Two novel mutations in the 3' untranslated region of the beta-globin gene that are associated with the mild phenotype of beta thalassemia

Evaluation of the Function of a Rare Variant in the 3'-Untranslated Region of the β-Globin Gene

β-Thalassemia (β-thal) is an inherited genetic disease that occurs because of the absence or reduction of β-globin chain synthesis. Genetic changes occur in different regions of the β-globin gene, but these mutations are less reported in the 3' untranslated region (3'-UTR). The objective of the present investigation was to evaluate the functional effect of a rare variant in the 3'-UTR of the β-globin gene. A variant at the first nucleotide of the 3'-UTR of the β-globin gene (HBB: c.*1G > A) was identified by DNA sequencing in an individual with low hematological indices and a normal hemoglobin (Hb) electrophoresis pattern. To evaluate the functional effect of this variant, the normal and mutated 3'-UTR of the β-globin gene was synthesized separately and sub cloned in the psiCHEK2 vector. Next, using the calcium phosphate method, the psiCHEK2 vectors containing normal and mutated 3'-UTR were transfected separately into the HEK293T cell line. Finally, the transfected cell line was analyzed by dual luciferase assay. The ratio of Renilla to firefly for the mutant sample was 1.26 ± 0.06, while for normal samples it was 1.12 ± 0.04. The results of the luciferase assay showed that there was no significant difference in the functional effect between the mutant and wild type construct. Therefore, it was concluded that this variant might not reduce the expression of the β-globin gene. Future studies by globin chain synthesis or to evaluate the expression of the gene in erythroid cells, might be necessary to understand the regulatory function of this mutation.

Identification of a Novel Mutation in the 3' Untranslated Region of the β-Globin Gene (HBB:c.*132C>G) in a Chinese Family

We describe a new β-globin mutation causing silent β-thalassemia (β-thal). The proband was a 5-year-old boy who presented with the phenotype of thalassemia intermedia. Molecular diagnoses revealed a genomic alteration at position 1606 of the HBB gene (HBB:c.*132C>G) in combination with a common β⁰-thal mutation (HBB:c.126_129delCTTT). The 3'-untranslated region (UTR) mutation was inherited from his father who showed a normal mean corpuscular volume (MCV) and Hb A₂ level. The discovery of rare mutations provides important information related to both genetic counseling for families involved.

β-Thalassemia Intermedia Caused by the β-Globin Gene 3' Untranslated Region: Another Case Report

The 3' untranslated region (3'UTR) is associated with mRNA stability because of its involvement in 3' end processing, polyadenylation, and mRNA capping. Mutations located in this area can cause a phenotype compatible with β⁺-thalassemia (β⁺-thal). We report a Chinese subject with β-thal intermedia (β-TI) who developed transfusion-dependent anemia. Molecular studies revealed that the patient was a compound heterozygote for two β-thal alleles: codons 41/42 (-TTCT) (HBB: c.126_129delCTTT) and term codon +32 (A>C) (HBB: c.*32A>C).

Quality of Life and Related Paraclinical Factors in Iranian Patients with Transfusion-Dependent Thalassemia

Background

Thalassemia is one of the most common genetic hematologic disorders in the world. Despite outstanding achievements in prenatal diagnosis and a decrease in the number of patients, thalassemia is still a significant issue in most parts of the world, especially in the Mediterranean countries. Understanding the factors associated with this condition is crucial to help clinicians and policymakers provides social and medical support for patients to facilitate their lives. This study aims to appraise the quality of life (QoL) and its related paraclinical factors in Iranian transfusion-dependent thalassemia patients.

Methods and Materials

This study is a cross-sectional study performed in the thalassemia clinic of Imam-Ali Hospital, Karaj, Iran. The demographic, clinical, and laboratory data of 100 patients with transfusion-dependent thalassemia were recorded. The patients' QoL was measured by the World Health Organization Quality of Life Instruments Brief (WHOQOL-BREF) version questionnaire. The results were analyzed using SPSS software.

Results

This study demonstrated that all four features of life are influenced in transfusion-dependent thalassemia patients. Also, higher educational status and lower serum ferritin levels were associated with better scores in assessing the QoL. On the other hand, an elevated level of AST (aspartate transaminase), ALT (alanine transaminase), and FBS (fasting blood sugar) are associated with lower scores.

Conclusion

All features of QoL are correlated to the patients' laboratory findings. Our data suggest that managing patients' laboratory indices is attributed to their higher QoL. We also suggest regular screening of patients' QoL to manage disease complications more efficiently.

Borderline HbA2 levels: Dilemma in diagnosis of beta-thalassemia carriers

There is inconsistency in the exact definition of diagnostic levels of HbA₂ for β thalassemia trait. While many laboratories consider HbA₂ ≥4.0 % diagnostic, still others consider HbA₂ ≥3.3 % or HbA₂ ≥3.5 % as the cut-off for establishing β thalassemia carrier diagnosis. This is because, over the years, studies have described β thalassemia carriers showing HbA₂ levels that lie above the normal range of HbA₂ but below the typical carrier range of β thalassemia. These, "borderline HbA₂ levels", though not detrimental to health, are significant in β thalassemia carrier diagnosis because they can lead to misinterpretation of results. In this review, we have evaluated the prevalence of borderline HbA₂ levels and discussed the causes of borderline HbA₂ values. We have also compiled an extensive catalogue of β globin gene defects associated with borderline HbA₂ levels and have discussed strategies to avoid misdiagnosing borderline HbA₂ β thalassemia carriers. Our analysis of studies that have delineated the cause of borderline HbA₂ levels in different populations shows that 35.4 % [626/1766] of all individuals with borderline HbA₂ levels carry a molecular defect. Among the positive samples, 17 % [299/1766] show β globin gene defects, 7.7 % [137/1766] show α thalassemia defects, 2.7 % [49/1766] show KLF1 gene mutations, 2.3 % [41/1766] show the co-inheritance of β and α thalassemia, 2.0 % [37/1766] show the co-inheritance of β and δ thalassemia and 1.8 % [32/1766] show α globin gene triplication. It appears that a comprehensive molecular work up of the β globin gene is the only definite method to detect borderline HbA₂ β thalassemia carriers, especially in populations with a high prevalence of the disease. The presence of associated genetic or acquired determinants may subsequently be assessed to identify the cause of borderline HbA₂.

Emerging Roles of RNA 3'-end Cleavage and Polyadenylation in Pathogenesis, Diagnosis and Therapy of Human Disorders

A crucial feature of gene expression involves RNA processing to produce 3′ ends through a process termed 3′ end cleavage and polyadenylation (CPA). This ensures the nascent RNA molecule can exit the nucleus and be translated to ultimately give rise to a protein which can execute a function. Further, alternative polyadenylation (APA) can produce distinct transcript isoforms, profoundly expanding the complexity of the transcriptome. CPA is carried out by multi-component protein complexes interacting with multiple RNA motifs and is tightly coupled to transcription, other steps of RNA processing, and even epigenetic modifications. CPA and APA contribute to the maintenance of a multitude of diverse physiological processes. It is therefore not surprising that disruptions of CPA and APA can lead to devastating disorders. Here, we review potential CPA and APA mechanisms involving both loss and gain of function that can have tremendous impacts on health and disease. Ultimately we highlight the emerging diagnostic and therapeutic potential CPA and APA offer.

NAA10 polyadenylation signal variants cause syndromic microphthalmia

BACKGROUND

A single variant in NAA10 (c.471+2T>A), the gene encoding N-acetyltransferase 10, has been associated with Lenz microphthalmia syndrome. In this study, we aimed to identify causative variants in families with syndromic X-linked microphthalmia.

METHODS

Three families, including 15 affected individuals with syndromic X-linked microphthalmia, underwent analyses including linkage analysis, exome sequencing and targeted gene sequencing. The consequences of two identified variants in NAA10 were evaluated using quantitative PCR and RNAseq.

RESULTS

Genetic linkage analysis in family 1 supported a candidate region on Xq27-q28, which included NAA10. Exome sequencing identified a hemizygous NAA10 polyadenylation signal (PAS) variant, chrX:153,195,397T>C, c.*43A>G, which segregated with the disease. Targeted sequencing of affected males from families 2 and 3 identified distinct NAA10 PAS variants, chrX:g.153,195,401T>C, c.*39A>G and chrX:g.153,195,400T>C, c.*40A>G. All three variants were absent from gnomAD. Quantitative PCR and RNAseq showed reduced NAA10 mRNA levels and abnormal 3' UTRs in affected individuals. Targeted sequencing of NAA10 in 376 additional affected individuals failed to identify variants in the PAS.

CONCLUSION

These data show that PAS variants are the most common variant type in NAA10-associated syndromic microphthalmia, suggesting reduced RNA is the molecular mechanism by which these alterations cause microphthalmia/anophthalmia. We reviewed recognised variants in PAS associated with Mendelian disorders and identified only 23 others, indicating that NAA10 harbours more than 10% of all known PAS variants. We hypothesise that PAS in other genes harbour unrecognised pathogenic variants associated with Mendelian disorders. The systematic interrogation of PAS could improve genetic testing yields.

Impact of Long-Term Dual Antiplatelet Therapy on Immature Platelet Count and Platelet Reactivity

The immature platelet count (IPC) is a potential marker of platelet reactivity. We assessed the relationship between IPC during chronic dual antiplatelet therapy (DAPT) and the response to antiplatelet drugs (acetylsalycilic acid + clopidogrel/ticagrelor). We included 286 patients: 167 (58.4%) patients received ticagrelor and 119 (41.6%) received clopidogrel. At a median follow-up of 46.5 days, the variation in IPC displayed an absolute median (interquartile range [IQR]) of −11.9 × 103/µL (−182.7 to 160.8), corresponding to a median percentage change in IPC ([%ΔIPC] IQR) of −0.3% (−21.9% to 35.5%), with an increase in IPC levels in those on ticagrelor and a decrease in IPC levels in those on clopidogrel. We observed an inverse association of lower platelet reactivity at different tests and a higher increase in IPC ( r = −0.14, P = .04 for arachidonic acid test; r = −0.12, P = .05 for collagen test; and r = −0.13, P = .02 for adenosine diphosphate test [ADP]). The rate of poor effectiveness of ADP antagonists was the only independent predictor of a ΔIPC above the third tertile (odds ratio [95% confidence interval] = 0.55 [0.32-0.99]; P = .048). We showed that in patients treated with chronic DAPT, an increase in IPC is significantly related to lower levels of platelet reactivity.

Co-heredity of silent CAP + 1570 T>C (HBB:c*96T>C) defect and severe β-thal mutation: a cause of mild β-thalassemia intermedia

INTRODUCTION

During an intensive screening program aimed at identifying the healthy carriers of thalassemia and the couples at risk of bearing an affected fetus, a rare single nucleotide variation (SNV), CAP + 1570 T > C (HBB:c*96T > C), located 12 nucleotides upstream of the polyadenylation signal in 3'UTR of the beta globin gene was identified. It was previously reported as a β+ thalassemia mutation and later as a plain polymorphism.

METHODS

Genotype identification of globin gene mutations was carried out using sequencing analysis, GAP-PCR, and MLPA methods.

RESULTS

CAP + 1570 T > C (HBB:c*96T > C) was found in 39 heterozygotes, in one case in homozygous state and in thirteen cases of co-inheritance of this nucleotide substitution with other mutations in globin genes. Carriers of this mutation showed a 'silent' phenotype without appreciable microcytosis and hypochromia, so they cannot be differentiated from noncarrier individuals. Compound heterozygotes for this mutation and severe β-thal mutations showed a variable phenotype ranging from β-thal carrier to mild form of β-thalassemia intermedia, revealing new aspects and allowing to better understand the clinical implications of this nucleotide substitution that can be classified as a silent β-thalassemic defect.

CONCLUSION

Data reported in this study indicate the need of investigating partner of β-thalassemia carrier by complete sequencing analysis of β-globin gene and of providing an appropriate genetic counseling for couples at risk undergoing prenatal diagnosis.

Novel Βeta (β)-Thalassemia Mutation in Turkish Children

Beta (β)-thalassemia is the most frequently observed hereditary blood disorder in the world. It is characterized by deficiency of hemoglobin β-globin gene and is also a profoundly heterogeneous both at the molecular and clinical level. In the case of β-thalassemia, there is reduced (β(+) type) or absent (β(o) type) synthesis of the beta chains of hemoglobin. β-Thalassemia clinically occurs in three main forms: major, intermedia and minor according to requirement of transfusion. The objective of this study was to evaluate β-thalassemia mutations in 89 patients ranging from 2 months to 16 years of age, who enrolled to Medical School Research and Training Hospital, Gaziantep University. The direct DNA sequence analysis was performed for mutation scanning of β-globin gene. 89 children with β-Thalassemia including all types were analyzed, 16 different β-thalassemia mutations were detected. We have also identified a novel mutation (HBB.c.-80delT, rs397509430) in the promoter region (-30 TATA box) of β-globin gene, and clinical data of patient having novel mutation was given. The β-Thalassemia mutations were determined as β-Thalassemia major type in 42 patients (47.19 %), β-Thalassemia intermedia in 4 (4.49 %), β-Thalassemia minor in 43, (48.31 %) patients. The most frequent mutation was IVS I-110 G>A, followed by IVS I-1 G>A, IVS I-6 T>C, IVS II-1 G>A, respectively.