When the abnormal haemoglobin S appears in homozygous form (Hb SS), it is referred to as sickle cell anaemia, and it can also affect individuals in combination with other abnormal haemoglobins such as sickle cell haemoglobin C disease (Hb SC) and sickle cell β-thalassaemia (Hb Sβ-Thal) (Okpala 2004). This evidence concerns the gene GSTM1 and sickle cell disease.