ATP13A3 and pulmonary arterial hypertension: ATP13A3 encodes a transmembrane cation transporter, which was recently shown to transport polyamines.8 Polyamines are small metabolites required for normal cell growth and proliferation, and elevated concentrations have been reported in multiple cancers and, more recently, PAH.20 21ATP13A3 is widely expressed in developing embryo and adult tissues,22 including pulmonary arterial smooth muscle cells (PASMC).3 Hypoxia, an environmental inducer of PAH, stimulates accumulation of spermine leading to increased PASMC proliferation in model systems.