Effect of HBB genotype on survival in a cohort of transfusion-dependent thalassemia patients in Cyprus

Survival and causes of death in patients with alpha and beta-thalassemia in Northern Thailand

BACKGROUND

Thalassemia is the most prevalent hereditary anaemia worldwide. Severe forms of thalassemia can lead to reduced life expectancy due to disease-related complications.

OBJECTIVES

To investigate the survival of thalassemia patients across varying disease severity, causes of death and related clinical factors.

PATIENTS AND METHODS

We conducted a retrospective review of thalassemia patients who received medical care at Chiang Mai University Hospital. The analysis focused on survival outcomes, and potential associations between clinical factors and patient survival.

RESULTS

A total of 789 patients were included in our study cohort. Among them, 38.1% had Hb H disease, 35.4% had Hb E/beta-thalassemia and 26.5% had beta-thalassemia major. Half of the patients (50.1%) required regular transfusions. Sixty-five patients (8.2%) had deceased. The predominant causes of mortality were infection-related (36.9%) and cardiac complications (27.7%). Transfusion-dependent thalassemia (TDT) (adjusted HR 3.68, 95% CI 1.39-9.72, p = 0.008) and a mean serum ferritin level ≥3000 ng/mL (adjusted HR 4.18, 95% CI 2.20-7.92, p < 0.001) were independently associated with poorer survival.

CONCLUSIONS

Our study highlights the primary contributors to mortality in patients with thalassemia as infection-related issues and cardiac complications. It also underscores the significant impact of TDT and elevated serum ferritin levels on the survival of thalassemia patients.

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/.

Unravelling the Complexity of the +33 C>G [HBB:c.-18C>G] Variant in Beta Thalassemia

The +33 C>G variant [NM_000518.5(HBB):c.-18C>G] in the 5' untranslated region (UTR) of the β-globin gene is described in the literature as both mild and silent, while it causes a phenotype of thalassemia intermedia in the presence of a severe β-thalassemia allele. Despite its potential clinical significance, the determination of its pathogenicity according to established standards requires a greater number of published cases and co-segregation evidence than what is currently available. The present study provides an extensive phenotypic characterization of +33 C>G using 26 heterozygous and 11 compound heterozygous novel cases detected in Cyprus and employs computational predictors (CADD, RegulomeDB) to better understand its impact on clinical severity. Genotype identification of globin gene variants, including α- and δ-thalassemia determinants, and rs7482144 (XmnI) was carried out using Sanger sequencing, gap-PCR, and restriction enzyme digestion methods. The heterozygous state of +33 C>G had a silent phenotype without apparent microcytosis or hypochromia, while compound heterozygosity with a β+ or β0 allele had a spectrum of clinical phenotypes. Awareness of the +33 C>G is required across Mediterranean populations where β-thalassemia is frequent, particularly in Cyprus, with significant relevance in population screening and fetal diagnostic applications.

Hemoglobinopathies (Sickle Cell Disease and Thalassemia)

Hematopoietic cell transplantation (HCT) using an HLA-matched sibling donor is a well-established curative therapy for pediatric patients with sickle cell disease (SCD) and transfusion-dependent thalassemias (TDT). In order to expand the donor pool, new approaches such as related haploidentical donor HCT have been used with encouraging results. These approaches aim for a higher overall survival, an effective reduction of acute and chronic GvHD and a reduced toxicity. Due to these alternative approaches and adult patients being increasingly transplanted, the number of HCT has dramatically increased in the last decade. Furthermore, different gene therapy and gene editing strategies are being developed in clinical trials, showing promising results.

Overall and complication-free survival in a large cohort of patients with β-thalassemia major followed over 50 years

We report data on survival and complications for a longitudinal cohort of 709 transfusion-dependent β-thalassemia major patients (51.1% males) born between 1970 and 1997 and followed through 2020 at seven major centers in Italy. Overall survival probability at 30 years was 83.6% (95%CI: 78.5-89.1) in the oldest birth cohort (1970-1974) compared with 93.3% (95%CI: 88.6-98.3) in the youngest birth cohort (1985-1997) (p = 0.073). Females showed better survival than males (p = 0.022). There were a total of 93 deaths at a median age of 23.2 years with the most frequent disease-related causes being heart disease (n = 53), bone marrow transplant (BMT) complication (n = 10), infection (n = 8), liver disease (n = 4), cancer (n = 3), thromboembolism (n = 2) and severe anemia (n = 1). There was a steady decline in the number of deaths due to heart disease from the year 2000 onwards and no death from BMT was observed after the year 2010. A progressive decrease in the median age of BMT was observed in younger birth cohorts (p < 0.001). A total of 480 (67.7%) patients developed ≥1 complication. Patients in younger birth cohorts demonstrated better complication-free survival (p < 0.001) which was comparable between sexes (p = 0.230). Independent risk factors for death in multivariate analysis included heart disease (HR: 4.63, 95%CI: 1.78-12.1, p = 0.002), serum ferritin >1000 ng/mL (HR: 15.5, 95%CI: 3.52-68.2, p < 0.001), male sex (HR: 2.75, 95%CI: 0.89-8.45, p = 0.078), and splenectomy (HR: 6.97, 95%CI: 0.90-54.0, p < 0.063). Survival in patients with β-thalassemia major continues to improve with adequate access to care, best practice sharing, continued research, and collaboration between centers.

A Novel Tool for the Analysis and Detection of Copy Number Variants Associated with Haemoglobinopathies

Several types of haemoglobinopathies are caused by copy number variants (CNVs). While diagnosis is often based on haematological and biochemical parameters, a definitive diagnosis requires molecular DNA analysis. In some cases, the molecular characterisation of large deletions/duplications is challenging and inconclusive and often requires the use of specific diagnostic procedures, such as multiplex ligation-dependent probe amplification (MLPA). Herein, we collected and comprehensively analysed all known CNVs associated with haemoglobinopathies. The dataset of 291 CNVs was retrieved from the IthaGenes database and was further manually annotated to specify genomic locations, breakpoints and MLPA probes relevant for each CNV. We developed IthaCNVs, a publicly available and easy-to-use online tool that can facilitate the diagnosis of rare and diagnostically challenging haemoglobinopathy cases attributed to CNVs. Importantly, it facilitates the filtering of available entries based on the type of breakpoint information, on specific chromosomal and locus positions, on MLPA probes, and on affected gene(s). IthaCNVs brings together manually curated information about CNV genomic locations, functional effects, and information that can facilitate CNV characterisation through MLPA. It can help laboratory staff and clinicians confirm suspected diagnosis of CNVs based on molecular DNA screening and analysis.

Adapting the ACMG/AMP variant classification framework: A perspective from the ClinGen Hemoglobinopathy Variant Curation Expert Panel

Accurate and consistent interpretation of sequence variants is integral to the delivery of safe and reliable diagnostic genetic services. To standardize the interpretation process, in 2015, the American College of Medical Genetics and Genomics (ACMG) and the Association for Molecular Pathology (AMP) published a joint guideline based on a set of shared standards for the classification of variants in Mendelian diseases. The generality of these standards and their subjective interpretation between laboratories has prompted efforts to reduce discordance of variant classifications, with a focus on the expert specification of the ACMG/AMP guidelines for individual genes or diseases. Herein, we describe our experience as a ClinGen Variant Curation Expert Panel to adapt the ACMG/AMP criteria for the classification of variants in three globin genes (HBB, HBA2, and HBA1) related to recessively inherited hemoglobinopathies, including five evidence categories, as use cases demonstrating the process of specification and the underlying rationale.

Global Globin Network Consensus Paper: Classification and Stratified Roadmaps for Improved Thalassaemia Care and Prevention in 32 Countries

The Global Globin Network (GGN) is a project-wide initiative of the Human Variome/Global Variome Project (HVP) focusing on haemoglobinopathies to build the capacity for genomic diagnosis, clinical services, and research in low- and middle-income countries. At present, there is no framework to evaluate the improvement of care, treatment, and prevention of thalassaemia and other haemoglobinopathies globally, despite thalassaemia being one of the most common monogenic diseases worldwide. Here, we propose a universally applicable system for evaluating and grouping countries based on qualitative indicators according to the quality of care, treatment, and prevention of haemoglobinopathies. We also apply this system to GGN countries as proof of principle. To this end, qualitative indicators were extracted from the IthaMaps database of the ITHANET portal, which allowed four groups of countries (A, B, C, and D) to be defined based on major qualitative indicators, supported by minor qualitative indicators for countries with limited resource settings and by the overall haemoglobinopathy carrier frequency for the target countries of immigration. The proposed rubrics and accumulative scores will help analyse the performance and improvement of care, treatment, and prevention of haemoglobinopathies in the GGN and beyond. Our proposed criteria complement future data collection from GGN countries to help monitor the quality of services for haemoglobinopathies, provide ongoing estimates for services and epidemiology in GGN countries, and note the contribution of the GGN to a local and global reduction of disease burden.

Primary HBB gene mutation severity and long-term outcomes in a global cohort of β-thalassaemia

In β-thalassaemia, the severity of inherited β-globin gene mutations determines the severity of the clinical phenotype at presentation and subsequent transfusion requirements. However, data on associated long-term outcomes remain limited. We analysed data from 2109 β-thalassaemia patients with available genotypes in a global database. Genotype severity was grouped as β⁰ /β⁰ , β⁰ /β⁺ , β⁺ /β⁺ , β⁰ /β⁺⁺ , β⁺ /β⁺⁺ , and β⁺⁺ /β⁺⁺ . Patients were followed from birth until death or loss to follow-up. The median follow-up time was 34·1 years. Mortality and multiple morbidity outcomes were analyzed through five different stratification models of genotype severity groups. Interestingly, β⁰ and β⁺ mutations showed similar risk profiles. Upon adjustment for demographics and receipt of conventional therapy, patients with β⁰ /β⁰ , β⁰ /β⁺ , or β⁺ /β⁺ had a 2·104-increased risk of death [95% confidence interval (CI): 1·176-3·763, P = 0·011] and 2·956-increased odds of multiple morbidity (95% CI: 2·310-3·784, P < 0·001) compared to patients in lower genotype severity groups. Cumulative survival estimates by age 65 years were 36·8% for this subgroup compared with 90·2% for patients in lower genotype severity groups (P < 0·001). Our study identified mortality and morbidity risk estimates across various genotype severity groups in patients with β-thalassaemia and suggests inclusion of both β⁺ and β⁰ mutations in strata of greatest severity.