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Hemoglobin (Hb) Ottawa [α15(A13)Gly>Arg], also known as Hb Siam, results from GGT>CGT mutation in codon 15 of either HBA1 or HBA2. Hb Ottawa carriers typically have normal hematology but when the variant is coinherited with either α or β thalassemia, microcytic red cell indices were observed. The percentage of variant detected using routine methodology was variable (14-33%), with a higher percentage found when co-inherited with an abnormal α-globin genotype. The case presented here involved an Indian male with microcytic red cell indices, who was heterozygous for Hb Ottawa (HBA2:c.46G>C) and β+ thalassemia (HBB:c.-138C>T). This case represents the first reported finding of Hb Ottawa in the Indian population, as well as the first time capillary zone electrophoresis (CZE) has been used to identify the variant. The abnormal red cell indices were attributed to co-inheritance of β+ thalassemia mutation (HBB:c.-138C>T), which alters binding of transcriptional factors to the HBB promoter and reduces transcription from the allele. The mild β+ thalassemia mutation has commonly been found in the Indian population.

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