Abnormal processing of β-Malay globin RNA

Hemoglobin Malay (α₂β₂19Asn→Ser) has been observed in a few Malaysian patients with thalassemia intermedia. The β^Malay substitution increases the homology of the cryptic splice site at codons 17/18/19 of the β-globin gene to the donor consensus splice sequence, suggesting that the β-thalassemia associated with this mutation may be due to the generation of a new splice site. To test this hypothesis, we constructed a hybrid gene where we replaced part of a normal β-globin gene with a PCR amplified region of the β^Malay gene. The expression of this mutant gene was studied in a heterologous transient expression system. The data show that nearly 25% of globin mRNA produced by this gene is abnormally spliced at the new splice site, providing a molecular mechanism for the β-thalassemia associated with the mutation.