HBB and autosomal dominant cerebellar ataxia: Sickle cell anemia (SCA, MIM #603903) is an autosomal recessive disorder of hemoglobin structure caused by the common HBB pathogenic variant (NM_000518.5):c.20A>T, p.(Glu7Val) which causes polymerization of deoxyhemoglobin, resulting in chronic intravascular hemolysis and intercurrent vaso-occlusive episodes.