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Haemoglobinopathies including β-thalassemia and sickle cell anaemia (SCA) are considered to be classical monogenic diseases. There is considerable clinical variability between patients inheriting identical β-globin mutations. The reasons for this variability are not well understood. Previous studies have suggested that a variety of genetic determents influence different clinical phenotypes. The genetic variants that modulate HbF levels have a very strong impact on ameliorating the clinical phenotype. In the present study 6,500 blood samples from suspected cases were analysed using HPLC, ARMS-PCR, RDB techniques. Patients with β-thalassemia and SCA were classified into mild, moderate, severe according to the severity score based on Hb levels, age of onset, age at which patients received their first blood transfusion, the degree of growth retardation and splenectomy. Patients with β-thalassemia and SCA were analysed for Xmn1 polymorphism and association between this polymorphism and severity of β-thalassemia and SCA was evaluated. We found a significant difference in genotypic and allelic frequencies of Xmn1 polymorphism between mild and moderate and mild and severe cases. There was a significant difference in high and low percentage of HbF in CC, CT and TT bearing individuals. The TT bearing individuals were found to have a high percentage of HbF in β-thalassemia as well as SCA. This study confirms that increased γG-globin expression associated with Xmn1 polymorphism ameliorates the clinical severity in β-thalassemia as well as SCA in the study population.

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