One group of genes associated with asthma are related to the epithelial barrier function (see summary in ref. [33]); these include PCDH1 (protocadherin-1), which is involved in cell adhesion and epithelial barrier formation [34] and CDHR3 (cadherin-related family member 3), which is also involved in cell adhesion as well as epithelial polarity and is the receptor for rhinovirus (RV) C, where the risk variant could increase susceptibility to infection [35,36,37]. This evidence concerns the gene PCDH1 and infection.