Gray platelet syndrome (GPS) is a rare inherited bleeding disorder characterized by macrothrombocytopenia, myelofibrosis, splenomegaly and typical gray appearance of platelets on Wright stained peripheral blood smear. The disease is Monarch Disease Ontology term MONDO_0007686 (gray platelet syndrome). Also known as: Alpha storage pool deficiency, BDPLT4, GPS, platelet alpha-granule deficiency, platelet-type bleeding disorder 4.