Sickle cell disease (SCD) is a hematologic disease in which a genetic alteration in the formation of hemoglobin (Hb) determines the formation of Hb S, instead of normal Hb A. When in homozygosis (Hb SS), the disease is called sickle cell anemia (SCA), with more evident signs and symptoms. The gene discussed is GSTM1; the disease is autosomal dominant cerebellar ataxia.