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Abstract
We studied 325 thalassemia intermedia patients from Iran, India, Pakistan, Thailand, Mauritius and Cyprus to examine factors which influence the phenotype. The β-thalassemia (thal) mutations were determined for 219 β-thal/β-thal and 106 β-thal/Hb E [β26(B8)Glu→Lys, GAG→AAG] thalassemia intermedia patients. Thirty-one different mutations were identified, and their combination gave rise to more than 44 different genotypes, of which 14 (31.8%) had the β0/β0, 21 (47.7%) the β0/β+ and nine (20.5%) the β+/β+ types. Thus, the β+-thal mutations were present in 68.2% of patients.
α-Thalassemia mutations were present in frequencies higher than in the general population of all ethnic groups studied, as 45% of the patients carried α-thal mutations. Correlation of α-thal mutations with β-globin mutations showed that the α-thal mutations were mainly co-inherited with the β+-thal mutations.
The XmnI Gγ polymorphic site at −158 (C→T) was positive (T) in nine (8.8%) of 102 patients of the β+/β+ genotype, and the percentage of both XmnI Gγ polymorphism [+/−] (T/C) and [+/+] (T/T) genotypes increased to 42.9 and 87.3, respectively, in the β0/β+ and β0/β0 patients. This polymorphism was found in the majority of β+-thal/Hb E compound heterozygote patients (88.6%), and β0-thal/Hb E patients (84.8%), suggesting that it could be linked to the Hb E chromosome. Therefore, the XmnI Gγ polymorphism at −158 (C→T) was associated with β0-thal mutations as well as the Hb E chromosome.
The present study demonstrates that in cases of thalassemia intermedia with β+ mutations, the common ameliorating factor is the presence of α-thal mutations, while in cases with β0 mutations, the common ameliorating factor is the presence of the XmnI Gγ polymorphism at −158 (C→T).