Development of a High Resolution Melting Curve Analysis for the Detection of Hemoglobin δ-Chain Variants in Thailand and Identification of Hb A2-Walsgrave [codon 52 (GAT>CAT), Asp→His; HBD:c.157G>C] in a Pregnant Woman from Southern Thailand.

Background: Delta-chain (δ-chain) variants are a group of rare hemoglobin (Hb) variants resulting from mutations within the δ-globin gene. Although quantification of Hb A2 levels is a useful screening tool for the beta-thalassemia trait, the coinheritance of a δ-globin gene mutation can lead to misinterpretation of diagnostic results. Objective: To identify an unreported Hb A2 variant in Thailand and to develop a high resolution melting (HRM) curve assay for the four δ-globin chain variants found in the Thai population. Materials and Methods: Allele-specific polymerase chain reaction (ASPCR) was used to analyze a total of 18 DNA samples for Hb variants comprising 10 wild-type controls, 4 Hb A2-Melbourne, 1 Hb A2-Lampang, 2 Hb A2-Kiriwong, and an unknown variant via HRM assays. Results: The unreported Hb A2 variant in Thailand was found to be Hb A2-Walsgrave resulting from δ-globin gene mutation at codon 52 (GAT>CAT). This was also confirmed using ASPCR. In addition, we demonstrated that the HRM curve profile for Hb A2-Melbourne, Hb A2-Lampang, Hb A2-Walsgrave, and Hb A2-Kiriwong could be identified so as to distinguish the mutant alleles from one another and from wild-type alleles. Conclusion: This HRM assay detected both known and unknown mutations with simultaneous differentiation between heterozygous and homozygous alleles on a polymerase chain reaction fragment spanning four of the δ-globin variants found in Thailand. This assay may help to support the prevention and control of thalassemias and hemoglobinopathies in Thailand.

Clinical and molecular characterization of Hb Hofu in eastern India.

INTRODUCTION: Hb Hofu (HBB:c. 380T>A) is a rare inherited hemoglobin abnormality with few case reports in the world literature. METHODS: Screening for the sickle cell gene mutation and other hemoglobinopathies was carried out using the sickle slide test, Hb electrophoresis, and HPLC under an ongoing central government project. RESULTS: We detected twelve Hb Hofu heterozygotes and three sickle Hb Hofu compound heterozygotes. The heterozygotes were asymptomatic except for one individual who had chronic kidney disease and moderate anemia. Only one HbS-Hofu case was symptomatic and presented with intermittent attacks of painful crisis. In the carrier state, the Hb Hofu eluted as a hump at the beginning of the HbA(0) window. But in HbS-Hofu cases, Hb Hofu eluted as a single peak in the HbA(0) window, with the HbA(2) levels being >4% consistently. CONCLUSION: HbS-Hofu has a variable clinical presentation. The retention time of Hb Hofu on HPLC is very close to that of HbA(0) and often elutes in the A0 window. Thus, there is every possibility of the HbS-Hofu chromatogram to be misinterpreted as that of a sickle cell trait/transfused sickle cell-beta-thalassemia case. This is the first time where Hb Hofu has been detected by HPLC, which is the widely accepted screening technique for hemoglobinopathies around the world.

Comparison of fast protein liquid chromatography (FPLC) with HPLC, electrophoresis & microcolumn chromatography techniques for the diagnosis of beta-thalassaemia.

BACKGROUND & OBJECTIVE: beta-thalassaemia is a genetic disorder and an important health problem around the world. Quantitative haemoglobin A(2) (HbA(2)) levels are used for the diagnosis of beta-thalassaemia. The conventional methods are high performance liquid chromatography (HPLC), electrophoresis, and microcolumn chromatography techniques. We established a fast protein liquid chromatography (FPLC) method, to measure quantitatively of HbA(2) levels, and compared its efficacy with conventional methods. METHODS: The FPLC method, using a DEAE Sepharose, Hi Trap anion-exchange column chromatography technique was set up for HbA(2) measurement. In this study, 220 blood samples were screened for haemoglobin type by FPLC technique and also using HPLC, microcolumn chromatography and electrophoresis. RESULTS: The FPLC results were highly correlated (r = 0.985, P<0.001) with those of HPLC for quantification of HbA(2) as well as cellulose acetate electrophoresis (r = 0.977) and microcolumn chromatography (r = 0.980). The FPLC method showed 100 per cent sensitivity and specificity, positive and negative predictive value for beta-thalassaemia diagnosis. In addition, the FPLC method was simple, rapid, low cost and reproducible. The HbA(2)/E range of FPLC for beta-thalassaemia was 6-10 per cent, HbE trait was 10-40 per cent, beta-thalassaemia/HbE was 40-60 per cent and homozygous HbE was more than 60 per cent. INTERPRETATION & CONCLUSION: Our findings suggested that FPLC method could be used as a cost-effective method for routine beta-thalassaemia diagnosis.

Effect of HbS in the determination of HbA2 with the Menarini HA-8160 analyzer and comparison with other instruments.

It is known that the presence of hemoglobin S (HbS) affects the determination of hemoglobin A(2) (HbA(2)) levels in clinical samples. We quantitated this effect using the Menarini HA-8160 analyzer and compared with other instruments (HELENA beta-thal quik column, TOSOH HLC-723G7 and BIORAD Variant II) using the HELENA SAS-MX alkaline gel electrophoresis kit as the reference method. The %HbA(2) values from the HA-8160 analyzer and the alkaline gel electrophoresis show a good linear correlation in the absence of HbS. A strong positive bias in the %HbA(2) values from the HA-8160 is apparent in the presence of HbS in the samples, when compared with the alkaline electrophoresis. The analytical imprecision and bias of the three HPLC instruments are comparable both in the presence and absence of HbS. The manual column method shows a lower bias in the absence of HbS but is more affected when HbS is present in the samples.

Separation of haemoglobin HbE and HbA by the fully automated, high-pressure liquid chromatography Tosoh HLC-723 G7 analyzer.

High-pressure liquid chromatography instruments specifically devised for separating haemoglobin (Hb) fractions have been increasingly employed by the hospital laboratories over the recent years since they allow easy and fast screening for several Hb variants. Although such instruments may be proposed as sensitive, specific and reliable alternatives to the classic electrophoretic techniques, a major drawback of this screening strategy is the almost identical retention time of several Hb variants. In particular, at least 18 Hb variants have been reported in the same retention window as HbA(2), including HbE, the second most common beta-chain variant in humans after sickle cell trait. Recently, we evaluated the performance characteristics of an improved buffer formulation originally conceived for Hb variants separation procedures on the fully automated high-pressure liquid chromatography instrument Tosoh G7. At variance with other fully automated high-pressure liquid chromatography analyzers, the elution pattern on the G7 in subjects heterozygous for HbE is characterized by the presence of four suggestive peaks (HbF, HbA, HbA(2) and HbE), confirming the effective separation of HbE from HbA(2). Because of its potential value in the diagnosis of the thalassaemia syndromes, the effective separation of HbA(2) from HbE can provide clinical laboratories with a valuable information for the diagnostic reasoning.

Effect of HbS in the determination of HbA2 with the Biorad Variant II analyzer.

OBJECTIVES: The effect of the presence of HbS in the determination of HbA2 using the Biorad Variant II analyzer. DESIGN AND METHODS: The effect of HbS presence in the samples was quantified using the HELENA SAS-MX alkaline gel electrophoresis kit as the reference method. RESULTS: The %HbA2 values from the Variant II analyzer and the HELENA SAS-MX alkaline gel electrophoresis kit show a good linear correlation in the absence of HbS. A strong positive bias in the %HbA2 values from the Variant II is apparent in the presence of HbS in the samples, when compared to the alkaline electrophoresis gel. CONCLUSION: The Variant II analyzer gives reliable results for %HbA2 determination when no HbS is detectable in the samples. When HbS is present, the gel electrophoresis method gives more accurate results.

Hb A2-Pasteur-Tunis [delta59(E3)Lys-->Asn, AAG-->AAC]: a new delta chain variant detected by DNA sequencing in a Tunisian carrier of the codon 39 (C-->T) beta0-Thalassemia mutation.

We describe a new delta-globin variant, Hb A2-Pasteur-Tunis [delta59(E3)Lys-->Asn, AAG-->AAC]. This hemoglobin (Hb) displayed an electrophoretic mobility faster than normal Hb A2 and was expressed at 2.2 %. The molecular defect was characterized by DNA sequencing and confirmed by a polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP)-designed protocol. Hb A2-Pasteur-Tunis was found in a carrier of a codon 39 (C-->T) beta0-thalassemia (thal), presenting with a normal Hb A2 level. Phenotype and genotype investigations revealed that the total Hb A2 level of the patient was that expected for a minor beta-thal (4.8%).

Beta thalassemia IVS-I-5(G-->C) heterozygosity masked by the presence of HbJ-Meerut in a Dutch-Indian patient.

We describe the genotype/phenotype correlation in a 35 year old anemic female referred to our laboratory because a fast eluting minor fraction on HPLC, mild hemolysis and hematological parameters suggesting a Thalassemia trait, eventually in combination with iron depletion. Direct sequencing of the alpha globin genes revealed heterozygosity for HbJ-Meerut, a Glu-->Ala substitution at residue 120 not justifying the hematological parameters. No other point mutations were found on the alpha genes and Gap-PCR excluded the 6 common deletion defects. Direct sequencing of the beta-globin genes revealed the IVS-I-5 (G-->C) transversion in absence of the elevated HbA2 levels usually measured in carriers of this beta-Thalassemia mutation. The HbA2 tetramer in the presence of HbJ-Meerut divides in two parts. One alphaN2/delta2 migrating on the right spot on HPLC. The other alphaJ2/delta2 migrating under the HbA fraction. Classic alkaline electrophoresis and the modern capillary electrophoresis CE showed these two tetramers and the reduction of the elevated HbA2 level of the beta-Thalassemia trait by at least 20% due to HbA2 Meerut.

Development and validation of an ELISA for hemoglobin-A2: a novel method for beta-thalassemia screening in developing countries.

Hemoglobin-A2 (HbA2) measurement in human hemolysates has great significance, since its level can indicate beta-thalassemia carrier status in otherwise healthy individuals. An ELISA for HbA2 using antiserum monospecific to the delta chain of HbA2 and affinity purified antirabbit gamma globulins (ARGG) conjugated to horseradish peroxidase (HRP) have been developed. The monospecific antiserum used does not cross react with other hemoglobins. Hemolysates from volunteers are used for measurement of HbA2. In a limited trial for beta-thalassemia carrier screening (n = 350), the results obtained with the developed ELISA are comparable with those obtained with a micro-column chromatography method (r > or = 0.89). The developed ELISA is simple, accurate, precise, inexpensive, and several samples can be processed simultaneously with ease, making this system a suitable candidate for transforming into a user friendly kit.

Crystallization and preliminary X-ray structural studies of hemoglobin A2 and hemoglobin E, isolated from the blood samples of beta-thalassemic patients.

Hemoglobin A(2) (alpha(2)delta(2)), a minor (2-3%) component of circulating red blood cells, acts as an anti-sickling agent and its elevated concentration in beta-thalassemia is a useful clinical diagnostic. In beta-thalassemia major, where there is a failure of beta-chain production, HbA(2) acts as the predominant oxygen delivery mechanism. Hemoglobin E, is another common abnormal hemoglobin, caused by splice site mutation in exon 1 of beta globin gene, when combines with beta-thalassemia, causes severe microcytic anemia. The purification, crystallization, and preliminary structural studies of HbA(2) and HbE are reported here. HbA(2) and HbE are purified by cation exchange column chromatography in presence of KCN from the blood samples of individuals suffering from beta-thalassemia minor and E beta-thalassemia. X-ray diffraction data of HbA(2) and HbE were collected upto 2.1 and 1.73 A, respectively. HbA(2) crystallized in space group P2(1) with unit cell parameters a=54.33 A, b=83.73 A, c=62.87 A, and beta=99.80 degrees whereas HbE crystallized in space group P2(1)2(1)2(1) with unit cell parameters a=60.89 A, b=95.81 A, and c=99.08 A. Asymmetric unit in each case contains one Hb tetramer in R(2) state.

Hemoglobin A2 quantification by capillary zone electrophoresis.

Hemoglobin A2 (HbA2) comprises about 2.2% of the total hemoglobin in the erythrocytes. The separation and quantitation of this minor hemoglobin by capillary electrophoresis (CE) using an arginine Tris buffer is described. Some of the variables affecting the accuracy and precision of HbA2 quantification are investigated. Furthermore, the quantification of this hemoglobin by CE is compared to that of a microcolumn chromatography method. The CE method is better suited than the microcolumn method for measuring HbA2 in the sickle cell trait.

Rapid analysis of hemoglobin variants by cation-exchange HPLC.

We investigated the use of a 3.5 x 0.46 cm HPLC column packed with 5-microns particles of porous (100 nm) silica coated with polyaspartic acid for hemoglobin analysis. A 13-min gradient was produced between two mobile phases. The method is capable of separating more than 35 commonly encountered hemoglobin variants within 12 min. Hemoglobin variants identified include Bart's, acetyl F, H, A1c, F, Camden, N-Baltimore, J-Baltimore, N-Seattle, Grady, Fannin-Lubbock, A G-Georgia, Lepore-Baltimore, P-Galveston, G-Coushatta, Lepore-Boston, E, Osu Christiansborg, A2, G-Philadelphia, Korle Bu, Russ, Richmond, D-Los Angeles, Deer Lodge, Montgomery, S, Q-Thailand, G-San Jose, A2', Hasharon, Q-India, Tampa, GS hybrid, C-Harlem, O-Arab, British Columbia, and C. Between-run precision of an in-house pooled hemoglobin control material, AFSCA2, gave CVs of 2-5% for the A, F, S, and C and 8% for the A2 over a 6-month period. The simplicity of sample preparation, high resolution of the system, and high accuracy of the method, combined with complete automation, make this an ideal methodology for the routine diagnosis of hemoglobin disorders in a clinical laboratory.

The estimation of Hb A2 in the presence of Hb C or Hb E by reverse phase high performance liquid chromatography.

Although Hb-C may be separated from Hb A2 by some ion exchange methods, most will not separate Hb E and Hb A2. The delta chain can be readily separated from the beta C, beta E and beta O-Arab chains by reverse phase HPLC. Hence, reverse phase HPLC provides a means of quantitatively determining Hb A2 in the presence of Hb C, Hb E, and Hb O-Arab. The procedure, although not highly accurate, does permit the detection of increased Hb A2, for example, in beta-thal heterozygotes and, therefore, is applicable to other conditions (Hb C, Hb E, Hb O-Arab).

Homozygosity for the delta-chain variant haemoglobin A2' (HbB2) (delta 16 Gly----Arg).

A healthy 20-year-old woman, belonging to the Kgalagadi tribe of Botswana, has been found to possess a variant Haemoglobin A2 as her only minor haemoglobin component. Fingerprinting and amino-acid analysis have shown that it is Haemoglobin A2' (delta 16 Gly----Arg). The one parent available for study is heterozygous for the Hb delta A2' allele and the variant haemoglobin accounts for 3% of the total haemoglobin in the proband. It is reasoned that the proband is, therefore, homozygous for the Hb delta A2' allele. No haematological abnormalities were evident.

Identification and quantification of hemoglobins A2 and Barts with an enzyme-labeled immunosorbent assay.

The presence and quantity of hemoglobins Barts and A2 in hemolysates from normal donors and individuals with alpha- and beta-thalassemia trait, respectively, were determined with an enzyme-labeled immunosorbent assay (ELISA). This technique requires the incorporation of monospecific antisera capable of specifically reacting only with these hemoglobins, e.g., with the delta chain of Hb A2 and gamma 4 chains of Hb Barts. By the ELISA, the mean percentage of Hb Barts in hemolysates from normal persons and persons with alpha-thalassemia was 0.25 (SD 0.07) and 6.1 (SD 0.40), respectively. Corresponding values for Hb A2 in hemolysates from normals and persons with beta-thalassemia were 3.1 (SD 0.22) and 5.9 (SD 0.21), respectively. The results obtained by the ELISA procedure were in good agreement with those determined by radioimmunoassay or microcolumn chromatography. The ELISA technique is more sensitive and specific than biochemical assays currently used to measure these hemoglobins and can detect 250 ng of Hb Barts in 100 micrograms of hemoglobin or 50 ng of Hb A2 in 5 micrograms of hemoglobin.

A new high-performance liquid chromatographic procedure to quantitate hemoglobin A1c and other minor hemoglobins in blood of normal, diabetic, and alcoholic individuals.

A new HPLC procedure is described for the separation and quantitation of minor human Hb variants. The cation exchanger, Synchropak CM 300, is a silica support with a bonded polymeric coating of carboxylic acid residues. The chromatogram is developed with 0.03M Bis-Tris-KCN buffers, pH 6.40, and a Na-acetate gradient increasing from 0 to 0.1125M. As many as 11 minor Hbs (including Hb A2) can be isolated. Some of these have been identified through rechromatography of the minor Hb zones obtained by Bio-Rex-70 chromatography. Quantitation of Hb A1c and Hb A2 is readily accomplished. Hb F0 and an unidentified minor Hb often observed in red cells of alcoholics co-chromatograph with Hb A1c. The method has been applied to blood samples of 10 normal adults, 13 diabetic patients, and nine alcoholic subjects. An excellent correlation exists between the Hb A1c percentages and the levels of Hb A1 determined by microcolumn chromatography. Some other minor Hbs, identified as components 9 and 10, which are (at least in part) Hb A0 with glucose attached to the alpha chains, are present in increased amounts in the blood of diabetic patients and others may be observed in patients who subject themselves to (severe) alcohol abuse. It is suggested that the new procedure is well-suited for detailed studies of the minor Hbs in patients with various abnormalities in carbohydrate metabolism.

High-performance liquid chromatography of human hemoglobins on a new cation exchanger.

We have investigated the use of a high-performance liquid chromatographic (HPLC) column packed with a unique weak cation exchanger prepared by coating silica with poly(aspartic acid) for hemoglobin analysis. The complete separation of hemoglobin Bart's F, A0, A2, S, C, D, E, G, SG, Winnipeg and Sealy was achieved by gradient elution within 30 min. The high resolution made it possible to distinguish hemoglobin variants such as Bart's, AC, AD, AE, AG, AS, ASG, CC, SC, SS, Winnipeg, Sealy and beta-chain variants with thalassemia such as S/beta +, S/beta 0 and S(C)-beta + thalassemia. Comparison of DEAE-cellulose column chromatography and our HPLC method for the quantitation of hemoglobin A2 yielded a good correlation. Hemoglobins A2, C and E are completely resolved on PolyCAT A columns in contrast to both cellulose acetate electrophoresis and DEAE-cellulose column chromatography. The high resolution of the system and the accuracy of the method combined with complete automation make this procedure useful for diagnosis of hemoglobin disorders in both a research and clinical laboratory environment.