The proband II1 (Fig. 1A), a young boy, presented with moderate anemia (Hb 78 g/L) and was preliminarily diagnosed with β-thalassemia intermedia based on blood testing, which confirmed microcytic (MCV 64.3 fL, RI: 80–100 fL) and hypochromic characteristics (MCH 20.2 pg, RI: 27–34 pg), elevated Hb A2 level (5.2%, RI: 2.5–3.5%) and Hb F level (8.3%, RI: 0–2%). The gene discussed is GSTM1; the disease is anemia (phenotype).