GSTM1 and thalassemia: Six of these variants (Hb Voreppe, Hb Quong Sze, Hb Sun Prarie, Hb Bibba, Hb Verona, Hb Attleboro) are unstable causing α-thalassemia phenotypes with two of them (Hb Utrecht and Hb Questembert) being very unstable and originating severe hemolytic anemia with an α-thalassemia like phenotype.