Alpha-thalassemia resulting from deletion of regulatory sequences far upstream of the alpha-globin structural genes.

We describe an alpha-thalassemia determinant in which alpha-globin expression is silenced by a deletion located 27 kb 5' to the transcription start site of the alpha 2-globin gene. This alpha-thalassemic determinant, (alpha alpha)MM, is a member of a newly described group of thalassemic mutations resulting from deletion of locus-controlling sequences critical to globin gene expression.