Severe thalassaemia intermedia caused by interaction of homozygosity for alpha-globin gene triplication with heterozygosity for beta zero-thalassaemia.

A 3-year-old child was evaluated for beta-thalassaemia intermedia. Molecular characterization including beta-globin gene sequence analysis revealed heterozygosity for a single beta-thalassaemia mutation, IVSI nt1 (G-->A). In addition the patient was found to be homozygous for alpha-globin gene triplication (alpha alpha alpha anti3.7/alpha alpha alpah anti3.7). The propositus has a significantly more severe phenotype than has been previously reported with this combination of genetic defects. In contrast, four individuals heterozygous for both triplicated alpha and for beta thalassaemia had a phenotype of thalassaemia minor, and a fifth had very mild thalassaemia intermedia.