Mutational spectrum of HBD gene in the Chinese population: Description of 36 mutations including 11 novel variants.

INTRODUCTION: Mutations in the hemoglobin subunit delta (HBD) gene (MIM#142000) are associated with decreased levels of the Hemoglobin A2 (Hb A2 ) fraction. We aimed to examine the prevalence of HBD gene mutations and summarize their characteristics in the Chinese population. METHODS: Individuals who exhibited Hb A2 levels below 1.8%, with or without Hb A2 variant peaks, were chosen for further investigation. Hemoglobin analysis was conducted using capillary electrophoresis. Common α and ß-thalassemia in China were detected using gap-PCR and reverse dot blot hybridization. The presence of HBD gene mutations was confirmed by DNA sequencing. RESULTS: A total of 188 patients were identified as carriers of the HBD gene mutation, with a prevalence of approximately 0.46%. We discovered 36 types of mutations, 30 of which resulted in δ-globin variants, while the remaining 6 resulted in δ-thalassemia. The most common mutation was HBD:c.-127 T > C, accounting for 87.2% of δ-thalassemia cases. In addition, we identified 11 novel HBD gene mutations and found 10 cases compounded with other common thalassemias. CONCLUSION: We observed a high prevalence of HBD gene mutations in southern China. Our findings provide a genetic basis for screening for δ-thalassemia and enrich the spectrum of HBD gene mutations.

Molecular characterization of a novel homozygous deletion in ß-globin cluster causing (δß)0-Thalassemia among Tunisian family.

BACKGROUND: Deletions in the ß-globin cluster are uncommon and cause thalassemia (thal) with hereditary persistence of fetal hemoglobin. They constitute a heterogenous group of disorders characterized by absent or reduced synthesis of adult hemoglobin (Hb A) and increased synthesis of fetal hemoglobin (Hb F). Although the clinical severity of these disorders are asymptomatic owing to the increased Hb F levels, the molecular basis is very heterogenous due to the large deletions in the ß-globin cluster spanning both HBD and HBB genes. Here, we describe a Tunisian family carrying a novel deletion mutation causing (δß)°-thalassemia. METHODS: The amounts of hemoglobin fractions were measured by capillary electrophoresis of hemoglobin. Amplification and sequencing of different regions on the ß-gene cluster were performed by Sanger method. RESULTS: Family study and genetic analysis revealed a large deletion mutation in the ß-globin cluster of 14.5 kb (NG_000,007.3:g. 58,253 to g.72837del14584) at the homozygous state in the patient and at heterozygous state at the other members of the family. This deletion removes the HBD and HBB genes. CONCLUSIONS: In our knowledge, this new large deletion is described for the first time in the Tunisian population and in the world, designed Tunisian(δß)0 in Ithanet database (IthaID: 3971). Therefore, it is important to identify the deletion leading to δß-thalassemia carriers at the molecular level, to highlight the importance of recognizing the clinical features and implementing appropriate testing to clarify the diagnosis and manage the condition.

Analysis of δ-globin gene alleles in Tunisians: description of three new delta-thalassemia mutations.

BACKGROUND: Thalassemia is one of the most prevalent worldwide autosomal recessive disorders characterized by a great molecular and clinical expression heterogeneity. Alpha and beta-thalassemia are the main two types observed in case of mutations affecting alpha and beta-globin genes respectively. Delta-thalassemia is noted when mutations occur on the delta-globin gene. In Tunisia, ß-thalassemia prevalence is estimated at 2.21% of carriers. However, few reports investigated the delta-globin gene. OBJECTIVES: In this work, we aimed to perform a molecular study to help define the molecular spectrum of δ-thalassemia mutations in Tunisia. PATIENTS AND METHODS: The study involved 7558 patients among whom we selected 179 individuals with abnormal HbA2 values or fractions. Hemoglobin analysis was performed using Capillary electrophoresis (CE) and high-performance liquid chromatography (HPLC). DNA sequencing was performed on ABI prism 310 Genetic Analyzer Applied Biosystems. CUPSAT (Cologne University Protein Stability Analysis Tool) was used for the prediction of protein stability changes upon missense mutations and mutants were modeled via DeepView-SwissPdbViewer and POV-Ray softwares for molecular dynamics simulation studies. RESULTS: We identified four mutations: HbA2-Yialousa described for the first time in Tunisia ( in 72.72% of cases) and 3 mutations reported for the first time in the world: (i) c.442 T > C Stop147Arg ext 15aa-stop observed in 18.18% of cases, (ii) c.187 G > C (Ala62Pro) noted in 4.54% of cases and (iii) c.93-1G > C found in 4.54% of cases. CONCLUSION: Our data provide genetic basis that would be especially useful in screening for beta-thalassemia trait during delta-beta thalassemia associations.

First report of the spectrum of δ-globin gene mutations among women of reproductive age in Fujian area-Discrimination of δ-thalassemia, α-thalassemia, and Iron Deficiency Anemia.

BACKGROUND: Low HbA2 level is an underlying of δ-thalassemia, α-thalassemia, and IDA. Interactions of these disorders can generate a wide spectrum of phenotype, which will pose diagnostic conundrum for clinical assessment, carrier screening, and genetic counseling. METHODS: Subjects with HbA2 levels below 2.0% with normal or reduced hematological parameters were recruited for further investigation. δ-globin gene mutations were identified by DNA sequencing of the HBD gene. Serum ferritin (SF) concentration was determined by the chemiluminescent microparticle immunoassay. The three common deletional α-thalassemia (--SEA /αα, -α3.7 /αα, and -α4.2 /αα) were detected using Gap-PCR, detection of the point mutations in the three nondeletional α-thalassemia (αCS α/αα,αQS α/αα,αWS α/αα), and the 17 common ß-thalassemia was performed using reverse dot blot hybridization (RDB). RESULTS: We had characterized the δ-globin gene mutations in 20 cases, revealing a frequency of 0.4% in the women of reproductive age (20/4 792). Two previously known mutations:-77 T > C and -30 T > C and 3 novel δ-globin gene defects: -44G > A,CD87C > T, and CD134T > A were found. In the selected cases, we also found 85 cases confirmed with (51.2%,85/166) IDA and 39 cases (23.5%,39/166) with common α-thalassemia. Subjects with δ-thalassemia had statistically higher levels of Hb, MCV, and MCH compared with other two groups, whereas statistically lower levels of RDW were seen in δ-thalassemia group. What's more, statistically higher levels of SF were seen in δ-thalassemia group, compared with IDA groups. CONCLUSION: We reported the spectrum of δ-thalassemia mutations for the first time with the frequency of 0.4% among women of reproductive age in Fujian area and found that -77T > C mutation was the most common mutation, followed by -30T > C mutation. What's more, 3 novel δ-globin gene defects: -44G > A,CD87C > T and CD134T > A were found. A thorough analysis of the hematological, electrophoretic characterization, and the level of SF was needed to suspect and further investigate the existence of IDA, α-thalassemia, and δ-thalassemia.

Genotypic-phenotypic heterogeneity of 뫧-thalassemia and hereditary persistence of fetal hemoglobin (HPFH) in India.

Large deletions in the ß-globin gene cluster lead to increased HbF levels by delaying the γ- to ß-globin switch process. However, these deletions when inherited as a homozygous condition or when co-inherited with ß-thalassemia result in variable clinical phenotypes. Individuals or families with a clinically presenting child, where the parents had HbF levels ≥ 10%, were further screened for the presence of large ß-globin cluster deletions. Six deletions in the ß-globin gene cluster were screened by GAP-PCR, and the uncharacterized deletions were further analyzed by gene dosage or by multiplex ligation-dependent probe amplification (MLPA). Among 192 individuals suspected for the inheritance of large deletions, 138 were heterozygous for large deletions, 45 were compound heterozygous of a large ß-globin cluster deletion and ß-thalassemia, and 9 were found to be homozygous for deletions. Among the heterozygotes, the Asian Indian inversion-deletion was found to be the most common deletion (39.9%), followed by the HPFH-3 deletion (30.0%). Other deletions 49.3 kb, δß-thalassemia (21.2%), and 32.6 kb deletion (4.4%) were also found to be prevalent in our population. Patients compound heterozygous or homozygous for HPFH-3 and 32.6 kb deletions showed a milder clinical presentation, as compared with the patients compound heterozygous or homozygous for the Asian Indian inversion-deletion and 49.3 kb δß-thalassemia. This comprehensive study highlights the mutation spectrum of large ß-globin cluster deletions and the clinical heterogeneity in the patients homozygous or compound heterozygous with ß-thalassemia, thus asserting the need for molecular characterization of these deletions.

Molecular epidemiology and hematologic characterization of 뫧-thalassemia and hereditary persistence of fetal hemoglobin in 125,661 families of greater Guangzhou area, the metropolis of southern China.

BACKGROUND: Individuals with δß-thalassemia/HPFH and ß-thalassemia usually present with intermedia or thalassemia major. No large-scale survey on HPFH/δß-thalassemia in southern China has been reported to date. The purpose of this study was to examine the molecular epidemiology and hematologic characteristics of these disorders in Guangzhou, the largest city in Southern China, to offer advice for thalassemia screening programs and genetic counseling. METHODS: A total of 125,661 couples participated in pregestational thalassemia screening. 654 subjects with fetal hemoglobin (HbF) level ≥ 5% were selected for further investigation. Gap-PCR combined with Multiplex ligation dependent probe amplification (MLPA) was used to screen for ß-globin gene cluster deletions. Gene sequencing for the promoter region of HBG1 /HBG2 gene was performed for all those subjects. RESULTS: A total of 654 individuals had hemoglobin (HbF) levels≥5, and 0.12% of the couples were found to be heterozygous for HPFH/δß-thalassemia, including Chinese Gγ (Aγδß)0-thal, Southeast Asia HPFH (SEA-HPFH), Taiwanese deletion and Hb Lepore-Boston-Washington. The highest prevalence was observed in the Huadu district and the lowest in the Nansha district. Three cases were identified as carrying ß-globin gene cluster deletions, which had not been previously reported. Two at-risk couples (0.0015%) were required to receive prenatal diagnosis. We also found 55cases of nondeletional-HPFH (nd-HPFH), including 54 with Italian nd-HPFH and one with the Aγ-197C-T heterozygous state. It is difficult to discriminate between Chinese Gγ (Aγδß)0-thal and Italian nd-HPFH carriers using hemoglobin (Hb) analysis. CONCLUSIONS: This study is the first to describe the familial prevalence of HPFH/δß-thalassemia and the high-risk rate in Greater Guangzhou Area, and the findings will support the implementation of thalassemia screening for three common deletions by gap-PCR. We also presented a systematic description of genotype-phenotype relationships which will be useful for genetic counseling and prenatal diagnostic services for ß-thalassemia intermedia.

Analysis of deletional hereditary persistence of fetal hemoglobin/δß-thalassemia and δ-globin gene mutations in Southerwestern China.

BACKGROUND: Deletional hereditary persistence of fetal hemoglobin (HPFH)/δß-thalassemia and δ-thalassemia are rare inherited disorders which may complicate the diagnosis of ß-thalassemia. The aim of this study was to reveal the frequency of these two disorders in Southwestern China. METHODS: A total of 33,596 subjects were enrolled for deletional HPFH/δß-thalassemia, and positive individuals with high fetal hemoglobin (Hb F) level were diagnosed by multiplex ligation-dependent probe amplification (MLPA). A total of 17,834 subjects were analyzed for mutations in the δ-globin gene. Positive samples with low Hb A2 levels were confirmed by δ-globin gene sequencing. Furthermore, the pathogenicity and construction of a selected δ-globin mutation were analyzed. RESULTS: A total of 92 suspected cases with Hb F ≥5.0% were further characterized by MLPA. Eight different deletional HPFH/δß-thalassemia were observed at a frequency of 0.024%. In addition, 195 cases suspected to have a δ-globin gene mutation (Hb A2 ≤2.0%) were characterized by molecular analysis. δ-Globin gene mutation was found at a frequency of 0.49% in Yunnan. The pathogenicity and construction for a selected δ-globin mutation was predicted. CONCLUSION: Screening of these two disorders was analyzed in Southwestern China, which could define the molecular basis of these conditions in this population.

Clinical variability and molecular characterization of Hbs/Gγ (Aγδß)0-thal and Hbs/HPFH in Indian sickle cell disease patients: AIIMS experience.

INTRODUCTION: In sickle cell disease (SCD) patients, among the predictors of survival, HbF levels play a significant role in lowering the morbidity and mortality. Coinheritance of 뫧 thalassemia and hereditary persistence of fetal hemoglobin (HPFH) may contribute to variable HbF levels in SCD patients, thus influencing their clinicopathological profile. Such cases are sparsely documented in the literature and thus, we screened the presence of 뫧 thalassemia and HPFH in 126 cases of SCD with high HbF. MATERIAL AND METHODS: A total 126 SCD individuals with raised HbF levels were the study subject. Capillary zone electrophoresis (CZE) was done for the quantitative assessment of hemoglobin variants. HbSC, HbSD, HbAS and HbSE cases were excluded. Asian Indian Gγ(Aγδß)0-thal, δß0-thal (Sicilian, 13.4 kb), (Chinese, 100 kb), HPFH-1 (Black, 106 kb), HPFH-2 (Ghanaian, 105 kb), HPFH-3 (Indian, 48.5 kb) were done by GAP-PCR. RESULTS: Out of 126, 78 cases (62%) were homozygous for SCD. The remaining 48 cases suspected to be heterozygous were furthered screened and 6/48 cases (12.5%) were found to be compound heterozygous. Out of these 6 cases,4(66.66%) had HbS/ δß- Gγ(Aγδß)0 and 2(33%) had HbS/HPFH compound heterozygous condition. None of the patients had δß0-thal (Sicilian, 13.4 kb), (Chinese, 100 kb), HPFH-1 (Black, 106 kb), HPFH-2 (Ghanaian, 105 kb). CONCLUSION: This study highlights the importance of understanding the complex patho-physiology of compound heterozygous cases of HbS/HPFH and HbS/뫧 thalassemia, as these infrequent conditions lead to change in phenotype and clinical severity of the disease. Insight into more such cases will open the window to better analyze the disease pathogenesis in these rare compound heterozygous conditions, as this will be beneficial to formulate proper management protocol in these patients.

Molecular and Hematological Characterization of Two Novel δ-Globin Gene Mutations Found in Chinese Individuals.

We identified two novel δ-globin gene mutations in two families during routine thalassemia screening. One missense mutation at codon 73 on the δ-globin gene [δ73(E17)Asp→Val, HBD: c.221A>T] which results in a Hb A2 variant homologous to the ß-globin gene variant called Hb Mobile [ß73(E17)Asp→Val, HBB: c.221A>T] and we have named this variant Hb A2-Henan. The other is a nonsense mutation [δ7(A4)Glu→Stop, HBD: c.22G>T] which gives rise to a stop codon (TAG) at codon 7, resulting in δ0-thalassemia (δ0-thal). The Hb A2 in one individual with homozygous HBD: c.22G>T was absent.

δ-Thalassemia with Complete Absence of Hb A2 in a Chinese Family.

A Chinese family with δ-thalassemia (δ-thal) was found, in which the daughter is homozygous for δ-thal (HBD: c.-127T>C) with complete deficiency of Hb A2 and the mother is a heterozygote with low level of Hb A2. The father, however, is a heterozygote with a normal Hb A2 value due to coinheritance of a ß-thalassemia (ß-thal). Although no abnormal clinical or hematological findings were noted in the individuals with δ-thal, one should keep in mind that ß-thal can be missed during routine preliminary screening when ß-thal and δ-thal coexist in a subject.

Contrasting co-inheritance of alpha and beta mutations in delta beta thalassemia and hereditary persistence of fetal hemoglobin: a study from India.

BACKGROUND AND OBJECTIVES: Coinheritance of 뫧 thalassemia and HPFH with inherited factors is sparsely documented and may affect treatment modalities. So, we screened the presence of α deletion and ß mutations in 뫧 thalassemia and HPFH disorders in 52 cases with high Hb F concentration. MATERIAL AND METHODS: Fifty-two individuals with raised HbF levels were study subjects. CZE was done for quantitative assessment of hemoglobin variants. Asian Indian inversion deletion break point type A, B and HPFH-3 were done by GAP-PCR. RESULTS: 18/52 cases of 뫧 Gγ (Aγδß)0 thalassemia and 28/52 cases of HPFH-3 deletion were characterized. 6/52 patients with raised HbF levels were negative for 뫧 Gγ (Aγδß)0 and HPFH-3 deletion. 9/18 (50%) were heterozygous for Gγ(Aγδß)0 break point type A, 6/18 (33%) were heterozygous for break point type B and 3/18 (17%) were homozygous. Of the nine patients heterozygous for Gγ(Aγδß)0 break point type A, three (33%) patients were double heterozygous with alpha 3.7 kb deletion and two (22%) patients showed compound heterozygosity with IVS 1-5(G-C) mutation. 4/9 (45%) patients were Gγ(Aγδß)0 heterozygous. DISCUSSION AND CONCLUSION: We found 5/18(27.ß) δß-thalassemia cases with co-inherited alpha 3.7 deletion and 3/18 (16ß) cases with IVS 1-5(G-C) mutation. Patients showed features of thalassemia intermedia phenotype among which those with co-inherited IVS 1-5(G-C) mutation showed severe phenotype as compared to those with co-inherited alpha 3.7 deletion. So, we highlight importance of genotyping of patients with 뫧 thalassemia or HPFH and coinheritance with inherited factors which plays crucial role in clinicopathological profile and setting up prenatal diagnostic protocol.

The prevalence and molecular characterization of (뫧)0 -thalassemia and hereditary persistence of fetal hemoglobin in the Chinese Zhuang population.

OBJECTIVE: To reveal the prevalence and molecular characterization of (δß)0 -thalassemia [(δß)0 -thal] and hereditary persistence of fetal hemoglobin (HPFH) in the Chinese Zhuang population. METHODS: A total of 105 subjects with fetal hemoglobin (Hb F) level ≥5% from 14 204 unrelated ones were selected for the study. Multiplex ligation dependent probe amplification was firstly used to analyze dosage changes of the ß-globin gene cluster for associated with (δß)0 -thal and HPFH mutations. The gap polymerase chain reaction was then performed to identify the deletions using the respective flanking primers. Hematologic data were recorded and correlated with the molecular findings. RESULTS: Twenty-one (0.15%) subjects were diagnosed with Chinese G γ(A γδß)0 -thal. Nine (0.06%) were diagnosed with Southeast Asia HPFH (SEA-HPFH) deletion. Seventy-five (0.53%) cases remained uncharacterized. Three genotypes for Chinese G γ(A γδß)0 -thal and SEA-HPFH deletion were identified, respectively. The genotype-phenotype relationships were discussed. CONCLUSION: Our study for the first time demonstrated that (δß)0 and HPFH were not rare events, and molecular characterized G γ(A γδß)0 -thal and HFPH mutations in the Chinese Zhuang population. The findings in our study will be useful in genetic counseling and prenatal diagnostic service of ß-thalassemia in this populations.

Delta-Beta Thalassaemia in a Pathan Family.

Delta-beta-thalassaemia (δß-thalassaemia) is a rare type of thalassaemia which mostly results from deletion of δ and ß genes with preservation of γ genes. δß-thalassaemia is classified into (δß)+ and (δß)0 types. The (δß)0-thalassemia is further divided into GγAγ(δß)0-thalassaemia and Gγ(Aγδß)0-thalassaemia. In heterozygous state, (δß)0mutations give rise to phenotype resembling ß-thalassaemia trait but with raised Hb-F, ranging from 5 to 20%, without a rise in Hb-A2. In homozygotes, the clinical picture is usually that of thalassaemia intermedia and the patients have 100% Hb-F. Workup of a 1-year child suffering from pallor, chronic ill health, and splenomegaly referred to our laboratory with the suspicion of ß-thalassaemia, ultimately resulted in a diagnosis on polymerase chain reaction as having homozygous inversion/deletion Gγ(Aγδß)0-thalassaemia. Her family members were also investigated.

[Analysis of haematological phenotype and mutation spectrum of δ-globin gene from Guangdong area in Chinese Han prenatal population].

Objective: To analyze the genotype-phenotype correlations among southern Chinese Han prenatal population in Guangdong area with δ-globin gene mutation, so as to enrich the delta-thalassemia gene mutations data. Methods: A total of 33 cases were selected in 7 580 patients during prenatal thalassemia trait screening, from January 2012 to May 2015(including 10 males and 23 females, aged 22-48 years old). Complete blood cell count was performed on a XE 4000i automatic hemocyte analyzer. Hb, HbF and HbA2 were tested by high performance liquid chromatography (HPLC). Genomic DNA was extracted from whole blood samples using a whole blood genomic DNA extraction kit. Polymerase chain reaction (PCR) was used to amplify three different fragments corresponding to the exons and the regulatory sequences using three different couples of primers for the δ-globin gene. Results: Twenty one of the 33 samples were positive for the δ-globin gene defects. Four previously known mutations were detected: including 12 cases for -77(T>C)[HBD c. -127 (T>C)](57.14%), 4 cases for -30 (T>C)[HBD c. -80 (T>C)](19.05%), 1 case for codon 10 (-G) (HBD c. 31delG)(4.76%), and 1 case for HBD c. 244 C>T(4.76%). Three new δ-globin gene defects which had not yet been reported in database were detected, including 1 case for HBD c. 22_24delGAG(4.76%), 1 case for HBD c. 347 C>T(4.76%), and one case for HBD c. 349 C>G(4.76%). Conclusions: -77 (T>C) is the most common mutation in Chinese southern prenatal population. Three new HBD gene mutations are referred in this report, which provide the valuable information for genetic counseling and prenatal diagnosis in Guangdong area.

Haemoglobinopathies that occur with decreased HbA2 levels: a gene mutation set involving the δ gene at a Spanish centre.

AIMS: Haemoglobin A2 (HbA2) consists of two globin chains, α and ß. Alterations in any of these genes influences the level of HbA2. Here, we present cases of structural Hb variants and thalassaemias which present either alone or together and reduce the level of HbA2 at varying degrees. Furthermore, we present a novel structural mutation in the δ globin gene, called Hb A2-Madrid. METHODS: The levels of HbA2 and HbF and the different haemoglobin variants were measured and analysed by ion exchange high performance liquid chromatography (HPLC, VARIANT II), the types of haemoglobins were determined by capillary zone electrophoresis (CZE) (Sebia) and the globin chains were determined by reversed-phase HPLC. Genetic analysis was performed by automatic sequencing of the α and δ genes as well as by multiple PCRs for the α globin genes. RESULTS: In α thalassaemia (n=94), the HbA2 levels ranged from 1.39% to 2.43%. Among individuals with δ thalassaemia (n=5), the HbA2 level of those with δ+ thalassaemia was 1.77%, and that of those with δ0 thalassaemia was 1.70%. Among the individuals with 뫧 thalassaemia (n=13), those who were homozygous lacked HbA2. All structural haemoglobinopathies (n=97) were heterozygous; the α chain variants (n=84) presented with an HbA2 level of 1.76%, while the δ chain variants (n=13) presented with a level of 1.75%. CONCLUSION: HbA2 is an essential parameter in the diagnostics of haemoglobinopathies. HPLC-EC and CZE allow the quantification of HbA2. Here, we show that quantification of HbA2 is critical for the identification of α, δ and ßδ thalassaemias. Structural variants are discovered by HPLC. Molecular genetics is required for the proper identification of the mutations. Only with this knowledge is genetic counselling possible.