Abstract
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.
Highlights
Contributions: BMP, conception, design, drafting and final approval of manuscript; analysis and interpretation of hematology data and CZE results; provided Figure 1 and Table 1
N mutation has commonly been found in the microcytic red cell indices have previously been described in two cases due to co-inheritance with α-thalassemia-16 and β0 thalassemia.[8]
This paper describes a case of double heterozygosity for Hb Ottawa (HBA2:c.46G>C) and β+ thalassemia (HBB:c.-138C>T) in a 47-year-old Indian male detected using CZE
Summary
A hemoglobinopathy/thalassemia screen was requested for the subject of this investigation after he was noted to have thalassemic carrier red blood cell indices. His full blood count, analyzed on an electronic Sysmex XN900 Two aberrant peaks were identified on the chromatogram; a major peak eluting in zone S (x-axis 214) constituting 26%, and a minor peak eluting in zone 1 (x-axis 276) constituting 1.4% (Figure 1). The association of the major peak with a corresponding slow HbA2 peak (minor peak) suggested the presence of a variant α-globin species. The presence of an α-globin variant meant the peak representing HbA2 (4.3%) and variant HbA2 (1.4%) should be added together to reflect the total HbA2 level of 5.7%.14
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