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.

Transfusion requirements and complication rate in β-thalassemia intermedia due to heterozygous β-globin gene mutation and triplicated α-globin genes

INTRODUCTION

The heterozygous condition for β-thalassemia mutation associated with an extra functional α-globin gene can produce a Thalassemia Intermedia (TI) phenotype. This genotype is the second in frequency in the French Thalassemia Registry NaThalY that prospectively collects laboratory and clinical data.

MATERIALS AND METHODS

The present report analyses transfusion needs, iron overload (ferritin, hepatic and cardiac iron concentrations), and complication rates in 45 patients included in NaThalY and presenting a heterozygous β0 or β+ -thalassemia mutation associated with a triplication at HBA locus. This cohort was compared to a cohort of patients with TI due to mutations in the beta-globin gene only and included in the French registry.

RESULTS

Patients with an extra functional α-globin gene showed a less severe anemia, lower transfusion needs and lower complication rates than those with TI related to the β-globin gene only. Nevertheless, some of them displayed complications such as cholelithiasis or extramedullary hematopoiesis. In addition, one third of the cohort needed transfusions and another third was under iron chelation.

CONCLUSION

The genotype associating a heterozygous β0 or β+ -thalassemia mutation with a triplication at HBA locus should be accurately diagnosed as it could lead to symptomatic anemia and to potential iron overload and iron-related complications even in patients with no transfusion need.

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.

Evaluation of endocrine complications in beta-thalassemia intermedia (β-TI): a cross-sectional multicenter study

BACKGROUND

Data on the prevalence and type of endocrine disorders in β-thalassemia intermedia (β-TI) patients are scarce. This multicenter study was designed to determine the prevalence of endocrine complications and the associated risk factors in a large group of β-TI patients.

METHODS

In this cross-sectional multicenter study, 726 β-TI patients, aged 2.5-80 years, registered at 12 thalassemic centers, from nine countries, were enrolled during 2017. In a subgroup of 522 patients (mean age 30.8 ± 12.1; range: 2.5-80 years) from Qatar, Iran, Oman, Cyprus, and Jordan detailed data were available.

RESULTS

Overall, the most prevalent complications were osteopenia/osteoporosis (22.3%), hypogonadism (10.1%), and primary hypothyroidism (5.3%). In the subgroup multivariate analysis, older age was a risk factor for osteoporosis (Odds ratio: 7.870, 95% CI: 4.729-13.099, P < 0.001), hypogonadism (Odds ratio: 6.310, 95% CI: 2.944-13.521, P < 0.001), and non-insulin-dependent diabetes mellitus (NIDDM; Odds ratio: 17.67, 95% CI: 2.217-140.968, P = 0.007). Splenectomy was a risk factor for osteoporosis (Odds ratio: 1.736, 95% CI: 1.012-2.977, P = 0.045). Hydroxyurea was identified as a "protective factor" for NIDDM (Odds ratio: 0.259, 95% CI: 0.074-0.902, P = 0.034).

CONCLUSIONS

To the best of our knowledge, this is the largest cohort of β-TI patients with endocrine disorders evaluated in extremely heterogenic thalassemic populations for age, clinical, hematological, and molecular composition. The study demonstrates that endocrine complications are less common in patients with β-TI compared with β-TM patients. However, regular monitoring with timely diagnosis and proper management is crucial to prevent endocrine complications in β-TI patients.

Molecular characterization of β-thalassemia intermedia in the West Bank, Palestine

BACKGROUND

We aimed to investigate the molecular basis of β-Thalassemia intermedia (TI) in the West Bank region and its management practices.

METHODS

This was a case series multi-center study and included 51 cases of TI. DNA sequencing was used to analyze β-globin gene mutations. Common α-globin gene mutations were screened by Gap-PCR (-α3.7, -α4.2, --MED, αααanti3.7) or DNA sequencing (α2-IVS II 5 nt del). XmnI -158 C > T polymorphisms of Gγ-globin gene was determined by RFLP-PCR.

RESULTS

Seven β-globin gene mutations were observed, namely IVS-I -6 C > T, IVS-I-110 G > A, IVS-II-1 G > A, IVS-I-1 G > A, Codon 37 Trp > Stop, beta - 101 and IVS-II-848 C > A. Ten genotypes were observed. Homozygosity for IVS-I-6 accounted for the majority of TI cases with a frequency of 74.5%. The second common β-globin gene genotype was homozygote IVS-I-110 G > A (5.8%) and homozygote IVS-II-1 G > A (5.8%). The remaining seven genotypes were each detected in about 2% of patients. α-Thalassemia mutations were seen in five patients (9.8%), and included (-α3.7, αααanti3.7 and α2-IVSII-5 nt del). XmnI polymorphism was observed in four patients (7.8%), three homozygotes and one heterozygote.

CONCLUSIONS

Homozygosity for the mild β-globin gene IVS-I-6 allele was the major contributing factor for the TI phenotype among the study subjects. The role of XmnI SNP and α-thalassemia mutations in ameliorating the TI phenotype was observed in few patients for each factor. The beta - 101 C > T mutation was diagnosed in one patient in homozygote state for the first time in Palestine.

Serum Hepcidin as a Diagnostic Marker of Severe Iron Overload in Beta-thalassemia Major

OBJECTIVES

To investigate potential usefulness of serum hepcidin in the diagnosis of iron overload in children with β-thalassemia.

METHODS

A study was conducted on 30 thalassemia major (TM), 30 thalassemia intermedia (TI) and 60 healthy children as controls. Serum hepcidin was measured by Human Hepcidin, ELISA Kit.

RESULTS

β-thalassemia patients had a higher serum hepcidin compared to the controls (p < 0.001). TM group had higher hepcidin and ferritin compared to the TI group (p = 0.034; < 0.001, respectively). Among controls, hepcidin did not correlate with age (r = 0.225, p = 0.084). Among β-thalassemia patients, it correlated positively with age (r = 0.4; p = 0.001), disease duration (r = 0.5; p < 0.001), transfusion frequency (r = 0.35; p = 0.007), total number of transfusions (r = 0.4; p = 0.003), and ferritin (r = 0.3; p = 0.027). Total hemoglobin and serum ferritin were significantly related to hepcidin, which tended to increase by 0.514 ng/ml with each 1 g/dl rise in hemoglobin (p = 0.023) and by 0.002 ng/ml with each 1 ng/ml rise in serum ferritin (p = 0.002). Iron overload [serum ferritin (SF) ≥ 1500 ng/ml] was independently associated with TM (p = 0.001) and elevated serum hepcidin (p = 0.02). The overall predictability of serum hepcidin in severe iron overload was statistically significant when compared to hepcidin to serum ferritin ratio.

CONCLUSIONS

Serum hepcidin is elevated in children with β-thalassemia; but this elevation is more evident in TM patients with severe iron overload. Thus, hepcidin can be a potential marker of severe iron overload in patients with TM. Further studies are recommended to compare serum hepcidin and serum ferritin in the prediction of severe iron overload in steady state and during infection or inflammation.

Liver transplantation from a deceased donor with β-thalassemia intermedia is not contraindicated: A case report

The use of extended criteria donors who might have previously been deemed unsuitable is an option to increase the organ supply for transplantation. This report presents a pediatric case of a successful liver transplantation from a donor with β-thalassemia intermedia. A patient, 6-year-old female, with a diagnosis of cryptogenic liver cirrhosis underwent deceased donor liver transplantation from a thalassemic donor. Extreme hyperferritinemia was detected shortly after transplantation. The most probable cause of hyperferritinemia was iron overload secondary to transplantation of a hemosiderotic liver. Hepatocellular injury due to acute graft rejection might have contributed to elevated ferritin levels by causing release of stored iron from the hemosiderotic liver graft. Iron chelation and phlebotomy therapies were started simultaneously in the early postoperative period to avoid iron-related organ toxicity and transplant failure. Follow-up with monthly phlebotomies after discharge yielded a favorable outcome with normal transplant functions. Thalassemia intermedia patients can be candidates of liver donors to decrease pretransplant waitlist mortality. After transplantation of a hemosiderotic liver, it is important to monitor the recipient in terms of iron overload and toxicity. Early attempts to lower iron burden including chelation therapy and/or phlebotomy should be considered to avoid organ toxicity and transplant failure.

A Large Cohort Study of Genotype and Phenotype Correlations of Beta- Thalassemia in Iranian Population

BACKGROUND

Thalassemia syndromes are the most prevalent single gene disorders in Iran. This study aimed to evaluate the effect of different types of beta-globin gene mutations, co-inheritance of alpha-globin gene mutations and/or Xmn1 SNP on disease phenotype in a large cohort of Iranian patients.

SUBJECTS AND METHODS

In total, 433 patients were clinically classified into β-thalassemia major (TM) or intermedia (TI). Multiplex PCR, ARMS-PCR, RFLP-PCR and DNA sequencing were performed to identify both α- and β-globin gene mutations and Xmn1 polymorphism as well. All data were compared and analyzed by SPSS software in TM and TI groups, consequently.

RESULTS

A total of 39 different β-globin mutations were identified. Among them, the most common were IVS IInt1 (40.33%) followed by IVS Int5 (9.56%), C30 (7.22%) and Fr8-9(7%). All patients were subjected to evaluate common α-globin gene deletions. The patients inherited concomitant mutations of α- and β-globin, showed no clinical modifications compared with those who had only β-globin mutation. The TI patients showed a significant increase in frequency of both heterozygous and homozygous form of the Xmn1 polymorphism. It was also found that β(0)/β(0) genotype patients, inherited the Xmn1 polymorphism required lesser blood transfusion.

CONCLUSION

No significant differences were observed, on the severity of disease, between patient's inherited defective α- and β-globin genes and ones with just β-globin gene mutation. Taking the results of this research into account, Xmn1 polymorphism can be considered as an important genetic factor modulating the severity of disease.

Pulmonary arterial hypertension in a patient with β-thalassemia intermedia and reversal with infusion epoprostenol then transition to oral calcium channel blocker therapy: review of literature

Pulmonary arterial hypertension (PAH) is a potentially life-threatening complication of thalassemia. A sexagenarian with β-thalassemia intermedia presented with new-onset dyspnea and syncope. Right heart catheterization confirmed severe PAH. Her functional class IV symptoms and severely elevated mean pulmonary artery pressure prompted the initiation of continuous epoprostenol therapy. Clinical follow-up documented significant improvement in functional class, 6-minute walk distance, and right ventricular size and function as well as pulmonary arterial pressure on echocardiogram. At the patient's request, epoprostenol was down-titrated and eventually discontinued. The patient was then safely transitioned to nifedipine therapy after verification of vasoresponsiveness.