Search

It is well known that modifiers play a role in ameliorating or exacerbating disease phenotypes in patients and carriers of recessively inherited disorders such as sickle cell disease and thalassemia. Here, we give an overview of the literature concerning a recently described association in carriers of SUPT5H Loss-of-Function variants with a beta-thalassemia-like phenotype including the characteristic elevated levels of HbA2. That SUPT5H acts as modifier in beta-thalassemia carriers became evident from three reported cases in whom combined heterozygosity of SUPT5H and HBB gene variants was observed to resemble a mild beta-thalassemia intermedia phenotype. The different SUPT5H variants and hematologic parameters reported are collected and reviewed to provide insight into the possible effects on hematologic expression, as well as potential disease mechanisms in carriers and patients.

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.

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.

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.

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.

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.

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。

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. 血红蛋白病（HBP）是一种在阿曼最常见的遗传性疾病，由于其高发的B型地中海贫血症及镰状细胞症，相关的预防措施对于这一国家来说，相当重要。产前诊断（PD）和选择性终止妊娠被证实是针对管控血红蛋白病（HBP）的最有效方法。然而，由于受到宗教、文化和伦理抵制堕胎的影响，产前诊断（PD）并不能在该国得以应用。我们对该国一部分血红蛋白病患夫妇做了一项关于产前诊断的意向调查。2011年一月至2012年一月，我们在马斯喀特（阿曼首都）的一家婚前诊所对35对夫妇做了相关的采访调查。调查的问卷是事先设置好的。大部分（94%）夫妇表示接受产前诊断如果相应的措施能得到广泛的普及，但是他们对于选择性终止妊娠的态度受到了其宗教价值观的极大影响。

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.

Genomic DNA of 3 patients, born as healthy carriers and developing a late-onset severe transfusion-dependent beta-thalassemia major was studied by high-density genome wide SNP array analysis. A mosaic loss of heterozygosity for almost the entire 11p was found, not attributable to deletions but involving mosaicism for segmental paternal isodisomy of 11p. Mitotic recombination leading to mosaic segmental uniparental isodisomy on chromosome 11p in multiple tissues has been described as a molecular disease mechanism for a subset of sporadic Beckwith-Wiedemann syndrome cases. A similar mechanism also seems to be involved in causing late-onset disease in carriers of recessive mutations in other genes located in 11p, such as late-onset beta-thalassemia major and sickle cell disease. We suggest that the loss of maternally imprinted IGF-2 and H19 genes may account for the selective advantage of hematopoietic cells containing this segmental paternal isodisomy of 11p carrying the β-thalassemia mutation.

We present a case of a 40-year-old female from Turkey, who was referred to our outpatient clinic for an undetermined thalassemia and sickle cell trait. At first consultation hemoglobin was decreased (71 g/L) with microcytosis (MCV 55.1 fL), and hypochromia (MCHC 239 g/L). The patient had severe iron deficiency. Brilliant cresyl blue staining showed >50% of the erythrocytes with typical Hemoglobin H (HbH) inclusions. High-performance liquid chromatography (HPLC) revealed normal levels of HbA2 and Hemoglobin F (HbF), and additionally a hemoglobin S (19%). Molecular diagnostics revealed the mutations α2 IVS-I donor site -5nt and a -- MED II deletion in the alpha gene complex and confirmed the heterozygote mutation of the beta-gene at codon 6 (HBB:c.20A>T; HbS). In conclusion, we present an extremely rare combination of HbH disease and sickle cell trait. This combination may explain the mild form of the HbH disease, with moderate anemia, splenomegaly but iron deficiency, rather than iron overload, as usually observed in HbH disease.

When the molecular background of couples requesting prevention is unclear, family analysis and tools to define rare mutations are essential. We report two novel deletion defects observed in an Italian and in a Turkish couple. The first proband presented with microcytic hypochromic parameters without iron deficiency, a normal HbA2 and an elevated HbF (10.6%). His father presented with a similar phenotype and his wife was heterozygous for the common Mediterranean codon 39 (HBB:c.118C>T) mutation. Having excluded point mutations and common deletions, Multiplex Ligation-dependent Probe Amplification was performed revealing an unknown Gγ(Aγδβ)0-thalassemia defect spanning from the Aγ gene to downstream of the β-globin gene provisionally named Leiden 69.5 kb deletion. In the second case, the wife presented with a mild thalassemic picture, normal HbA2, elevated HbF (18.5%) and a β/α globin chain synthesis ratio of 0.62, without iron deficiency or any known β-thalassemia defect, while the husband was a simple carrier of the common Mediterranean IVS-I-110 (HBB:c.93-21 G>A) mutation. A new large deletion involving the β-gene and part of the δ-gene was identified by Multiplex Ligation-dependent Probe Amplification provisionally named “Leiden 7.4 kb”.

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.

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.