Molecular characteristics of α+-thalassemia (3.7 kb deletion) in Southeast Asia: Molecular subtypes, haplotypic heterogeneity, multiple founder effects and laboratory diagnostics

A large cohort of Hb H disease in northeast Thailand: A molecular revisited, diverse genetic interactions and identification of a novel mutation

BACKGROUND AND AIMS

To update the molecular characteristics of α-thalassemia in northeast Thailand, the molecular basis and genetic interactions of Hb H disease were examined in a large cohort of patients.

MATERIALS AND METHODS

A study was done on 1,170 subjects with Hb H disease and various genetic interactions encountered during 2009-2023. Hb and DNA analyses were carried out.

RESULTS

As many as 40 genotypes with several known, previously undescribed, and novel mutations were observed. These included 698 subjects (59.8 %) of Hb H disease, 357 (30.6 %) with EABart's disease, 63 (5.4 %) with EEBart's disease, 18 (1.7 %) with abnormal Hbs, 17 (1.5 %) with β-thalassemia, and 4 (0.4 %) with EFBart's or EFABart's disease. The molecular basis of 13 subjects (1.1 %) remains unknown. The α0-thalassemia included --SEA (n = 1,139, 97.4 %) and --THAI (n = 21, 1.8 %). Two rare mutations were identified in 3 subjects (0.3 %) with --SA and --CR deletions. For α+-thalassemia, -α3.7 kb del (n = 626, 53.5 %), Hb Constant Spring (n = 415, 35.5 %), -α4.2 kb del (n = 44, 3.8 %), Hb Paksé (n = 36, 3.1 %), and Hb Q-Thailand (n = 19, 1.6 %), were detected. Ten rarer α+-thalassemia were identified, including a novel mutation, namely the Hb Chumphae (HBA2:c.32T>A). The Hb H-Lansing-Ramathibodi, Hb H-Jax, and Hb H-Chumphae are hitherto undescribed in this region. PCR-based diagnostic methods for these α-thalassemia defects were described.

CONCLUSIONS

This study confirms the diverse heterogeneity and genetic interactions causing Hb H disease in northeast Thailand. The results should prove useful for laboratory diagnosis and genetic counseling of this genetic disorder in the region.

Development of pre-implantation genetic testing protocol for monogenic disorders (PGT-M) of Hb H disease

Hb H disease is the most severe form of α-thalassemia compatible with post-natal life. Compound heterozygous α0-thalassemia- SEA deletion/α+-thalassemia- 3.7kb deletion is the commonest cause of Hb H disease in Thailand. Preimplantation genetics testing for monogenic disorders (PGT-M) is an alternative for couples at risk of the disorder to begin a pregnancy with a healthy baby. This study aims to develop a novel PCR protocol for PGT-M of Hb H disease- SEA/-3.7kb using multiplex fluorescent PCR. A novel set of primers for α+-thalassemia- 3.7kb deletion was developed and tested. The PCR protocol for α0-thalassemia- SEA deletion was combined for Hb H disease- SEA/-3.7kb genotyping. The PCR protocols were applied to genomic DNA extracted from subjects with different thalassemia genotypes and on whole genome amplification (WGA) products from clinical PGT-M cycles of the families at risk of Hb Bart's. The results were compared and discussed. The results showed three PCR products from α+-thalassemia- 3.7kb primer set, and three from α0thalassemiaSEA primer set. The results were consistent with the known thalassemia genotypes. The novel -α3.7 primers protocol was also tested on 37 WGA products from clinical PGT-M cycles giving accurate genotyping results and a satisfying amplification efficiency with the ADO rates of 2.7%, 0%, and 0% for HBA2, HBA1, and internal control fragments, respectively. This novel PCR protocol can precisely distinguish Hb H disease- SEA/-3.7kb from other genotypes. Additionally, this is the first PCR protocol for Hb H disease- SEA/-3.7kb which is optimal for PGT-M.

Retrospective study and implementation of a low-cost LAMP-turbidimetric assay for screening α0-thalassemia (SEA deletion): preventing and controlling Hb Bart's hydrops fetalis syndrome in Thailand

Homozygous α0-thalassemia (SEA deletion) or Hb Bart's hydrops fetalis syndrome is a significant public health issue in Thailand and Southeast Asia. A prevention and control program has been implemented in this region. This study focuses on retrospective laboratory data collected between January 2021 and April 2023 at a single center. Additionally, we developed a low-cost LAMP-turbidimetric assay to propose in the screening strategy. A total of 3,623 samples underwent screening tests (MCV, MCH, and DCIP), including 1,658 couple screenings (84.25%) and 310 single pregnant screenings (15.75%). Negative screenings, which did not require further investigation, were found in 75.51% for couple screenings and 46.58% for single pregnant screenings. At hemoglobin (Hb) analysis identified 129 couples which had fetuses at risk of severe thalassemia, whereas molecular analysis during the retrospective period revealed 210 samples with different genotypes. These remaining samples were validated using the low-cost LAMP-turbidimetric assay to detect α0-thalassemia (SEA deletion). The developed LAMP turbidimetric assay demonstrated a sensitivity and specificity of 100% (36/36 × 100) and 97.7% (170/174 × 100), respectively, when compared with gap-PCR. Furthermore, we propose a strategy involving the addition of the low-cost LAMP-turbidimetric assay before performing the gold standard. This strategy represents a cost-saving of USD 2,608 based on 210 samples that required DNA analysis. Finally, the developed LAMP turbidimetric assays offer advantages such as reduced time, workload, cost savings, no need for highly developed instruments, and a straightforward interpreting process. Therefore, implementation of LAMP assays into routine settings would be improve the efficiency of prevention and control program for severe thalassemia disease in this region.

Identification of double heterozygous -α4.2Ⅰ/-α4.2Ⅱ using third-generation sequencing

OBJECTIVE

The 4.2 kb deletion (-α4.2/) is a common a+-thalassemia with a carrier rate, followed by the South-East Asian deletion (-SEA) and the 3.7 kb deletion (-α3.7/). There are few reports about 4.2 kb deletion sub-types. Herein, we present a patient with double heterozygous -α4.2Ⅰ/-α4.2Ⅱwho was identified using third-generation sequencing (TGS).

METHODS

Hematology and hemoglobin fraction analysis were carried out by complete blood count (CBC) and capillary electrophoresis (CE). Gap-PCR was used to detect the common deletional α-thalassemia, and multiple ligation-dependent probe amplification (MLPA) was performed to screen the large deletion. Sanger sequencing identified the variant. The different deletions were confirmed by TGS.

RESULTS

CBC showed the patient with microcytic hypochromic anemia, and CE indicated the presence of a Hb variant. Gap-PCR and MLPA detected 4.2 kb deletion homozygotes (-α4.2/-α4.2). The Hb variant was confirmed as Hb Q-Thailand by Sanger sequencing. The patient was identified as compound heterozygous of 4.2 kb deletion and Hb Q-Thailand (-α4.2/-α4.2-Q-Thailand, -α4.2Ⅰ/-α4.2Ⅱ) using TGS.

CONCLUSIONS

Hb Q-Thailand (-α4.2-Q-Thailand/) complex 4.2 kb deletion heterozygote (-α4.2/) is easily misdiagnosed as 4.2 kb homozygous using Gap-PCR and MLPA. The TGS enables the identification of the two different 4.2 kb deletion sub-types.

Direct cord blood LAMP colorimetric phenol red assay for detecting α0-thalassemia (SEA deletion); the validation and post-natal screening in Thailand

Post-natal or newborn screening for thalassemia and hemoglobinopathies is useful for genetic counseling and managing thalassemia in children. We characterized thalassemia genotypes in newborns from the eastern part of Thailand. The results demonstrated a high heterogeneity of thalassemia and hemoglobinopathies with seventeen genotypes. We focused on α0- thalassemia (Southeast Asian [SEA] deletion) in this study. We developed and validated the loop-mediated isothermal amplification (LAMP) colorimetric assay for detecting α0- thalassemia (SEA deletion) using simple direct cord blood sampling compared to genomic DNA. A total of 160 cord blood samples were evaluated with the LAMP assay. The sensitivity and specificity of the LAMP colorimetric assay for α0-thalassemia (SEA deletion) using direct cord blood showed 100% (6/6 x 100) and 98.05% (151/154 x 100) whereas, genomic DNA showed 100% (6/6 x 100) and 100% (154/154 x 100), respectively. Moreover, we demonstrated other simple screening tools for α0-thalassemia with %Hb Bart's, MCV, and MCH values and found that these parameters were not diagnostic in our samples. The direct cord blood with colorimetric LAMP assay is simple, rapid, and does not require a post-LAMP step compared to conventional PCR. These techniques could be applied in post-natal or large population screening for α0-thalassemia (SEA deletion). Finally, this could support early prevention of complications, early management, genetic counseling for α-thalassemia disease in children, or a long-term prevention and control program of severe thalassemia in Thailand.

Hemoglobin profile and molecular characteristics of the complex interaction of hemoglobin Doi-Saket [α9(A7) asn > lys, HBA2:c.30C > a], a novel α2α1 hybrid globin variant, with hemoglobin E [β26(B8) Glu > lys, HBB:c.79G > A] and deletional α+-thalassemia in a Thai family

BACKGROUND

An increasing number of α-hemoglobin (Hb) variants is causing various clinical symptoms; therefore, accurate identification of these Hb variants is important.

OBJECTIVE

This study aimed to describe the molecular and hematological characteristics of novel Hb Doi-Saket that gives rise to a typical α+-thalassemia phenotype in carriers with and without other hemoglobinopathies.

MATERIALS AND METHODS

Biological samples from a proband and his family members were analyzed. Hematological profiles were analyzed using a standard automated cell counter. Hb was analyzed by capillary electrophoresis and high-performance liquid chromatography. Mutations and globin haplotype were identified by DNA analysis. Novel diagnostic tools based on allele-specific polymerase chain reaction (PCR) and PCR-restriction fragment length polymorphism were developed.

RESULTS

Hb analysis showed a major abnormal Hb fraction, moving slower than HbA, and a minor Hb fraction alongside HbA2 in the proband, his father, and son. DNA analysis of the α-globin gene identified the -α3.7 deletion and in cis the C > A mutation on codon 9 of the α2α1 gene, corresponding to Hb Doi-Saket [α9(A7) Asn > Lys]. This mutation could be identified using newly developed allele-specific PCR-based assays. The Hb Doi-Saket al.lele was significantly associated with haplotype [- + M + + 0 -]. Interaction of αDoi-Saket with βE globin chains led to a new Hb variant (HbE Doi-Saket). Phenotypic expression was clinically silent in heterozygotes and might present slight microcytosis.

CONCLUSIONS

Hb Doi-Saket emphasizes a great diversity present in α-globin gene. The mutation in this family from Thailand was linked to -α3.7 and caused mild microcytosis in the carriers. The combination of this variant with deletions in α genes might cause a severe clinical phenotype. Different methods of separation can provide useful information in diagnosis, and a complete molecular approach is needed for confirmation before considering patient management.

Molecular and haematological characterisation of haemolytic anaemia associated with biallelic KLF1 mutations: a case series

AIMS

Krüppel-like factor 1 (KLF1) is an erythroid-specific transcription factor playing an important role in erythropoiesis and haemoglobin (Hb) switching. Biallelic KLF1 mutations can cause haemolytic anaemia with thalassaemia-like syndromes but are rarely reported. We explore the KLF1 mutations in Thai subjects with unexplainable haemolytic anaemia.

METHODS

The study was done on 57 subjects presented with haemolytic anaemia and elevated Hb F without β-thalassaemia diseases. Hb analysis was performed using capillary electrophoresis. Analyses of α-thalassaemia, β-thalassaemia and KLF1 genes were performed using PCR-based methods and DNA sequencing.

RESULTS

Thirteen subjects with compound heterozygous for a known and five new genetic KLF1 interactions were identified, including KLF1:c.519_525dupCGGCGCC/c.892G>C with class 3/2 (n=8), and each subject with new genetic interaction, including KLF1:c.-154C>T;643C>T/c.983G>A with class 3/2, KLF1:c.-154C>T;643C>T/c.809C>G with class 3/2, KLF1:c892G>C/c.983G>A with class 2/2, KLF1:c.892G>C/c.1001C>G with class 2/2 and KLF1:c.1001C>G/c.1003G>A with class 2/2. Most of them had anaemia with Hb levels ranging from 45 to 110 g/L, hypochromic microcytosis, aniso-poikilocytosis, increased Hb F levels (17.9%-47.4%), small amounts of Hb Bart's, regular blood transfusion, hyperbilirubinaemia, increased serum ferritin and nucleated red blood cell.

CONCLUSIONS

Biallelic KLF1 mutations associated with anaemia may not be uncommon in Thailand. Characteristics of haemolytic anaemia, abnormal red cell morphology with nucleated red blood cells and elevated Hb F, and presenting small amounts of Hb Bart's without thalassaemia diseases are useful markers to further investigation of the KLF1 gene.

Molecular basis of non-deletional HPFH in Thailand and identification of two novel mutations at the binding sites of CCAAT and GATA-1 transcription factors

High Hb F determinants are genetic defects associated with increased expression of hemoglobin F in adult life, classified as deletional and non-deletional forms. We report the first description of non-deletional hereditary persistence of fetal hemoglobin (HFPH) in Thailand. Study was done on 388 subjects suspected of non-deletional HPFH with elevated Hb F expression. Mutations in the Gγ- and Aγ-globin genes were examined by DNA analysis and rapid diagnosis of HPFH mutations were developed by PCR-based methods. Twenty subjects with five different mutations were identified including three known mutations, - 202 Aγ (C>T) (n = 3), - 196 Aγ (C>T) (n = 3), and - 158 Aγ (C>T) (n = 12), and two novel mutations, - 117 Aγ (G>C) (n = 1) and - 530 Gγ (A>G) (n = 1). Interaction of the - 117 Aγ (G>C) and Hb E (HBB:c.79G>A) resulted in elevation of Hb F to the level of 13.5%. Two plain heterozygous subjects with - 530 Gγ (A>G) had marginally elevated Hb F with 1.9% and 3.0%, whereas the proband with homozygous - 530 Gγ (A>G) had elevated Hb F of 11.5%. Functional prediction indicated that the - 117 Aγ (G>C) and - 530 Gγ (A>G) mutations dramatically alter the binding of transcription factors to respective γ-globin gene promotors, especially the CCAAT and GATA-1 transcription factors. Diverse heterogeneity of non-deletional HFPH with both known and new mutations, and complex interactions of them with other forms of thalassemia are encountered in Thai population.

Prospective screening for δ-hemoglobinopathies associated with decreased hemoglobin A2 levels or hemoglobin A2 variants: A single center experience

BACKGROUND

δ-hemoglobinopathies may lead to misdiagnosis of several thalassemia syndromes especially β-thalassaemia carrier, it is important to evaluate the δ-globin gene defects in areas with high prevalence of globin gene disorders. We describe a prospective screening for δ-hemoglobinopathies in a routine setting in Thailand.

METHODS

Study was done on a cohort of 8,471 subjects referred for thalassemia screening, 317 (3.7%) were suspected of having δ-globin gene defects due to reduced hemoglobin (Hb) A₂ levels and/or appearance of Hb A₂-variants on hemoglobin analysis. Hematologic and DNA analysis by PCR and related assays were carried out.

RESULTS

DNA analysis of δ-globin gene identified seven different δ-globin mutations in 24 of 317 subjects (7.6%). Both known mutations; δ^-77(T>C) (n=3), δ^-68(C>T) (n=1), δ^-44(G>A) (n=8), Hb A₂-Melbourne (n=5), δ^{IVSII-897(A>C)} (n=5), and Hb A₂-Troodos (n=1) and a novel mutation; the Hb A₂-Roi-Et (n=1) were identified. This Hb A₂-Roi-Et, results from a double mutations in-cis, δ^{CD82(AAG>AAT)} and δ^{CD133(GTG>ATG)}, was interestingly found in combination with an in trans, 12.6 kb deletional δβ⁰-thalassemia in an adult Thai woman who had no Hb A₂ and elevated Hb F. A multiplex-allele-specific PCR was developed to detect these novel δ-globin gene defects.

CONCLUSIONS

The result confirms a diverse heterogeneity of δ-hemoglobinopathies in Thailand which should prove useful in a prevention and control program of thalassemia in the region.

Molecular basis of a high Hb A2/Hb Fβ-thalassemia trait: a retrospective analysis, genotype-phenotype interaction, diagnostic implication, and identification of a novel interaction with α-globin gene triplication

Background

β ⁰-thalassemia deletion removing 5´β-globin promoter usually presents phenotype with high hemoglobin (Hb) A₂ and Hb F levels. We report the molecular characteristics and phenotype-genotype correlation in a large cohort of the β ⁰-thalassemia with 3.4 kb deletion.

Methods

A total of 148 subjects, including 127 heterozygotes, 20 Hb E-β-thalassemia patients, and a double heterozygote with α-globin gene triplication, were recruited. Hb and DNA analysis were performed to identify thalassemia mutations and four high Hb F single nucleotide polymorphisms (SNPs) including four base pair deletion (-AGCA) at ^A γ-globin promoter, rs5006884 on OR51B6 gene, -158 ^G γ-XmnI, BCL11A binding motifs (TGGTCA) between 3´^A γ-globin gene and 5´δ-globin gene.

Results

It was found that heterozygous β ⁰-thalassemia and Hb E-β ⁰-thalassemia with 3.4 kb deletion had significantly higher Hb, hematocrit, mean corpuscular volume, mean corpuscular hemoglobin and Hb F values as compared with those with other mutations. Co-inheritance of heterozygous β ⁰-thalassemia with 3.4 kb deletion and α-thalassemia was associated with even higher MCV and MCH values. The Hb E-β ⁰-thalassemia patients carried a non-transfusion-dependent thalassemia phenotype with an average Hb of around 10 g/dL without blood transfusion. A hitherto undescribed double heterozygous β ⁰-thalassemia with 3.4 kb deletion and α-globin gene triplication presented as a plain β-thalassemia trait. Most of the subjects had wild-type sequences for the four high Hb F SNPs examined. No significant difference in Hb F was observed between those of subjects with and without these SNPs. Removal of the 5´β-globin promoter may likely be responsible for this unusual phenotype.

Conclusions

The results indicate that β ⁰-thalassemia with 3.4 kb deletion is a mild β-thalassemia allele. This information should be provided at genetic counseling and prenatal thalassemia diagnosis.

The -α3.7III subtype of α+-thalassemia was identified in China

OBJECTIVE

The 3.7 kb deletion (-α^3.7) in the α-globin cluster, which characterizes α⁺-thalassemia, has been reported to have a carrier rate of 4.78% in southern China. Three -α^3.7 subtypes have been identified worldwide. However, the -α^{3.7 III} subtype has not previously been identified in China. Herein, we reported identification of the -α^{3.7 III} subtype in a Chinese patient.

METHODS

We used gap-PCR and a liquid chip system to detect α-thalassemia mutations. Multiple ligation-dependent probe amplification was performed to detect the large deletion. We finally used Sanger sequencing and single molecule real-time sequencing to characterize and confirm the genotype.

RESULTS

The proband, characterized as -α^{3.7 III} heterozygous, showed microcytosis and hypochromic red cells, with a mean corpuscular volume of 78 fL and mean corpuscular hemoglobin of 25.4 pg. The proband's mutation was inherited from her father, who had normal blood parameters.

CONCLUSION

We first identified the -α^{3.7 III} subtype in China. Consequently, all -α^3.7 subtypes have now been identified in the Chinese population. Therefore, attention should be paid to -α^{3.7 III} in clinical prenatal diagnosis, given that commonly used methods such as gap-PCR may lead to misdiagnosis or missed diagnosis.

Anemia, iron deficiency, and thalassemia among the Thai population inhabiting at the Thailand-Lao PDR-Cambodia triangle

Anemia is a major public health problem in many areas of Southeast Asia. Ascertaining anemia and defining its underlying causes is essential for providing appropriate care, management, and establishment of a control program. Limited studies on these have been carried out on people living at the borders of Thailand, Lao PDR, and Cambodia. This cross-sectional study was done in four areas along the borders of Thailand, Lao PDR, and Cambodia. Blood specimens were collected from subjects aged 15-18 years in four districts including Kantharalak, Si Sa Ket province (n = 36), Nam Khun (n = 109), Nam Yuen (n = 98), and Na Chaluai (n = 128), Ubon Ratchathani province, Thailand. RBC parameters were recorded, and serum ferritin (SF) level was measured. Diagnosis of thalassemia and hemoglobinopathies was based on hemoglobin (Hb) and DNA analyses. Measurement of C-reactive protein was performed to exclude false-negative result of iron deficiency. The prevalence of anemia was found to be 25.1%. ID accounted for only 10.5%. Various types of thalassemia were identified in 67.7% of the subjects. The overall prevalence of thalassemia included 3.5% α⁰-thalassemia, 0.8% β-thalassemia, 47.7% Hb E, and 53.6% α⁺-thalassemia. The proportions of ID, thalassemia and combined ID and thalassemia among anemic subjects were 6.5%, 66.6%, and 20.4%, respectively. The results indicate that thalassemia and hemoglobinopathies rather than ID are major causes of anemia in Thailand-Lao PDR-Cambodia triangle. This information should prove useful for implementing an anemia control program in the regions.

Analysis of rare thalassemia genetic variants based on third-generation sequencing

Thalassemia is a group of common hereditary anemias that cause significant morbidity and mortality worldwide. However, precisely diagnosing thalassemia, especially rare thalassemia variants, is still challenging. Long-range PCR and long-molecule sequencing on the PacBio Sequel II platform utilized in this study could cover the entire HBA1, HBA2 and HBB genes, enabling the diagnosis of most of the common and rare types of thalassemia variants. In this study, 100 cases of suspected thalassemia were subjected to traditional thalassemia testing and third-generation sequencing for thalassemia genetic diagnosis. Compared with traditional diagnostic methods, an additional 10 cases of rare clinically significant variants, including 3 cases of structure variants and 7 cases of single nucleotide variations (SNVs) were identified, of which a case with − α^3.7 subtype III (− α^3.7III) was first identified and validated in the Chinese population. Other rare variants of 11.1 kb deletions (− 11.1/αα), triplicate α-globin genes (aaa^3.7/αα) and rare SNVs have also been thoroughly detected. The results showed that rare thalassemia variants are not rare but have been misdiagnosed by conventional methods. The results further validated third-generation sequencing as a promising method for rare thalassemia genetic testing.

Diagnostic value of fetal hemoglobin Bart's for evaluation of fetal α-thalassemia syndromes: application to prenatal characterization of fetal anemia caused by undiagnosed α-hemoglobinopathy

Background

To evaluate whether the quantification of fetal hemoglobin (Hb) Bart’s is useful for differentiation of α-thalassemia syndromes in the fetus and to characterize the fetal anemia associated with fetal α-hemoglobinopathy.

Methods

A total of 332 fetal blood specimens collected by cordocentesis were analyzed using capillary electrophoresis and the amount of Hb Bart’s was recorded. The result was evaluated against thalassemia genotypes determined based on Hb and DNA analyses. Prenatal Hb and DNA characterization of the fetal anemia observed in two families was done.

Results

Among 332 fetuses investigated, Hb and DNA analyses identified 152 fetuses with normal genotypes. The remaining 180 fetuses carried α-thalassemia with several genotypes. Variable amounts of Hb Bart’s were identified in all fetuses with α-thalassemia, which could be used for simple differentiation of fetal α-thalassemia genotypes. These included α⁺- and α⁰-thalassemia traits, homozygous α⁺-thalassemia and Hb Constant Spring (CS), Hb H disease, Hb H-CS and Hb H-Quong Sze diseases, homozygous α⁰-thalassemia causing the Hb Bart’s hydrops fetalis and a remain uncharacterized α-thalassemia defect. The previously undescribed interactions of Hb Queens Park and Hb Amsterdam A1 with Hb E were detected in two fetuses with Hb Bart’s of 0.5%. The Hb Queens Park-AEBart’s disease was also noted in one pregnant woman. Prenatal analysis of the fetuses with severe fetal anemia and cardiomegaly with Hb Bart’s of 9.0% and 13.6% revealed unexpectedly the homozygous Hb CS and a compound heterozygosity of Hb CS/Hb Pakse’ with Hb E heterozygote, respectively.

Conclusions

The usefulness of detecting and differentiation of fetal α-thalassemia syndromes by quantifying of Hb Bart’s was demonstrated. Apart from the fatal condition of Hb Bart’s hydrops fetalis associated with homozygous α⁰-thalassemia, homozygous Hb CS and a compound Hb CS/Hb Pakse’ could result in severe fetal anemia and fetal complications, prenatal diagnosis is highly recommended. The simple Hb Bart’s quantification of fetal blood should prove helpful in this matter.

Direct PCR assays without DNA extraction for rapid detection of hemoglobin Constant Spring and Pakse' genes: application for carrier screening and prenatal diagnosis

Hemoglobin Constant Spring (Hb CS) and Hb Pakse' (PS) are the common non-deletional α⁺-thalassemia found in Thailand. These two variants can cause severe thalassemia syndromes, especially in fetus and neonate. Molecular diagnosis is the only confirmatory method because Hb CS and Hb PS are usually missed by routine screening and Hb analysis. Therefore, we aimed to develop rapid direct PCR for the diagnosis of Hb CS and PS genes. Multiplex direct PCR assays for identifying the Hb CS and PS genes in whole blood (WB) and amniotic fluid (AF) specimens were developed. The assays were firstly validated on 290 unrelated whole blood specimens. Hb CS and PS carriers were identified in 67 (23.1%) and 6 (2.1%) cases, respectively. A 100% concordant result as compared to routine PCR assay was observed. The direct PCR assays have been applied successfully for prenatal diagnosis in two families. The result showed that the fetuses were affected by homozygous Hb CS and compound heterozygous Hb CS/Hb PS. Accurate prenatal diagnosis of these families was observed using the newly developed assays. These assays should be applicable in routine thalassemia diagnostics as well as in the large-scale screening of Hb CS and PS in the region.

Prenatal Genetic Counseling in a Chinese Pregnant Woman With Rare Thalassemia: A Case Report

Background: Prenatal genetic counseling can be difficult, especially when it is related to fetuses with a rare thalassemia. An intronic variant located far from obvious regulatory sequences in the HBB gene could be very difficult to evaluate as it may affect the mRNA processing or cause β-thalassemia (β-thal). In the present study, a Chinese pregnant woman with HbJ-Bangkok and a very rare change in the second intron of the HBB gene [IVS-II-806(G>C), NM_000518.4, HBB: c.316-45G>C] in combination with α+-thalassemia was reported, which can assist in prenatal genetic counseling. Case Report: A 26-year-old pregnant woman presented at the obstetric clinic for a routine pregnancy check at 12 weeks of gestation. Red blood counts and high-performance liquid chromatography (HPLC) were consistent with clinical manifestations of anemia. Multiplex gap-polymerase chain (gap-PCR) displayed rightward deletion (-α3.7/αα). Direct DNA sequencing of the δ-globin gene showed no mutation. Sanger sequencing of the β-globin gene showed a previously undescribed condition of double heterozygosity for HbJ-Bangkok and a very rare change in the second intron of the HBB gene [IVS-II-806(G>C), NM_000518.4, HBB: c.316-45G>C] that has not been previously reported in the HbVar database. Thus, a rare combination of α+-thal and a compound heterozygosity of HbJ-Bangkok and [IVS-II-806(G>C)] with α+-thal (-α3.7/αα) was finally diagnosed. Prenatal genetic counseling was made based on the genotype and phenotype analyses. Conclusion: This study enlarges the mutation spectrum of β-globin gene and emphasizes DNA analysis in resolving unusual patterns in Hb analysis and the importance of sharing the observed rare undefined mutations and the possible interactions with known molecular defects, which can assist in prenatal genetic counseling.

δ-Hemoglobinopathies in Thailand: screening, molecular basis, genotype-phenotype interaction, and implication for prevention and control of thalassemia

The δ-globin gene defects are clinically silent but interaction with β-thalassemia can lead to a misdiagnosis of β-thalassemia carrier. We report an extensive molecular characterization of δ-hemoglobinopathies in Thailand. Study was done on 32,108 subjects, encountered at the thalassemia screening. Six different approaches based on the reduced Hb A₂ or appearance of Hb A₂-derivative were established for selective recruitment of subjects. Among 32,108 subjects, a total of 296 subjects were suspected of having δ-globin gene defects. Of these 296 subjects, Hb and DNA analyses identified δ-hemoglobinopathies with 10 different mutations in 34 (0.11%) of them. These included a novel mutation, [δ^{CD30(AGG>GGG)} (n = 1)], 5 previously undescribed in Thailand, [δ^-44(G>A) (n = 7), Hb A₂-Troodos (n = 5), δ^{IVSII-897(A>C)} (n = 4), δ^-68(C>T) (n = 2), and Hb A₂-Indonesia (n = 1)], and 4 mutations previously found in Thailand, [Hb A₂-Melbourne (n = 9), δ^-77(T>C) (n = 3), Hb A₂' (n = 1), and Hb A₂-Kiriwong (n = 1)]. Genetic heterogeneities seen included interactions of δ-globin gene defects with heterozygous Hb E, β-thalassemia, α-thalassemia, and in cis locations of the Hb A₂-Troodos and Hb E mutations found for the first time. Rapid identification methods of these δ-globin gene mutations were developed. The results should prove useful to a prevention and control program of hemoglobinopathies in the region.

Forager and farmer evolutionary adaptations to malaria evidenced by 7000 years of thalassemia in Southeast Asia

Thalassemias are inherited blood disorders that are found in high prevalences in the Mediterranean, Southeast Asia and the Pacific. These diseases provide varying levels of resistance to malaria and are proposed to have emerged as an adaptive response to malaria in these regions. The transition to agriculture in the Holocene has been suggested to have influenced the selection for thalassemia in the Mediterranean as land clearance for farming encouraged interaction between Anopheles mosquitos, the vectors for malaria, and human groups. Here we document macroscopic and microscopic skeletal evidence for the presence of thalassemia in both hunter-gatherer (Con Co Ngua) and early agricultural (Man Bac) populations in northern Vietnam. Firstly, our findings demonstrate that thalassemia emerged prior to the transition to agriculture in Mainland Southeast Asia, from at least the early seventh millennium BP, contradicting a long-held assumption that agriculture was the main driver for an increase in malaria in Southeast Asia. Secondly, we describe evidence for significant malarial burden in the region during early agriculture. We argue that the introduction of farming into the region was not the initial driver of the selection for thalassemia, as it may have been in other regions of the world.

Prevalence of Alpha(α)-Thalassemia in Southeast Asia (2010-2020): A Meta-Analysis Involving 83,674 Subjects

Alpha(α)-thalassemia is a blood disorder caused by many types of inheritable α-globin gene mutations which causes no-to-severe clinical symptoms, such as Hb Bart's hydrops fetalis that leads to early foetal death. Therefore, the aim of this meta-analysis was to provide an update from year 2010 to 2020 on the prevalence of α-thalassemia in Southeast Asia. A systematic literature search was performed using PubMed and SCOPUS databases for related studies published from 2010 to 2020, based on specified inclusion and exclusion criteria. Heterogeneity of included studies was examined with the I2 index and Q-test. Funnel plots and Egger's tests were performed in order to determine publication bias in this meta-analysis. Twenty-nine studies with 83,674 subjects were included and pooled prevalence rates in this meta-analysis were calculated using random effect models based on high observed heterogeneity (I2 > 99.5, p-value < 0.1). Overall, the prevalence of α-thalassemia is 22.6%. The highest α-thalassemia prevalence was observed in Vietnam (51.5%) followed by Cambodia (39.5%), Laos (26.8%), Thailand (20.1%), and Malaysia (17.3%). No publication bias was detected. Conclusions: This meta-analysis suggested that a high prevalence of α-thalassemia occurred in selected Southeast Asia countries. This meta-analysis data are useful for designing thalassemia screening programs and improve the disease management.

Micromapping of Thalassemia and Hemoglobinopathies Among Laos, Khmer, Suay and Yer Ethnic Groups Residing in Lower Northeastern Thailand

Northeastern (NE) Thailand is one of the areas with a prevalence of thalassemias and hemoglobinopathies. Data on the prevalence of the diseases in minorities in the region has been limited. This study aimed to survey the thalassemias and hemoglobinopathies that take into account ethnicity. Four ethnic groups, including Laos (n = 162), Khmer (n = 145), Suay (n = 134), and Yer (n = 101) inhabiting the lower region of NE Thailand, were selected to represent the study populations. The results demonstrated that an extremely high prevalence of Hb E (HBB: c.79G>A) (>50.0%) was observed in the Khmer, Suay and Yer ethnic groups. The highest prevalence of α⁺-thalassemia (α⁺-thal) [-α^3.7 (rightward)] deletion was found in the Khmer ethnic group (48.28%). The -α^4.2 (leftward) deletion (α⁺-thal) was restricted to the Yer ethnic group. Yer and Suay had a high incidence of Hb Constant Spring (Hb CS; HBA2: c.427T>C) as well as Hb Paksé (HBA2: c.429A>T). As the prevalence of α⁰-thalassemia (α⁰-thal) is relatively high in Suay (7.46%), couples who are members of Suay ethnic population should be urged to undergo hematological screening before planning a pregnancy to control the Hb Bart's hydrops fetalis. Micromapping of thalassemias and hemoglobinopathies herein described will be helpful in genetic counseling and public education campaigns, which should be carried out in appropriate languages, with exhibitions at the village levels. This information will be of benefit for the long-term effort to reduce the burden of severe thalassemia disease in the region.