TBX4 and pulmonary arterial hypertension: Mutations in the BMP receptor type IA and type 1B [BMPR1A and BMPR1B, also called activin receptor-like kinase 6 (ALK6)], caveolin-1 (CAV1), eukaryotic initiation translation factor 2 alpha kinase 4 (EIF2AK4), potassium two-pore-domain channel subfamily K member 3 (KCNK3), SMAD family members 4 and 9 (SMAD4 and SMAD9), and T-box 4 (TBX4) have all been identified as less frequent or rare causes of PAH (9).