CD34 and pulmonary arterial hypertension: Studies exploring EPC counts and function in patients with pulmonary arterial hypertension (PAH) have also been undertaken, with one study reporting increased CD34+/KDR+/CD133+ EPC levels in patients with PAH, and reduced OEC tubulogenesis and increased proliferation in PAH patients with the bone morphogenetic protein receptor type II mutation [33], and another study reporting increased OEC levels in PAH patients treatment with treprostinil (a parenteral prostanoid) [34].