Signaling through several tyrosine kinases, including platelet-derived growth factor receptor (PDGFR) α, PDGFRβ, colony stimulating factor 1 receptor (CSF1R), and mast/stem cell growth factor receptor kit (c-KIT), contribute to the cycle of inflammation and proliferation involved in PAH pathogenesis and progression. The gene discussed is PDGFRB; the disease is pulmonary arterial hypertension.