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.