Search

Hemoglobin Grange-Blanche [beta 27(B9) Ala----Val] is a new variant found in a Portuguese family. The carriers present moderate erythrocytosis. Upon isoelectric focusing, Hb Grange-Blanche was slightly more cathodic than Hb A. beta Grange-Blanche chain migrated like the G gamma chain when submitted to electrophoresis in the presence of urea-Triton X-100. The precentage of Hb Grange-Blanche was about 50% in the heterozygous state. Oxygen affinity was increased (P50 = 22 mmHg), but heme-heme interaction was normal. An abnormal tryptic peptide (beta T3) was isolated using HPLC. Its composition allowed us to deduce unambiguously the amino acid change. The latter is the third mutation found in position 27 of the beta-chain. Because of its normal expression and its elevated affinity for oxygen, Hb Grange-Blanche contrasts with Hb Knossos [beta 27(B9) Ala----Ser], a beta-thalassemic variant with low affinity.

We have previously described the first homozygous cases of Hb Knossos in an Algerian family. The Hb A2 was completely absent, ascertaining the presence of a δ°-thalassemia determinant in cis of the βKnossoss gene. Here, we investigate the affected δ-globin gene. The complete DNA sequence of the gene and its 5′ and 3′ flanking regions was determined. Only two nucleotide changes were recorded: a C → T substitution at −199 and an AT insertion at −448 upstream from the cap site. To examine the involvement of these changes in gene function, the δ-gene was subcloned in an expression vector and introduced into COS cells. Analysis of RNA derived from these cells, using an S1 protection assay and dot-blot hybridization, revealed qualitatively and quantitatively normal transcription. The loss of δ-globin gene activity in vivo may be due to the alteration of a tissue-specific control.