EUROPEAN JOURNAL OF HUMAN GENETICS, vol.7, no.3, pp.345-356, 1999 (SCI-Expanded)
We have studied 31 beta-thalassaemia intermedia, 30 beta-thalassaemia major patients and 50 normal individuals from Turkey, determining the relationship between the nucleotide variations in beta-globin gene cluster, the altered levels of foetal haemoglobin and the relative ratios of beta- and gamma mRNAs, We have found in P-thalassaemia intermedia patients with high foetal haemoglobin expression that the three nucleotide variations in the 5' sequences of the gamma globin genes, A-->G at G gamma-1396, the T-->C at A gamma-228, and the GA-->AG at A gamma-603/4, are linked to haplotype II in haplotypic homozygotes and the (AT)(8)N-14(AT)(7) motif in beta LCR, Conversely, the three single nucleotide substitutions in the 5' sequences of gamma globin genes, the G-->A at G gamma-1225, the A-->G at A gamma + 25 and the C-->G at A gamma - 369, which have a strong linkage with haplotype I, V or VI in haplotypic homozygotes and the (AT)(10)N-12(AT)(12) and the (AT)(9)N-12(AT)(12) motifs in HS-2 of beta LCR are all associated with low foetal haemoglobin levels. The number of nucleotide changes in beta-globin gene cluster implied in our study are not the primary cause of the differences in haemoglobin F levels, They perhaps may contribute to the variations in the clinical severity observed among beta thalassaemia intermedia and major patients with other yet unknown gene conversions.