Decreased Hb A2 level at less than 1.8−2.0% has been used to screen δ-hemoglobinopathies in subjects with normal Hb type of A2A (Mosca et al., 2009; Singha, Fucharoen & Fucharoen, 2021; Morgado et al., 2007). The gene discussed is GSTM1; the disease is hemoglobinopathy.