The development of drug-induced thrombocytopenia, a severe autoimmune response triggered by formation of antibodies recognizing heparin/heparin mimetic-PF4 complexes [11], was quite unexpected as preclinical studies in rats and monkeys provided no evidence of thrombocytopenia and no indication that the development of anti-heparin-PF4 complex antibodies could result from administering PI-88 to patients. This evidence concerns the gene PF4 and Thrombocytopenia.