KLF1 and thalassemia: Results from these studies collectively reveal that the causes of borderline HbA2 levels may include heterozygosity for β-thalassemia, presence of KLF1 gene mutations, α thalassemia, co-inheritance of β and δ thalassemia, co-inheritance of β and α thalassemia, α globin gene triplication or the presence of hereditary persistence of fetal hemoglobin.