The erythrocyte count cutoff for SMA was determined to be 2.4 × 1012/l in homozygous α+-thalassaemia, 2.2 × 1012/l in heterozygotes, and 2.0 × 1012/l in normal individuals (Figure 3), because of differences in MCH values among genotypes. This evidence concerns the gene SMN1 and thalassemia.