Heparin-induced thrombocytopenia (HIT) is an immune-mediated and potentially lethal response to heparin administration leading to the formation of IgG antibodies directed against the heparin/platelet factor 4 (PF4) complex with consequent platelet activation, release of prothrombotic microparticles, platelet clumping, and thrombocytopenia.1 The gene discussed is PF4; the disease is Thrombocytopenia.