The co‐inheritance of alpha‐thalassaemia in SCA modifies red cell indices (Embury et al, 1984; Stevens et al, 1986; Kulozik et al, 1988) and red cell rheology (Serjeant et al, 1983), and, in some reports, increases total Hb (Embury et al, 1982). This evidence concerns the gene GSTM1 and autosomal dominant cerebellar ataxia.