An approximately 300 bp deletion involving part of the 5' beta-globin gene region is observed in members of a Turkish family with beta-thalassemia.

Detailed gene mapping analyses of genomic DNA from two Turkish subjects with a beta-thalassemia trait demonstrated an approximately 300 bp deletion, which is located between the Rsa I restriction site 128 bp 5' to the Cap site and the Acc I restriction site 284 bp 3' to the same Cap site; it includes the 5' beta promoter region, the first exon, and (part of) the IVS-I. Heterozygotes for this and two other beta-thalassemia types, which are also caused by deletions involving 5' beta promoter sequences, appear to have higher hemoglobin (Hb) A2 levels, perhaps because the loss of this promoter results in an increased transcription of the delta globin gene, as delta and beta promoters may be influenced by the same enhancing sequences 3' to the beta globin gene.