Elevated HbF associated with an unstable hemoglobin, hemoglobin Saint Etienne: Hb synthesis in blood BFUe in culture

The red blood cells of a patient heterozygous for the unstable Hb Saint Etienne (092 His → Gin) contained 19% of fetal hemoglobin (Hb). Study of his family suggested that the proband had inherited the Swiss type of hereditary persistence of fetal hemoglobin (HPHF) from his father who had 1.2% of HbF and 8% of F cells. In order to gain further insight into the mechanism of the elevated production of HbF in the proband, hemoglobin synthesis was studied in 14-day cultures of blood erythroid burst-forming units (BFUe). The culture of cells from the proband and from his father resulted in an average production of 30% HbF, while HbF synthesis in the mother's BFUe was only 12%. These findings suggest that individuals with the Swiss HPHF may have a proportion of circulating precursors that possesses a high potential for HbF synthesis in vitro as compared to normal controls. The elevated production in vivo of HbF in the proband can therefore be regarded as an expression of this high potential for HbF synthesis, which occurs under the influence of an increased erythropoietic stimulation induced by the unstable hemoglobin. Study of single erythroid bursts derived from the proband's blood cells showed a reciprocal relationship between synthesis of HbF and of Hb Saint Etienne, while the amount of HbA remained constant. This result suggests that the increased synthesis of HbF seen in the propositus is linked to one chromosome only, i.e., that which bears the Saint Etienne mutation.