Twelve Cases of Hb Manitoba [α102(G9)Ser→Arg]: the Fluctuation in the Variant Expression

Abstract

Hb Manitoba [α102(G9)Ser→Arg] is a rare α chain variant with diverse ethnic origins. It is mildly unstable with an expression of around 10.0–14.2% in the heterozygous state in most literature. In this study, 12 cases of Hb Manitoba [11 cases carried Hb Manitoba II (HBA1: c.309C>A) and one case carried Hb Manitoba IV (HBA1: c.307A>C)] were detected during a wide-spectrum study of α chain variants in the UK. Fluctuation in variant expression from 6.9 to 15.2% of total Hb on high performance liquid chromatography (HPLC) would pose a diagnostic dilemma in routine laboratories. Focusing on the variant expression, the median of Hb Manitoba was around 11.5% of total Hb in three cases, apparently with normal hemoglobin (Hb), and normal red blood cell (RBC) indices. Two cases showed a higher expression (13.9 and 15.2%) and five cases showed a lower expression (6.9–9.9%). The common α-thalassemia (α-thal) –α^3.7 (rightward) deletion coexisted with one case of increased Hb Manitoba expression. Iron (or other nutrient) deficiency was likely the cause of decreased Hb Manitoba percentage in this study. The α73(EF2)Val→Val (α2) (HBA2: c.222G>T) polymorphism is published for the first time and coexisted with two cases. The Cap +14 (C>G) (HBA2: c.-24C>G) polymorphism coexisted with another case in a heterozygous state. In conclusion, the fluctuation in variant expression can cause a diagnostic dilemma, especially in routine laboratories. Screening for the common –α^3.7 deletion and iron deficiency is recommended when an α chain variant is suspected.

Keywords:

• α Variant
• HBA2: c.-24C>G
• HBA2: c.222G>T
• Hb Manitoba
• hemoglobin (Hb)

Disclosure statement

The authors report no conflicts of interest. The authors alone are responsible for the content and writing of this article. The views expressed in this publication are those of the authors and not necessarily those of the Department of Health.

Additional information

Funding

This study was supported by the European Commission grant for the project ‘eInfrastructure for Thalassemia Research Network,’ Coordination Action, ITHANET [RI-2004–026539], and also by the Oxford Partnership Comprehensive Biomedical Research Center with funding from the Department of Health’s National Institute of Health Biomedical Research Center’s funding scheme.