In RBCs from patients with SCA, there is an aberrant response to O2 tension such that KCC activities are the highest and similar in fully oxygenated and fully deoxygenated RBCs while reaching at nadir at about the P50 for saturation of Hb with O2 (Gibson et al., 1998b). The gene discussed is GSTM1; the disease is autosomal dominant cerebellar ataxia.