Quantitation of three types of gamma chain of HbF by high pressure liquid chromatography; application of this method to the HbF of patients with sickle cell anemia or the S-HPFH condition

A modification of a high pressure liquid chromatographic (HPLC) procedure is described that enables the complete separation and quantitation of the A gamma T, A gamma I, and G gamma chains in human fetal hemoglobin. The method, which is fast and accurate, requires 5 to 2000 micrograms Hb F. The purity of the Hb F is not essential and admixture of up to 70% adult Hb does not interfere with the determination. The method has been applied to the Hb F of 64 Black SS patients and 7 persons with the Hb S-HPFH (G gamma A gamma type) conditions. (A) Both "adult" G gamma to A gamma (2:3) and "newborn" G gamma to A gamma (3:2) ratios were observed in adult SS patients, 8 yr and older. Only 12% of the SS patients had the "newborn" ratio. This high G gamma to A gamma ratio may be due to a modification of the genetic switch mechanism that regulates the change of this ratio after birth. (B) Intermediate G gamma to A gamma ratios were only found in young SS patients, 5 yr of age or less. The results suggest a delayed switch of the newborn leads to adult ratio in sickle cell anemia. (C) The A gamma T chain was present in only 6% of all SS patients. One patient is homozygous for this variant chain. (D) Three of the 7 subjects with Hb S-HPFH were positive for the A gamma T chain. Its percentage was low, which suggests that the A gamma T chain gene is in trans of the HPFH determinant. (E) Quantitation of the three gamma chain types is also possible in the Hb F from Hb S heterozygotes with (nearly) normal Hb F levels. Such an analysis is useful for an evaluation of genetic conditions involving variations in the production of (different types of) Hb F.