Mutations in other TGFβ family member genes—activin A, receptor type II-like 1 (ACVRL1), endoglin (ENG), BMP receptor type 1A (BMPR1A) and type 1B (BMPR1B)—as well as 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-box4 (TBX4) have all been identified as less frequent or rare causes of PAH [5–8]. This evidence concerns the gene TBX4 and pulmonary arterial hypertension.