A Single-Tube Multiplex Gap-Polymerase Chain Reaction for the Detection of Eight β-Globin Gene Cluster Deletions Common in Southeast Asia

α-Globin mutations and Genetic Variants in γ-globin Promoters are Associated with Unelevated Hemoglobin F Expression of Atypical β0-thalassemia/HbE

BACKGROUND

Excessive expression of hemoglobin F (HbF) is a characteristic feature and important diagnostic marker of β0-thalassemia/HbE disease. However, some patients may exhibit low-HbF levels, leading to misdiagnosis and precluding genetic counseling. The genetic factors influencing these differences in HbF expression in this atypical disease are not completely understood.

AIMS

To investigate determinants contributing to the non-elevation of HbF expression in β0-thalassemia/HbE disease.

METHODS

We studied 231 patients with β0-thalassemia/HbE confirmed by DNA analysis; classified them into the low-HbF (n = 62) and high-HbF (n = 169) groups; analyzed hematological parameters and hemoglobin levels in both groups; and characterized mutations in β- and α-globin genes and genetic variants in γ-globin promoters.

RESULTS

Both groups showed similar rates of type β0-thalassemia mutations but significantly different proportions of α-globin mutations: approximately 88.7% (95% confidence interval [CI] = 66.8-115.5) and 39.1% (95% CI = 30.2-49.7) in the low- and high-HbF groups, respectively. The results revealed single-nucleotide polymorphisms (SNPs) at -158 (C>T) in the Gγ-globin promoters and novel SNPs at the 5' untranslated region position 25 (G>A) in Aγ-globin promoters. The distribution of CC genotypes of the Gγ-globin promoter in the low-HbF group was significantly higher than that in the high-HbF group.

CONCLUSIONS

Cases with HbE predominance with low-HbF levels and undetectable HbA may not be as conclusive as those with homozygous HbE until DNA analysis is performed. Concomitant inheritance of α-thalassemia is an important inherent factor modifying HbF expression in a typical β0-thalassemia/HbE, and SNPs with the CC genotype in the Gγ-globin promoter may indicate unelevated HbF expression in patients with this disease.

Awareness and practical evaluation of correct use of iron chelators; a study to track the ambiguities of thalassemia patients on their medications in Iran

PURPOSE

This study aimed to evaluate the knowledge, attitude, and practice toward iron chelating agents (ICAs) in Iranian thalassemia major patients.

METHODS

A total of 101 patients with thalassemia major were involved in this cross-sectional survey. A deep medication review was done, and participants' knowledge, attitude, and practice were evaluated by a validated instrument based on a 20-scoring system.

RESULTS

Statistical analyses showed 52 patients (51.5%) had a poor knowledge level (scores < 10) about their medications, 37 (36.6%) had a moderate level (scores 10-15), and 12 (11.9%) had a satisfactory level (scores > 15). Seventy-seven (76.2%) patients have positive beliefs regarding the dependence of their current health status on taking iron chelators, and 63 (62.4%) believed that they would become very ill without taking medication. The results also showed that the mean practice score in patients who received deferoxamine was 5.81 ± 3.50; in the patients who received deferiprone and those who received deferasirox, the mean scores were 7.36 ± 5.15 and 14.94 ± 4.14. Also, the knowledge and practice level had a direct linear correlation based on the regression analyses (P < 0.001).

CONCLUSION

In conclusion, results of the present research suggests that the patients' knowledge about the administration, adverse events, and necessity of ICAs was not satisfactory. Improving the knowledge of thalassemia patients toward their medicines through educational interventions is highly recommended to improve their practice level.

Justification of Universal Iron Supplementation for Infants 6-12 months in Regions with a High Prevalence of Thalassemia

Introduction

Many clinicians hesitate to adopt a universal infant iron supplementation program due to the risk of increased iron absorption for those with thalassemia. We aimed to determine thalassemia prevalence in 6- to 12-month-old infants, along with the iron status of those with and without thalassemia.

Methods

We performed a cross-sectional descriptive study of infants attending the Well Baby Clinic at Thammasat University Hospital for routine checkups. Complete blood count, hemoglobin electrophoresis, iron parameters, and molecular genetics for common α- and β-thalassemia were evaluated.

Results

Overall, 97 of 206 (47%) participants had thalassemia minor, the majority having Hb E traits. None had thalassemia intermedia or major. Familial history of anemia or thalassemia presented an increased risk of detecting thalassemia minor in offspring (OR 5.18; 95% CI 2.60-10.33, p=0.001). There were no statistical differences in transferrin saturation, serum ferritin and hepcidin between iron-replete infants with thalassemia minor and those without. However, one-third of infants with thalassemia minor (31/97) also had iron deficiency anemia (IDA), with a similar risk of having iron deficiency to infants without thalassemia. There was no hepcidin suppression in our infants with thalassemia minor as compared to controls.

Conclusions

Both thalassemia and IDA are endemic to Southeast Asia. Infants with thalassemia minor, particularly with Hb E and α-thalassemia traits, are at risk of IDA. Our short-term universal iron supplementation program for 6- to 12-month-old infants does not appear to increase the risk of those with thalassemia minor developing iron overload in the future.

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.

Molecular diagnosis of hereditary hemolytic anemias: Recent updates

Hereditary hemolytic anemia (HHA) is a heterogeneous group of disorders due to genetically caused defects in red blood cell membrane structure, enzymes, heme and globin synthesis, erythroid proliferation, and differentiation. Traditionally, the diagnostic process is complex and includes a plethora of tests from routine to highly specialized ones. The inclusion of molecular testing has significantly improved the diagnostic yield. The value of molecular testing is broader than just rendering the correct diagnosis, as it may also guide therapeutic decisions. As more molecular modalities become available for clinical use, it is imperative to understand their benefits and disadvantages pertaining to the HHA diagnostics. Re-evaluation of the traditional diagnostic workflow may also bring forth additional benefits. This review focuses on the current state of molecular testing for HHA.

Third-Generation Sequencing as a New Comprehensive Technology for Identifying Rare α- and β-Globin Gene Variants in Thalassemia Alleles in the Chinese Population

CONTEXT.—

Identification of rare thalassemia variants requires a combination of multiple diagnostic technologies.

OBJECTIVE.—

To investigate a new approach of comprehensive analysis of thalassemia alleles based on third-generation sequencing (TGS) for identification of α- and β-globin gene variants.

DESIGN.—

Enrolled in this study were 70 suspected carriers of rare thalassemia variants. Routine gap-polymerase chain reaction and DNA sequencing were used to detect rare thalassemia variants, and TGS technology was performed to identify α- and β-globin gene variants.

RESULTS.—

Twenty-three cases that carried rare variants in α- and β-globin genes were identified by the routine detection methods. TGS technology yielded a 7.14% (5 of 70) increment of rare α- and β-globin gene variants as compared with the routine methods. Among them, the rare deletional genotype of -THAI was the most common variant. In addition, rare variants of CD15 (G>A) (HBA2:c.46G>A), CD117/118(+TCA) (HBA1:c.354_355insTCA), and β-thalassemia 3.5-kilobase gene deletion were first identified in Fujian Province, China; to the best of our knowledge, this is the second report in the Chinese population. Moreover, HBA1:c.-24C>G, IVS-II-55 (G>T) (HBA1:c.300+55G>T) and hemoglobin (Hb) Maranon (HBA2:c.94A>G) were first identified in the Chinese population. We also identified rare Hb variants of HbC, HbG-Honolulu, Hb Miyashiro, and HbG-Coushatta in this study.

CONCLUSIONS.—

TGS technology can effectively and accurately detect deletional and nondeletional thalassemia variants simultaneously in one experiment. Our study also demonstrated the application value of TGS-based comprehensive analysis of thalassemia alleles in the detection of rare thalassemia gene variants.

Next-Generation Sequencing (NGS) and Third-Generation Sequencing (TGS) for the Diagnosis of Thalassemia

Thalassemia is one of the most heterogeneous diseases, with more than a thousand mutation types recorded worldwide. Molecular diagnosis of thalassemia by conventional PCR-based DNA analysis is time- and resource-consuming owing to the phenotype variability, disease complexity, and molecular diagnostic test limitations. Moreover, genetic counseling must be backed-up by an extensive diagnosis of the thalassemia-causing phenotype and the possible genetic modifiers. Data coming from advanced molecular techniques such as targeted sequencing by next-generation sequencing (NGS) and third-generation sequencing (TGS) are more appropriate and valuable for DNA analysis of thalassemia. While NGS is superior at variant calling to TGS thanks to its lower error rates, the longer reads nature of the TGS permits haplotype-phasing that is superior for variant discovery on the homologous genes and CNV calling. The emergence of many cutting-edge machine learning-based bioinformatics tools has improved the accuracy of variant and CNV calling. Constant improvement of these sequencing and bioinformatics will enable precise thalassemia detections, especially for the CNV and the homologous HBA and HBG genes. In conclusion, laboratory transiting from conventional DNA analysis to NGS or TGS and following the guidelines towards a single assay will contribute to a better diagnostics approach of thalassemia.

The hemoglobinopathies, molecular disease mechanisms and diagnostics

Hemoglobinopathies are the most common monogenic disorders in the world with an ever increasing global disease burden each year. As most hemoglobinopathies show recessive inheritance carriers are usually clinically silent. Programmes for preconception and antenatal carrier screening, with the option of prenatal diagnosis are considered beneficial in many endemic countries. With the development of genetic tools such as Array analysis and Next Generation Sequencing in addition to state of the art screening at the hematologic, biochemic and genetic level, have contributed to the discovery of an increasing number of rare rearrangements and novel factors influencing the disease severity over the recent years. This review summarizes the basic requirements for adequate carrier screening analysis, the importance of genotype–phenotype correlation and how this may lead to the unrevealing exceptional interactions causing a clinically more severe phenotype in otherwise asymptomatic carriers. A special group of patients are β‐thalassemia carriers presenting with features of β‐thalassemia intermedia of various clinical severity. The disease mechanisms may involve duplicated α‐globin genes, mosaic partial Uniparental Isodisomy of chromosome 11p15.4 where the HBB gene is located or haplo‐insufficiency of a non‐linked gene SUPT5H on chromosome 19q, first described in two Dutch families with β‐thalassemia trait without variants in the HBB gene.

Molecular and hematological studies in a cohort of beta zero South East Asia deletion (β°-thal SEA) from Malaysian perspective

ABSTRACT

We report the haematological parameters and molecular characterization of beta zero (β°) South East Asia (SEA) deletion in the HBB gene cluster with unusually high levels of Hb F compared to a classical heterozygous beta zero (β°)-thalassaemia.

METHODS

Retrospective study on 17 cases of (β°) South East Asia (SEA) deletion from 2016 to 2019 referred to Institute for Medical Research were conducted. The clinical information and haematological profiles were evaluated. The mutation was analyzed, and the results were compared with other β°-thalassaemia groups. For HBB gene genotyping, all the cases were subjected for multiplex gap-PCR, 5 cases were subjected for HBB gene sequencing for exclusion of compound heterozygous with other beta variants. Co-inheritance of α-thalassaemia were determined using multiplex gap-PCR and multiplex ARMS-PCR.

RESULTS

Seventeen cases were positive for β°-thal SEA deletion. Fifteen cases were heterozygous and two were compound heterozygous for β°-thal SEA deletion. The results were compared with 182 cases of various heterozygous β° deletions and mutations. The mean Hb for heterozygous β°-thal SEA deletion (13.44 ± 1.45 g/dl) was normal and significantly higher than heterozygous IVS 1-1 and Codon 41/42 (post hoc test, p < 0.05). The medians for the MCV and MCH of β°-thal SEA deletion were significantly higher than for all heterozygote β°-thalassaemia traits (Mann Whitney test, p < 0.05). Patients with β°-thal SEA deletion had elevated levels of Hb A2 consistent with β-thalassaemia traits, with Hb F levels consistent with HPFH or δβ-thalassaemia carriers. The median for Hb A2 was 4.00 + 1.00%, similar to that observed in other β°-thalassaemia groups except for IVS 1-1 mutation (median 5.30 + 0.45%) and β°-Filipino (∼45 kb deletion) deletion (median 6.00 + 0.58). Interestingly, we found that Hb F levels for β°-thal SEA deletion were statistically higher than other β°-thalassaemia mutations (median 19.00 + 5.50%, p < 0.05), except for the β°-thal 3.5 kb deletion group.

CONCLUSION

We conclude that β°-thal SEA deletion has a unique haematological parameters of beta zero thalassaemia trait. We affirm to classifying this deletion as SEA-HPFH based on previous studies considering the phenotype features rather than the molecular defect of β°-thal SEA deletion, as this will make it easier to offer genetic counselling to affected individuals.

Genetics background of β-thalassemia (3.5 kb deletion) in Southern Thailand: Haplotype analysis using novel reverse dot blot hybridization

β-thalassemia (β-thal) (3.5 kb deletion or NC_000011.10:g.5224302-5227791del3490bp) is a common mutation in southern Thailand. This study aimed to determine genetic diversity in subjects with β-thal (3.5 kb deletion) alleles and to ascertain the origin of this mutation using haplotype and phylogenetic analysis. The study was carried out on members of the southern Thai population, including 45 normal individuals, 116 heterozygous β-thal (3.5 kb deletion) and one homozygous β-thal (3.5 kb deletion). The 5'-haplotype in β-globin gene cluster was examined using newly developed reverse dot blot hybridization (RDB) and compared with polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP). The results showed 100% concordance between the haplotype patterns of these two methods. From a total of 324 chromosomes, nine haplotypes were segregated. Haplotype H2 (+ - - - -) was the predominant haplotype observed in all 118 β-thal (3.5 kb deletion) chromosomes, which revealed a single origin. The phylogenetic tree demonstrated that β-thal (3.5 kb deletion) has an older genetic defect in this region. Moreover, the developed RDB is simple, less time-consuming, inexpensive, and does not restriction enzyme digestion.

Direct Amplification of Whole Blood and Amniotic Fluid Specimens for Prenatal and Postnatal Diagnosis of Hb E-β 0-Thalassemia Diseases

OBJECTIVE

Prenatal and postnatal diagnosis of hemoglobin E-β 0-thalassemia can be made using polymerase chain reaction (PCR) analysis mostly on purified DNA. We have establihed a direct amplification method without DNA extraction on whole blood (WB) and amniotic fluid (AF) specimens to diagnose the disease.

METHODS

Three reactions of WB PCR assays and 7 reactions of AF PCR tests were developed for postnatal and prenatal diagnosis, respectively. Assays were validated against routine tests in a blinded trial.

RESULTS

The results showed 100% concordance with routine DNA PCR assays. Among 309 β-thalassemia carriers, 191 patients (61.8%) carried common β-thalassemia mutations. Among 448 AF specimens, 116 (25.9%) fetuses were found to be affected, 247 (55.1%) fetuses were carriers, and 85 (19%) fetuses were unaffected.

CONCLUSION

We found that WB and AF PCR assays are simple, rapid, and reliable. The developed techniques could be applicable in routine settings.

Establishment and application of a novel method based on single nucleotide polymorphism analysis for detecting β-globin gene cluster deletions

β-Globin gene mutations reduce or terminate the production of beta globin chains, of which approximately 10% are large deletions within the β-globin gene cluster. Because gene deletion leads to loss of heterozygosity at single nucleotide polymorphism (SNP), a novel method for detecting β-globin gene cluster deletions based on SNP heterozygosity analysis was established in this study. The location range of SNPs was selected according to the breakpoint of β-globin gene cluster deletions. SNPs were screened using bioinformatics analysis and population sequencing data. A novel method which enables genotyping of multiplex SNPs based on tetra-primer ARMS-PCR was designed and optimized. Forty clinical samples were tested in parallel by this method and MLPA to verify the performance of this method for detecting β-globin gene cluster deletion. Six informative SNPs were obtained, achieving heterozygote coverage of 93.3% in normal individuals. Genotyping of six SNPs were successfully integrated into two multiplex tetra-primer ARMS-PCR reactions. The sensitivity, specificity, positive predictive value and negative predictive value of the method for detecting β-globin gene cluster deletion were 100%, 96.30%, 92.86%, and 100%, respectively. This is a simple, cost-effective and novel method for detecting β-globin gene cluster deletions, which may be suitable for use in combination with MLPA for thalassemia molecular testing.

Association Between Genetic Polymorphisms and Hb F Levels in Heterozygous β-Thalassemia 3.5 kb Deletions

Single nucleotide polymorphisms (SNPs) in several genetic modifying factors have been related to Hb F levels, including ^Gγ XmnI polymorphism, B-cell lymphoma/leukemia 11 A (BCL11A), HBS1L-MYB intergenic polymorphism (HMIP) and a mutation in the Krüppel-like factor 1 (KLF1). This study aimed to determine whether genetic variability of these modifying factors affects Hb F levels in heterozygous β-thalassemia (β-thal) 3.5 kb deletion (NC_000011.10: g.5224302-5227791del13490bp). A total of 111 β-thal 3.5 kb deletion carriers with Hb F levels ranging from 0.9 to 18.4% was recruited for this study. Genotyping of SNPs including HBG2 rs7482144, HMIP rs4895441 and rs9399137, BCL11A rs4671393 and KLF1 rs2072596 was identified. Multiple regression analyses showed that only two SNPs (HMIP rs4895441 and rs9399137) influenced Hb F levels. Interestingly, a combination of these two SNPs was associated with higher Hb F levels. Our study is the first to demonstrate that the rs4895441, rs9399137 of HMIP are associated with elevated Hb F levels in the heterozygous β-thal 3.5 kb deletion.

Simultaneous Characterization of Deletional and Nondeletional Globin Gene Mutations by Multiplex Real-Time-Polymerase Chain Reaction and High-Resolution Melting Curve Analysis

Both deletional and nondeletional globin gene mutations are common in Southeast Asians. Normally, deletional gene mutations are characterized separately from nondeletional gene mutations. Therefore, we developed a new approach of multiplex real-time polymerase chain reaction (qPCR) followed by high-resolution melting (HRM) analysis without a fluorescently-labeled probe for the simultaneous detection of deletional and nondeletional gene mutations in a single tube. Three sets of primer pairs were used to establish the qPCR-HRM method that was used to genotype more than 20 different globin genotypes. Twenty known genotypes were used to optimize the qPCR and HRM conditions. Eight genotypes were used to determine the reproducibility of the method. A total of 351 blinded known DNA samples were used for the validation study in three separate reactions and revealed 16 distinct patterns of fragments and/or HRM. The melting temperatures (Tm) of the 3.5 kb, - -^THAI, HBB-FR2 (exon 1 of the HBB gene), - -^SEA (Southeast Asian), α2 and 3'-ψζ1 fragments were 79.44, 81.01, 86.47, 87.89, 90.54 and 94.15 °C, respectively. The HRM analysis was performed with the HBB-FR2 fragment to differentiate several alleles. We report a rapid and high-throughput technique that showed 100.0% concordance and low variability for each run. Our developed technique is one of the alternative techniques recommended for screening samples with both deletional and nondeletional globin gene mutations.

The prevalence and molecular characterization of (δβ)0 -thalassemia and hereditary persistence of fetal hemoglobin in the Chinese Zhuang population

Objective

To reveal the prevalence and molecular characterization of (δβ)⁰‐thalassemia [(δβ)⁰‐thal] and hereditary persistence of fetal hemoglobin (HPFH) in the Chinese Zhuang population.

Methods

A total of 105 subjects with fetal hemoglobin (Hb F) level ≥5% from 14 204 unrelated ones were selected for the study. Multiplex ligation dependent probe amplification was firstly used to analyze dosage changes of the β‐globin gene cluster for associated with (δβ)⁰‐thal and HPFH mutations. The gap polymerase chain reaction was then performed to identify the deletions using the respective flanking primers. Hematologic data were recorded and correlated with the molecular findings.

Results

Twenty‐one (0.15%) subjects were diagnosed with Chinese ^Gγ(^Aγδβ)⁰‐thal. Nine (0.06%) were diagnosed with Southeast Asia HPFH (SEA‐HPFH) deletion. Seventy‐five (0.53%) cases remained uncharacterized. Three genotypes for Chinese ^Gγ(^Aγδβ)⁰‐thal and SEA‐HPFH deletion were identified, respectively. The genotype‐phenotype relationships were discussed.

Conclusion

Our study for the first time demonstrated that (δβ)⁰ and HPFH were not rare events, and molecular characterized ^Gγ(^Aγδβ)⁰‐thal and HFPH mutations in the Chinese Zhuang population. The findings in our study will be useful in genetic counseling and prenatal diagnostic service of β‐thalassemia in this populations.

Gap-PCR Screening for Common Large Deletional Mutations of β-Globin Gene Cluster Revealed a Higher Prevalence of the Turkish Inversion/Deletion (δβ)0 Mutation in Antalya

OBJECTIVE

Although the calculated carrier frequency for point mutations of the β-globin gene is around 10% for Antalya Province, nothing is known about the profile of large deletional mutations involving the β-globin gene. In this study, we aimed to screen common deletional mutations in the β-globin gene cluster in patients for whom direct DNA sequencing was not able to demonstrate the mutation(s) responsible for the disease phenotype.

MATERIALS AND METHODS

Thirty-one index cases selected with a series of selection events among 60 cases without detected β-globin gene mutation from 580 thalassemia-related cases tested by direct sequencing over the last 4 years in our diagnostic center were screened for the most common 8 different large deletional mutations of the β-globin gene cluster by gap-PCR.

RESULTS

We detected 1 homozygous and 9 heterozygous novel unrelated cases for the Turkish inversion/deletion (δβ)0 mutation in our series of 31 cases. Our study showed that the Turkish inversion/deletion (δβ)0 mutation per se accounts for 16.6% of the unidentified causative alleles and also accounts for 1.5% of all detected mutations over the last 4 years in our laboratory.

CONCLUSION

Since molecular diagnosis of deletional mutations in the β-globin gene cluster warrants different approaches, it deserves special attention in order to provide prenatal diagnosis and prevention opportunities to the families involved. We conclude that the Turkish inversion/deletion (δβ)0, as the most prevalent deletional mutation detected so far, has to be routinely tested for in Antalya, and the gap-PCR approach has valuable diagnostic potential in the patients at risk.

Screening for common β-globin gene cluster deletions in Chinese individuals with increased hemoglobin F

INTRODUCTION

The aim of this study was to determine the prevalence of β-globin gene cluster deletions in individuals with increased Hb F levels in a Chinese population.

METHODS

Subjects with HbF levels ≥ 10% were selected for further investigation. Gap-PCR was used to screen for three common β-globin gene cluster deletions: Chinese ((A) γδβ)(0)-thalassemia, Southeast Asian (SEA) deletion and Hb Lepore. Multiplex ligation-dependent probe amplification (MLPA) was used to analyze dosage changes of the β-globin gene cluster for those not associated with one of the three common deletions.

RESULTS

One hundred and thirty-one individuals had an increased Hb F level; among these, 51 (38.9%) were showed to have Chinese ((A) γδβ)(0)-thalassemia (n = 37) or SEA deletion (n = 14). A single case of Hb Lepore-Boston-Washington was detected. MLPA only detected 2 deletions in three cases of the remaining 80 patients. Gap-PCR confirmed that they included a 1357 bp β-globin gene deletion (NG_000007.3:g.69997_71353del1357) in one case and a HBG2-HBG1 fusion gene consisting of exons 1 and 2 of HBG2 ((G) γ-globin gene) and exon 3 of HBG1 ((A)γ-globin gene) (HBG2:c.315 + 573_HBG1: c.315 + 572del) in two cases.

CONCLUSION

The Chinese ((A) γδβ)(0)-thalassemia and SEA deletion are the most common large deletions of β-globin gene cluster in Chinese. Gap-PCR for the detection of these two deletions should be used in thalassemia screening program in China where the incidence of β-thalassemia is high.

A novel (A)γδβ(0)-thalassemia caused by DNA deletion-inversion-insertion of the β-globin gene cluster and five olfactory receptor genes: Genetic interactions, hematological phenotypes and molecular characterization

OBJECTIVE

To report the phenotypes and genetic basis of a novel (A)γδβ(0)-thalassemia found in Thai individuals with several forms of thalassemia.

DESIGNS AND METHODS

An initial study was done in an adult Thai woman who had hypochromic microcytic red cells with unusually 100% Hb F. Extended study was carried out on her parents and another 17 unrelated individuals with elevated Hb F. Hb analysis was performed by capillary electrophoresis and DNA analysis was done using PCR. A novel diagnostic method based on multiplex PCR assays was developed.

RESULTS

DNA analysis of the proband revealed the homozygosity for a novel deletion of 118.3 kb, removing the entire (A)γ, ψβ, δ-, β-globin and five olfactory receptor (OR) genes with an insertion of a 179 bp inverted DNA sequence located behind the OR52A5 gene located downstream and an insertion of 7 orphan nucleotides. Her parents were both carriers of this mutation. Further screening in suspected cases in our series unexpectedly led to identification of an additional 17 cases with this mutation in different genotypes including plain heterozygote, homozygote, compound heterozygote with Hb E, and double heterozygote with several forms of α-thalassemia. Hematological features associated with these genetic interactions are presented.

CONCLUSIONS

Haplotype analysis indicated a single origin of this novel deletion-inversion-insertion (A)γδβ(0)-thalassemia in the Thai population. Differentiation of this mutation and other high Hb F determinants documented previously could be done by using a developed multiplex PCR assay.

Advances in technologies for screening and diagnosis of hemoglobinopathies

Hemoglobinopathies constitute the most common monogenic disorders worldwide, caused by mutations in the globin genes that synthesize the globin chains of hemoglobin. Synthesis may be reduced (thalassemia) or underlie abnormal hemoglobins. Mutation interactions produce a wide range of disorders. For neonatal and antenatal screening, identification of affected newborns or carriers is achieved by hematological tests. DNA analysis supports definitive diagnosis, and additionally facilitates prenatal diagnosis procedures. Most methods used today have been developed over several decades, with few recent advances in hematology methods. However, DNA methods evolve continuously. With global migration and multiethnic societies the trend is from targeted, population-specific methods towards generic methods, such as Sanger sequencing (point mutations) and multiplex ligation probe amplification (deletions). DNA microarrays constitute an advanced DNA method for some mutation categories. The newest DNA technology is next-generation sequencing. Although not completely ready for routine use currently, next-generation sequencing may soon become a reality for some hemoglobin diagnostic laboratories.

State of the art and new developments in molecular diagnostics for hemoglobinopathies in multiethnic societies

For detecting carriers of thalassemia traits, the basic part of diagnostics consists of measurement of the hematological indices followed by mostly automatic separation and measurement of the Hb fractions, while direct Hb separation either on high pressure liquid chromatography or capillary electrophoresis is sufficient to putatively identify carriers of the common Hb variants like HbS, C, E, D, and O-Arab. A putative positive result is reported together with an advice for parents, partner, or family analysis. For couples, presumed at-risk confirmation at the DNA level is essential. In general, this part of diagnostics is done in specialized centers provided with sufficient experience and the technical tools needed to combine hematological and biochemical interpretation with identification of the mutations at the molecular level. State-of-the-art tools are usually available in centers that also provide prenatal diagnosis and should consist of gap-PCR for the common deletions, direct DNA sequencing for all kind of point-mutations and the capacity to uncover novel or rare mutations or disease mechanisms. New developments are MLPA for large and eventually unknown deletion defects and microarray technology for fine mapping and primer design for breakpoint analysis. Gap-PCR primers designed in the region flanking the deletion breakpoints can subsequently be used to facilitate carrier detection of uncommon deletions in family members or isolated populations in laboratories where no microarray technology or MLPA is available.