In particular, PAE mutations have been described in genes such as FGFR2, FGFR3, HRAS, PTPN11, KRAS, and RET (Qin et al. 2007; Choi et al. 2012; Shinde et al. 2013; Maher et al. 2016) and more recently in six new genes (BRAF, CBL, MAPK1, MAPK2, RAF1, and SOS1) (Maher et al. 2018), all acting in the receptor tyrosine kinase (RTK)-RAS signaling pathway and expressed in spermatogonial stem cells (SSCs). The gene discussed is RAF1; the disease is pulmonary artery enlargement.