Application of the polymerase chain reaction (PCR) in the diagnosis of Hb S-beta(+)-thalassemia

Isoelectric focusing of the hemolysate prepared from a two-year-old American black boy with microcytic hypochromia showed the presence of a high percentage (63.3%) of such Hb variant as Hb S, while the levels of Hb A, Hb F and Hb A2 were 20.0%, 12.7%, and 4.0%, respectively. The ratio of the non-alpha-chain to the alpha-chain of the biosynthesized globin chains was 0.49. The variant was identified as Hb S by amino acid analysis of the abnormal peptide (beta T-1) and digestion of DNA amplified by the polymerase chain reaction with enzyme Eco 81 I. This was further confirmed by DNA sequencing. DNA sequencing of a beta-gene without the beta s-mutation revealed a nucleotide change of T to C in the polyadenylation signal sequence AATAAA 3' to the beta-gene, resulting in beta(+)-thalassemia. These results are consistent with the existence of a beta s-gene and a beta(+)-thalassemia gene in trans.     

Two siblings with unusually mild homozygous β-thalassemia: A didactic example of the effect of a nonallelic modifier gene on the expressivity of a monogenic disorder

Two adult Black sibs with homozygous β-thalassemia had severe deficiency of β-chain production but an unusually mild clinical course and almost normal hematocrit values. Their father had the typical hematological findings of β-thalassemia trait but the mother, in addition to the β-thalassemia trait, had elevated F cells (42.2%). Elevated F cells were also present in a hematologically normal sister of the affected providing evidence that a gene for heterocellular hereditary persistence of fetal hemoglobin (HPFH) was also running in this family. The unusually mild clinical course of the two homozygotes is attributed to their inheritance from their mother of the heterocellular HPFH gene. The gene for heterocellular HPFH is nonallelic to the β-globin locus and apparently acted as a modifier of the homozygous β-thalassemia phenotype by facilitating F-cell production and thus diminishing the pathophysiological consequences of the β-thalassemia defect. The effect of heterocellular HPFH on the expression of homozygous β-thalassemia or Hb S genotypes is an impressive example of the pathophysiological basis of changes in the expressivity of monogenic disorders due to action of nonallelic modifiers.     

G gamma beta + type of hereditary persistence of fetal haemoglobin in association with Hb C.

This report describes a Negro family with the G gamma beta + type of hereditary persistence of fetal haemoglobin. Family members with levels of haemoglobin F of 17 to 23% had normal red cell indices, balanced globin chain synthesis, and a pancellular distribution of the fetal haemoglobin, showing that these subjects have a form of HPFH. The production of Hb A and C in addition to the large amount of Hb F in one family member showed that there was an active beta A gene in cis to the HPFH determinant, while structural analysis of the Hb F revealed the presence of only G gamma chains. The criteria for the diagnosis of G gamma beta + HPFH, and the relevance of such conditions to the control of globin gene expression, are discussed.     

Globin chain synthesis in Hb J Baltimore-beta (+)-thalassemia

An American black family in whom hemoglobin J Baltimore and beta (+)-thalassemia genes coexisted is described. The proposita is a 23-year-old woman with a hemoglobin (Hb) level of 11.5 g/dl, microcytic, hypochromic indices, increased values of Hbs A2 and F, and alpha/non-alpha synthetic ratio of 1.52. Hbs A and J Baltimore (beta 16 Gly---Asp) constituted 12% and 81.3%, respectively, of her total hemoglobin. Her sister had a very similar peripheral blood picture, but Hbs A and J Baltimore constituted 6.8% and 85.5%, respectively, of her total hemoglobin, and the alpha/non-alpha synthetic ratio was 1.39. The mother had beta(+)-thalassemia trait only, a moderate degree of anemia, and greater synthetic imbalance (alpha/non-alpha raio of 1.73). These findings suggest that the presence of the Hb J Baltimore gene ameliorates the effects of a coexistent beta-thalassemia gene.     

Flow cytometric measurement of hemoglobin F in RBCs: diagnostic usefulness in the distinction of hereditary persistence of fetal hemoglobin (HPFH) and hemoglobin S-hPFH from other conditions with elevated levels of hemoglobin F

The cellular distribution of hemoglobin F is important for evaluating persistently elevated hemoglobin F levels, such as in hereditary persistence of fetal hemoglobin (HPFH) or delta/beta-thalassemia, and for differentiating homozygous hemoglobin S (or hemoglobin S-beta(0)-thalassemia) from hemoglobin S-HPFH, traditionally done by using the Kleihauer-Betke (K-B) acid elution test. We evaluated a flow cytometric method using an anti-hemoglobin F antibody as a replacement for the K-B test. We used 172 specimens representing a variety of conditions: HPFH trait, 19 cases; delta/beta-thalassemia trait, 8 cases; hemoglobin S-HPFH, 10 cases. By flow cytometry, all cases of HPFH trait gave a hemoglobin F pattern comparable to the homocellular pattern obtained by the K-B test; all cases of delta/beta-thalassemia tested gave a pattern comparable to a K-B heterocellular pattern. Most cases of hemoglobin S-HPFH gave a homocellular distribution of hemoglobin F whereas all cases of homozygous hemoglobin S with elevated hemoglobin F levels gave a heterocellular pattern. Flow cytometry provides a more rapid and objective method for assessing cellular distribution of hemoglobin F and is useful for patient evaluation when HPFH trait, delta/beta-thalassemia trait, or hemoglobin S-HPFH trait is suspected.     

Thalassaemia intermedia in a family with beta 0-thalassaemia and Hb Hasharon.

A Brazilian family of Italian descent is described in which the beta-thalassaemia gene is interacting with an alpha chain variant Hb Hasharon (alpha 47 Asp leads to His). One patient who was affected by homozygous beta 0-thalassaemia and heterozygous alpha Hasharon displayed the clinical picture of thalassaemia intermedia. Her haemolysate contained 8.6% Hb F Hasharon (alpha 2 Hasharon gamma 2) and 1.1% Hb A2, the remaining haemoglobin being Hb F. Hb A was not detected. Globin chain synthesis in reticulocytes showed non-alpha/total alpha ratios of 0.29, 0.39, and 0.73 respectively for the patient, the mother, and the father, who is heterozygous for both the beta 0-thalassemia and Hb Hasharon genes. The possible contribution of Hb Hasharon heterozygosity to the less severe expression of homozygous beta 0-thalassaemia is discussed.     

Clinical and haematological evaluation of beta thalassaemia intermedia with increased Hb F and Hb A2 in heterozygotes: beta thalassaemia intermedia I.

Family studies were performed in 10 patients from seven different families with homozygous beta zero thalassaemia intermedia and in three patients with homozygous beta+ or compound heterozygous beta+ and beta zero thalassaemia intermedia. In nine of the 10 families at least one of the parents was found to have raised Hb A2 and Hb F. In the heterozygotes with increased Hb A2 and Hb F, the means of Hb F and MCV were significantly higher than those observed in regular Hb A2 thalassaemia heterozygotes. However, the severity of imbalance in in vitro haemoglobin synthesis was similar in these two groups. The imbalance in the alpha/non-alpha synthetic ratio was heterogeneous in the patients, being 2.1 and 4.0. Segregation of the raised Hb F from the Hb A2 beta thalassaemia determinant was found to be possible in only one of the 36 heterozygotes. This may exclude the possibility of the presence of an additional determinant responsible for the activation of the gamma chain. The G gamma/A gamma ratio of Hb F was that of the fetal type (G gamma was between 50 and 71% of the total gamma chain). The A gamma T variant of gamma chain was not detected in cis of the beta zero thalassaemia determinant characterised by increased Hb F and Hb A2. A retrospective study of 180 patients with beta thalassaemia and their parents indicated that the combined rise in Hb A2 and Hb F was more common in the heterozygous parents (11 out of 30 parents) of the patients with beta zero thalassaemia than it was in the parents of patients with beta+ thalassaemia (three out of 140 parents). The presence of increased Hb A2 and Hb F in the heterozygote may in some cases determine the relative mildness of the disease.     

Incidental findings of variant hemoglobin during hemoglobin a1c testing

A variant hemoglobin fraction may be an incidental finding during HbA(1c) analysis using the G8 Tosoh HPLC analyzer, but it is unclear if the retention times and fraction patterns can reliably predict the findings of a high-performance liquid chromatography (HPLC) β-thalassemia program (Bio Rad Variant II analyzer). We chose 100 samples sent for HbA(1c) determinations (G8 Tosoh) with an incidental finding of variant hemoglobin and did a reflex test using the Bio Rad Variant II analyzer (β-thalassemia program). Two observers attempted to predict the results with that analyzer from fraction patterns and retention times of the hemoglobin variants detected with the G8. They independently identified all hemoglobin variants (HbS, Hb Setif, HbC, and HbD) by their patterns and retention times. We conclude that HPLC confirmation of certain variant hemoglobin fractions found incidentally during HbA(1c) testing on the G8 Tosoh is not necessary.     

Delta beta (F)-thalassaemia in Sardinia.

A population survey carried out in southern sardinia on more than 5000 people has shown that delta beta (F)-thalassaemia, with a gene frequency of 0-00088, is a rare trait in this population. We examined the members of three families segregating for both delta beta- and beta(0)-thalassemia and a number of delta beta carriers identified during the screening. The doubly heterozygous children suffer from a mild form of Cooley's disease with non-alpha/alpha biosynthetic ratios within the range of values observed in beta (0)-thalassaemia homozygotes. Three of them have been transfusion dependent for some time. The delta beta carriers, although in many respects showing the usual picture of delta beta-thalassaemia, such as abnormal red cell indices, normal Hb A2, Hb F heterogeneously distributed in the erythrocytes, and low beta/alpha synthetic ratios, have unusually high levels of Hb F (range 10 to 20%) and particularly low glycine content (range 0.02 to 0.14 residues) in the isolated gamma CB3 peptide. These results have led us to the conclusion that the delta beta-thalassaemia found in Sardinia is different from the similar kind of delta beta defect found in Negroes and in other Mediterranean populations, including continental Italians.     

Rapid diagnosis of thalassemias and other hemoglobinopathies by capillary electrophoresis system

Basic diagnosis of hemoglobinopathies can be performed by analysis of erythrocyte indices as well as by the separation and quantification of the common hemoglobin (Hb) fractions Hb A(2), Hb S, Hb C, Hb D, Hb E, and Hb F. This study used an automatic capillary zone electrophoresis system to diagnose various types of hemoglobinopathies common in the Thai population. A total of 459 adults were recruited, which consisted of normal, various types of thalassemia carriers, and thalassemia patients with different genotypes. Hb types and quantification of all Hb components were determined by an automated capillary zone electrophoresis. The automatic capillary electrophoresis system can separate and quantitate Hbs A, F, E, A(2), Constant Spring (CS), H, and Bart's in a way that is comparable with other Hb analysis methods. Moreover, the Hb A(2) peak can be distinguished clearly from the Hb E peak in individuals who carry Hb E. The slightly increased levels of Hb A(2), 3.5% +/- 0.4%, which is shown in the carriers of Hb E, confirm that Hb E is the silent phenotype of beta(+)-thalassemia.     

Cord blood study on β-thalassemia and hemoglobin E

We describe hematologic data from 18 newborn infants including follow-up data. Of these, ten were the offspring of patients with β-thal/Hb E disease and the remainder were infants who were found to have a decrease in red cell osmotic fragility during a random cord blood examination. The results of the cord blood study showed that two infants having normal red cell osmotic fragility with about 2% Hb E + Hb A + Hb F at birth represented Hb E heterozygosity. Eleven babies had slightly decreased red cell osmotic fragility, a mild degree of microcytosis and poikilocytosis, and hemoglobin types of Hb A + Hb F with no elevation of Hb A₂ at birth. They subsequently had hematologic findings consistent with the β-thal heterozygosity. The means of hematological values of cord blood in the β-thal trait infants appeared to be statistically different from those in the normal infants only with respect to increased red cell count and reduced MCH. One infant was thought to have the β-thal trait but had a greater degree of thalassemic changes in red cells; subsequently he turned out to have homozygous β-thalassemia. Four newborn infants with hypochromia and numerous target cells had 4-7% Hb E + Hb F without Hb A. Follow-up examination showed two cases of Hb E homozygosity; however, the others, who had obvious microcytosis and poikilocytosis in cord blood, finally developed β-thal/Hb E disease. Thus, a careful study on red cell osmotic fragility, morphology and starch gel electrophoresis at birth allows detection and diagnosis of β- thal heterozygosity, β-thal homozygosity, Hb E heterozygosity, Hb E homozygosity and double heterozygosity for β-thal and Hb E.     

Clinical and haematological evaluation of beta thalassaemia intermedia characterised by unusually low Hb F and increased Hb A2: beta thalassaemia intermedia II.

A total of 15 patients from different families with thalassaemia intermedia was studied. Haematological studies showed that the fetal haemoglobin was only slightly raised, being between 2 and 11.5% of the total haemoglobin. Haemoglobin A2 was high in all cases. The family study indicated that homozygosity or compound heterozygosity for beta thalassaemia was present in five patients, while dominant inheritance was observed in three. In seven patients family studies were not sufficient to predict the genotype. Haematological findings in the parents of the homozygous patients were as severe as those seen in common Hb A2 beta thalassaemia traits. The decrease in MCH and MCV was more severe and the Hb A2 higher in homozygous patients than in cases of common beta thalassaemia major (p less than 0.01, p less than 0.01, and p less than 0.001 respectively). The imbalance in in vitro globin synthesis was more severe in classical beta thalassaemia major than in homozygous patients in this study (p less than 0.01). However, the imbalance in alpha/non-alpha synthetic ratios showed variation among the homozygous and heterozygous patients in this study (2.1 to 4.0). Haematological severity and Hb F value showed some slight variation among affected persons of the same family in the case of patients with severe beta thalassaemia heterozygosity. The G gamma/A gamma ratio of haemoglobin F was found to be close to that of the adult level. Haematological studies suggested that clinical and haematological findings were more severe in patients with homozygous beta thalassaemia than in patients with heterozygosity for beta thalassaemia. The prevalence of thalassaemia intermedia with low Hb F and increased Hb A2 was found to account for 3% of the Turkish beta thalassaemic patients diagnosed before the age of 8 years.     

Clinical, haematological, and genetic studies of type 2 normal Hb A2 beta thalassaemia.

The clinical and haematological phenotype as well as chain synthesis data were studied in 35 doubly heterozygous patients with either normal Hb A2 and Hb F, type 2 beta thalassaemia and beta (high A2) thalassaemia (26 patients), or type 2 and other rare beta or delta beta variants (nine patients). Patients doubly heterozygous for type 2 and beta zero or delta beta zero thalassaemia variants had no detectable Hb A, indicating that the type 2 normal A2 beta thalassaemia is primarily the result of a beta zero gene. The clinical phenotype varied from severe thalassaemia major to mild thalassaemia intermedia, and was mainly related to the thalassaemia variant with which the type 2 normal A2 beta thalassaemia was combined, and the proportion of Hb A produced in beta + thalassaemia patients. Haematological and chain synthesis data were similar in heterozygotes with type 2 and beta zero or beta + (high A2) thalassaemia. Hb A2 levels were within the normal range (2.3 to 3.6%) though absolute values (Hb A2 per RBC) ranged from low normal (0.5 pg/RBC) to increased levels (1.0 pg/RBC.) The variation of Hb A2, as well as the presence of Hb A2 in a type 2/delta beta high F patient and the complete absence of HbA2 in a homozygous type 2 patient, indicate that there are at least two genotypes of type 2, one beta zero and the other delta beta zero. This has been recently proven by gene mapping studies. For clinicians, routine haematological and family studies are sufficient for the proper treatment and prevention of doubly heterozygous type 2 patients.     

Interference of hemoglobin Hope on beta-thalassemia diagnosis by the capillary electrophoresis Method

The β-chain hemoglobin (Hb) variants interfere with the diagnosis of β-thalassemia trait using high-performance liquid chromatography (HPLC) and capillary electrophoresis (CE). We analyzed the effect of Hb Hope, a β-chain Hb variant frequently found in the Thai population, on β-thalassemia trait diagnosis. HPLC and CE were used to quantify the level of HbA(2) in 11 whole blood samples containing Hb Hope. The levels of Hb Hope detected by both methods were similar. An elevated HbA(2) level was found in all samples analyzed by the CE method, while 1 was increased when analyzed by HPLC, which was a compound heterozygous of Hb Hope and α-thalassemia-1 SEA-type deletion. Of 11 samples, 6 had mean corpuscular volumes within the reference range. All samples showed negative results for molecular analysis of β(0)-thalassemia codon 17, 41/42, and 71/72 mutations and β-thalassemia 3.5-kb deletion. Therefore, Hb Hope interfered with the diagnosis of β-thalassemia trait analyzed by CE but not by HPLC.     

Hemoglobin binding to A beta and HBG2 SNP association suggest a role in Alzheimer's disease

From a normal human brain phage display library screen we identified the gamma (A)-globin chain of fetal hemoglobin (Hb F) as a protein that bound strongly to A beta1-42. We showed the oxidized form of adult Hb (metHb A) binds with greater affinity to A beta1-42 than metHb F. MetHb is more toxic than oxyhemoglobin because it loses its heme group more readily. Free Hb and heme readily damage vascular endothelial cells similar to Alzheimer's disease (AD) vascular pathology. The XmnI polymorphism (C-->T) at -158 of the gamma (G)-globin promoter region can contribute to increased Hb F expression. Using family-based association testing, we found a significant protective association of this polymorphism in the NIMH sibling dataset (n=489) in families, with at least two affected and one unaffected sibling (p=0.006), with an age of onset >50 years (p=0.010) and >65 years (p=0.013), and families not homozygous for the APOE4 allele (p=0.041). We hypothesize that Hb F may be less toxic than adult Hb in its interaction with A beta and may protect against the development of AD.     

Thalassemia and erythroid transcription factor KLF1 mutations associated with borderline hemoglobin A2 in the Thai population

IntroductionElevated hemoglobin (Hb) A₂ is an important diagnostic marker for β-thalassemia carriers. However, diagnosis of cases with borderline Hb A₂ may be problematic. We described the molecular characteristics found in a large cohort of Thai subjects with borderline Hb A₂.Material and methodsExamination was done on 21,657 Thai subjects investigated for thalassemia at Khon Kaen University, Thailand. A total of 202 subjects with borderline Hb A₂ (3.5–4.0%) were selectively recruited and hematological parameters were recorded. DNA variants in α-, β-, δ-globin, and Krüppel-like factor 1 (KLF1) genes were examined using PCR.ResultsAmong 202 subjects, DNA analysis identified carriers of α⁺-thalassemia (n = 48; 23.8%), β-thalassemia (n = 22; 10.9%) and KLF1 mutations (n = 48; 23.8%). No molecular defect was observed in the remaining 84 (41.5%) subjects. Interaction of KLF1 and α-thalassemia was observed in 10 cases. Of the 22 β-thalassemia carriers, five β⁺-thalassemia mutations were identified with lower MCV and higher Hb A₂. Seven KLF1 mutations were detected in 10 genotypes in subjects with higher MCV and Hb F. No β⁰-thalassemia, α-globin gene triplication or δ-globin gene mutation was detected.ConclusionsA large proportion of subjects with borderline Hb A₂ are not β-thalassemia carriers and for those with β-thalassemia, only mild β⁺-thalassemia mutations were detected. Evaluation of the patients using Hb A₂, Hb F and MCV values will help in selecting cases for further molecular analysis. The results should explain the unusual phenotype of the cases and facilitate a thalassemia screening program in the region.     

云南省100例异常血红蛋白E患者的血液学和基因型分析

目的分析云南省异常血红蛋白E(hemoglobin E,Hb E)杂合子及Hb E合并地中海贫血(简称地贫)病例的血液学表型和基因型特征。方法对100例高效液相色谱分析提示为Hb E异常血红蛋白携带病例进行血细胞分析,并用Gap-PCR和PCR-寡核苷酸探针反向斑点杂交法检测α-和β-珠蛋白基因常见突变类型。结果100例疑似Hb E携带的病例,经基因诊断全部检出β-珠蛋白链CD26突变(HBB:c.79G>A),其中Hb E杂合子90例,Hb E合并αα/-α3.7突变7例,Hb E合并αα/--SEA突变2例,1例为Hb E合并-α3.7/-α3.7。Hb E杂合子血液学表型分析结果:Hb A2(26.02±3.64)%,Hb F(1.35±1.25)%,平均红细胞体积(78.83±4.68)fl,平均红细胞血红蛋白含量(26±1.54)pg,平均血红蛋白浓度(329.65±10.73)g/L,血红蛋白(141.08±16.53)g/L;Hb E复合α地贫时,α地贫基因的突变类型不同,血液学表型结果不同。结论云南省Hb E及Hb E合并α地贫的发生率较高,高效液相色谱能够有效检出Hb E,Hb E合并其它α地贫基因突变时,有较大差异的表型变化;仅依靠血液学结果进行产前筛查会造成Hb E漏诊。     

A molecular marker associated with mild hemoglobin H disease

The clinical spectrum of HbH disease varies from a benign disorder to a severe anemia which is blood-transfusion dependent. Heterogeneity at the clinical level is now being understood in terms of the underlying molecular defects. In this study a mild phenotype found in a group of patients with HbH disease is associated with two types of alpha-thalassemia. These are: alpha+-thalassemia (-alpha 3.7/) and alpha 0-thalassemia (--SEA/). In contrast, a second group with more severe HbH disease has a non-deletional alpha-thalassemia defect instead of alpha+-thalassemia (genotype alpha alpha T/--SEA). In the majority of cases, the basis for non-deletional alpha-thalassemia is Hb Constant Spring.     

脐血毛细管电泳在产前诊断重型地中海贫血中的应用

目的探讨脐血毛细管电泳在产前诊断重型地中海贫血中的应用价值。方法对71例夫妻双方患有同型地中海贫血的孕妇进行脐静脉穿刺术,抽取脐血同时进行地中海贫血基因检测和血红蛋白毛细管电泳。结果重型α地中海贫血胎儿脐血Hb Bart’s含量高达72.9%∽89.8%,而Hb H病、轻型α地中海贫血及静止型α地中海贫血胎儿脐血Hb Bart’s含量分别为18.4%∽24.3%、2.1%∽5.7%及0.3%∽0.6%,正常胎儿脐血中未检出Hb Bart’s。重型β地中海贫血胎儿脐血Hb A含量极低,为0%∽0.6%,而轻型β地中海贫血胎儿和正常胎儿脐血Hb A含量分别为2.2%∽5.2%和2.5%∽9.4%。脐血Hb Bart’s和Hb A定量分析能准确的检出胎儿重型地中海贫血。结论毛细管电泳具有操作简便及自动化的优点,能准确诊断胎儿重型地中海贫血,可以作为产前诊断的一种常规方法。     

Evaluation of a dual hemoglobin A(2)/A(1c) quantitation kit on the bio-rad variant II automated hemoglobin analyzer

CONTEXT: Quantitation of hemoglobin (Hb) A(1c) and investigation of hemoglobinopathy on the Bio-Rad Variant analyzers require a switch between 2 separate kits that is time consuming and causes errors. OBJECTIVE: Evaluation of a new Variant II HbA(2)/HbA(1c) Dual kit capable of both Hb A(1c) quantitation and hemoglobinopathy investigation on a single kit. DESIGN: We evaluated Hb A(1c), Hb A(2), and Hb F quantitation for precision, linearity, and correlation with current methodology. We also evaluated detection of Hb variants and correlation of Hb Barts quantitation. SETTING: Hamilton Regional Laboratory Medicine Program, Provincial Hemoglobinopathy Laboratory, St Joseph's Healthcare Site, Hamilton, Ontario. PATIENTS: Patient blood samples submitted for Hb A(1c) quantitation or hemoglobinopathy investigation. MAIN OUTCOME MEASURES: Precision, linearity, linear regression, and reference interval validation. RESULTS: We provide tables and figures illustrating precision, linearity, linear regression, and quantitation of Hb variants. We validated reference intervals for Hb A(1c), Hb A(2), and Hb F. CONCLUSIONS: The dual kit provides precise Hb A(1c), Hb A(2), and Hb F quantitation. The results show good linearity and correlate well with the results of current methods. We detected all clinically important Hb variants and a wide variety of rare variants. The dual kit has several advantages: it eliminates the need for extensive kit switch over; improves utility for newborn screening because of its quantification of Hb Barts; permits quantification of Hb A(1c) using the beta-Thal method; and eliminates the need for separate Hb A(2) reference intervals for patients with Hb S because of its accurate quantitation of Hb A(2) in the presence of Hb S.