The deletion in a type of δ0-β0-thalassaemia begins in an inverted AluI repeat

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Abstract
In hereditary persistence of fetal haemoglobin (HPFH) and delta 0-beta 0-thalassaemia, increased levels of fetal haemoglobin (HbF) are found in adult individuals. HbF production is particularly noticeable in the former condition in which HbF levels of 20-40% are found in heterozygous patients, as opposed to 5-20% in delta 0-beta 0-thalassaemia. In a minority of these cases, no obvious abnormalities have been found in the globin gene region by DNA mapping, indicating that small deletions or perhaps even point mutations in critical DNA sequences in the globin gene cluster may be responsible for these conditions. However, most cases of HPFH and delta 0-beta 0-thalassaemia are associated with extensive deletions in the globin gene cluster. Genetic data and gene mapping investigations provided some evidence for the location of a regulatory area, whose deletion results in continuing activity of gamma-globin genes in adults, in a DNA region between the A gamma- and delta-globin genes, possibly 3-4 kilobases (kb) 5' to the delta gene. The precise nature of these sequences is of great interest, because it might help elucidate the molecular mechanisms regulating globin gene expression during development. Recently, Jagadeeswaran et al. cloned the DNA encompassing the region of a gene deletion in a type of HPFH and showed that the 5' end point of the deletion lies in the middle of an AluI repetitive DNA sequence. We have now cloned the corresponding region from the DNA of a delta 0 -beta 0-thalassaemia patient and we report here that the deletion ends in a different AluI sequence, congruent to 700 nucleotides 3' to the AluI repeat involved in the HPFH deletion, and in the opposite orientation.