GSTM1 and autosomal dominant cerebellar ataxia: Sickle cell disease (SCD), also known as sickle cell anemia (SCA) is one of the structural hemoglobinopathies that occurs due to a single nucleotide mutation from GAG to GTG, which changes the amino acid of a Beta-globin chain of Hb from glutamate (hydrophilic) to valine (hydrophobic).