A nucleotide change at a splice junction in the human β-globin gene is associated with β ⁰-thalassemia

β ⁰-thalassemia is a heterogeneous group of disorders associated with absence of β-globin. In a survey of DNAs from patients with β ⁰-thalassemia of diverse ethnic origins, a change at the splice junction at the 5' end ot the large intervening sequence (IVS 2) of the human β-globin gene has been found in one patient of Italian and another two of Iranian ethnic origins. The enzyme Hph I recognizes a change at this site and generates a larger-than-normal fragment of DNA, which hybridizes specifically to a β-globin IVS 2 probe. No other changes in β-globin gene DNA structure or organization are detectable by extensive restriction endonuclease analysis. The enzyme HinfI which recognizes a sequence beginning three nucleotides from the 5' end of the IVS 2 splice junction, produces normal fragments and localizes the defect to a G-G-T sequence at the 5'-end IVS 2 splice junction. This sequence is known to be remarkably conserved in all globin genes from many species and in most other genes examined to date. Thus, in at least some β ⁰-thalassemia patients, the β ⁰-thalassemia defect is associated with a nucleotide change at a splice junction. These patients provide unique examples of naturally occurring defects in splice junctions of eukaryotic genes associated with absence of specific gene function.