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The switch from fetal to adult globin gene expression occurs around birth when fetal hemoglobin (HbF) production gradually declines within a few months. Much effort is underway to clarify the molecular basis of this mechanism, since impaired hemoglobin switching leading to persistent expression of fetal globin genes in adults (HPFH) offers therapeutic potential for hemoglobinopathies (S.L. Thein. Br. J. Haematol2004; 124: 264–74). In order to identify and study regulatory factors putatively involved in ?-globin gene expression, we examined the reticulocyte mRNAs differently expressed in three siblings (one brother, 54 years-old and two sisters 35- and 37-years old, respectively). The eldest brother had been referred to Umberto I Hospital for evaluation of a severe condition of ß-thalassemia intermedia on chronic transfusion therapy since 1990. Both of his sisters resulted clinically affected by a milder form of thalassemia intermedia, non-transfusion dependent, showing Hb values around 8.4 g/dL, Hb A2 levels from 6.0 to 7.9% and HbF ranging from 14.5 to 27.6%, values higher than those resulted in their brother (5.9% Hb A2 and 7.2% HbF). Molecular analysis was performed on DNA extracted from peripheral leucocytes and revealed the same ß-globin gene cluster genotype for all these subjects who resulted homozygous for the ß+ IVSI-6 (C?T) mutation associated to haplotype VI chromosomes. Different levels of HbF were thus presumably responsible of different clinical phenotypes. To investigate the possible causes of the variations in ?-globin gene expression, extensive sequence analysis was performed on putative regulatory regions within the ß-globin gene cluster (Zhi-Hong Lu et al., Blood1996; 87: 1604–11). Results showed the same genetic background in all the siblings. It was thus supposed that genetic determinants external to the ß-globin gene cluster were responsible of the different ?-globin gene expression. To explore this hypothesis, the reticulocyte transcriptome was analyzed by a differential mRNA display approach. Reticulocytes were isolated from peripheral blood and total RNA extracted for all family members. Our study revealed several bands differentially displayed in the sample from the more severely affected sibling respect to his sisters. Selected bands were cloned in a pGEM T-vector (Promega, WI) and sequenced. Comparative sequence searches were performed using the BLAST algorithm. Preliminary data gave, for two of the clones originated from bands with increased expression in the brother, a complete homology (greater than 95%) with the cDNA sequence of a cold shock domain protein, displaying features of a repressor factor for several hematopoietic genes (Horwitz M. et al. JBC1994; 269: 14130–39; P. Coles et al. Nucleic Acids Res1996; 12: 2311–17).