Phenotypic and molecular diversity of haemoglobin H disease: a Greek experience

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.

Αlpha-thalassemia: A practical overview

α-Thalassemia is an inherited blood disorder characterized by decreased synthesis of α-globin chains that results in an imbalance of α and β globin and thus varying degrees of ineffective erythropoiesis, decreased red blood cell (RBC) survival, chronic hemolytic anemia, and subsequent comorbidities. Clinical presentation varies depending on the genotype, ranging from a silent or mild carrier state to severe, transfusion-dependent or lethal disease. Management of patients with α-thalassemia is primarily supportive, addressing either symptoms (eg, RBC transfusions for anemia), complications of the disease, or its transfusion-dependence (eg, chelation therapy for iron overload). Several novel therapies are also in development, including curative gene manipulation techniques and disease modifying agents that target ineffective erythropoiesis and chronic hemolytic anemia. This review of α-thalassemia and its various manifestations provides practical information for clinicians who practice beyond those regions where it is found with high frequency.

Molecular patterns of alpha-thalassemia in the kingdom of Saudi Arabia: identification of prevalent genotypes and regions with high incidence

BACKGROUND

Alpha-thalassemia (α-thalassemia) is one of the most common monogenic diseases in Saudi Arabia and is associated with significant morbidity. Premarital testing programs in Saudi Arabia reduce the burden of hemoglobinopathy disorders, and ongoing monitoring is required. We aimed to explore the molecular nature of α-globin genes and identify the most common genotypes and regions with a high risk of α-thalassemia in Saudi Arabia.

METHODS

This retrospective study was conducted between January 2021 and December 2022. Six hundred twenty-five samples from patients with microcytic hypochromic anemia in Saudi Arabia were analyzed using reverse dot blot hybridization (RDBH)-based multiplex-PCR, which screens for the known 21 mutations of α-globin genes.

RESULTS

Seven mutations in the α-globin gene were identified in 88.96% (556) patients. The most frequent abnormality of a-globin genes was -α3.7 (62.3%), followed by α2IVS1(-5nt) (20.7%) and α2 polyA-1 (α2T.Saudi) (14.1%). Interestingly, α2 polyA-2 (α2T.Turkish) was identified in Saudi and presented with -MED, causing Haemoglobin H disease. The incidence of α-thalassemia in Saudi Arabia's cities showed significant differences (P = 0.004). Jeddah City had the highest percentage of cases (25%), followed by Makkah (23%), Taif (13.3%), and Al-Ahassa (12.4%).

CONCLUSION

The study provides current knowledge about the molecular nature of α- thalassemia, highlights the common genotypes that could contribute to disease occurrence in the Saudi population, and sheds light on Saudi regions with a high incidence. It also recommends further studies in a larger population and with differently composed molecular assays to verify these findings.

Severity scoring system to guide transfusion management in pediatric non-deletional HbH

BACKGROUND

Hemoglobin (Hb) H is generally recognized as mild thalassemia, despite its actual phenotypic diversity. A disease severity scoring system to guide initiation of regular transfusion among severely affected pediatric patients has not previously been reported.

METHODS

Patients with HbH were classified into transfusion-dependent thalassemia (TDT) and non-transfusion-dependent thalassemia (NTDT) as a surrogate for disease severity. Alpha-globin genotypes and relevant clinical parameters associated with TDT were identified. Univariate and multiple logistic regression analyses were performed to yield the most suitable severity scoring system.

RESULTS

From 246 patients with a median age of 14.3 (interquartile range 9.9-18.4) years initially enrolled into the study, the chance of having severe disease and developing TDT was remarkable only among patients with non-deletional HbH, for whom the scoring system was developed. Univariate and multiple logistic regression analyses resulted in three retained parameters associated with TDT, β-coefficients of which were used to develop the score. The final scoring system comprised age at diagnosis <2 years (score = 1), spleen size ≥3 cm (score = 1) and Hb at steady-state <7 (score = 4) or 7-8 g/dL (score = 3). A cutoff score ≥4 was associated with severe disease likely requiring regular transfusion (sensitivity 89.3%, specificity 81.4%), given regular transfusion resulted in maintained growth. The scoring system was validated in the second cohort of 77 non-deletional HbH, from which comparable sensitivity and specificity were obtained.

CONCLUSION

The newly developed scoring system was practical and helpful to highlight severely affected pediatric non-deletional HbH patients with potential needs of regular transfusion. This can be used as a guide for optimal treatment and disease monitoring in the future.

An analysis of the distribution and spectrum of alpha thalassemia mutations in Rasht City, North of Iran

Background

Alpha thalassemia is one of the most common hereditary hemoglobin disorders worldwide, particularly in the Middle East, including Iran. Therefore, determining the spectrum and distribution of alpha thalassemia mutation is a fundamental component of preventive approaches and management strategies.

Methods

The present study reviews the genetic testing and blood laboratory results of 455 candidates eligible for marriage who were suspected of being thalassemia carriers and on whom genetic testing was performed from 21 March 2013 to 31 December 2020 in Rasht City.

Results

A total of 114 (25.05%) alpha thalassemia cases were identified. Fifteen different alpha mutations were found. The most common mutation among the study population was -α^3.7 deletion in 55 patients (48.24%), followed by Hb Constant Spring (C.S) in 21 patients (18.42%) and poly A2 in 16 (14.03%). Also, most of the patients were silent carriers. The deletion type of mutation was much more common than non-deletion mutations.

Conclusion

Our study reveals genetic heterogeneity and alpha thalassemia diversity among the Rasht City population. We expect that these findings will help guide premarital screening and genetic counseling, prenatal diagnosis of thalassemia, preventive strategy development, as well as a compilation of the alpha thalassemia catalog in Guilan province.

Benign Cardiac Effects of Hemoglobin H Disease

BACKGROUND/AIMS

Hemoglobin H (HbH) disease is associated with iron overload, but whether this results in serious cardiac or vascular sequelae is unresolved.

METHODS

We identified 39 adult subjects (age 42 ± 12 years, 13 men) with HbH disease who had undergone echocardiography, 27 of whom had also undergone cardiac and liver magnetic resonance assessment of iron loading using T2*-weighted imaging.

RESULTS

None of the subjects had a history of heart failure or arrhythmias. There were 13/39 subjects with a ferritin level within the sex-based normal range and only 4/39 had ferritin >1,000 ng/ml. Left ventricular (LV) and left atrial dilatation was common, but LV ejection fraction was normal (≥55%) in all subjects. Age was positively correlated with log ferritin in the 27 nontransfused subjects (r = 0.43) and was inversely correlated with the transmitral E wave and E/A ratio (r = -0.69 and r = -0.79, respectively), but no relation of log ferritin with E or E/A was evident. The peak tricuspid regurgitation velocity was normal in 24/29 subjects for whom this was obtained, and it was no more than mildly elevated in the other 5. None of the tested subjects had an abnormal cardiac T2* reading, but half had evidence of liver iron loading.

CONCLUSION

No myocardial iron loading or serious cardiac or vascular sequelae were identified in this cohort with HbH disease.