukin-4 receptor (IL4R; Soto-Ramírez et al. 2013) gene loci. Here, IL4R is linked to asthma.