Sickle cell disease (SCD) refers to haemoglobinopathies consisting of at least one haemoglobin (Hb) S allele expressed as homozygous (HbS/S, most common and fatal), heterozygous (HbS/C, which is less severe), two phenotypes of sickle beta (β) thalassemia (HbS/β+ thalassemia and HbS/βo_thalassemia) and other rare forms such as HbS/D, HbS/O and HbS/E (Serjeant & Vichinsky 2018). Here, GSTM1 is linked to Schnyder corneal dystrophy.