Molecular Detection of Alpha Thalassemia: A Review of Prevalent Techniques

Unveiling the molecular landscape of δ-thalassemia and δ-globin variants in southern China: novel mutations, gene spectrum, and implications for thalassemia diagnosis

Objectives

δ-thalassemia and δ-globin variants are rare hemoglobinopathies. However, co-inheritance of β-thalassemia and δ-globin gene mutations may affect the diagnosis of β-thalassemia carriers when based on the elevated Hb A2. This study aimed to identify and characterize δ-thalassemia and δ-globin variants in Southern China.

Methods

Ninety samples with suspected δ-globin gene mutations from 15,642 participants were selected for further molecular analysis based on their Hb A2 level (≦1.8%) and hematological parameters. Additionally, 37 samples with suspected δ-globin gene mutations were sent from other hospital to our laboratory for identification. GAP-PCR and PCR-reverse dot blot (PCR-RDB) were used to detect common α- and β-thalassemia in the Chinese population, and Sanger sequencing was used to identify δ-globin gene mutations.

Results

Among 15,642 samples examined, samples with δ-globin gene mutations were identified in 127 (0.81%) cases with as many as 28 different genotypes, including 81 (0.52%) cases of δ-thalassemia and 46 (0.29%) cases of δ-globin variants. The most prevalent δ-thalassemia and δ-globin variants of this study were HBD:c.-127T>C (75.3%, 61/81) and Hb A2-Melbourne (54.3%, 25/46). Most of the samples were heterozygous (87.4%, 111/127), and only two cases of homozygous were detected. There were three double heterozygotes and 11 cases of combined α/β-globin mutations. Notably, we also identified eight cases of novel mutations in the δ-globin gene. In both heterozygous and homozygous cases, δ-globin mutations maintained hematological parameters within normal ranges, while their co-occurrence with α- or β-thalassemia manifested as a thalassemia phenotype characterized by significantly reduced MCV and MCH values.

Conclusion

The study reveals that δ-globin gene mutations are prevalence in the South China and necessitates integration of δ-globin screening into existing thalassemia prevention protocols.

A novel case of Hb Bart's hydrops fetalis following prenatal diagnosis: Case report from Huizhou, China

Objective

Presentation of a novel case of a patient with Hb Bart's hydrops fetalis, which was accurately identified by SMRT sequencing leading to expand the mutation spectrum of α-thalassemia.

Case report

A 26-year-old pregnant woman and her husband underwent molecular analysis of thalassemia due to abnormal hematological results. The molecular analysis showed that the pregnant woman carried -α3.7/--SEA, while her husband exhibited a negative result. Accordingly, the pregnant woman continued the pregnancy until the 19-week gestational age. She was subsequently referred to our department for genetic counseling due to abnormal ultrasound findings in the fetus. A novel deletional α-thal mutation was detected for the husband by MLPA, and the precise location of the mutation was determined through SMRT sequencing, which revealed a 45.2 kb deletion. Later, an interventional umbilical cord blood puncture was offered for the pregnant woman. The cord blood was subjected to capillary electrophoresis, which revealed apparent Hb Bart's and Hb Portland peaks associated with Hb Bart's hydrops fetalis syndrome.

Conclusion

It is imperative that Hb Bart's hydrops fetalis syndrome be diagnosed with the utmost expediency. If results of molecular analysis are not consistent with the clinical hematological findings, the presence of a novel thalassemia could be suspected. To identify the novel genotype, the SMRT sequencing represents an effective method for achieving an accurate diagnosis.

Sonographic Assessment of Splenic Manifestations in Sickle Cell Disease Patients and Its Relation to Hematological Parameters: A Cross-Sectional Study in Basra, Iraq

Background Hemoglobinopathies, such as sickle cell disease (SCD), are inherited disorders of hemoglobin (Hb) synthesis. SCD presents with complex clinical manifestations, including anemia, painful episodes, and organ damage due to recurrent vaso-occlusion. The spleen is one of the first organs affected in SCD patients, with hyposplenism typically occurring by age five. However, older patients may show variations in splenic size, which can complicate the diagnosis. Objective This study aimed to investigate the radiological manifestations of the spleen in patients with SCD using sonographic assessment and the relationship between these manifestations and the patient's clinical and laboratory findings. Methodology This descriptive cross-sectional study was carried out at the Basra Hematology Center, which is the largest center for hematological diseases in the southern part of Iraq. It was carried out over a three-month period from May 22 to August 22, 2024. A total of 81 patients aged 15 and above, diagnosed with SCD, and attending the outpatient clinic at Basra Hematology Center in Basra city were included. Participants were identified through medical records and referrals from private outpatient clinics. Inclusion criteria ensured participants had a confirmed SCD diagnosis and met the age requirements. Exclusion criteria eliminated individuals with sickle cell trait, other hemolytic anemias, leukemia, relevant co-morbidities, or those who declined participation. After obtaining informed consent, each patient was interviewed by the research team, their blood was taken for lab tests, and then an ultrasound scan of their spleen was performed. Results Regarding the demographic characteristics of patients, age showed a statistically significant difference across the groups (p=0.017), indicating that marked splenomegaly is associated with younger individuals (mean age of 19.50 ± 4.95 years) compared to autosplenectomy, which is linked to older patients (mean age of 35.42 ± 11.84 years). Regarding radiological findings, splenic size was categorized into normal size, splenomegaly, small spleen, and autosplenectomy. Increased echogenicity is more frequently seen in the small spleen group (87.5%, p<0.001). Focal lesions, such as infarctions, were relatively uncommon and did not show significant variation across the groups. However, the presence of Gamna-Gandy bodies (GGB) was reported in a few patients and did not vary significantly among spleen status groups. The laboratory data showed notable significant differences in several key blood parameters. Hb levels were significantly lower in patients with marked splenomegaly (6.65 ± 0.21 g/dl) compared to other groups (p=0.01). White blood cell count (WBC) and platelet count (PLT) were significantly higher in the autosplenectomy group (WBC 12.29 ± 5.67 x 10³/μL; PLT 426.16 ± 222.85 x 10³/μL), both with p-values <0.001. Conclusion This study examined splenic changes in SCD patients, finding that autosplenectomy is more common in older patients, while splenomegaly is prevalent in younger ones. Increased splenic echogenicity indicated fibrosis, and patients with splenomegaly showed lower hemoglobin levels. Autosplenectomy was associated with higher WBC and PLT levels. Although elevated HbF and certain genetic factors seemed protective against splenic atrophy, these findings were not statistically significant, warranting further research.

Global Globin Network and adopting genomic variant database requirements for thalassemia

Thalassemia is one of the most prevalent monogenic disorders in low- and middle-income countries (LMICs). There are an estimated 270 million carriers of hemoglobinopathies (abnormal hemoglobins and/or thalassemia) worldwide, necessitating global methods and solutions for effective and optimal therapy. LMICs are disproportionately impacted by thalassemia, and due to disparities in genomics awareness and diagnostic resources, certain LMICs lag behind high-income countries (HICs). This spurred the establishment of the Global Globin Network (GGN) in 2015 at UNESCO, Paris, as a project-wide endeavor within the Human Variome Project (HVP). Primarily aimed at enhancing thalassemia clinical services, research, and genomic diagnostic capabilities with a focus on LMIC needs, GGN aims to foster data collection in a shared database by all affected nations, thus improving data sharing and thalassemia management. In this paper, we propose a minimum requirement for establishing a genomic database in thalassemia based on the HVP database guidelines. We suggest using an existing platform recommended by HVP, the Leiden Open Variation Database (LOVD) (https://www.lovd.nl/). Adoption of our proposed criteria will assist in improving or supplementing the existing databases, allowing for better-quality services for individuals with thalassemia. Database URL: https://www.lovd.nl/.

Uncommon Combination of Hemoglobin Jax and Hemoglobin Constant Spring Leading to Microcytic Anemia

BACKGROUND Thalassemia and hemoglobin (Hb) variants are the most common hereditary red blood cell disorders worldwide. Alpha-thalassemia and alpha-globin variants are caused by mutations of the alpha-globin genes (HBA2 and HBA1), resulting in impaired alpha-globin production and structurally abnormal globin, respectively. Clinical severity of alpha-thalassemia correlates with the number of affected alpha-globin genes, yielding a spectrum of clinical manifestations from mild to severe anemia. Routine diagnosis involves Hb analysis and PCR-based methods, yet identifying rare variants necessitates comprehensive clinical and hematologic laboratory data. The knowledge of phenotype and genotype correlation is useful for genetic counseling and treatment planning. CASE REPORT A 59-year-old Thai woman presented with chronic anemia. Her baseline Hb level ranged between 8.0 and 9.0 g/dL, with no history of transfusion. Physical examination showed mild pallor, without enlarged liver and spleen. Laboratory investigations showed microcytic, hypochromic anemia and abnormal Hb peak by Hb analysis (retention time 4.58 min by HPLC method). Common alpha-globin gene deletions, including the Southeast-Asian/Thai 3.7 kb and 4.2 kb deletions were tested using gap-PCR, with none of these deletions detected. Direct DNA sequencing revealed a compound heterozygosity of Hb Jax (HBA2: c.44G>C) and Hb Constant Spring (HBA2: c.427T>C). CONCLUSIONS Compound heterozygosity of Hb Jax and Hb Constant Spring results in microcytic anemia. Hb Jax can be identified by Hb analysis, and diagnosis can be confirmed by direct DNA sequencing method. Coinheritance of Hb Jax and alpha-globin variants should be considered in cases with microcytic anemia and a specific Hb peak seen in Hb chromatogram.

Severe Transfusion-Dependent Thalassemia in Compound Heterozygote Palestinian Siblings with Two α-Globin Gene Defects, Hb Taybe D HBA1: C.119_121delCCA Mutation and HBA2: C.*94A > G Mutation

Alpha and Beta Thalassemia are autosomal recessive anemias that cause significant morbidity and mortality worldwide, especially in the Middle East and North Africa (MENA) region where carrier rates reach up to 50%. We report the case of two siblings of Palestinian origin born who presented to our tertiary healthcare center for the management of severe transfusion dependent hemolytic anemia. Before presentation to our center, the siblings were screened for a-thalassemia using the Alpha-globin StripAssay. They were found to carry the α2 polyA-1 [AATAAA > AATAAG] mutation in the heterozygous form, which was insufficient to make a diagnosis. No pathogenic variants were detected on Sanger sequencing of the HBB gene. Full sequencing of the a-gene revealed compound heterozygous variants (HBA1:c.119_121delCCA and the previously detected HBA2:c.*+94A > G Poly A [A->G]) with trans inheritance. This report highlights the impact of non-deletional mutations on α-globin chain stability. The compound heterozygosity of a rare α-globin chain pathogenic variant with a polyadenylation mutation in the probands leads to clinically severe a-thalassemia. Due to the high carrier status, the identification of rare mutations through routine screening techniques in our populations may be insufficient. Ongoing collaboration among hematologists, medical geneticists, and counselors is crucial for phenotypic-genotypic correlation and assessment of adequate genetic testing schemes.

Advances in screening of thalassaemia

Thalassaemia is a common hereditary haemolytic anaemia. Mild cases of this disease may be asymptomatic, while patients with severe thalassaemias require high-dose blood transfusions and regular iron removal to maintain life or haematopoietic stem cell transplantation to be cured, imposing an enormous familial and social burden. Therefore, early, timely, and accurate screening of patients is of great importance. In recent years, with the continuous development of thalassaemia screening technologies, the accuracy of thalassaemia screening has also improved significantly. This article reviews the current research on thalassaemia screening.

The need to perform α-thalassemia genetic testing in Italian patients with β-thalassemia trait: A case report

Here, we describe a case report of a Sardinian woman diagnosed as pure beta-thalassemia carrier for her anemia who underwent to alpha-thalassemia genetic testing that revealed she was heterozygous for both thalssemias. This allowed to reach a conclusive diagnosis useful for family counseling and for assess the reproductive risk.

Applications of next generation sequencing in the screening and diagnosis of thalassemia: A mini-review

Thalassemias are a group of inherited blood disorders that affects 5-7% of the world population. Comprehensive screening strategies are essential for the management and prevention of this disorder. Today, many clinical and research laboratories have widely utilized next-generation sequencing (NGS) technologies to identify diseases, from germline and somatic disorders to infectious diseases. Yet, NGS application in thalassemia is limited and has just recently surfaced due to current demands in seeking alternative DNA screening tools that are more efficient, versatile, and cost-effective. This review aims to understand the several aspects of NGS technology, including its most current and expanding uses, advantages, and limitations, along with the issues and solutions related to its integration into routine screening and diagnosis of thalassemias. Hitherto, NGS has been a groundbreaking technology that offers tremendous improvements as a diagnostic tool for thalassemia in terms of its higher throughput, accuracy, and adaptability. The superiority of NGS in detecting rare variants, solving complex hematological problems, and providing non-invasive alternatives to neonatal diagnosis cannot be overlooked. However, several pitfalls still preclude its use as a stand-alone technique over conventional methods.