Suppression of Hb Bart's to improve tissue oxygenation and fetal development in homozygous alpha-thalassemia

Intra-uterine reduction of Hb Bart's only reached with exchange transfusions.

A Novel Tool for the Analysis and Detection of Copy Number Variants Associated with Haemoglobinopathies

Several types of haemoglobinopathies are caused by copy number variants (CNVs). While diagnosis is often based on haematological and biochemical parameters, a definitive diagnosis requires molecular DNA analysis. In some cases, the molecular characterisation of large deletions/duplications is challenging and inconclusive and often requires the use of specific diagnostic procedures, such as multiplex ligation-dependent probe amplification (MLPA). Herein, we collected and comprehensively analysed all known CNVs associated with haemoglobinopathies. The dataset of 291 CNVs was retrieved from the IthaGenes database and was further manually annotated to specify genomic locations, breakpoints and MLPA probes relevant for each CNV. We developed IthaCNVs, a publicly available and easy-to-use online tool that can facilitate the diagnosis of rare and diagnostically challenging haemoglobinopathy cases attributed to CNVs. Importantly, it facilitates the filtering of available entries based on the type of breakpoint information, on specific chromosomal and locus positions, on MLPA probes, and on affected gene(s). IthaCNVs brings together manually curated information about CNV genomic locations, functional effects, and information that can facilitate CNV characterisation through MLPA. It can help laboratory staff and clinicians confirm suspected diagnosis of CNVs based on molecular DNA screening and analysis.

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.

Hemoglobinopathy screening in primary care in the Netherlands: exploring the problems and needs of patients and general practitioners

The prevalence of hemoglobinopathies in The Netherlands is increasing due to migration. Hemoglobinopathies are severe hereditary diseases. An informed reproductive choice by at-risk couples, such as pre-implantation diagnosis or termination of affected pregnancies, can be made if carriers are detected prior to conception. Using a qualitative design, the needs and wishes of patients, carriers and general practitioners were evaluated regarding carrier detection of hemoglobinopathies in primary care practice. 30 semi-structured interviews were established with 10 general practitioners, 10 patients and 10 carriers. The interviews were audio-recorded, transcribed verbatim and analysed using content analysis to identify recurring themes. Three themes were generated regarding carrier detection of hemoglobinopathies: (1) a need for more information about hemoglobinopathy, (2) a need for indications when to refer for analysis (carrier diagnostics) and (3) insight concerning organization and roles in care for hemoglobinopathy carriers and patients. These themes reflected a need to increase awareness of hemoglobinopathy, improve competences among general practitioners through better education and improvement of communication with patients and their unidentified family members. This study shows the scope of the problem and the critical need for action to improve informed reproductive decision making for the at-risk population.

Adapting the ACMG/AMP variant classification framework: A perspective from the ClinGen Hemoglobinopathy Variant Curation Expert Panel

Accurate and consistent interpretation of sequence variants is integral to the delivery of safe and reliable diagnostic genetic services. To standardize the interpretation process, in 2015, the American College of Medical Genetics and Genomics (ACMG) and the Association for Molecular Pathology (AMP) published a joint guideline based on a set of shared standards for the classification of variants in Mendelian diseases. The generality of these standards and their subjective interpretation between laboratories has prompted efforts to reduce discordance of variant classifications, with a focus on the expert specification of the ACMG/AMP guidelines for individual genes or diseases. Herein, we describe our experience as a ClinGen Variant Curation Expert Panel to adapt the ACMG/AMP criteria for the classification of variants in three globin genes (HBB, HBA2, and HBA1) related to recessively inherited hemoglobinopathies, including five evidence categories, as use cases demonstrating the process of specification and the underlying rationale.

Evaluation of in silico predictors on short nucleotide variants in HBA1, HBA2, and HBB associated with haemoglobinopathies

Haemoglobinopathies are the commonest monogenic diseases worldwide and are caused by variants in the globin gene clusters. With over 2400 variants detected to date, their interpretation using the American College of Medical Genetics and Genomics (ACMG)/Association for Molecular Pathology (AMP) guidelines is challenging and computational evidence can provide valuable input about their functional annotation. While many in silico predictors have already been developed, their performance varies for different genes and diseases. In this study, we evaluate 31 in silico predictors using a dataset of 1627 variants in HBA1, HBA2, and HBB. By varying the decision threshold for each tool, we analyse their performance (a) as binary classifiers of pathogenicity and (b) by using different non-overlapping pathogenic and benign thresholds for their optimal use in the ACMG/AMP framework. Our results show that CADD, Eigen-PC, and REVEL are the overall top performers, with the former reaching moderate strength level for pathogenic prediction. Eigen-PC and REVEL achieve the highest accuracies for missense variants, while CADD is also a reliable predictor of non-missense variants. Moreover, SpliceAI is the top performing splicing predictor, reaching strong level of evidence, while GERP++ and phyloP are the most accurate conservation tools. This study provides evidence about the optimal use of computational tools in globin gene clusters under the ACMG/AMP framework.

Recommendations for diagnosis and treatment of methemoglobinemia

Methemoglobinemia is a rare disorder associated with oxidization of divalent ferro‐iron of hemoglobin (Hb) to ferri‐iron of methemoglobin (MetHb). Methemoglobinemia can result from either inherited or acquired processes. Acquired forms are the most common, mainly due to the exposure to substances that cause oxidation of the Hb both directly or indirectly. Inherited forms are due either to autosomal recessive variants in the CYB5R3 gene or to autosomal dominant variants in the globin genes, collectively known as HbM disease. Our recommendations are based on a systematic literature search. A series of questions regarding the key signs and symptoms, the methods for diagnosis, the clinical management in neonatal/childhood/adulthood period, and the therapeutic approach of methemoglobinemia were formulated and the relative recommendations were produced. An agreement was obtained using a Delphi‐like approach and the experts panel reached a final consensus >75% of agreement for all the questions.

Cyanosis, hemolysis, decreased HbA1c and abnormal co-oximetry in a patient with hemoglobin M Saskatoon [HBB:c.190C > T p.His64Tyr]

We describe a first Dutch case of Hb M Saskatoon (HBB:c.190C > T p.His64Tyr) in a 47-year-old female Dutch patient who presented with cyanosis, hemolysis, and abnormal co-oximetry. A mean corpuscular volume (MCV) of 105 fL caused by reticulocytosis (160 × 10⁹/L) and low red blood cell count (3.6 × 10¹²/L) suggested an increased erythrocyte turnover. An HPLC glyco-globin analysis revealed a decreased HbA1c fraction of 12.3 mmol/mmol, HbA0 of 93.3% and an additional unidentified fraction at 1.2 min. DNA sequencing revealed a missense mutation in the HBB gene, (HBB:c.190C > T p.His64Tyr), known as Hb M Saskatoon, a variant which has been previously identified as an unstable hemoglobin variant leading to methemoglobinemia and anemia. In this report, we describe the clinical and remarkable laboratory aspects of our patient with Hb M Saskatoon, and the consequences for treatment and drug use.

The Evolving Role of Next-Generation Sequencing in Screening and Diagnosis of Hemoglobinopathies

During the last few years, next-generation sequencing (NGS) has undergone a rapid transition from a research setting to a clinical application, becoming the method of choice in many clinical genetics laboratories for the detection of disease-causing variants in a variety of genetic diseases involving multiple genes. The hemoglobinopathies are the most frequently found Mendelian inherited monogenic disease worldwide and are composed of a complex group of disorders frequently involving the inheritance of more than one abnormal gene. This review aims to present the role of NGS in both screening and pre- and post-natal diagnostics of the hemoglobinopathies, and the added value of NGS is discussed based on the results described in the literature. Overall, NGS has an added value in large-scale high throughput carrier screening and in the complex cases for which common molecular techniques have some inadequacies. It is proven that the majority of thalassemia cases and Hb variants can be diagnosed using routine analysis involving a combined approach of hematology, hemoglobin separation, and classical DNA methods; however, we conclude that NGS can be a useful addition to the existing methods in the diagnosis of these disorders.

Breakpoint characterization of a rare alpha0 -thalassemia deletion using targeted locus amplification on genomic DNA

Introduction

The high‐sequence homology of the α‐globin‐gene cluster is responsible for microhomology‐mediated recombination events during meiosis, resulting in a high density of deletion breakpoints within a 10 kb region. Commonly used deletion detection methods, such as multiplex ligation‐dependent probe amplification (MLPA) and Southern blot, cannot exactly define the breakpoints. This typically requires long‐range PCR, which is not always successful. Targeted locus amplification (TLA) is a targeted enrichment method that can be used to sequence up to 70 kb of neighboring DNA sequences without prior knowledge about the target site.

Methods

Genomic DNA (gDNA) TLA is a technique that folds isolated DNA, ensuring that adjacent loci are in a close spatial proximity. Subsequent digestion and religation form DNA circles that are amplified using fragment‐specific inverse primers, creating a library that is suitable for Illumina sequencing.

Results

Here, we describe the characterization of a rare 16 771 bp deletion, utilizing gDNA TLA with a single inverse PCR primer set on one end of the breakpoint. Primers for breakpoint PCR were designed to confirm the deletion breakpoints and were consequently used to characterize the same deletion in 10 additional carriers sharing comparable hematologic data and similar MLPA results.

Conclusions

The gDNA TLA technology was successfully used to identify deletion breakpoints within the alpha‐globin cluster. The deletion was described only once in an earlier study as the ‐‐^gb, but as it was not registered correctly in the available databases, it was not initially recognized as such.

Hemoglobin Yamagata [β132(H10)Lys→Asn; (HBB: c.399A>T)]: a mosaic to be put together

OBJECTIVES

Artifactually altered glycated hemoglobin (HbA_1c) concentrations are frequently linked to hemoglobin (Hb) variants. Their expression and detection require in-depth analysis.

METHODS

Cation exchange high performance liquid chromatography (HPLC) (Bio-Rad Variant™ II; Trinity Biotech Premier Hb9210 Resolution), capillary electrophoresis (CE) (Sebia Capillarys 2 Flex Piercing) and mass spectrometry (MS) (Waters) were used for variant detection; Sanger sequencing, multiplex ligation-dependent probe amplification (MLPA) and next generation sequencing (NGS) were used for DNA analysis; HbA_1c was measured with cation exchange HPLC (Bio-Rad Variant™ II; Arkray Adams HA-8180V; Tosoh HLC-723 G7), CE (Sebia Capillarys 2 Flex Piercing), boronate affinity HPLC (Trinity Biotech Hb9210 Premier), immunoassay (Cobas c501 Tina-quant HbA_1c Gen. 3; Nihon Kohden CHM-4100 Celltac chemi HbA_1c HA-411V) and enzymatic assay (Abbott Architect c 8000 HbA_1c).

RESULTS

Hb Yamagata [β132(H10)Lys→Asn; (HBB: c.399A>T)] was identified in the proband by MS after the observation of an abnormal peak in HPLC and CE. A mosaic expression of this variant was detected by NGS (mutant: 8%; wild type: 92%), after negative results in Sanger sequencing. Hb Yamagata interfered with HbA_1c measurements by cation exchange HPLC and CE whereas immuno and enzymatic assay values showed good agreement with boronate affinity HPLC measurement.

CONCLUSIONS

A mosaicism of Hb Yamagata was found in a patient with altered HbA_1c values. This rare gene variant was detected only by advanced technologies as MS and NGS. The variant interfered with common HbA_1c determination methods.

Usefulness of NGS for Diagnosis of Dominant Beta-Thalassemia and Unstable Hemoglobinopathies in Five Clinical Cases

Unstable hemoglobinopathies (UHs) are rare anemia disorders (RADs) characterized by abnormal hemoglobin (Hb) variants with decreased stability. UHs are therefore easily precipitating, causing hemolysis and, in some cases, leading to dominant beta-thalassemia (dBTHAL). The clinical picture of UHs is highly heterogeneous, inheritance pattern is dominant, instead of recessive as in more prevalent major Hb syndromes, and may occur de novo. Most cases of UHs are not detected by conventional testing, therefore diagnosis requires a high index of suspicion of the treating physician. Here, we highlight the importance of next generation sequencing (NGS) methodologies for the diagnosis of patients with dBTHAL and other less severe UH variants. We present five unrelated clinical cases referred with chronic hemolytic anemia, three of them with severe blood transfusion dependent anemia. Targeted NGS analysis was performed in three cases while whole exome sequencing (WES) analysis was performed in two cases. Five different UH variants were identified correlating with patients’ clinical manifestations. Four variants were related to the beta-globin gene (Hb Bristol—Alesha, Hb Debrousse, Hb Zunyi, and the novel Hb Mokum) meanwhile one case was caused by a mutation in the alpha-globin gene leading to Hb Evans. Inclusion of alpha and beta-globin genes in routine NGS approaches for RADs has to be considered to improve diagnosis’ efficiency of RAD due to UHs. Reducing misdiagnoses and underdiagnoses of UH variants, especially of the severe forms leading to dBTHAL would also facilitate the early start of intensive or curative treatments for these patients.

A Small Key for a Heavy Door: Genetic Therapies for the Treatment of Hemoglobinopathies

Throughout the past decades, the search for a treatment for severe hemoglobinopathies has gained increased interest within the scientific community. The discovery that ɤ-globin expression from intact HBG alleles complements defective HBB alleles underlying β-thalassemia and sickle cell disease, has provided a promising opening for research directed at relieving ɤ-globin repression mechanisms and, thereby, improve clinical outcomes for patients. Various gene editing strategies aim to reverse the fetal-to-adult hemoglobin switch to up-regulate ɤ-globin expression through disabling either HBG repressor genes or repressor binding sites in the HBG promoter regions. In addition to these HBB mutation-independent strategies involving fetal hemoglobin (HbF) synthesis de-repression, the expanding genome editing toolkit is providing increased accuracy to HBB mutation-specific strategies encompassing adult hemoglobin (HbA) restoration for a personalized treatment of hemoglobinopathies. Moreover, besides genome editing, more conventional gene addition strategies continue under investigation to restore HbA expression. Together, this research makes hemoglobinopathies a fertile ground for testing various innovative genetic therapies with high translational potential. Indeed, the progressive understanding of the molecular clockwork underlying the hemoglobin switch together with the ongoing optimization of genome editing tools heightens the prospect for the development of effective and safe treatments for hemoglobinopathies. In this context, clinical genetics plays an equally crucial role by shedding light on the complexity of the disease and the role of ameliorating genetic modifiers. Here, we cover the most recent insights on the molecular mechanisms underlying hemoglobin biology and hemoglobinopathies while providing an overview of state-of-the-art gene editing platforms. Additionally, current genetic therapies under development, are equally discussed.

Further evaluation of the world health organization international reference reagent for Haemoglobin A2 measurement

INTRODUCTION

The accurate measurement of HbA₂ is essential for the detection of β-thalassaemia carriers and as no single calibrant is used by the various manufacturers of analysers, differences are seen in results obtained. The World Health Organization International Reference Reagent for HbA₂ (WHO IRR 89/666) was made available to diagnostic laboratories in the 1980s and remains the only international reference material available. A previous study (2015) demonstrated that the WHO IRR remained suitable for use as an HbA₂ standard as tested by 52 participants in the UK NEQAS Haematology Abnormal Haemoglobins Programme. This study was undertaken to include simultaneous analysis of three whole blood specimens over a range of HbA₂ values with the WHO IRR and to include participants from laboratories outside of the UK.

METHOD

Three whole blood specimens with HbA₂ levels ranging from 2.4% to 5.7% and the WHO IRR were distributed to 56 laboratories located in 14 different countries. Participants were requested to test the specimens at defined intervals and return results accompanied by chromatograms or electropherograms produced.

RESULTS

Differences found in results from different analyser groups reflect the bias found in the 2015 study in that bias is seen according to the methodology used and also varies in relation to the level of analyte being measured.

CONCLUSION

Results of measurements from whole blood specimens and the lyophilized WHO IRR standard did not show any deterioration of the IRR, and it remains suitable for use. Linearity and calibration of analysers remain a problem.

A roadmap for the standardization of hemoglobin A2

BACKGROUND

Standardization of laboratory tests can be a long process, and this is the case with regards to the methods used to measure hemoglobin A₂ (HbA₂), an important marker for beta-thalassemia and other thalassemic conditions. The IFCC standardization project started in 2004, and it took at least 15 years before developing a reference measurement procedure, defining and producing calibrators and certified reference materials.

METHODS

A series of steps have to be undertaken in order to promote the standardization in the field, a process involving a number of stakeholders (manufacturers, scientific societies, national health bodies, laboratory professionals, clinicians). In this work we describe some possible process indicators, in order to assure that the standardization will have internal and external validity and be effective for a long time. These indicators concern the inter-method studies, elaboration of External Quality Assessment Schemes, and the evaluation of the yearly distributions of HbA₂ measurements collected in selected laboratories.

RESULTS

Preliminary results are reported concerning the yearly distributions of HbA₂, collected in two different locations, and using different analytical methods. Median yearly values were found very constant over the years, but different between methods. On the other side, results obtained on the same specimens using two different techniques, proved that results by capillary electrophoresis in 2 out of the 3 years of observation, were significantly lower than those by HPLC.

CONCLUSION

In this document we report what has been done so far, and what has to be done to achieve the standardization of the measurement of HbA₂ worldwide.

A Woman with Missing Hb A2 Due to a Novel (εγ)δβ0-Thalassemia and a Novel δ-Globin Variant Hb A2-Gebenstorf (HBD: c.209G>A)

A woman completely lacking Hb A₂ on the high performance liquid chromatography (HPLC) analysis, presented with a novel deletional (εγ)δβ⁰-thal and a δ-globin gene variant. This combination causes a β-thalassemia (β-thal) minor phenotype. The woman was referred by a hematologist due to abnormal blood counts. Multiplex ligation-dependent probe amplification (MLPA) and microarray analysis showed a heterozygous, 177 kb long deletion that removed the locus control region enhancer plus the ε, ^Gγ and ^Aγ genes. Additional sequencing revealed a novel variant HBD: c.209G>A, p.Gly70Asp in the heterozygous state, called Hb A₂-Gebenstorf. The combination of the two variants explains the lack of Hb A₂ in this woman.

ATR-16 syndrome: mechanisms linking monosomy to phenotype

Background

Deletions removing 100s–1000s kb of DNA, and variable numbers of poorly characterised genes, are often found in patients with a wide range of developmental abnormalities. In such cases, understanding the contribution of the deletion to an individual’s clinical phenotype is challenging.

Methods

Here, as an example of this common phenomenon, we analysed 41 patients with simple deletions of ~177 to ~2000 kb affecting one allele of the well-characterised, gene dense, distal region of chromosome 16 (16p13.3), referred to as ATR-16 syndrome. We characterised deletion extents and screened for genetic background effects, telomere position effect and compensatory upregulation of hemizygous genes.

Results

We find the risk of developmental and neurological abnormalities arises from much smaller distal chromosome 16 deletions (~400 kb) than previously reported. Beyond this, the severity of ATR-16 syndrome increases with deletion size, but there is no evidence that critical regions determine the developmental abnormalities associated with this disorder. Surprisingly, we find no evidence of telomere position effect or compensatory upregulation of hemizygous genes; however, genetic background effects substantially modify phenotypic abnormalities.

Conclusions

Using ATR-16 as a general model of disorders caused by CNVs, we show the degree to which individuals with contiguous gene syndromes are affected is not simply related to the number of genes deleted but depends on their genetic background. We also show there is no critical region defining the degree of phenotypic abnormalities in ATR-16 syndrome and this has important implications for genetic counselling.

An Unusual Compound Heterozygosity for Hb O-Arab (HBB: c.364G>A) and Hb D-Los Angeles (HBB: c.364G>C)

We report a newborn with a compound heterozygosity for Hb O-Arab (HBB: 364G>A) and Hb D-Los Angeles (HBB: 364G>C). To the best of our knowledge, the combination of these two hemoglobin (Hb) variants has not been identified and reported before. The variants of the proband and parents were identified by high-performance liquid chromatography (HPLC) and capillary electrophoresis (CE). DNA analysis was performed to confirm the variants. The levels of Hb variants of the proband were determined post-partum, at 3 months and 1 year after birth. Blood count analysis after 1 year revealed that the proband had a mild microcytic anemia. Furthermore, HPLC and CE analysis revealed an equal distribution of Hb D-Los Angeles compared to Hb O-Arab at the age of 1 year. The follow-up of the patient, suggested that the Hb combination is clinically silent or mild.

Characterization of Two Deep Intronic Variants on the β-Globin Gene with Inconsistent Interpretations of Clinical Significance

Sequence variants located in the introns of the β-globin gene may affect the mRNA processing and cause β-thalassemia (β-thal). Sequence variants that change one of the invariant dinucleotides at the exon-intron boundaries may have fatal consequences for normal mRNA splicing. Intronic variants located far from obvious regulatory sequences can be more difficult to evaluate. There is a potential for misinterpretation of such sequence variants. Hence, thorough evaluation of patient data together with critical use of databases and in silico prediction tools are important. Here, we describe two rare sequence variants in the second intron of the β-globin gene, HBB: c.316-70C>G and HBB: c.316-125A>G (NM_000518.4), both previously reported as variants causing β-thal, and later as benign sequence variants. Due to the limited number of published cases and inconsistent interpretations, the significance of these sequence variants has been unclear. We have identified these two sequence variants in multiple individuals, alone and in a variety of combinations with other δ- and β-globin defects, and we find no influence of the sequence variants on the phenotype.

Diagnosis of Haemoglobinopathies: New Scientific Advances

The molecular defects underlying haemoglobinopathies are both deletions and point mutations in the alpha- or beta-globin genes or gene-clusters. To detect point mutations causing alpha- or beta-thalassaemia, direct sequencing is the method of choice to detect the widest spectrum of molecular defects. The most established approach in DNA diagnostics to screen for the most common deletion defects causing alpha-thalassaemia or beta-thalassaemia is gap- PCR, Multiplex Ligation-dependent Probe Amplification (MLPA) and Sanger Sequencing technology to detect breakpoint sequences of previously uncharacterized deletions/duplications. We demonstrate the recent advances in the determination of duplications and deletions causing alpha- or beta-thalassemia, using Next Generation Sequencing, array Comparative Genome Hybridization and Target Locus Amplification. We present three cases in which the use of advanced technologies allow the diagnosis of unexpected disease genotypes.

Molecular basis of α-thalassemia

α-Thalassemia is an inherited, autosomal recessive, disorder characterized by a microcytic hypochromic anemia. It is one of the most common monogenic gene disorders in the world population. The clinical severity varies from almost asymptomatic, to mild microcytic hypochromic, and to a lethal hemolytic condition, called Hb Bart's Hydrops Foetalis Syndrome. The molecular basis are usually deletions and less frequently, point mutations affecting the expression of one or more of the duplicated α-genes. The clinical variation and increase in disease severity is directly related to the decreased expression of one, two, three or four copies of the α-globin genes. Deletions and point mutations in the α-globin genes and their regulatory elements have been studied extensively in carriers and patients and these studies have given insight into the α-globin genes are regulated. By looking at naturally occurring deletions and point mutations, our knowledge of globin-gene regulation and expression will continue to increase and will lead to new targets of therapy.

Hb Melusine and Hb Athens-Georgia: potentially underreported in the Belgian population? Four cases demonstrating the lack of detection using common CE-HPLC methods either for glycated hemoglobin (HbA1C) analysis or Hb variant screening

OBJECTIVE AND IMPORTANCE

Suspected hemoglobin (Hb) variants, detected during HbA_1C measurements should be further investigated, determining the extent of the interference with each method.

CLINICAL PRESENTATION

This is the first report of Hb Melusine and Hb Athens-Georgia in Caucasian Belgian patients. Intervention & Technique: Since common CE-HPLC methods for HbA_1C analysis or Hb variant screening are apparently unable to detect these Hb variants, their presence might be underestimated. HbA_1C analysis using CZE, however, alerted for their presence. Moreover, in case of Hb Melusine, even Hb variant screening using CZE was unsuccessful in its detection.

CONCLUSION

Fortunately, carriage of Hb Melusine or Hb Athens-Georgia variants has no clinical implications and, as shown in this report, no apparent difference in HbA_1C should be expected.

Hb Olivet (HBA1: C.40G > A; p.Ala14Thr), a Novel Silent Hemoglobin Variant in Two Families of Distinct Origin

We report two families, members of which are carriers of a novel hemoglobin (Hb) variant that was named Hb Olivet [α13(A11)Ala→Thr (α1) (GCC > ACC); HBA1: c.40G > A; p.Ala14Thr]. The analysis of these cases allowed a clear description of this anomaly that behaves as a silent Hb. In the first family, of Portuguese ethnicity living in France, the proband, a 24-year-old male and his 57-year-old mother, both appeared to be carriers. The son presented with borderline mean corpuscular volume (MCV), while the mother was normocytic and normochromic. Hemoglobin separation on capillary electrophoresis (CE) was normal, while a slightly asymmetric peak was observed on high performance liquid chromatography (HPLC). In a second family, originally from Surinam but living in The Netherlands, the proband, a 6-year-old girl, showed a mild microcytosis at low ferritin levels. The abnormal Hb was inherited from the mother who was clearly iron depleted, was not present in the sister and brother of the proband. The microcytic hypochromic anemia was only shown in two out of a total of four carriers. It therefore seems likely that iron depletion is causative as two carriers are completely normal. Characterization and genotype/phenotype correlation are briefly described.

Haplotypes, Sub-Haplotypes and Geographical Distribution in Omani Patients with Sickle Cell Disease

Despite the fact that patients homozygous for the sickle cell disease (SCD) mutation have an identical genotype, the severity of the disease can be extremely variable. The hemoglobin (Hb) S mutation has been described on five different haplotypes with different clinical expression. Identifying the genotypes, haplotypes and sub-haplotypes of the β gene cluster in Oman needs to be studied in more details to establish a correlation between the genotype/haplotype and phenotype diversity observed in SCD patients for prognostic purposes, accurate diagnosis and thus planning for the best tailored treatment. We have investigated 125 HbS homozygotes from different parts of Oman and determined their haplotypes and sub-haplotypes and correlated this to the hematological and clinical expression. We have found 11 haplotype combinations differently distributed in the country, with the Asian/Asian HbS haplotype being the most predominant. Sub-haplotypes was only found among patients with CAR/OmanI haplotype. As expected, the correlation between haplotypes, sub-haplotypes and disease severity was mainly associated with HbF expression. Our study on haplotype/phenotype correlation has shown which major haplotypes occur in the different regions of Oman. Furthermore, neither the haplotype or sub-haplotype nor the HbF alone appeared to be fully associable with the variable clinical phenotypes. External factors do occur and are associated with the expression of the disease.尽管镰状细胞突变病（SCD）患者拥有相同的基因类型，但患者的病患程度却大相径庭。血红蛋白（Hb）S突变有五种不同的单体型，各种类型在临床表现上也不相同。为了识别在阿曼地区β基因簇的基因型、单体型，亚单体型，需要研究更多以SCD患者预后为目的，关于其观察到的基因型、单体型，表型多样性之间联系的更多细节，以便作出准确的诊断，为各个患者量身制定治疗方案。我们研究了125个来自阿曼不同地区的HbS纯合体，并确认了它们的单体型和亚单体型血液学上的临床表现。我们已找到了该国家11个单体型组合的不同分布，其中以亚洲/亚洲HbS单体型为主要类型。亚单体型只在CAR/OMANI单体型患者中被发现。正如之前所料，单体型、亚单体型和病患程度之间的联系主要与HbF表现相关。我们关于单体型和亚单体型之间联系的研究显示出了阿曼地区最为主要的单体类型。此外，无论是单体型、亚单体型还是HbF，都被证明与该疾病不同的临床表现没有紧密的联系。外部因素是该疾病不同表现的致因。

Hb Lansing (HBA2: c.264C > G) and a new β promoter transversion [-52 (G > T)]: an attempt to define the phenotype of two mutations found in the Omani population

We report two examples showing how problematic it can be to define the phenotype of new or rare globin genes mutations. We describe two mutations observed for the first time in the Omani population: the first was found in the consanguineous parents of a deceased newborn with hepatomegaly, cardiomegaly and severe hemolytic anemia, putatively homozygous for the rare Hb Lansing (HBA2: c.264C > G) variant. The second is a novel β-globin gene promoter mutation [-52 (G > T)] observed in four independent patients. Two with borderline/elevated Hb A2, α-thalassemia (α-thal) and hypochromic red cell indices, and two heterozygotes for Hb S (HBB: c.20A > T), α-thal and with Hb A/Hb S ratios possibly indicating a very mild β(+)-thalassemia (β(+)-thal) mutation.

Broader spectrum of β-thalassemia mutations in Oman: regional distribution and comparison with neighboring countries

The objective of this study was to expand and study the molecular spectrum of β-thalassemia (β-thal) mutations in Oman by examining cases from seven different regions and comparing the prevalence with neighboring countries. A total of 446 cases of β hemoglobinopathies was obtained and analyzed to determine the frequency and distribution of the different β alleles. The molecular spectrum of β-thal in Oman revealed the presence of 32 mutations from different origins and 11 alleles are reported for the first time in the Omani population. The wide heterogeneous spectrum of β-thal mutations found can be associated with the history of trade and migration as well as the past domination from other countries. The presented data will facilitate the development of a comprehensive prevention strategy in Oman.

Aberrant glycated haemoglobin (HbA1c) results leading to haemoglobinopathy diagnosis in four Belgian patients

INTRODUCTION

We report four cases in which haemoglobinopathy screening was triggered following aberrant HbA1c analysis. Either the HbA1c assay was unable to produce a quantifiable result or it showed the presence of an extra fraction and/or the result was discordant with the clinical context.

CASE REPORT

In the reported four patients, all from Caucasian, Belgian descent, Hb analysis was performed using cation-exchange high performance liquid chromatography. If necessary, additional Hb electrophoresis was carried out to establish a preliminary (biochemical) diagnosis. Definitive diagnosis was obtained for every sample through DNA-analysis. Three patients were carriers of Hb J-Toronto and one of Hb Stanleyville-II.

DISCUSSION

This report underlines the importance of correct interpretation of HbA1c results to avoid mismanagement of (diabetic) patients. Since neither the RBC indices, the clinical context, nor the ethnicity of these patients was suspicious for an underlying haemoglobinopathy, the aberrant HbA1c result was the only indicator for further investigation. Laboratory personnel and clinicians should be aware of the possibility of uncommon, sometimes clinically unsuspected, Hb variants to cause aberrant HbA1c values, even in populations with low prevalence for haemoglobinopathies. Further analysis should be prompted to obtain definitive diagnosis. Alternative methods for monitoring glycaemic control should be used.

Primary Prevention of Hemoglobinopathies by Prenatal Diagnosis and Selective Pregnancy Termination in a Muslim Country: Oman

Hemoglobinopathies (HBP) are the most common genetic disorder in Oman and are in need of prevention programs due to the high incidence of β-thalassemia major and sickle cell disease. Prenatal diagnosis (PD) and selective pregnancy termination is shown to be the most effective prevention tool for the control of HBP. However, PD is not available in Oman thus far because abortion is subject to religious, cultural and ethical issues. We have examined the attitude of a number of Omani HBP carrier couples towards prenatal diagnosis and selective abortion. We have interviewed 35 couples at risk visiting the main premarital clinic in Muscat between Jan 2011 and Jan 2012. Couples were interviewed using a pre-structured questionnaire. The majority would have accepted prenatal diagnosis (94%) if the service would be available in the country but pregnancy termination was greatly influenced by religious values.

Molecular spectrum of α-globin gene defects in the Omani population

We describe the molecular characterization of α-globin gene defects in a cohort of 634 Omani patients. A total of 21 different α gene mutations were found in 484 subjects. Overall, we identified three different large deletions, three small deletions, 11 point mutations [two on the α2 polyadenylation signal (polyA) (HBA2: c.*94A>G), and nine α chain variants], three ααα(anti 3.7) triplication, a 21 nucleotide (nt) duplication on the α1 gene and two novel (presumed) polymorphisms on the α 3.7 kb hybrid gene, namely -5 (C>T) and +46 (C>A). Of these defects, 15 have not been previously reported in the Omani population. This large heterogeneity of α-thalassemia (α-thal) observed in the Omani population could be expected in neighboring Arab countries. The high frequency of α-thal, solely or in association with β-globin gene defects, emphasize the necessity of adding α-thal testing to pre marital programs for accurate genetic counseling.

Providing Appropriate Genetic Information to Healthy Multi-Ethnic Carriers of Hemoglobinopathy in The Netherlands

The aims of this study are: (i) to enquire whether informing healthy hemoglobinopathy carriers about their condition is a welcome initiative in The Netherlands; (ii) to study whether using information letters and thorough explanation is associated with presence or absence of undesired feelings or emotions. We have approached 100 multi-ethnic carriers previously diagnosed in our lab. All subjects had previously received our information letter through their physician who was supposed to have provided an explanation of the letter if required. We have enquired whether the subjects had experienced negative or positive emotions after receiving our diagnosis and explanation and to which degree, if they were sufficiently informed and satisfied and if they would have considered prevention in case of risk. The rate negative versus positive feelings was calculated using a numerical distribution. We have registered negative feelings in a rate that was directly proportional to the lack of information. While the number of registered negative feelings in well-informed carriers was very low it was more present in badly informed. Nevertheless, all participants found carrier information a welcome initiative and over 80% of them declared to be in favor of prenatal diagnosis in case of risk. Carrier information is essential for an informed reproductive choice and is welcome in a multi-ethnic society. Unfortunately, information is not always consequently provided and should therefore be imbedded in the ongoing national screening for Rhesus and infectious diseases available to all women in early pregnancy.

HbA2 Measurements in β-Thalassemia and in Other Conditions

Quite a few papers have been written on the significance of elevated hemoglobin (Hb) A2 as a parameter for the diagnosis of β-thalassemia trait, on the cutoff values to be used in diagnostics and on the significance and effects of factors reducing or elevating the expression of HbA2 and last but not least on the need for reliable measurement methods and precise calibrations with accurate standards. However, little has been published on the causes that elevate or reduce the HbA2 levels in β- and a-thalassemia and in other conditions. For a better understanding of the value of a precise measurement of this parameter we summarize and elucidate in this review the direct and indirect mechanisms that cause the variations in HbA2 expression and that influence the value of this parameter in particular conditions. We conclude by explaining the advantages and disadvantages of trusting on a precise measurement in the complete diagnostic contest.