An interplay of alleviating mutations in the clinical phenotype of beta-thalassaemia intermedia.

Prediction of a beta-thalassaemia major phenotype from the beta-genotype is generally relatively straightforward. However, despite the ability to accurately define the beta-thalassaemia mutations, prediction of a beta-thalassaemia intermedia phenotype from the genotype sometimes remains problematic and this has important implications in genetic counselling and prenatal diagnosis. We report a 11-year-old Indian male child with a thalassaemia intermedia phenotype. beta-Globin gene analysis of the family showed that he was a compound heterozygote with the -88 (C-->T) beta+-mutation and the IVS1 nt 130 (G-->C) beta0-mutation. Both these mutations are rare among Indians. The propositus was also found to be heterozygous for the XmnI polymorphism and had a normal alpha-genotype. In this family interplay of two alleviating mutations (a milder promoter mutation along with a gene for raised HbF) might have synergistically compensated for lack of globin chains in the patient. Hence, the nature of the beta-genotype as well as the knowledge of the presence or absence of alleviating factors will help the clinician to decide whether early commencement of a regular transfusion regime is necessary.