Lina Oggiano

The term delta beta-thalassemia with normal HbF has been recently proposed to define heterogenous delta and beta globin gene molecular defects involving the same chromosome in cis. Here, we describe a Sardinian family in which three members showing microcytosis, border-line HbA2 levels and normal HbF proved to be heterozygotes for delta(+) 27 and beta(0) 39 point mutations in cis by allele specific oligonucleotide hybridization as well as by ECO 0 109 I endonuclease digestion and electrophoresis. As some of these beta-thalassemia carriers shows normal HbA2 levels, knowledge of the molecular basis of this novel delta beta-thalassemia silent phenotype would be useful in thalassemia screening and genetic counselling.

The -117(G-->A)A gamma hereditary persistence of fetal hemoglobin (Greek HPFH) and beta zero 39-thal mutations are rather frequent in Sardinia so that their interaction is to be expected. Characterization of eight compound heterozygotes for these defects indicated that HPFH was linked to haplotype VII and beta zero 39-thal to haplotype II. Haplotype II beta zero 39-thal chromosome carries the A gamma T gene which is a useful marker of gamma-gene expression. Since the Hb F level in these compound heterozygotes was significantly higher than in 46 -117 HPFH carriers, the A gamma I, A gamma T, and G gamma globin level was determined. A gamma T was underexpressed while G gamma was significantly increased, which suggest that in -117 A gamma HPFH/beta zero 39-thal healthy subjects the increase in Hb F production is determined only by the -117 mutated A gamma gene and the adjacent G gamma gene.

In this paper we report an unusual Sardinian family, in which the heterozygosity for beta zero 39-thalassaemia and for triple alpha-globin gene complex have been found in two members: the former showing a high HbA2 mild thalassaemia intermedia syndrome, the latter, her daughter, showing a normal HbA2 thalassaemia trait. Molecular analysis revealed the daughter to also be a carrier of a delta+27-thalassaemia point mutation, which in trans to the beta zero 39 defect invariably normalizes the HbA2 levels.