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

Large-Scale Analysis of the Thalassemia Mutation Spectrum in Guizhou Province, Southern China, Using Third-Generation Sequencing

This study aimed to comprehensively characterize the molecular spectrum of thalassemia by retrospectively analyzing genetic screening results from a large cohort of individuals. Peripheral blood samples were collected from 26 047 individuals seeking care at the Departments of Obstetrics and Gynecology, Pediatrics, Reproductive Medicine, and Hematology across multiple regional hospitals in Guizhou Province, China. Thalassemia gene mutations were analyzed using targeted third-generation sequencing (TGS) to assess the mutation spectrum in this population. Of the cohort, 5099 individuals were identified as thalassemia carriers, yielding an overall carrier rate of 19.58%. The carrier rates differed significantly between the southern and northern regions of Guizhou (p < 0.001). α-thalassemia included 40 distinct genotypes, β-thalassemia comprised 33 genotypes, and cases with concurrent α- and β-thalassemia mutations exhibited 47 unique genotypes. A total of 17 distinct mutations were identified in the α-thalassemia gene and 26 in the β-thalassemia gene. The mutation spectrum in Guizhou showed significant differences when compared to other southern Chinese populations, with notable regional variations within Guizhou itself. This study highlights the substantial genetic diversity and distinct mutation patterns of thalassemia in Guizhou Province. These findings provide valuable insights into the distribution of thalassemia genotypes and alleles, which can inform genetic counseling and prenatal screening strategies tailored to this population.

Prevalence and Molecular Characteristics of Hemoglobin Variants in Laibin City, Central Guangxi of Southern China

This study investigated hemoglobin (Hb) variant prevalence and molecular characteristics in Laibin City, Central Guangxi, China. Using capillary electrophoresis (CE), 33,958 individuals from six regions within Laibin area were screened, with hematological parameters analyzed via automated cell counters. Gap-PCR/RDB-PCR identified common α/β-thalassemia mutations, while Sanger sequencing characterized Hb variants. Single-molecule real-time (SMRT) sequencing was performed to identify breakpoints in a sample with a large duplication and to detect multiple mutations in another sample. Multiple ligation-dependent probe amplification (MLPA) was used for duplication validation. Among 231 Hb variant carriers (0.68% prevalence), 18 mutation types were identified: 7 α-chain, 6 β-chain, and 5 δ-chain variants. Hb New York was most frequent (30.3%, 70/231), followed by Hb E (27.3%, 63/231) and Hb Q-Thailand (20.8%, 48/231). Two novel variants-Hb Laibin (HBA2: c.44T>C) and Hb Anti-Lepore Laibin-were discovered, alongside China's first reported Hb Matsue-Oki case. In conclusion, we observed a high carrying rate of Hb variants in Laibin City. Our findings contribute to the increasing number and diverse heterogeneity of Hb variants in Central Guangxi, which should be useful for genetic counseling and the prevention of hemoglobinopathies. The flexible application of a diverse array of molecular detection techniques is essential to avoid missed diagnoses and achieve high diagnostic efficiency.

First clinical and pedigree study of rare HBB: c.316-90 A > G variant in β-globin gene in Chinese population using third-generation sequencing

INTRODUCTION

β-thalassemia is a common genetic disease mainly caused by point mutations in the β-globin gene, eliciting a high prevalence in South China. The aim of the present study is to identify a rare HBB: c.316-90 A > G variant and provide the clinical and hematological features in two unrelated Chinese families.

METHODS

In this study, we collected eight subjects from two unrelated Chinese families. Conventional thalassemia gene testing was performed to investigate common α and β-thalassemia variants based on the PCR reverse dot hybridization technique. Third-generation sequencing (TGS) was utilized to examine the rare or novel HBA1, HBA2 and HBB gene variants, which will be further verified using Sanger sequencing.

RESULTS

A rare HBB: c.316-90 A > G variant was identified in the proband of Family 1 using TGS, and exhibited remarkably low levels of hemoglobin (Hb), Hb A2, MCV and MCH. The other members in Family 1 did not have the HBB: c.316-90 A > G variant and elicited normal hematological screening results. In Family 2, the proband also carried the HBB: c.316-90 A > G variant and exhibited low levels of MCV, MCH and Hb A2, but with normal Hb value. However, pedigree analysis results revealed that the proband's mother and nephew also carried the HBB: c.316-90 A > G variant, but with normal hematological screening results.

CONCLUSION

This study first conducts clinical and hematological analysis of the HBB: c.316-90 A > G variant in two unrelated Chinese families, which provides valuable data for genetic counseling of the corresponding individuals.

Screening and Diagnosis of Rare Thalassemia Variants: Is Third-Generation Sequencing Enough?

CONTEXT.—

Rare thalassemia subtypes are often undiagnosed because conventional testing methods can only identify 23 common types of α- and β-thalassemia.

OBJECTIVE.—

To assess a comprehensive approach for the screening and diagnosis of rare thalassemia.

DESIGN.—

The study cohort included 72 individuals with suspected rare thalassemia variants. Screening was conducted by next-generation sequencing (NGS) combined with third-generation sequencing (TGS) and chromosomal microarray analysis (CMA)/copy number variation sequencing.

RESULTS.—

Of the 72 individuals with suspected rare thalassemia, 49 had rare α- or β-gene variants. NGS combined with gap polymerase chain reaction detected a total of 42 cases, resulting in a positive detection rate of 58.3%. Additionally, 4 α-globin genetic deletions were identified by TGS, which increased the variant detection rate by 5.6%. Two samples with a microdeletion of chromosome 16 or 11 were detected by CMA, which increased the detection rate by 2.8%. For one sample, reanalysis of the NGS and TGS data confirmed the presence of the β41-42/βN and βN/βN mosaic. The HBB:c.315 + 2delT mutation was initially reported in Guangdong Province, China. Two HBB gene mutations (HBB:c.315 + 5G>C and HBB:c.295G>A) and 4 rare HBA gene deletions (-11.1, -α27.6, -α2.4, and -α21.9) were initially identified in the Zhonshan region. The hematologic phenotypes of all rare cases in this study were clarified.

CONCLUSIONS.—

Rare thalassemia variants are more common than previously thought. Despite advancements in TGS, there is still no foolproof method for detection of all types of thalassemia. Thus, a comprehensive approach is necessary for accurate screening and diagnosis of rare thalassemia variants.

Application of third-generation sequencing technology for identifying rare α- and β-globin gene variants in a Southeast Chinese region

BACKGROUND

Third-generation sequencing (TGS) based on long-read technology has been gradually used in identifying thalassemia and hemoglobin (Hb) variants. The aim of the present study was to explore genotype varieties of thalassemia and Hb variants in Quanzhou region of Southeast China by TGS.

METHODS

Included in this study were 6,174 subjects with thalassemia traits from Quanzhou region of Southeast China. All of them underwent common thalassemia gene testing using the DNA reverse dot-blot hybridization technology. Subjects who were suspected as rare thalassemia carriers were further subjected to TGS to identify rare or novel α- and β-globin gene variants, and the results were verified by Sanger sequencing and/or gap PCR.

RESULTS

Of the 6,174 included subjects, 2,390 (38.71%) were identified as α- and β-globin gene mutation carriers, including 40 carrying rare or novel α- and β-thalassemia mutations. The αCD30(-GAG)α and Hb Lepore-Boston-Washington were first reported in Fujian province Southeast China. Moreover, the βCD15(TGG> TAG), βIVS-II-761, β0-Filipino(~ 45 kb deletion), and Hb Lepore-Quanzhou were first identified in the Chinese population. In addition, 35 cases of Hb variants were detected, the rare Hb variants of Hb Jilin and Hb Beijing were first reported in Fujian province of China. Among them, one case with compound αααanti3.7 and Hb G-Honolulu variants was identified in this study.

CONCLUSION

Our findings may provide valuable data for enriching the spectrum of thalassemia and highlight the clinical application value of TGS-based α- and β-globin genetic testing.

Molecular characterization of similar Hb Lepore Boston-Washington in four Chinese families using third generation sequencing

Hemoglobin (Hb) Lepore is a rare deletional δβ-thalassemia caused by the fusion between delta-beta genes, and cannot be identified by traditional thaltassemia gene testing technology. The aim of this study was to conduct molecular diagnosis and clinical analysis of Hb Lepore in four unrelated Chinese families using third generation sequencing. Decreased levels of mean corpuscular volume (MCV), mean corpuscular hemoglobin (MCH) and an abnormal Hb band were observed in the probands of the four families. However, no common α and β-thalassemia variants were detected in the enrolled families using polymerase chain reaction-reverse dot blot hybridization based traditional thalassemia gene testing. Further third-generation sequencing revealed similar Hb Lepore-Boston-Washington variants in all the patients, which were resulted from partial coverage of the HBB and HBD globin genes, leading to the formation of a delta-beta fusion gene. Specific gap-PCR and Sanger sequencing confirmed that all the patients carried a similar Hb Lepore-Boston-Washington heterozygote. In addition, decreased levels of MCH and Hb A2 were observed in the proband's wife of family 2, an extremely rare variant of Hb Nanchang (GGT > AGT) (HBA2:c.46G > A) was identified by third-generation sequencing and further confirmed by Sanger sequencing. This present study was the first to report the similar Hb Lepore-Boston-Washington in Chinese population. By combining the utilization of Hb capillary electrophoresis and third-generation sequencing, the screening and diagnosis of Hb Lepore can be effectively enhanced.

Long read sequencing on its way to the routine diagnostics of genetic diseases

The clinical application of technological progress in the identification of DNA alterations has always led to improvements of diagnostic yields in genetic medicine. At chromosome side, from cytogenetic techniques evaluating number and gross structural defects to genomic microarrays detecting cryptic copy number variants, and at molecular level, from Sanger method studying the nucleotide sequence of single genes to the high-throughput next-generation sequencing (NGS) technologies, resolution and sensitivity progressively increased expanding considerably the range of detectable DNA anomalies and alongside of Mendelian disorders with known genetic causes. However, particular genomic regions (i.e., repetitive and GC-rich sequences) are inefficiently analyzed by standard genetic tests, still relying on laborious, time-consuming and low-sensitive approaches (i.e., southern-blot for repeat expansion or long-PCR for genes with highly homologous pseudogenes), accounting for at least part of the patients with undiagnosed genetic disorders. Third generation sequencing, generating long reads with improved mappability, is more suitable for the detection of structural alterations and defects in hardly accessible genomic regions. Although recently implemented and not yet clinically available, long read sequencing (LRS) technologies have already shown their potential in genetic medicine research that might greatly impact on diagnostic yield and reporting times, through their translation to clinical settings. The main investigated LRS application concerns the identification of structural variants and repeat expansions, probably because techniques for their detection have not evolved as rapidly as those dedicated to single nucleotide variants (SNV) identification: gold standard analyses are karyotyping and microarrays for balanced and unbalanced chromosome rearrangements, respectively, and southern blot and repeat-primed PCR for the amplification and sizing of expanded alleles, impaired by limited resolution and sensitivity that have not been significantly improved by the advent of NGS. Nevertheless, more recently, with the increased accuracy provided by the latest product releases, LRS has been tested also for SNV detection, especially in genes with highly homologous pseudogenes and for haplotype reconstruction to assess the parental origin of alleles with de novo pathogenic variants. We provide a review of relevant recent scientific papers exploring LRS potential in the diagnosis of genetic diseases and its potential future applications in routine genetic testing.

Comparison of Third-Generation Sequencing and Routine Polymerase Chain Reaction in Genetic Analysis of Thalassemia

CONTEXT.—

Thalassemia is the most widely distributed monogenic autosomal recessive disorder in the world. Accurate genetic analysis of thalassemia is crucial for thalassemia prevention.

OBJECTIVE.—

To compare the clinical utility of a third-generation sequencing-based approach termed comprehensive analysis of thalassemia alleles with routine polymerase chain reaction (PCR) in genetic analysis of thalassemia and explore the molecular spectrum of thalassemia in Hunan Province.

DESIGN.—

Subjects in Hunan Province were recruited, and hematologic testing was performed. Five hundred four subjects positive on hemoglobin testing were then used as the cohort, and third-generation sequencing and routine PCR were used for genetic analysis.

RESULTS.—

Of the 504 subjects, 462 (91.67%) had the same results, whereas 42 (8.33%) exhibited discordant results between the 2 methods. Sanger sequencing and PCR testing confirmed the results of third-generation sequencing. In total, third-generation sequencing correctly detected 247 subjects with variants, whereas PCR identified 205, which showed an increase in detection of 20.49%. Moreover, α triplications were identified in 1.98% (10 of 504) hemoglobin testing-positive subjects in Hunan Province. Seven hemoglobin variants with potential pathogenicity were detected in 9 hemoglobin testing-positive subjects.

CONCLUSIONS.—

Third-generation sequencing is a more comprehensive, reliable, and efficient approach for genetic analysis of thalassemia than PCR, and allowed for a characterization of the thalassemia spectrum in Hunan Province.

Third-generation sequencing identified two rare α-chain variants leading to hemoglobin variants in Chinese population

BACKGROUND

Rare and novel variants of HBA1/2 and HBB genes resulting in thalassemia and hemoglobin (Hb) variants have been increasingly identified. Our goal was to identify two rare Hb variants in Chinese population using third-generation sequencing (TGS) technology.

METHODS

Enrolled in this study were two Chinese families from Fujian Province. Hematological screening was conducted using routine blood analysis and Hb capillary electrophoresis analysis. Routine thalassemia gene testing was carried out to detect the common mutations of α- and β-thalassemia in Chinese population. Rare or novel α- and β-globin gene variants were further investigated by TGS.

RESULTS

The proband of family 1 was a female aged 32, with decreased levels of mean corpuscular volume (MCV), mean corpuscular hemoglobin (MCH), Hb A2, and abnormal Hb bands in zone 5 and zone 12. No common thalassemia mutations were detected by routine thalassemia analysis, while a rare α-globin gene variant Hb Jilin [α139(HC1)Lys>Gln (AAA>CAA); HBA2:c.418A>C] was identified by TGS. Subsequent pedigree analysis showed that the proband's son also harbored the Hb Jilin variant with slightly low levels of MCH, Hb A2, and abnormal Hb bands. The proband of family 2 was a male at 41 years of age, exhibiting normal MCV and MCH, but a low level of Hb A2 and an abnormal Hb band in zone 12 without any common α- and β-thalassemia mutations. The subsequent TGS detection demonstrated a rare Hb Beijing [α16(A14)Lys>Asn (AAG>AAT); HBA2:c.51G>T] variant in HBA2 gene.

CONCLUSION

In this study, for the first time, we present two rare Hb variants of Hb Jilin and Hb Beijing in Fujian Province, Southeast China, using TGS technology.

Case report: Identification of a novel triplication of alpha-globin gene by the third-generation sequencing: pedigree analysis and genetic diagnosis

BACKGROUND

Thalassemia, a common autosomal hereditary blood disorder worldwide, mainly contains α- and β-thalassemia. The α-globin gene triplicates allele is harmless for carriers, but aggravates the phenotype of β-thalassemia. Therefore, it is particularly crucial to accurately detect the structural variants of α-globin gene clusters.

CASE REPORT

We reported a 28-year-old man, the proband, with microcytic hypochromic anemia. From pedigree analysis, his mother and sister had hypochromic microcytosis, and his father was normal. Genetic testing of thalassemia identified a novel α-globin gene triplicate named αααanti4.2del726bp (NC_000016.10:g.170769_174300dupinsAAAAAA) by third-generation sequencing (TGS) in the proband and his father, which was further validated by multiplex ligation-dependent probe amplification (MLPA) and Sanger sequencing. The genotypes of the proband's mother and sister were both -α3.7/αα compounded with heterozygous HBB:c.126_129delCTTT. They were categorized as silent α-thalassemia with co-inheritance of β-thalassemia trait. The proband's genotype additionally had the α-globin gene triplicates compared with his mother and sister, which increased the imbalance between α/β-globin, so the proband had more severe hematological parameters. The proband's wife was diagnosed as HBA2:c.427T > C heterozygosis, and his daughter had the novel α-globin gene triplicates compounded with HBA2:c.427T > C, therefore the girl might be asymptomatic.

CONCLUSION

The identification of the novel α-globin gene triplicates provides more insight for the research of thalassemia variants and indicates that TGS has significant advantages on genetic testing of thalassemia for the reliability, accuracy and comprehensiveness.

The Development of Plant Genome Sequencing Technology and Its Conservation and Application in Endangered Gymnosperms

Genome sequencing is widely recognized as a fundamental pillar in genetic research and legal studies of biological phenomena, providing essential insights for genetic investigations and legal analyses of biological events. The field of genome sequencing has experienced significant progress due to rapid improvements in scientific and technological developments. These advancements encompass not only significant improvements in the speed and quality of sequencing but also provide an unparalleled opportunity to explore the subtle complexities of genomes, particularly in the context of rare species. Such a wide range of possibilities has successfully supported the validation of plant gene functions and the refinement of precision breeding methodologies. This expanded scope now includes a comprehensive exploration of the current state and conservation efforts of gymnosperm gene sequencing, offering invaluable insights into their genomic landscapes. This comprehensive review elucidates the trajectory of development and the diverse applications of genome sequencing. It encompasses various domains, including crop breeding, responses to abiotic stress, species evolutionary dynamics, biodiversity, and the unique challenges faced in the conservation and utilization of gymnosperms. It highlights both ongoing challenges and the unveiling of forthcoming developmental trajectories.

Third-generation sequencing for genetic disease

Third-generation sequencing (TGS) has led to a brave new revolution in detecting genetic diseases over the last few years. TGS has been rapidly developed for genetic disease applications owing to its significant advantages such as long read length, rapid detection, and precise detection of complex and rare structural variants. This approach greatly improves the efficiency of disease diagnosis and complements the shortcomings of short-read sequencing. In this paper, we first briefly introduce the working mechanism of one of the most important representatives of TGS, single-molecule real-time (SMRT) sequencing by Pacific Bioscience (PacBio), followed by a review and comparison of the advantages and disadvantages of different sequencing technologies. Finally, we focused on the progress of SMRT sequencing applications in genetic disease detection. Future perspectives on the applications of TGS in other fields were also presented. With the continuous innovation of the SMRT technologies and the expansion of their fields of application, SMRT sequencing has broad clinical application prospects in genetic diseases detection, and is expected to become an important tool for the molecular diagnosis of other diseases.

Long-Read Sequencing Identified a Large Novel δ/β-Globin Gene Deletion in a Chinese Family

Objective

Increasingly rare thalassemia has been identified with the advanced use of long-read sequencing based on long-read technology. Here, we aim to present a novel δ/β-globin gene deletion identified by long-read sequencing technology.

Methods

Enrolled in this study was a family from the Quanzhou region of Southeast China. Routine blood analysis and hemoglobin (Hb) capillary electrophoresis were used for hematological screening. Genetic testing for common α- and β-thalassemia was carried out using the reverse dot blot hybridization technique. Long-read sequencing was performed to detect rare globin gene variants. Specific gap-polymerase chain reaction (gap-PCR) and/or Sanger sequencing were further used to verify the detected variants.

Results

None of the common α- and β-thalassemia mutations or deletions were observed in the family. However, decreased levels of MCV, MCH, and abnormal Hb bands were observed in the family members, who were suspected as rare thalassemia carriers. Further, long-read sequencing demonstrated a large novel 7.414 kb deletion NG_000007.3:g.63511_70924del partially cover HBB and HBD globin genes causing delta-beta fusion gene in the proband. Parental verification indicated that the deletion was inherited from the proband's father, while none of the globin gene variants were observed in the proband's mother. In addition, the novel δ/β-globin gene deletion was further verified by gap-PCR and Sanger sequencing.

Conclusion

In this study, we first present a large novel δ/β-globin gene deletion in a Chinese family using long-read sequencing, which may cause δβ-thalassemia. This study further enhances that long-read sequencing would be applied as a sharp tool for detecting rare and novel globin gene variants.

Third generation sequencing transforms the way of the screening and diagnosis of thalassemia: a mini-review

Thalassemia is an inherited blood disorder imposing a significant social and economic burden. Comprehensive screening strategies are essential for the prevention and management of this disease. Third-generation sequencing (TGS), a breakthrough technology, has shown great potential for screening and diagnostic applications in various diseases, while its application in thalassemia detection is still in its infancy. This review aims to understand the latest and most widespread uses, advantages of TGS technologies, as well as the challenges and solutions associated with their incorporation into routine screening and diagnosis of thalassemia. Overall, TGS has exhibited higher rates of positive detection and diagnostic accuracy compared to conventional methods and next-generation sequencing technologies, indicating that TGS will be a feasible option for clinical laboratories conducting in-house thalassemia testing. The implementation of TGS technology in thalassemia diagnosis will facilitate the development of effective prevention and management strategies, thereby reducing the burden of this disease on individuals and society.

Identification of rare thalassemia variants using third-generation sequencing

Routine PCR, Sanger sequencing, and specially designed GAP-PCR are often used in the genetic analysis of thalassemia, but all these methods have limitations. In this study, we evaluated a new third-generation sequencing-based approach termed comprehensive analysis of thalassemia alleles (CATSA) in subjects with no variants identified by routine PCR, Sanger sequencing, and specially designed GAP-PCR. Hemoglobin testing and routine PCR tests for 23 common variants were performed for 3,033 subjects. Then, Sanger sequencing and specially designed GAP-PCR were performed for a subject with no variants identified by routine PCR, no iron deficiency, and positive hemoglobin testing. Finally, the new CATSA method was conducted for the subjects with no variants identified by Sanger sequencing and specially designed GAP-PCR. In the 49 subjects tested by CATSA, eight subjects had variants identified. Sanger sequencing and independent PCR confirmed the CATSA result. In addition, it is the first time that Hb Lepore was identified in Hunan Province. In total, traditional methods identified variants in 759 of the 3,033 subjects, while CATSA identified additional variants in eight subjects. CATSA showed great advantages compared to the other genetic testing methods.