Despite sharing the same deleterious genetic mutation in the HBB beta globin gene, persons with homozygous HbSS (sickle cell anemia, SCA) have marked variability in their laboratory profiles and clinical disease expression.[1] Understanding the phenotypic variability of SCA is a desirable goal, since the identification of children with increased likelihood of severe disease manifestations could prompt early intervention with targeted and preventive therapy. The gene discussed is HBB; the disease is autosomal dominant cerebellar ataxia.