Concomitant loss of CalDAG-GEFI (Cdg1–/–) normalized both platelet count and platelet life span in R3hlb/hlb mice, suggesting that unrestrained Rap1 activation leading to enhanced platelet clearance is the main reason for thrombocytopenia in Rasa3-mutant mice. The gene discussed is RASA3; the disease is Thrombocytopenia.