Fetal hemoglobin expression in the compound heterozygous state for nondeletional HPFH and beta-thalassemia

Nondeletional Hereditary Persistence of Fetal Hemoglobin (ndHPFH) are benign conditions due to heterogeneous point mutations occurring at either the A-gamma or G-gamma gene promoters and are characterized by high HbF levels in adult life. Increased HbF levels in compound heterozygotes for HPFH and for beta-thalassemia have been attributed to overexpression of gamma-globin genes in cis both o HPFH and on beta-thal determinant.
The beta-globin gene cluster HpII carries the HbF A-gamma-T variant which is linked to -4bp deletion at
-225 to -222 to A-gamma promoter. The -4bp del is in turn associated with decreased A-gamma-T expression. Therefore the -4bp represents an useful marker in studying gamma-globin expression.