Frontier Research

Hb A2-Kiriwong – A Novel Hb A2 Variant in a Southern Thai Individual

Walailak Frontier 12, February 2019

 

 

Hb A2-Kiriwong – A Novel Hb A2 Variant in a Southern Thai Individual

 

Compound Heterozygotes for Hb A2-Kiriwong and Homozygous a-Thalassemia 2

 

The thalassemias and hemoglobinopathies are a large group of genetic disorders that have  high prevalence in Thailand. Many of them are caused by mutations in α- and/or β-globin genes, δ- and γ-globin gene mutations are relatively rare. Mutations can occur on the δ-globin gene that affect the structure and/or the level of the δ-globin chains. Structural abnormalities of δ-globin chain will produce a second peak and usually visible Hb A2 fraction and can be detected by high performance liquid chromatography (HPLC) method or other Hb separation techniques. An individual with δ-globin gene defect normally demonstrates normal red blood cell morphology. Therefore, DNA analysis is required, because δ-globin gene defects can mask the diagnosis of β-thalassemia. Heterozygote β-thalassemia is usually characterized by low mean corpuscular volume (MCV) and high Hb A2 levels (> 3.5%). Compound heterozygotes for β-thalassemia and δ-globin gene mutation may have reduced MCV/MCH with normal Hb A2 levels. In this study, we report a novel δ-globin chain variant in a Southern Thai individual.

A total of 931 samples from Southern Thailand were collected for this study. Complete blood count (CBC) was conducted by automated hematology analyzer and hemoglobin typing was separated by automated high performance liquid chromatography (HPLC). The hematological data was as follows: Hb 12.6 g/dL, Hct 41.0%, MCV 69.5 fL, MCH 21.4 pg and RDW 13.1%. The blood smear showed hypochromic microcytic red blood cells. Hemoglobin analysis results showed Hb A 86.9%, Hb A2+A2-Kiriwong 2.4 % and Hb F 0.3 %. This sample was suspected as a d-globin variant. The mutation of the d-globin gene was subsequently characterized by DNA sequencing and confirmed by a polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP). DNA sequencing of the d-globin gene revealed a novel d-globin variant caused by a mutation at codon 77 [NM_000519.3(HBD):c.233A>G (p.His77Arg)]. In addition, homozygous α-thalassemia 2 (-α3.7/-α3.7) was observed in this case. In addition, DNA sequencing of the whole β-globin gene was performed and confirmed that this case had no β-thalassemia mutation. In summary, the red blood cell abnormality found in this case was likely the result from the homozygous α-thalassemia 2. Hb A2-Kiriwong is now available on HbVar: A database of Human Hemoglobin Variants and Thalassemias and which can be accessed via LINK

Sources:

  • Nuinoon M, Jeenduang N, Kesornsit A, Horpet D, Plyduang T. Hematological and Molecular Characterization of a Novel Hb A2 Variant with Homozygous a-Thalassemia-2 in a Southern Thai Individual. Hemoglobin 2017;41(3):213-5

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