RAF1 and pulmonary artery enlargement: To date the majority of known PAE mutations affect the RTK or components of its downstream RAS-ERK signaling pathway (FGFR3, HRAS, PTPN11, KRAS, RET, RAF1, PTPN11, BRAF, CBL, MAPK1, MAPK2) (Tiemann-Boege et al. 2002; Qin et al. 2007; Goriely et al. 2009; Choi et al. 2012; Shinde et al. 2013; Maher et al. 2016, 2018).