A laboratory strategy for genotyping haemoglobin H disease in the Chinese

A specific early eluting peak in Bio-Rad Variant II cation-exchange high-performance liquid chromatography (CE-HPLC) for the screening of alpha-thalassaemia in a Chinese population

The early eluting peaks in the first minute of cation-exchange high-performance liquid chromatography (CE-HPLC) are often not analysed in haemoglobin pattern studies, except for haemoglobin (Hb) Bart's and Hb H peaks. In this study, we described the presence of a specific α-thalassaemia early eluting peak (αEEP) at the retention time of 0.24 min generated by Variant II CE-HPLC (β-Thalassaemia Short Program; Bio-Rad Laboratories). We have evaluated the utility of αEEP for the screening of α-thalassaemia trait in our local Chinese population in comparison to the Hb H inclusion body test. A total of 303 blood samples presenting with microcytosis were sent for haemoglobin pattern study and were analysed for the presence or absence of αEEP and Hb H inclusions. Twenty cases with a normal mean corpuscular volume were assessed as a control. Discordant results between the αEEP and the Hb H inclusion test were reviewed with the α-globin genotyping test performed. The concordance rate of the αEEP and the Hb H inclusion body test was 96.0% (κ=0.921, p<0.001). Eight of 303 cases (2.6%) were initially negative for the Hb H inclusion test but positive for the αEEP. All eight cases were found to have occasional Hb H inclusion bodies upon review. Four of 303 cases (1.3%) were negative for the αEEP but positive for the Hb H inclusion test. Of these four cases, two (50%) showed heterozygous Southeast Asian (SEA) type deletion, one (25%) showed Hb Quong Sze mutation, and one (25%) showed no mutation detected upon molecular testing. All the Hb E trait cases with no Hb H inclusions and the negative control group showed the absence of the αEEP. The sensitivity and specificity of αEEP for detecting SEA deletion were 93.8% and 100% respectively, which is superior to the Hb H inclusion test (sensitivity 81.3%, specificity 95.2%). The αEEP is found to be a more sensitive method than the Hb H inclusion body test in the screening of α-thalassaemia trait in our Chinese population, in which SEA type deletion is prevalent. Further study is needed to explore the utility of the αEEP in the screening of α-thalassaemia traits in other populations. The exact nature of the αEEP is yet to be defined.

Hemoglobin H Disease and Growth: A Comparative Study of DHbH and NDHbH Patients

Background

Hemoglobin H disease (HbH), a hemoglobinopathy resulting from abnormal alpha globin genes, is classified into two categories: deletional HbH (DHbH) and non-deletional HbH (NDHbH). The alpha-mutation genotypes exhibit a range of clinical anemias, which differentially impact patient growth.

Objectives

This retrospective study assessed the growth of HbH patients at Siriraj Hospital, Mahidol University.

Methods

Patients diagnosed with HbH between January 2005 and April 2021 were analyzed using growth standard scores of the Thai Society for Pediatric Endocrinology (2022 version) and BMI-for-age Z scores of the World Health Organization. Growth failure was defined as a patient's height for age exceeding two standard deviations below the mean.

Results

Of the 145 HbH patients, 75 (51.7%) had NDHbH, with --SEA/αCSα being the most common genotype (70 patients; 93.3%). The mean baseline hemoglobin level was significantly lower in NDHbH patients than in DHbH patients (8.16 ± 0.93 g/dL vs. 9.51 ± 0.68 g/dL; P < 0.001). Splenomegaly and growth failure prevalences were higher in NDHbH patients (37.3% vs. 0%, with P < 0.001, and 22.7% vs. 8.6%, with P = 0.020, respectively). Multivariable analysis revealed splenomegaly > 3 cm was associated with growth failure (OR = 4.28; 95% CI, 1.19-15.39; P = 0.026).

Conclusions

NDHbH patients exhibited lower hemoglobin levels and more pronounced splenomegaly than DHbH patients. Growth failure can occur in both HbH types but appears more prevalent in NDHbH. Close monitoring of growth velocity is essential, and early treatment interventions may be required to prevent growth failure.

Hematological Characteristics of Hb Constant Spring (HBA2: c.427T>C) Carriers in Mainland China

Hb Constant Spring (Hb CS) (HBA2: c.427T>C) is a common α-globin variant causing α-thalassemia (α-thal) phenotypes in mainland China. In this study, we evaluated the efficiency of erythrocyte parameters and capillary electrophoresis (CE) in the determination of Hb CS in blood samples from Hb CS carriers. Based on molecular diagnosis, there were 462 patients carrying Hb CS: 411 Hb CS heterozygotes, seven carried Hb H-Hb CS disease, 18 compound heterozygotes for Hb CS/α⁺-thal, and 26 double heterozygotes for Hb CS and β-thalassemia (β-thal). Forty-three cases had no Hb CS peak visible on CE, including all 26 cases of double heterozygotes for Hb CS and β-thal, and 17 cases of heterozygotes carrying only Hb CS. Hb CS heterozygotes, those without a Hb CS peak, presented with lower hemoglobin (Hb), mean corpuscular volume (MCV) and mean corpuscular Hb (MCH) values than those with a Hb CS peak. The MCV <80.0 fL yielded a detection rate of 87.8% for screening individuals carrying Hb CS. Therefore, we emphasize that if one partner of a couple has tested positive for α⁰-thal, the other should be subjected to detailed screening for this nondeletional allele using molecular analysis, regardless of his/her red cell indices and electrophoretic chromatogram.

Detection of Hb H disease caused by a novel mutation and --SEA deletion using capillary electrophoresis

Background

Hb H disease is a serious type of α‐thalassemia which cause moderate anemia while misdiagnosis by routine genetic analysis in a rare or novel Hb H disease.

Methods

The study was done on three patients and one fetus in a suspected Hb H disease family. Hb analysis was carried out using capillary electrophoresis (CE), and hematological analysis was conducted with an automated cell counter. Common α‐ and β‐thalassemia mutations were detected by routine genetic analysis (gap‐PCR and RDB‐PCR). Novel mutation diagnostic methods were based on DNA sequencing.

Results

Capillary electrophoresis revealed clinical feature of classic Hb H disease in the proband, and hematology analysis showed moderate anemia (Hb 87 g/L). But routine genetic analysis was found that it was only a heterozygote for the ‐‐^SEA deletion. DNA sequencing of α‐globin genes (α1 and α2) identified the breakpoints between nts 34162 and 34171 at α2 gene, named CD 90‐93 (‐AGCTTCGG) mutation. The genotype of proband and fetus was the same ‐‐^SEA/‐α^CD90‐93. His father was homozygous for the novel mutation (‐α^CD90‐93/‐α^CD90‐93), and his mother was heterozygote for the ‐‐^SEA deletion.

Conclusions

Our study for the first time described the novel mutation CD 90‐93 (‐AGCTTCGG). CE is a way to avoid misdiagnosis of rare or novel Hb H disease.

Molecular prenatal diagnosis of alpha and beta thalassemia in pregnant Hakka women in southern China

BACKGROUND

To date, there has been no systematic study of DNA-based prenatal diagnosis of thalassemia in pregnant Hakka women in southern China.

METHODS

A total of 279 pregnant Hakka women with confirmed cases of thalassemia who had been treated at the Meizhou People's Hospital in China's Guangdong Province from January 2014 to December 2016 were here enrolled. Genomic DNA was extracted from peripheral blood of couples and villus, amniotic fluid, or fetal cord blood. DNA-based diagnosis was performed on the tissues of fetuses whose parents had tested positive for α- and β-globin gene mutations were found using polymerase chain reaction (PCR) and flow-through hybridization technique. Follow-up visits were performed 6 months after the fetuses were born. Prenatal diagnosis was performed on 279 fetuses in at-risk pregnancies.

RESULTS

Here, 211 α-thalassemia fetuses were confirmed, including 41 (19.43%) that tested positive for Bart's hydrops syndrome and 15 (7.11%) for Hb H disease. There were 103 (48.81%) heterozygotes. β-thalassemia was confirmed in 68 fetuses, including 23 (33.82%) with severe thalassemia and 27 (39.71%) heterozygotes. Another 12 cases were confirmed with α+β-thalassemia, including three cases of severe β-thalassemia. DNA-based testing prenatal diagnosis of thalassemia was found to be highly reliable.

CONCLUSIONS

Our findings provide key information for clinical genetic counseling of prenatal diagnosis for major thalassemia in pregnant Hakka women in southern China.

Genetic basis of persistent red blood cell microcytosis in the Chinese unexplained by phenotypical testing

AIMS

Hypochromic microcytic anaemia is the hallmark phenotype of thalassaemia. Current phenotypical tests do not provide a diagnosis in a small proportion of patients with red blood cell microcytosis. We aim to evaluate the genetic basis of red cell microcytosis in these cases in our Chinese population.

METHODS

We identified from a large cohort of 1684 unselected requests for thalassaemia testing 23 Chinese subjects who had unexplained microcytosis after phenotypical iron and haemoglobin studies. In 18 of these subjects with available DNA, extensive genotypical analysis of the α and β globin gene cluster was performed, including gap-PCR, multiplex amplification-refractory mutation system, Sanger sequencing and multiplex ligation-dependent probe amplification.

RESULTS

Occult single and double α globin gene (HBA1, HBA2) deletions and α thalassaemic haemoglobinopathies (Haemoglobin Quong Sze, Haemoglobin Constant Spring) were the genetic basis for the microcytosis. Occult β globin gene (HBB) mutations and δ globin gene (HBD) abnormalities masking β thalassaemia are not seen.

CONCLUSIONS

A cost-effective genotyping approach for the detection of these occult globin gene mutations can be proposed. The identification of these mutations is important for making a diagnosis and for the provision of accurate genetic counselling. (This paper adds to our understanding of the genetic basis of red blood cell microcytosis in clinical practice, and it provides a cost-effective approach for genotyping in diagnostic laboratories).

Diagnosis and prevention of thalassemia

Thalassemia is the most common monogenic inherited disease worldwide and it affects most countries to various extents. This review summarizes the current approaches to phenotypic and genotypic diagnosis of thalassemia in clinical practice. Prevention strategies that encompass carrier screening, genetic counseling and prenatal diagnosis are discussed. The importance of public education and an awareness of a changing perception regarding this group of diseases are emphasized. It also addresses the impact of the rapidly increasing knowledge in disease severity modification by hemoglobin F (Hb F).

Mutations in Kruppel-like factor 1 cause transfusion-dependent hemolytic anemia and persistence of embryonic globin gene expression

In this study, we report on 8 compound heterozygotes for mutations in the key erythroid transcription factor Krüppel-like factor 1 in patients who presented with severe, transfusion-dependent hemolytic anemia. In most cases, the red cells were hypochromic and microcytic, consistent with abnormalities in hemoglobin synthesis. In addition, in many cases, the red cells resembled those seen in patients with membrane defects or enzymopathies, known as chronic nonspherocytic hemolytic anemia (CNSHA). Analysis of RNA and protein in primary erythroid cells from these individuals provided evidence of abnormal globin synthesis, with persistent expression of fetal hemoglobin and, most remarkably, expression of large quantities of embryonic globins in postnatal life. The red cell membranes were abnormal, most notably expressing reduced amounts of CD44 and, consequently, manifesting the rare In(Lu) blood group. Finally, all tested patients showed abnormally low levels of the red cell enzyme pyruvate kinase, a known cause of CNSHA. These patients define a new type of severe, transfusion-dependent CNSHA caused by mutations in a trans-acting factor (Krüppel-like factor 1) and reveal an important pathway regulating embryonic globin gene expression in adult humans.

Molecular characterisation of Haemoglobin Constant Spring and Haemoglobin Quong Sze with a Combine-Amplification Refractory Mutation System

BACKGROUND

The interaction of the non-deletional α(+)-thalassaemia mutations Haemoglobin Constant Spring and Haemoglobin Quong Sze with the Southeast Asian double α-globin gene deletion results in non-deletional Haemoglobin H disease. Accurate detection of non-deletional Haemoglobin H disease, which is associated with severe phenotypes, is necessary as these mutations have been confirmed in the Malaysian population.

METHODS

DNA from two families with Haemoglobin H disease was extracted from EDTA-anticoagulated whole blood and subjected to molecular analysis for α-thalassaemia. A duplex polymerase chain reaction was used to detect the Southeast Asian α-globin gene deletion. Polymerase chain reaction-restriction fragment length polymorphism analysis was then carried out to determine the presence of Haemoglobin Constant Spring and Haemoglobin Quong Sze. A combine-amplification refractory mutation system protocol was optimised and implemented for the rapid and specific molecular characterisation of Haemoglobin Constant Spring and Haemoglobin Quong Sze in a single polymerase chain reaction.

RESULTS AND CONCLUSIONS

The combine-amplification refractory mutation system for Haemoglobin Constant Spring and Haemoglobin Quong Sze, together with the duplex polymerase chain reaction, provides accurate pre- and postnatal diagnosis of non-deletional Haemoglobin H disease and allows detailed genotype analyses using minimal quantities of DNA.