The identification of multiple unrelated patients with similar phenotypes and exactly the same de novo CDC42 mutation enabled us to confirm that these patients represent a new syndromic form of thrombocytopenia, which was eponymized as “Takenouchi-Kosaki syndrome” (OMIM #616737). The gene discussed is CDC42; the disease is macrothrombocytopenia-lymphedema-developmental delay-facial dysmorphism-camptodactyly syndrome.