As a general rule, classic HIT features a moderate degree of thrombocytopenia, moderate thrombotic risk, and rapid platelet count recovery after heparin cessation; in contrast, aHIT and the other anti-PF4 disorders feature more severe thrombocytopenia, very high thrombosis risk (>95%), prolonged thrombocytopenia irrespective of heparin administration, and often overt, decompensated disseminated intravascular coagulation (DIC). This evidence concerns the gene PF4 and Thrombocytopenia.