Sickle-cell disease (SCD) is a group of inherited blood disorders in which a mutation in the β-globin (HBB) gene causes red blood cells to produce abnormal hemoglobin, known as Hb S. SCD is characterized by an autosomal-recessive pattern of inheritance, implying that for a child to manifest the condition, they must inherit an Hb S allele from both parents (HbSS) or one Hb S allele and another β-globin variant, such as Hb C or β-thalassemia (HbSC, HbS/β-thal). The gene discussed is GSTM1; the disease is Schnyder corneal dystrophy.