Prenatal Molecular Diagnosis of β-Thalassemia and Sickle Cell Anemia in the Syrian Population

The Spectrum of α-Thalassemia Mutations in Syrian Patients

α-Thalassemia (α-thal) is a globally prevalent genetic disorder of hemoglobin (Hb) structure where the rate of α-globin chain synthesis is reduced or absent due to the presence of α-globin mutation(s). The aim of this study is to define the spectrum of α-globin gene mutations and evaluate their allele frequency in a group of α-thal carriers. A total of 55 individuals with possible α-thal patients were referred from the thalassemia centers in Syria. They have unexplained hypochromia and microcytosis. All patients were genetically tested for 21 common α-globin gene mutations using reverse hybridization kit. Seven different α-globin gene mutations and 13 different genotypes were detected in 55 patients. The two most frequently encountered mutations were -α3.7 deletion (47.1%) and --MED mutation (21.4%). The most commonly observed genotype was -α3.7/αα (40%), followed by --MED/αα genotype (21.8%). We determined the most common α thalassemia mutations in the Syrian patients. α-Thalassemia mutations with deletions were mostly observed in our study.

Whole-exome sequencing analysis of amniotic fluid cells in 5 pregnant women with thalassemia: Case report

RATIONALE

While thalassemia is a monogenic disease that is relatively common worldwide, there is no recognized radical cure for thalassemia in current medical practice. Prenatal diagnosis is the most important contribution to thalassemia prevention, but due to its technical limitations, rare thalassemia mutations cannot be detected; and the birth of thalassemic babies cannot be completely circumvented. Whole-exome sequencing can, however, compensate for this shortcoming.

PATIENT CONCERNS

We report the results of whole exon sequencing of amniotic cells in 5 pregnant women with thalassemia.

DIAGNOSIS

Prenatal diagnosis revealed that 4 of them were α thalassemia carriers and 1 of them was β thalassemia carrier.

INTERVENTIONS AND OUTCOMES

We collected amniotic fluid of 5 pregnant women (age range: 25-27 years, Mean ± SD: 28 ± 1.8) with thalassemia. The gestational ages ranged between 16 and 19 weeks. The cells were separated from the amniotic fluid and passaged until a sufficient number of cells were obtained for exome sequencing. We therefore employed whole-exome sequencing of amniotic fluid cells from thalassemic carriers to validate prenatal diagnostic results and to identify novel mutation sites. We found that 4 of 5 samples are SEA which is consistent with the clinical prenatal diagnosis. However, 2 of 5 samples were point mutations in the HBB gene, and were thus different from the clinical prenatal diagnosis.

CONCLUSION

The identifications from this study showed that prenatal diagnosis has limitations. Whole-exome sequencing can compensate for this shortcoming. And this study would add new insights into understanding of molecular mechanisms in thalassemia.

A rare gene variation cap +1 (A>C) (HBB: c. -50A>C) associated with codon 5 (-CT) (HBB: c.17_18delCT) mutation in Syrian family

Background

CAP+1 [A>C] (HBB:c.‐50A>C) is a rare silent β‐thalassemia (β‐thal) mutation. Carrier individuals of this mutation show borderline hemoglobin (Hb), mean corpuscular volume (MCV) and Hb A2 levels. This mutation was previously reported in combination with different β‐thalassemia mutations, leading to variable phenotypes.

Case presentation

Here, we describe for the first time the combination of silent CAP+1 [A>C] (HBB:c.‐50A>C) mutation with β⁰ codon 5 [‐CT] (HBB:c.17_18delCT) mutation in a Syrian proband, leading to beta thalassemia intermedia (TI).

Conclusions

The compound heterozygotes of the silent CAP+1 (A>C) together with another severe beta gene mutation, are phenotypically severe enough to present at an early age and require appropriate therapeutic modalities.

Genotype/Phenotype Correlation of β-Thalassemia in Syrian Patients: A Cross-Sectional Study

β-Thalassemia (β-thal) is an inherited blood disorder caused by reduced or absent synthesis of β-globin chains leading to imbalance of globin chain synthesis. β⁰-Thalassemia (β⁰-thal), refers to the complete absence of β-globin chain production on the affected allele. β⁺-Thalassemia (β⁺-thal) refers to alleles with some residual production of β-globin chain. We studied the correlation of genotype/phenotype of β-thal disease in Syrian patients. A cross-sectional study was carried out on 260 patients with β-thal. Genotyping was determined by a DNA sequencing technique. Routine investigations were performed to assess the complete blood count (CBC), serum ferritin, Hb A₂ and Hb F levels. We found that the β⁰/β⁰ genotype was the most common in our patients followed by β⁺/β⁺ and β⁰/β⁺. Patients with β⁰/β⁰ received transfusions at an earlier age and more frequently when compared to those with β⁰/β⁺ and β⁺/β⁺ genotypes. Moreover, patients with β⁰/β⁰ had higher levels of Hb F and lower levels of Hb A₂ compared to those with β⁰/β⁺ and β⁺/β⁺ genotypes. All patients with β-thal intermedia (β-TI) carry the β⁺/β⁺ genotype, while all patients with β⁰/β⁰ and β⁰/β⁺ genotypes presented with transfusion-dependent β-thal major (β-TM).

A First Case of Hemoglobin Castilla [Beta 32(B14) Leu>Arg; HBB: c.98T>G] Associated with [IVS-I-1 (G>A); HBB:c.92+1G>A] Mutation Found in a Syrian Betathalassemia Patient

Beta thalassemia (β-thal) is one of the most common worldwide inherited hemoglobinopathies. Proper identification and diagnosis of hemoglobin (Hb) variants provide a major challenge. In this report, we describe a 1-year-old boy, presented with the diagnosis of β-TM (beta thalassemia major), has received regular blood transfusions. The molecular analysis revealed the presence of rare Hb Castilla [Beta 32(B14) Leu>Arg; HBB: c.98T>G] variant associated with β0 [IVS-I-1 (G>A); AG^GTTGGT- >AGATTGGT beta0] (HBB:c.92+1G>A) Mutation in beta-globin (β-globin) gene. To our knowledge, this is the first report of Hb Castilla [Beta 32(B14) Leu>Arg] in ExonII of β-globin gene which were found in Syrian male proband. However, we should investigate abnormal hemoglobins in patients with beta thalassemia to determine whether they have involvement with β-thalassemia mutations in the clinical case of the patients or not.

Use of an automated pyrosequencing technique for confirmation of sickle cell disease

BACKGROUND

The diagnosis of sickle cell disease (SCD) is made by hemoglobin assays such as high-performance liquid chromatography (HPLC), isoelectric focusing and cellulose acetate or citrate agar electrophoresis. These assays are easy to perform and used in large-scale newborn screening in many countries. These tests however may not easily differentiate Sβ0 thalassemia from SS or identify other hemoglobin variants, and in this case, hemoglobin (HBB) gene sequencing may be necessary.

OBJECTIVES

To develop a high throughput DNA based confirmatory assay for SCD and to detect mutations in the HBB gene.

METHODS

We developed an automated pyrosequencing technique (PyS) based on QIAGEN technology (Hilden, Germany) to detect homozygous or heterozygous hemoglobin S mutations as well as hemoglobin C mutations. The technique was tested on 2,748 samples from patients enrolled in a multi-center SCD cohort in Brazil. Patients were previously tested using HPLC to diagnose SCD as part of routine clinical care. Any subjects with discrepant results between HPLC and PyS or with heterozygous hemoglobin S detected had Sanger sequencing of the HBB gene.

RESULTS

We identified 168 samples with discrepant results between HPLC and PyS and 100 with concordant PyS = heterozygous S and HPLC, which would suggest SB-thalassemia or other heterozygous S variants. The PyS assay correctly identified 1906 (98.7%) of the 1930 HbSS and 628 (98.7%) of the 636 HbSC samples. Of the 179 remaining samples, PyS correctly indicated S heterozygosis in 165 (92.2%). Of the 165 heterozygous S samples confirmed by Sanger as consistent with Sβ thalassemia genotype, 84 samples were classified as Sβ0 thalassemia and 81 as Sβ+ thalassemia. The most frequent beta thalassemia mutations of Sβ0 and Sβ+ were HBB: c.118C>T (Gln40Stop) and HBB c.92 + 6T> C, respectively.

DISCUSSION

The PyS proved to be satisfactory for large-scale confirmatory testing of hemoglobin mutation. Moreover, with this study we were able to describe the most common β+ and β0 mutations in SCD patients with Sβ-thalassemia in a large multi-institutional SCD cohort in Brazil.

Sickle cell retinopathy. A focused review

PURPOSE

To provide a focused review of sickle cell retinopathy in the light of recent advances in the pathogenesis, multimodal retinal imaging, management of the condition, and migration trends, which may lead to increased prevalence of the condition in the Western world.

METHODS

Non-systematic focused literature review.

RESULTS

Sickle retinopathy results from aggregation of abnormal hemoglobin in the red blood cells in the retinal microcirculation, leading to reduced deformability of the red blood cells, stagnant blood flow in the retinal precapillary arterioles, thrombosis, and ischemia. This may be precipitated by hypoxia, acidosis, and hyperosmolarity. Sickle retinopathy may result in sight threatening complications, such as paracentral middle maculopathy or sequelae of proliferative retinopathy, such as vitreous hemorrhage and retinal detachment. New imaging modalities, such as wide-field imaging and optical coherence tomography angiography, have revealed the microstructural features of sickle retinopathy, enabling earlier diagnosis. The vascular growth factor ANGPTL-4 has recently been identified as a potential mediator of progression to proliferative retinopathy and may represent a possible therapeutic target. Laser therapy should be considered for proliferative retinopathy in order to prevent visual loss; however, the evidence is not very strong. With recent development of wide-field imaging, targeted laser to ischemic retina may prove to be beneficial. Exact control of intraoperative intraocular pressure, including valved trocar vitrectomy systems, may improve the outcomes of vitreoretinal surgery for complications, such as vitreous hemorrhage and retinal detachment. Stem cell transplantation and gene therapy are potentially curative treatments, which may prevent retinopathy.

CONCLUSIONS

There is lack of evidence regarding the optimal management of sickle retinopathy. Further study is needed to determine if recent progress in the understanding of the pathophysiology and diagnosis of sickle retinopathy may translate into improved management and outcome.

Hb Knossos (HBB: c.82G > T), β-globin CD 5 (-CT) (HBB: c.17_18delCT) and δ-globin CD 59 (-a) (HBD: c.179delA) mutations in a Syrian patient with β-thalassemia intermedia

Background

Beta thalassemia (β-thal) is an inherited hemoglobin disorder characterized by reduced synthesis of the hemoglobin that results in microcytic hypochromic anemia. β-Thalassemia intermedia (TI) is a clinical term of intermediate gravity between the carrier state and β-thalassemia major (β -TM).

Case presentation

We describe a 12-year-old male proband originating from Al-Quneitra province - southwest Syria. Hematological investigations revealed, pallor and anemia (Hb 9 g/dl). The mean cell volume (MCV) 64 fL; mean cell hemoglobin (MCH) 21.8 pg. Capillary electrophoresis (CE) electropherogram revealed low level of Hb A1 (36.2%), high level of Hb F (62.2%) and low level of Hb A2 (1.6%). The proband requires blood transfusion occasionally. Direct DNA sequencing and Polymerase chain reaction-restriction fragment length polymorphism (PCR/RFLP) for mutations detection were used. The molecular analysis revealed the presence of rare β⁺ Hb Knossos codon 27 (G > T) (HBB: c.82G > T) variant associated with β⁰ codon 5 [−CT] (HBB: c.17_18delCT) mutation in beta-globin (β-globin) gene and δ⁰ codon 59 [−A] (HBD: c.179delA) mutation in delta-globin (δ-globin) gene. The proband tested negative for the common deletional forms of alpha thalassemia (α-thal). Polymorphism of the Xmn-I locus (HBG2: c.-211C > T) revealed that the proband had a homozygous [TT] for Xmn-1 locus.

Conclusions

To our knowledge, this is the first report of beta thalassemia intermedia due to combination of Hb Knossos /codon 5 [−CT] associated with δ⁰ codon 59 [−A] in Syrian patient. On the other hand, in Syria, β-thal carriers who have low level of Hb A2 due to decreased δ-chain production, different δ-thal gene mutations must be screened to avoid the failure diagnosis of β-thal disease.

Description of a Rare β-Globin Gene Mutation: -86 (C>G) (HBB: c.-136C>G) Observed in a Syrian Family

We present the description of a β-thalassemia (β-thal) -86 (C>G) (HBB: c.-136C>G) mutation in a Syrian family from Damascus, As-Suwayda Province, Syria, who was referred to the laboratory for prenatal diagnosis (PND). The mutation was found in the mother in a homozygous state, while it was in the father and in the amniotic fluid sample in a heterozygous state. This mutation is located at -86 within the proximal CACCC box in the promoter of the β-globin gene and is possibly linked with a phenotype of β⁺-thal. Polymerase chain reaction-restriction fragment length polymorphism (PCR/RFLP) analysis indicated that the -86 mutation was linked with haplotype I [+ - - - - + +]. We propose that Lebanon may be the origin of this mutation. To the best of our knowledge, this is the first report describing this mutation in As-Suwayda Province. These findings provide novel information on the region-specificity of this mutation in southwestern Syria.

Effectiveness of β-thalassemia prenatal diagnosis in Southern Iran: a cohort study

AIM

The aim of this study was to evaluate the effectiveness of prenatal diagnosis (PND) for the prevention of thalassemia in Southern Iran.

METHODS

From 2004 to 2012 1346 couples with β-thalassemia minor were referred to our center. Mutation analyses utilized different methods including polymerase chain reaction-based technique of amplification refractory mutation system (ARMS), Restriction Fragment Length Polymorphism Analysis of PCR-Amplified Fragments (PCR-RFLP) and Gel Electrophoresis and direct sequencing. Haplotype analysis of the β-globin gene cluster was done routinely using the PCR-RFLP technique.

RESULTS

Of the 1346 couples, 884 (66%) requested PND. They had a total of 985 pregnancies (954 singleton and 31 twin pregnancies): the 1016 fetuses underwent chorionic villus sampling (CVS). Thalassemia major was diagnosed in 266 cases (26.2%), and termination of pregnancy was requested by the parents in 264 of them (99%). Thalassemia trait was detected in 499 (49.1%) and 251 cases (24.7%) showed no β-thalassemia mutations. There were three misdiagnoses (0.4%) (affected children diagnosed as carriers at PND). A unique pattern of thalassemia mutations was present in the study population, with IVS II-I (G→A), C36-37(-T), IVS I-5(G>C), -25bpdel (252-276), IVS I-110(G>A) and C44 (-C) being present in 62% of cases.

CONCLUSION

The pattern of distribution of thalassemia mutations differs among ethnic groups within the same country.