Influence of Xmn 1(G)γ (HBG2 c.-211 C → T) Globin Gene Polymorphism on Phenotype of Thalassemia Patients of North India.

Beta (β) thalassemia is the most common single gene disorder in India. It has been reported that in patients with β-thalassemia in the presence of Xmn 1(G)γ polymorphic site the level of fetal hemoglobin (HbF) is increased thereby reducing the severity of disease. To determine the prevalence of Xmn 1(G)γ polymorphic site and its effect on the clinical phenotype and HbF level in 39 β-thalassemia major and 62 thalassemia intermedia patients, along with response to hydroxyurea therapy in thalassemia intermedia cases. Status of Xmn 1(G)γ polymorphism was determined by polymerase chain reaction-restricted fragment length polymorphism procedure. The HbF level was determined using high performance liquid chromatography. Genotypes and allele frequencies of the Xmn 1(G)γ polymorphism did not vary significantly between the various thalassemia groups. HbF levels were observed to be significantly increased and age at presentation was significantly greater in presence of Xmn 1(G)γ polymorphic site on both alleles as compared to its absence in thalassemia major but not in thalassemia intermedia cases. The response of hydroxyurea in thalassemia intermedia was found only in a few patients irrespective of their Xmn 1(G)γ status. Xmn 1(G)γ polymorphisms appear to significantly influence HbF levels and age at presentation in thalassemia major but not in thalassemia intermedia patients. Small numbers precluded a definitive correlation of the polymorphism with response to hydroxyurea therapy.