The direct sequencing of the α2-globin gene in an individual carrying the common Mediterranean deletion (αα/--MED) revealed a +14 C→G DNA polymorphism; first described in the Hellenic population. The phenotype was typical for heterozygous α0-Thalassemia.

Tha α2-globin gene of this subject was specifically amplified by PCR in which one of the two primers was biotinylated at the 5′ end, the amplified meterial was subsequently mixed with magnetic beads coated with streptavidin (Dynabeads M280-Streptavidin, Dynal). Single-stranded templates were then available for the sequencing reactions. The one base substitution was confirmed by hybridization of the amplified α2-globin gene with radiolabeled allele specific oligonucleotides (PCR-ASO).

The C→G substitution occurs at a position 14 bp downsteam from the cap site of α2 globin mRNA; in the 5′ untranslated region. It was first detected by denaturing gradient gel electrophoresis (DGGE) during a screening program for non deletional α-Thalassemias in the Dutch population(K.L.Harteveld, 1996).

In order to assess the frequency of this allele in the Hellenic population we collected blood samples from 111 random selected, unrelated individuals, originating from several different geographic regions.

Genomic DNA of all samples was prepared from white blood cells and examined for the presence of the +14 C--G substitution by PCR-ASO hybridization. The population sample was also tested for the presence of Thalassemia. Haematologic examinations and haemoglobin analysis were performed according to standard methods, while the molecular studies included a standardized PCR strategy for the detection of the common severe [--MED, -(α)20.5] and mild (-α3.7) α-Thalassemia deletions and PCR-ASO hybridizations specific for four non deletional types of α-Thalassemia.

The results showed that 68 individuals were normal (non thalassemic), 21 were β- or δβ- Thalassemia carriers, 12 remained undiagnosed(possible iron-deficiency anaemia) and 10 were α-Thalassemia heterozygotes. From the 222 chromosomes examined, 7 carried deletions of the α-globin gene cluster (5 the -α3.7/ and 2 the --MED/) and 3 carried the IVS-1 splice donor site 5 bp deletion.From the non deletional 215 chromosomes, 24 had the C→G single base change (11.2%). The frequency of the polymorphism in the 68 normal individuals was quite the same (10.3%).

In conclusion, because of the small sample size these results can be taken only as indications for the frequency of this polymorphism in the Hellenic population. A larger sample is needed to estimate the real value of this frequency.