VDR and respiratory syncytial virus bronchiolitis: Several studies have shown that polymorphisms in innate immunity-related genes as well as various cytokines, surfactant protein D (SFTPD), Toll-like receptors 4 (TLR 4), inflammation gene myxovirus (influenza virus) resistance 1 (MX1) protein or vitamin D receptor (VDR) lead to genetic susceptibility to RSV bronchiolitis [220,221,222,223,224].