Hemoglobin Hekinan [alpha (2)27(B8)Glu----Asp beta 2] detected in Guyana

Comprehensive Hematological and molecular Characterization of hemoglobin Hekinan [α27(B8)Glu→Asp(α1), HBA1:c.84G > T] in a Large Thai cohort

BACKGROUND

Hemoglobin (Hb) Hekinan is a prevalent α-globin variant frequently missed in thalassemia screening centers using high-performance liquid chromatography (HPLC) or capillary electrophoresis. This study aims to investigate the hematological and molecular characteristics of Hb Hekinan in a large cohort.

METHODS

Hb variants were identified using isoelectric focusing (IEF) and HPLC. Hb Hekinan was confirmed by direct DNA sequencing. Additional genetic determinants, including α-thalassemia, β-thalassemia and other variants, were detected using multiplex GAP-PCR, ARMS-PCR or direct DNA sequencing as appropriate.

RESULTS

Among 61,997 Hb typing samples, 149 cases of Hb Hekinan were identified in Thai individuals and classified into 8 genotypic groups. These included 104 Hb Hekinan heterozygotes, 10 Hb Hekinan coexisting with α+-thalassemia, 3 Hb Hekinan with non-deletional α-variants, 6 Hb Hekinan with α0-thalassemia, 21 double heterozygote for Hb Hekinan and HbE, 3 Hb Hekinan with β-thalassemia trait, 1 triple heterozygotes (Hb Hekinan/α0-thalassemia/Hb E) and 1 quadruple heterozygote for Hb Hekinan/α+-thalassemia/Hb E/Hb Hope. Hb Hekinan was well-separated from Hb A using IEF but was frequently missed with HPLC. On HPLC, Hb Hekinan could only be identified when coexisting with α0-thalassemia. All cases presented with either normal Hb levels or mild anemia.

CONCLUSIONS

Hb Hekinan is a prevalent α-globin variant that is often undetected by HPLC but reliably identified using IEF. These findings highlight the importance of incorporating IEF for accurate diagnosis of Hb Hekinan. Most cases are clinically benign, even when interacting with other thalassemia syndromes or Hb variants.

Interactions of electrophoretically silent hemoglobin Hekinan II [HBA1:c.84G>T] with various forms of α-thalassemias and other hemoglobinopathies: novel insights into the molecular and hematological characteristics and genetic origins

To determine the molecular basis, genotype - phenotype relationship, and genetic origin of Hemoglobin (Hb) Hekinan associated with several forms of α-thalassemia and other hemoglobinopathies for a better understanding of its diverse clinical phenotypes. Seventeen participants with suspected abnormal Hb were studied. Hb analysis was performed using high-performance liquid chromatography (HPLC) and capillary electrophoresis (CE). Mutational and α-haplotypic and structural analyses were conducted, and the effects of mutations on globin-chain stability were determined. All participants harbored Hb Hekinan II (HBA1:c.84 G>T) co-inherited with another α-globin gene anomaly. Three novel genotypes, (ααHekinan/αCSα), (ααHekinan/αCSα,βA/βE), and (ααHekinan/αCSα,βE/βE), were characterized. Despite being co-inherited with both α- and β-Hb variants Hb Hekinan II led to minimal changes in erythrocyte parameters, suggesting a non-pathological nature. HPLC but not CE revealed a distinct small shoulder-like Hb pattern. Thai Hb Hekinan II was strongly associated with haplotype [+ - S + - - -] and the possibility of four different haplotypes, while two Burmese Hb Hekinan II were associated with haplotypes [± - S + - + -] and [± - S + - - -]. The novel genotypes identified provide a fresh perspective on Hb Hekinan II diversity. HPLC has superior identification capabilities for samples of Hb Hekinan II co-inherited with α-thalassemia. Thai and Burmese Hb Hekinan II have diverse origins.

Mutations in the paralogous human alpha-globin genes yielding identical hemoglobin variants

The human alpha-globin genes are paralogues, sharing a high degree of DNA sequence similarity and producing an identical alpha-globin chain. Over half of the alpha-globin structural variants reported to date are only characterized at the amino acid level. It is likely that a fraction of these variants, with phenotypes differing from one observation to another, may be due to the same mutation but on a different alpha-globin gene. There have been very few previous examples of hemoglobin variants that can be found at both HBA1 and HBA2 genes. Here, we report the results of a systematic multicenter study in a large multiethnic population to identify such variants and to analyze their differences from a functional and evolutionary perspective. We identified 14 different Hb variants resulting from identical mutations on either one of the two human alpha-globin paralogue genes. We also showed that the average percentage of hemoglobin variants due to a HBA2 gene mutation (alpha2) is higher than the percentage of hemoglobin variants due to the same HBA1 gene mutation (alpha1) and that the alpha2/alpha1 ratio varied between variants. These alpha-globin chain variants have most likely occurred via recurrent mutations, gene conversion events, or both. Based on these data, we propose a nomenclature for hemoglobin variants that fall into this category.

Two cases of compound heterozygosity for Hb Hekinan [alpha27(B8)Glu-->Asp (alpha1)] and alpha-thalassemia in Thailand

Two unrelated cases of compound heterozygosity for Hb Hekinan [alpha27(B8)Glu-->Asp (alpha1) and alpha-thalassemia have been found in Thailand. Mutations were established at protein level by peptide mapping and at the DNA level by direct sequence analysis. Proband S.S. had genotype - -SEA/alpha2(A)alpha1Hekinan, betaA/betaE, while an unrelated proband, S.J., is the first case described with the genotype - -SEA/alpha2(A)alpha1Hekinan, betaA/betaA. Both alpha1Hekinan mutations were located in the alpha1 locus. Hb Hekinan could not be accurately estimated by HPLC, since it was poorly separated from Hb A. However IEF gave good separation of Hb Hekinan and Hb A, leading to estimates of Hb Hekinan (alpha Hekinan 2/beta A 2 and alpha Hekinan 2/beta E 2) level as 40-43% of total Hb.

Laboratory diagnosis of a compound heterozygosity for Hb Hekinan [alpha27(B8) Glu-Asp] and a deletional alpha-thalassaemia 2 in Thailand

We report the haematological and molecular characterization of a previously undescribed condition of compound heterozygosity for haemoglobin (Hb) Hekinan [alpha27(B8) Glu-Asp] and a deletional alpha-thalassaemia 2 detected in a Thai individual. Hb analysis demonstrated that although this Hb variant co-migrates with Hb A on cellulose acetate electrophoresis and cation-exchange high-performance liquid chromatography (HPLC), the HPLC procedure using a weak cation-exchange material with polyaspartic acid could clearly differentiate the two Hb. The variant could then be confirmed using the polymerase chain reaction-restriction fragment-length polymorphism (PCR-RFLP) analysis of the amplified alpha1-globin gene.

Complex interaction of Hb Hekinan [alpha27(B8) Glu-Asp] and Hb E [beta26(B8) Glu-Lys] with a deletional alpha-thalassemia 1 in a Thai family

Hemoglobin (Hb) Hekinan (alpha27; Glu-Asp) is a rare alpha-chain variant found mainly in Japanese and Chinese whereas Hb E (beta26; Glu-Lys) is common among Southeast Asians. We report a hitherto undescribed condition in which these two variants co-segregate. The proband was a 25-yr-old Thai woman who was encountered with the presence of mild hypochromic microcytosis with Hb 8.2 g/dL, hematocrit (Hct) 26.0%, Mean Corpuscular Value (MCV) 68.6 fL, Mean Corpuscular Hemoglobin (MCH) 21.6 pg and Mean Corpuscular Hemoglobin Concentration (MCHC) 31.5 g/dL. Although Hb electrophoresis at alkaline pH did not show any abnormal band except Hb E in addition to Hb A, high performance liquid chromatography analysis revealed abnormal peaks at the Hb A and Hb E positions. DNA analysis of the proband revealed a GAG-GAT mutation at codon 27 of the minor alpha1-globin gene for Hb Hekinan in trans to the South-east Asian (SEA) deletional alpha-thalassemia 1 determinant and a GAG-AAG mutation at codon 26 of the beta-globin gene for Hb E. She was therefore a triple heterozygote for these three anomalies. Family study identified that her mother was a double heterozygote for Hb Hekinan and Hb E without alpha-thalassemia whereas her father was a classical Hb H disease patient. The genotype-phenotype relationship observed in this Thai family with complex hemoglobinopathies is presented and a simple DNA assay based on the polymerase chain reaction methodology for rapid diagnosis of Hb Hekinan is described.

Hb Hekinan observed in three Chinese from Macau; identification of the GAG----GAT mutation in the alpha 1-globin gene

Hb Hekinan, an alpha chain variant that is characterized by a Glu----Asp mutation at position alpha 27, was observed in three Chinese females attending a prenatal clinic in Macau. The relative quantities of the stable hemoglobin were 13-14% (average 13.3%); its identification was greatly aided by the separation and purification of the peptides by reversed phase high performance liquid chromatography. Dot-blot analysis of amplified DNA with 32P-labeled probes located the mutation in codon 27 of the minor alpha 1-globin gene; the change involved a GAG (coding for glutamic acid) to GAT (coding for aspartic acid) mutation.