HBA1 and Alpha-thalassemia: Second is theco-inheritance of alpha globin locus defect, either an alpha-thalassemia deletion(α-thal) which is often observed in β-thal patients, resulting as a positivemodifier or, conversely, the presence of additional copies of HBA2or HBA1 genes which causes a more severe form of β-thal (Ben-Salah et al., 2017; Theodoridou et al., 2018;Clark et al., 2018; Harteveld et al., 2008).