Non-deletional mutations in patients with alpha (–α3.7 deletion) thalassaemia trait: accurate diagnosis and reproductive implications

Abstract

Background and Aim Alpha-thalassaemia is often caused by deletion of alpha (α) globin gene/s on chromosome 16p. Non-deletional mutations (α T ), detected on a globin gene sequencing, are uncommon. Rarely, these two types of mutations co-exist. The current PCR primers for α globin sequencing selectively amplify the α1 and α2 globin genes in patients without deletional α thalassaemia. A problem arises in patients with the –α 3.7 deletion, as the α1 primers also amplify the –α 3.7 fusion gene. It is important to establish if α T occurs on the α1 or –α 3.7 gene, as the latter results in an alpha 0 phenotype, and the reproductive risk of Hb Bart’s hydrops fetalis. We aimed to design new primers to localise non-deletional α mutation in patients with the –α 3.7 deletion. Method The Beacon Designer (Premier Biosoft International) was used to design novel α1 gene specific primers Fα1 (located 992bp prior to α1-globin ATG site) and Rα1 (701bp downstream to α1-globin stop codon). The –α 3.7 allele was also sequenced. Results and Discussion We were able to correctly localise the non-deletional mutation (α T ) in all nine cases investigated. In six, α T was localised to the a1 gene, whereas in three patients, α T was localised to the –α 3.7 fusion gene (αα/ –α 3.7T ). It is important to identify and localise these mutations as they can cause alpha 0 thalassaemia, with important reproductive implications.