GSTM1 and autosomal dominant cerebellar ataxia: Sickle cell anemia (SCA) is a hereditary hemoglobin (Hb) disorder associated with a very specific molecular lesion, which is the exchange of glutamic acid for valine in the sixth residue of the Hb beta chain, originating the S Hb. It is characterized by intermittent episodes of vascular occlusion and end-organ damage.