Normal Hb A2β-Thalassemia Trait: Frameshift Mutation (HBB: c.187_251dup) inCiswith the Hb A2’δ-Globin Gene Missense Mutation (HBD: c.49G>C)

Hb A2-Guangxi [δ79 (EF3) Asp→Asn, HBD: C.238G > A] and polyA + 70 (HBD: C.*200G > A): Two Novel δ-Globin Gene Mutations Identified in a Chinese Family

We report the molecular and hematological identifications of two novel δ-globin gene mutations found in Guangxi Zhuang Autonomous Region, China. Capillary electrophoresis of the proband showed 1.3% Hb A2, accompanied by a minor unknown peak (0.7%) within the Z1 zone. High-performance liquid chromatography also revealed the presence of 1.5% Hb A2 and a 0.6% unknown peak. Routine genetic testing (Gap-PCR and reverse dot-blot hybridization) for common α-thalassemia was performed, and no mutations were observed. Sanger sequencing identified a heterozygous mutation for GAC > AAC at codon 79 (HBD:c.238G > A) and G > A at polyA + 70 (HBD:c.*200G > A) of the δ-globin gene. This variant was named Hb A2-Guangxi [δ79 (EF3) Asp→Asn, HBD:c.238G > A] after the geographic origin of the proband.

A New δ-Globin Gene Variant: Hb A2-Yulin [δ46(CD5)Gly→Arg,HBD: C.139G > A]

We report a new δ-chain hemoglobin (Hb) variant observed in a 5-year-old female living in Yulin, Guangxi, China. Capillary electrophoresis revealed splitting of the Hb A2 peak into two fractions (Hb A2 and Hb A2 variant), and the Hb A2 variant was also detected by high-performance liquid chromatography. However, it could not be detected using matrix-assisted laser desorption lonization-time of flight mass spectrometry. CD41-42 (-TCTT) heterozygosity was observed on the HBB gene by PCR and reverse dot-blot hybridization. Sanger sequencing showed a new transition (G > A) at codon 46 of the HBD gene, resulting in glycine changing to arginine. Based on the patient's place of residence, the new variant was named Hb A2-Yulin [δ46(CD5)Gly→Arg,HBD:c.139G > A].

Phenotypic Expression of Known and Novel Hemoglobin A2-Variants, Hemoglobin A2-Mae Phrik [Delta 52(D3) Asp > Gly, HBD:c.158A > G], Associated with Hemoglobin E [Beta 26(B8) Glu > Lys, HBB:c.79G > A] in Thailand

The interactions of δ-globin variants with α- and β-thalassemia or other hemoglobinopathies cause complex thalassemic syndromes and potential diagnostic problems. Understanding the molecular basis and phenotypic expression is crucial. Four unrelated Thai subjects with second hemoglobin (Hb) A2 fractions were studied. A standard automated cell counter was used to acquire initial hematological data. Hb analysis was carried out by capillary electrophoresis (CE) and high-performance liquid chromatography (HPLC) assays. Globin gene mutations and haplotype were identified by appropriate DNA analysis. An allele-specific polymerase chain reaction method was developed to provide a simple molecular diagnostic test. Hb analysis revealed a Hb A2 variant in all cases. DNA analysis of the δ-globin gene identified the Hb A2-Melbourne [δ43(CD2)Glu > Lys] variant in combination with Hb E in three cases. Analysis of the remaining case identified a novel δ-Hb variant, namely Hb A2-Mae Phrik [δ52(D3)GAT > GGT; Asp > Gly], found in association with Hb E and α+-thalassemia, indicative of the as yet undescribed combination of triple heterozygosity of globin gene defects. An allele-specific PCR-based assay was successfully developed to identify this variant. The β-haplotype of the Hb A2 Mae-Phrik allele was strongly associated with haplotype [+ − − − − ± +]. This study advanced our understanding of the phenotypic expression of known and novel δ-Hb variants coinherited with other globin gene defects, routinely causing problems with diagnosis. Therefore, knowledge and recognition of this Hb variant and molecular assessments are crucial to improving diagnosis.

Known and new hemoglobin A2 variants in Thailand and implication for β-thalassemia screening

BACKGROUND

We reported molecular and hematological characteristics of δ-globin chain variants and addressed diagnostic consideration of complex hemoglobinopathies caused by their interactions with α- and β-thalassemias.

METHODS

Study was done on four unrelated Thai subjects with second Hb A2 fractions. Hb analysis was carried out using automated HPLC and capillary electrophoresis. Mutations were identified by DNA analysis. Novel diagnostic methods based on PCR-RFLP and allele specific PCR were developed.

RESULTS

Hb analysis revealed Hb A2 variant in all cases. DNA analysis of δ-globin gene identified the Hb A2-Melbourne [δ43(CD2)Glu→Lys] in combination with α(+)-thalassemia, α(0)-thalassemia and β(0)-thalassemia in the first three cases, respectively. Analysis of the remaining case identified a novel δ-Hb variant namely the Hb A2-Lampang [δ47(CD6)GAT→AAT; Asp→Asn] found in association with Hb E and α(+)-thalassemia. These mutations could be identified using PCR-RFLP and allele specific PCR assays developed.

CONCLUSIONS

It is necessary to recognize the Hb A2 variant and to combine the amounts of Hb A2 and Hb A2-variant for a total Hb A2 value to make better diagnostic of these complex syndromes. Co-inheritance of these multiple globin gene defects could lead to complex hemoglobinopathies requiring comprehensive Hb and molecular assessments.