Haemoglobin (Hb) G-Philadelphia, Hb Stanleyville-II, Hb G-Norfolk, Hb Matsue-Oki and Hb Mizushi can form a panel of α-chain variants that overlap in their phenotype: the novel use of StyI to screen for Hb G-Philadelphia

Molecular understanding of unusual HbE-β+-thalassemia with Hb phenotype similar to HbE heterozygote: simple and rapid differentiation using HbE levels

BACKGROUND

Low HbF expression in HbE-β+-thalassemia may lead to misdiagnosis of HbE heterozygosity. We aimed to characterize the β- and α-globin genes and the modifying factors related to HbF expression in patients with an Hb phenotype similar to that of HbE heterozygotes. Furthermore, screening tools for differentiating HbE-β+-thalassemia from HbE heterozygotes have been investigated.

PARTICIPANTS AND METHODS

A total of 2133 participants with HbE and HbA with varying HbF levels were recruited. Polymerase chain reaction-based DNA analysis and sequencing were performed to characterize β- and α-globin genes. DNA polymorphism at position -158 nt 5' to Gγ-globin was performed by XmnI restriction digestion. Receiver operating characteristic (ROC) curves were constructed using the area under the curve (AUC). Cutoff values of HbA2, HbE, and HbF levels for the differentiation of HbE-β+-thalassemia from HbE heterozygotes were determined.

RESULTS

Five β+-thalassemia mutations trans to βE-gene (β-87(C>A), β-31(A>G), β-28(A>G), β19(A>G), and β126(T>G)) were identified in 79 patients. Among these, 54 presented with low HbF levels, and 25 presented with high HbF levels. ROC curve analysis revealed an excellent AUC of 1.000 (95% confidence interval:1.000-1.000) for HbE levels, and a cut-off point of ≥35.0% had 100.0% sensitivity, specificity, and Youden's index for differentiating HbE-β+-thalassemia from HbE heterozygotes. The proportion of α-thalassemia mutations was 46.3 and 8.0% among HbE-β+-thalassemia patients with low and high HbF levels, respectively. Two rare α-thalassemia mutations (Cap +14(C>G) and initiation codon (ATG>-TG)) of α2-globin genes were identified. The genotype and allele of the polymorphism at -158 nt 5' to Gγ-globin was found to be negatively associated with HbF expression.

CONCLUSIONS

HbE-β+-thalassemia cannot be disregarded until appropriate DNA analysis is performed, and the detection of α-thalassemia mutations should always be performed under these conditions. An HbE level ≥35.0% may indicate screening of samples for DNA analysis for HbE-β+-thalassemia diagnosis.

Eleven Cases of Hb J-Paris-I [HBA2: c.38C>A (or HBA1)]: A Stable α Chain Variant Elutes in the P3 Window on High-Performance Liquid Chromatography

Hb J-Paris-I [HBA2: c.38C>A (or HBA1)] is a stable fast-moving hemoglobin (Hb) that elutes in the P3 window on high performance liquid chromatography (HPLC). The mutation can happen on either the α1- or α2-globin gene. Codon 12 changes from GCC to GAC to replace the alanine amino acid with aspartic acid. This change is external with no clinical significance. The elution in the P3 wave on HPLC can interfere with the glycated Hb assay by HPLC. In this study, data of 11 cases of Hb J-Paris-I were thoroughly presented. The majority of the cases were of Indian ethnicity. The mean value of Hb J-Paris-I on HPLC was 26.7 ± 2.0%. The retention time (RT) was 1.75 ± 0.03 min. The isoelectric focusing (IEF) mean value was -5.6 (range -6.1 to -4.9). Hb A₂ was consistently reduced to 1.8 ± 0.3%. A fraction of 0.8% corresponding to the Hb A₂-J-Paris-I (α₂^J-Paris-Iδ₂) is likely to be concealed within the A₀ peak of Hb A on HPLC. Interestingly, two cases were associated with two different polymorphisms [HBA2: c.-24C>G or Cap +14 (C>G) and HBA2: c.*136A>G polymorphism] without apparent effect on the variant expression.

Eight Cases of Hb Winnipeg [HBA2: c.226G>T (or HBA1)]: A Detailed Study

Hb Winnipeg [α75(EF4)Asp→Tyr (α2); HBA2: c.226G>T (or HBA1)] is a stable α-globin chain variant described in a few articles. The majority of reported cases in older articles were clustered in Canada. It can occur on both α1- and α2-globin genes and in different populations. In this study, eight cases of Hb Winnipeg were characterized by DNA sequencing during a wide-spectrum study of suspected α-globin gene variants collected in the United Kingdom. All cases detected peaked in the S window between 4.4 and 4.54 min. on high performance liquid chromatography (HPLC). The isoelectric focusing (IEF) averaged at 6.21 below Hb A. All the mutations were detected on the α1-globin gene except in one case. The ethnic origin of the majority of the patients was Canadian. Only one case was associated with the common polymorphism HBA2: c.-24C>G (or HBA1) [Cap +14 (C>G)] on both α-globin genes without any apparent effect on the variant expression. All cases were detected in a heterozygous state. Hb Winnipeg expression was consistently lower than the theoretical value for α chain variants, ranging between 11.8 and 15.8% of total hemoglobin (Hb). This study gave more details about Hb Winnipeg that may help in presumptive diagnosis, especially in routine laboratories.

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

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.

Fifteen Cases of Hb J-Meerut: The Rare Association with Hb E and/or HBA1: c.-24C>G (or HBA2) Variants

Hb J-Meerut [HBA2: c.362C>A (or HBA1)] is a rare, stable, nonpathogenic α-globin gene variant that peaks in the area between the P3 and A₀ windows on high performance liquid chromatography (HPLC). Few cases from different ethnic origins have been published but the majority were Asian Indians. Coinheritance with other hemoglobin (Hb) variants are rarer and can change the Hb J-Meerut phenotype making a diagnostic dilemma. In this study, we have reported 15 cases of Hb J-Meerut, discovered during a wide spectrum study of α-globin chain variants in the UK. The diagnosis was confirmed by forward and reverse DNA sequencing of the α1- and α2-globin genes. The average of the Hb J-Meerut expression was 20.9% of total Hb and characterized by a retention time (RT) of 1.9 min. (on average) on HPLC. The median of isoelectric focusing (IEF) was 5.6 mm above Hb A. Among the 15 cases studied, one case coinherited the Hb E (HBB: c.79G>A) mutation in heterozygosity and another case was associated with the Cap +14 (C>G) [HBA1: c.-24C>G (or HBA2)] variant. We noticed that the coinheritance of the Hb E mutation reduced the Hb J-Meerut expression with the formation of a hybrid peak missed on the HPLC chromatograph. We also noticed an increased expression of Hb J-Meerut in the case showing the coinheritance of the HBA2: c.-24C>G (or HBA1) variant.

A Wide Spectrum Study of α-Globin Chain Variants: Cases from the UK

Over many years, cases of suspected α-globin chain variants were collected from different parts of the UK. The suspicion was based on the clinical picture, high performance liquid chromatography (HPLC) variant percentage, retention time (RT) and isoelectric focusing (IEF). DNA sequencing and the restriction enzyme EaeI were used for definitive diagnosis. One hundred and forty-eight variants were confirmed on one or both of the two α-globin genes (HBA2, HBA1). These cases were identified as 46 different α-globin chain variants. The most common variants were Hb J-Meerut [HBA2: c.362C>A (or HBA1)] (10.1%) and Hb Q-India (HBA1: c.193G>C) (8.1%), followed by Hb J-Paris-I [HBA2: c.38C>A (or HBA1)] and Hb Manitoba II (HBA1: c.309C>A) (7.4% for each). Other α variants were detected at lower frequencies. Two novel alleles were also detected: Hb Walsgrave [α116(GH4)Glu→Val (HBA2: c.350A>T)] and Hb Coombe Park [α127(H10)Lys→Glu (HBA2: c.382A>G)]. The majority of the ethnic origin was Indian. The positive predictive value for α variant identification by HPLC-RT analysis was 65.9%, 41.9% by IEF, and using both RT and IEF, the value was 72.1%. The number of variants was higher in HBA1 than in HBA2 genes and in exons 1 and 2 than in exon 3. There was no clustering of mutations in consecutive codons. This study, the characterization of a wide spectrum of α-globin chain variants, can facilitate the presumptive diagnosis of these variants prior to screening by a panel of amplification refractory mutation system-polymerase chain reaction (ARMS-PCR), and a definitive diagnosis by DNA sequencing.

β-Globin Gene Sequencing of Hemoglobin Austin Revises the Historically Reported Electrophoretic Migration Pattern

Context.—Hemoglobin (Hb) Austin was defined in 1977, using amino acid sequencing of samples from 3 unrelated Mexican-Americans, as a substitution of serine for arginine at position 40 of the β-globin chain (Arg40Ser). Its electrophoretic migration on both cellulose acetate (pH 8.4) and citrate agar (pH 6.2) was reported between Hb F and Hb A, and this description persists in reference literature.

Objectives.—To review the clinical features and redefine the diagnostic characteristics of Hb Austin.

Design.—Eight samples from 6 unrelated individuals and 2 siblings, all with Hispanic surnames, were submitted for abnormal Hb identification between June 2010 and September 2011. High-performance liquid chromatography, isoelectric focusing (IEF), citrate agar electrophoresis, and bidirectional DNA sequencing of the entire β-globin gene were performed.

Results.—DNA sequencing confirmed all 8 individuals to be heterozygous for Hb Austin (Arg40Ser). Retention time on high-performance liquid chromatography and migration on citrate agar electrophoresis were consistent with that identification. Migration on IEF, however, was not between Hb F and Hb A, as predicted from the report of cellulose acetate electrophoresis. By IEF, Hb Austin migrated anodal to (“faster than”) Hb A.

Conclusions.—Hemoglobin Austin (Arg40Ser) appears on IEF as a “fast,” anodally migrating, Hb variant, just as would be expected from its amino acid substitution. The cited historic report is, at best, not applicable to IEF and is probably erroneous. Our observation of 8 cases in 16 months suggests that this variant may be relatively common in some Hispanic populations, making its recognition important. Furthermore, gene sequencing is proving itself a powerful and reliable tool for definitive identification of Hb variants.