GSTM1 and acute chest syndrome: In addition, five studies practiced HU therapy in accordance with recommendation 6 (usage of HU in SCA patients who have a history of stroke) [29, 30, 34, 35, 57], and two studies [29, 42] in accordance with recommendation 7 (usage of HU in adult Hb S-β+ thalassaemia patients who experience ≥ 3 pain crises in 12-month period or having a history of ACS).