We screened for mutations in the NOTCH3, HES1, and HES5 genes in 41 IPAH/HPAH patients who had no mutations in BMPR2, ALK1, ENG, SMAD1/4/8, BMPR1B, or CAV1 (Fig. 1). The gene discussed is SMAD1; the disease is idiopathic pulmonary arterial hypertension.