Modifier genes in Mendelian disorders: the example of hemoglobin disorders

Chronic disease prevalence in a population with structural hemoglobin disorders undergoing diabetes diagnosis: A bayesian approach

Background

Structural disorders of hemoglobin are a group of rare and fatal genetic diseases that disrupt the transport and exchange of oxygen in the blood, causing tissue damage and ultimately leading to chronic conditions. The hemoglobin (Hb) S variant predominantly impacts individuals of Afro-descendant heritage. A significant concentration of the Afro-descendant population in Colombia, notably 12.5 %, is found in the city of Cali. Previous research has identified this city's structural hemoglobin disorders prevalence rate of 3.78 %. The aim of this study was to determine the prevalence of HbC, HbS, HbF, and HbA2 variants within a population who underwent HbA1c testing, as well as the prevalence of chronic diseases among patients with these hemoglobin alterations, at a high-complexity hospital in the city of Cali from 2015 to 2019.

Methods

A descriptive observational study was conducted, involving a study population that comprised patients with both suspected and monitored diagnoses of diabetes. The cohort was selected from a high-complexity hospital in Cali. A total of 15,608 patients were included in the analysis, all of whom underwent HbA1C measurement through capillary electrophoresis, which also offers an indirect diagnosis of certain structural disorders of hemoglobin. Bayesian methods were employed for frequency analysis.

Results

Among the 15,608 patients assessed, 63.6 % (n = 9920) were women. The overall prevalence of structural hemoglobin disorders was 1.98 % (n = 287, 95 % CI = 1.77 %-2.21 %). The co-occurrence of diabetes and kidney disease emerged as the most prevalent combination of pathologies observed in individuals with HbC, for both men and women across various age groups: 18-42 (58.3 % and 50.0 % respectively), 43-55 (50.0 % for both), 56-65 (50.0 % and 37.5 % respectively), and >65 years (66.7 % and 57.1 % respectively).

Conclusions

The observed prevalence of the studied variants exceeded 1 %, a threshold underscored by the World Health Organization (WHO) as epidemiologically significant. Among HbC and HbS-positive patients, the elevated prevalence of diabetes and kidney disease is a guiding factor in developing proactive prevention strategies.

Acute soft head syndrome in a teenager with sickle cell anemia: A case report

Key Clinical Message

Sickle cell disease (SCD) rarely presents with acute soft head syndrome (ASHS) often posing a diagnostic dilemma. Recovery is typically spontaneous, however, in the context of lack of awareness and limited brain imaging it could potentially lead to poor outcome.

Abstract

ASHS is a rare complication of SCD, invariably occurring near puberty with hitherto elusive pathogenic mechanisms. ASHS often resolves spontaneously on conservative management, however, lack of awareness in the context of limited access to brain imaging could pose diagnostic challenges resulting in inappropriate management and untoward outcome. We present a case of a teenager who presented with subtle symptoms for which the diagnosis of sickle cell anemia (SCA) was delayed until he developed ASHS. LTM was a 16 years old boy with a history of recurrent joints pain since the age of 6 years, with a family history of SCA, but had initial negative sickling test. He presented with episodes of multiple joints pain, unprovoked scalp and left orbital swelling, low-grade fever and mild headache without any evidence for bleeding diathesis. The diagnosis of SCA was confirmed by hemoglobin electrophoresis. Computed tomography (CT) scan of the head revealed subgaleal heamatoma (SGH) and intraorbital haematoma without intracranial hemorrhage (ICH). He was managed conservatively with analgesics and hydration together with antibiotics for associated sepsis with complete resolution of clinical symptoms within 2 weeks. This case represents a rare scenario for a relatively mild SCA phenotype presenting with ASHS whose diagnosis poses an enigma in the resource-limited contex. It is therefore, prudent to recognize ASHS to avoid judicious interventions which could potentially result in untoward clinical outcome.

Allogeneic hematopoietic stem cell transplantation to cure sickle cell disease: A review

Sickle cell disease (SCD) had first been mentioned in the literature a century ago. Advancement in the molecular basis of the pathophysiology of the disease opens the door for various therapeutic options. Though life-extending treatments are available for treating patients with SCD, allogeneic hematopoietic stem cell transplantation (HSCT) is the only option as of yet. A major obstacle before HSCT to cure patients with SCD is the availability of donors. Matched sibling donors are available only for a small percentage of patients. To expand the donor pool, different contrasting approaches of allogeneic HSCT like T-cell replete and deplete have been tested. None of those tested approaches have been without the risk of GvHD and graft rejection. Other limitations such as transplantation-related infections and organ dysfunction caused by the harsh conditioning regimen need to be addressed on a priority basis. In this review, we will discuss available allogeneic HSCT approaches to cure SCD, as well as recent advancements to make the approach safer. The center of interest is using megadose T-cell-depleted bone marrow in conjugation with donor-derived CD8 veto T cells to achieve engraftment and tolerance across MHC barriers, under reduced intensity conditioning (RIC). This approach is in phase I/II clinical trial at the MD Anderson Cancer Centre and is open to patients with hemoglobinopathies.

β-Thalassemia Intermedia: Interaction of α-Globin Gene Triplication With β-thalassemia Heterozygous in Spain

Objectives

To verify with hematimetric data that the diagnosis and clinical grade of β-TI can be established when a triplication of alpha genes (αααanti 3.7) and heterozygous β-thalassemia coexist.

Materials and Methods

Retrospective study in which 73 patients of Caucasian origin participated, who simultaneously showed a triplication or quadruplication of genes α and β-thalassemia.

Screening for the most frequent α-thalassemia mutations as well as gene triplication (αααanti 3.7) was carried out by multiplex PCR followed by reverse hybridization with a commercial Alpha-Globin StripAssay kit and confirmed by MLPA (Multiplex ligation-dependent probe amplification). The molecular diagnosis of β-thalassemia was carried out by automatic sequencing according to the Sanger method.

Results

The genotypes have been classified into three groups according to the number of α globin genes and the severity of the alteration in the β globin gene. All had a mutation in the HBB gene (β0-thalassemia, β+-thalassemia severe, and β+-thalassemia mild). Group I patients who have coherent 6 α genes and groups II and III with 5 α globin genes. In group III, the patients were carriers of mutations affecting the β and δ globin genes. The most significant hematological parameters were hemoglobin levels, MCV, RDW, and the percentage of Hb F.

Conclusions

In group I, regardless of the distribution of the 6 α globin genes, homozygous triplication (ααα/ααα) or heterozygous quadruplication (αααα/αα), the association with heterozygous β-thalassemia results in severe to moderate anemia that may or may not require transfusion therapy, is the severity of the HBB gene mutation that would determine the clinical variation. Group II patients phenotypically behaved like mild thalassemia intermedia, except for one case that presented thalassemic trait because it also presented an associated α-thalassemia (ααα/-α3.7). Finally, group III patients behaved as a thalassemic trait since all were carriers of mutations that increase the overexpression of γ genes.

POGZ Is Required for Silencing Mouse Embryonic β-like Hemoglobin and Human Fetal Hemoglobin Expression

Fetal globin genes are transcriptionally silenced during embryogenesis through hemoglobin switching. Strategies to derepress fetal globin expression in the adult could alleviate symptoms in sickle cell disease and β-thalassemia. We identified a zinc-finger protein, pogo transposable element with zinc-finger domain (POGZ), expressed in hematopoietic progenitor cells. Targeted deletion of Pogz in adult hematopoietic cells in vivo results in persistence of embryonic β-like globin expression without affecting erythroid development. POGZ binds to the Bcl11a promoter and erythroid-specific intragenic regulatory regions. Pogz+/- mice show elevated embryonic β-like globin expression, suggesting that partial reduction of Pogz expression results in persistence of embryonic β-like globin expression. Knockdown of POGZ in primary human CD34+ progenitor cell-derived erythroblasts reduces BCL11A expression, a known repressor of embryonic β-like globin expression, and increases fetal hemoglobin expression. These findings are significant, since new therapeutic targets and strategies are needed to treat β-globin disorders.

Genotype-phenotype correlation among beta-thalassemia and beta-thalassemia/HbE disease in Thai children: predictable clinical spectrum using genotypic analysis

Introduction

Beta-thalassemia is a group of inherited hemolytic anemias and one of the most common genetic disorders in Thailand. The clinical spectrum of beta-thalassemia disease ranges from mild to severe clinical symptoms including mild beta-thalassemia intermedia (TI) and severe beta-thalassemia major (TM).

Objective

This study aimed to determine the correlation between beta-globin gene (HBB) mutations and their phenotypic manifestations by evaluating patients' clinical characteristics, transfusion requirements, growth and hematologic parameters, and hemoglobin typing among pediatric patients treated at Phramongkutklao Hospital.

Materials and methods

Seventy beta-thalassemia patients, including 63 with beta-thalassemia/hemoglobin E (HbE) and 7 with either homozygous or compound heterozygous beta-thalassemia, were enrolled in this study. Their clinical presentation, growth parameters and laboratory findings were reviewed and analyzed. The mean follow-up time was 10.52±5.62 years. Mutation analysis in each individual was performed using multiplex amplification refractory mutation system (M-ARMS), direct DNA sequencing of beta-globin gene and gap PCR for 3.4 kb deletion detection.

Results

All 7 homozygous and compound heterozygous beta-thalassemia patients were classified in TM. Among 63 patients with beta-thalassemia/HbE, 58 were classified in TM and 4 were classified in TI. Mean age at diagnosis was 0.8±0.49 years for homozygous or compound heterozygous beta-thalassemia and 3.43±3.5 years for beta-thalassemia/HbE. The most common HBB mutation was HBB:c.126_129delCTTT [codon 41/42 (-TCTT)] found in 34 alleles (48.6%). The height for age was also lower in homozygous beta-thalassemia patients (<3rd percentile) compared to compound heterozygous beta-thalassemia patients (25-50th percentile).

Conclusion

This study revealed a genotype-phenotype correlation of the most prevalent beta-thalassemia in Thai children using diagnostic capacity in genotypic analysis of HBB mutation. Our findings can provide a better prediction of clinical manifestation and severity by early identification of the type of the HBB mutations.

Monogenic diseases in India

Studies on monogenic diseases are considered valuable because they give insights and expand our knowledge on gene function and regulation. Despite all the current advancement in science and technology, a deep understanding and knowledge as to why only those particular genes are affected in a disease is still vague. We also lack profound illumination as to why only certain mutations are seen in a disease. Though useful from a research perspective, a majority of these diseases are lethal resulting in death of the affected individual. Unfortunately, in the fast - growing land of India, the incidence of monogenic diseases is very high with few counter-measures in place. This article encompasses a list of all monogenic diseases ever to be reported in India with special focus on five diseases which has been stated to have the highest incidence in India. Here, we discuss about the limited research carried out in India on these high incidence monogenic diseases, the other diseases related to those genes, the range of treatments available for these diseases in India in contrast to its availability around the world and the need to develop treatment strategies to reduce the mortality and morbidity due to these rare but daunting diseases.

Genotype-Phenotype Correlations of β-Thalassemia Mutations in an Azerbaijani Population

β-Thalassemia is the most common inherited disorder in Azerbaijan. The aim of our study was to reveal genotype-to-phenotype correlations of the most common β-thalassemia mutations in an Azerbaijani population. Patients with codon 8 (-AA), IVS-I-6 (T>C), and IVS-II-1 (G>A) mutations, which are reportedly the most common β-globin gene mutations among the local population, were tested for hematologic parameters. Fifty-five previously tested patients with known genotypes were included in the study. Hematologic indices and hemoglobin fractions were tested in order to reveal the phenotypic manifestation of the mutations. The results obtained indicate that clinical presentation varies between different β-globin gene mutations: individuals with IVS-I-6 (T>C) mutations showed milder presentation than those with codon 8 (-AA) and IVS-II-1 (G>A), which is associated with the molecular basis of the mutations. These data can be of assistance to predict clinical presentation and select the best possible therapeutic approach via early genotype identification.

Emerging cellular and gene therapies for congenital anemias

Congenital anemias comprise a group of blood disorders characterized by a reduction in the number of peripherally circulating erythrocytes. Various genetic etiologies have been identified that affect diverse aspects of erythroid physiology and broadly fall into two main categories: impaired production or increased destruction of mature erythrocytes. Current therapies are largely focused on symptomatic treatment and are often based on transfusion of donor-derived erythrocytes and management of complications. Hematopoietic stem cell transplantation represents the only curative option currently available for the majority of congenital anemias. Recent advances in gene therapy and genome editing hold promise for the development of additional curative strategies for these blood disorders. The relative ease of access to the hematopoietic stem cell compartment, as well as the possibility of genetic manipulation ex vivo and subsequent transplantation in an autologous manner, make blood disorders among the most amenable to cellular therapies. Here we review cell-based and gene therapy approaches, and discuss the limitations and prospects of emerging avenues, including genome editing tools and the use of pluripotent stem cells, for the treatment of congenital forms of anemia. © 2016 Wiley Periodicals, Inc.

Small island, big genetic discoveries

Three new studies have identified new genes and sequence variants implicated in blood lipids, inflammatory markers, hemoglobin levels and adult height variation in Sardinia. These reports highlight the usefulness of large-scale genotype imputation based on whole-genome sequencing, particularly in isolated populations, in studying the genetics of complex human phenotypes.

From genome-wide association study hits to new insights into experimental hematology

Despite significant improvements in our knowledge of the mechanisms of normal and pathological hematopoiesis, our current understanding is most likely an oversimplification of the complexity of regulatory networks at play. Thus, considerable efforts have been made to catalogue the total sum of germline alterations in individual genomes affecting human hematopoiesis. These efforts ultimately led to the discovery of a large number of new genes not previously implicated in blood formation. Although identification of novel genes is important in revealing the profiles of genetic variations associated with normal hematopoiesis, further functional studies are necessary to improve our understanding of the mechanism(s) involved in these processes. In this review, we summarize the knowledge gained from genome-wide association studies to elucidate the relationship between genetics and blood cell traits. We discuss the most important recent advances, with an emphasis on functional follow-up studies that have been particularly useful in providing an insight into novel regulatory processes that influence blood cell formation and function. We also discuss potential future directions and challenges in the field.

Lessons and Implications from Genome-Wide Association Studies (GWAS) Findings of Blood Cell Phenotypes

Genome-wide association studies (GWAS) have identified reproducible genetic associations with hundreds of human diseases and traits. The vast majority of these associated single nucleotide polymorphisms (SNPs) are non-coding, highlighting the challenge in moving from genetic findings to mechanistic and functional insights. Nevertheless, large-scale (epi)genomic studies and bioinformatic analyses strongly suggest that GWAS hits are not randomly distributed in the genome but rather pinpoint specific biological pathways important for disease development or phenotypic variation. In this review, we focus on GWAS discoveries for the three main blood cell types: red blood cells, white blood cells and platelets. We summarize the knowledge gained from GWAS of these phenotypes and discuss their possible clinical implications for common (e.g., anemia) and rare (e.g., myeloproliferative neoplasms) human blood-related diseases. Finally, we argue that blood phenotypes are ideal to study the genetics of complex human traits because they are fully amenable to experimental testing.

Prevalence of depression and anxiety in adult patients with β-thalassemia major and intermedia

OBJECTIVE

To evaluate and compare the prevalence and risk factors for anxiety and depression in adults with beta-thalassemia major (TM) and intermedia (TI).

METHOD

A cross-sectional study of TI and TM patients at a Chronic Care Center in Lebanon. A total of 80 patients agreed to participate (32 TI (median age 24 years) and 48 TM (median age 23 years)). The Beck Depression Inventory (BDI) and State-Trait Anxiety Inventory (STAI) questionnaires were used to assess the depression and anxiety levels of patients, respectively. Data on patient demographics, clinical complications, and socioeconomic status were also collected.

RESULTS

Patients with TM had a significantly longer median duration with a known thalassemia diagnosis than patients with TI (p < 0.001). A considerable proportion of patients had depression (35.0%), State (S)-anxiety (22.5%) or Trait (T)-anxiety (36.2%). Patients with TI had a higher median S-anxiety score compared with TM (p = 0.035), although the median T-anxiety and depression scores were similar. On linear regression analysis, the significant association between the thalassemia diagnosis (TM versus TI) and S-anxiety score (beta: 5.740; 95% CI: 0.201 to 11.278; p = 0.042) was no longer observed upon adjustment for the co-variate duration with a known thalassemia diagnosis (beta: 3.162; 95% CI: -2.949 to 9.274; p = 0.306).

CONCLUSIONS

A considerable proportion of adult patients with TM and TI show evidence of depression and anxiety. Patients with TI are more liable to state anxiety than TM patients of a similar age, which is attributed to a shorter duration of living with a thalassemia diagnosis.

Detection and impact of rare regulatory variants in human disease

Advances in genome sequencing are providing unprecedented resolution of rare and private variants. However, methods which assess the effect of these variants have relied predominantly on information within coding sequences. Assessing their impact in non-coding sequences remains a significant contemporary challenge. In this review, we highlight the role of regulatory variation as causative agents and modifiers of monogenic disorders. We further discuss how advances in functional genomics are now providing new opportunity to assess the impact of rare non-coding variants and their role in disease.

Gene-centric association study of acute chest syndrome and painful crisis in sickle cell disease patients

Patients with sickle cell disease (SCD) present with a wide range of clinical complications. Understanding this clinical heterogeneity offers the prospects to tailor the right treatments to the right patients and also guide the development of novel therapies. Several environmental (eg, nutrition) and nonenvironmental (eg, fetal hemoglobin levels, α-thalassemia status) factors are known to modify SCD severity. To find new genetic modifiers of SCD severity, we performed a gene-centric association study in 1514 African American participants from the Cooperative Study of Sickle Cell Disease (CSSCD) for acute chest syndrome (ACS) and painful crisis. From the initial results, we selected 36 single nucleotide polymorphism (SNPs) and genotyped them for replication in 387 independent patients from the CSSCD, 318 SCD patients recruited at Georgia Health Sciences University, and 449 patients from the Duke SCD cohort. In the combined analysis, an association between ACS and rs6141803 reached array-wide significance (P = 4.1 × 10(-7)). This SNP is located 8.2 kilobases upstream of COMMD7, a gene highly expressed in the lung that interacts with nuclear factor-κB signaling. Our results provide new leads to gaining a better understanding of clinical variability in SCD, a "simple" monogenic disease.

How genetic modifiers influence the phenotype of spinal muscular atrophy and suggest future therapeutic approaches

Both complex disorders and monogenetic diseases are often modulated in their phenotype by further genetic, epigenetic or extrinsic factors. This gives rise to extensive phenotypic variability and potentially protection from disease manifestations, known as incomplete penetrance. Approaches including whole transcriptome, exome, genome, methylome or proteome analyses of highly discordant phenotypes in a few individuals harboring mutations at the same locus can help to identify these modifiers. This review describes the complexity of modifying factors of one of the most frequent autosomal recessively inherited disorders in humans, spinal muscular atrophy (SMA). We will outline how this knowledge contributes to understanding of the regulatory networks and molecular pathology of SMA and how this knowledge will influence future approaches to therapies.

Gene therapy for hemoglobinopathies: progress and challenges

Hemoglobinopathies are genetic inherited conditions that originate from the lack or malfunction of the hemoglobin (Hb) protein. Sickle cell disease (SCD) and thalassemia are the most common forms of these conditions. The severe anemia combined with complications that arise in the most affected patients raises the necessity for a cure to restore hemoglobin function. The current routine therapies for these conditions, namely transfusion and iron chelation, have significantly improved the quality of life in patients over the years, but still fail to address the underlying cause of the diseases. A curative option, allogeneic bone marrow transplantation is available, but limited by the availability of suitable donors and graft-vs-host disease. Gene therapy offers an alternative approach to cure patients with hemoglobinopathies and aims at the direct recovery of the hemoglobin function via globin gene transfer. In the last 2 decades, gene transfer tools based on lentiviral vector development have been significantly improved and proven curative in several animal models for SCD and thalassemia. As a result, clinical trials are in progress and 1 patient has been successfully treated with this approach. However, there are still frontiers to explore that might improve this approach: the stoichiometry between the transgenic hemoglobin and endogenous hemoglobin with respect to the different globin genetic mutations; donor cell sourcing, such as the use of induced pluripotent stem cells (iPSCs); and the use of safer gene insertion methods to prevent oncogenesis. With this review we will provide insights about (1) the different lentiviral gene therapy approaches in mouse models and human cells; (2) current and planned clinical trials; (3) hurdles to overcome for clinical trials, such as myeloablation toxicity, insertional oncogenesis, and high vector expression; and (4) future perspectives for gene therapy, including safe harbors and iPSCs technology.

Hydroxyurea responsiveness in β-thalassemic patients is determined by the stress response adaptation of erythroid progenitors and their differentiation propensity

β-thalassemia is caused by mutations in the β-globin locus resulting in loss of, or reduced, hemoglobin A (adult hemoglobin, HbA, α2β2) production. Hydroxyurea treatment increases fetal γ-globin (fetal hemoglobin, HbF, α2γ2) expression in postnatal life substituting for the missing adult β-globin and is, therefore, an attractive therapeutic approach. Patients treated with hydroxyurea fall into three categories: i) 'responders' who increase hemoglobin to therapeutic levels; (ii) 'moderate-responders' who increase hemoglobin levels but still need transfusions at longer intervals; and (iii) 'non-responders' who do not reach adequate hemoglobin levels and remain transfusion-dependent. The mechanisms underlying these differential responses remain largely unclear. We generated RNA expression profiles from erythroblast progenitors of 8 responder and 8 non-responder β-thalassemia patients. These profiles revealed that hydroxyurea treatment induced differential expression of many genes in cells from non-responders while it had little impact on cells from responders. Part of the gene program up-regulated by hydroxyurea in non-responders was already highly expressed in responders before hydroxyurea treatment. Baseline HbF expression was low in non-responders, and hydroxyurea treatment induced significant cell death. We conclude that cells from responders have adapted well to constitutive stress conditions and display a propensity to proceed to the erythroid differentiation program.

The relation of vascular endothelial growth factor (VEGF) gene polymorphisms on VEGF levels and the risk of vasoocclusive crisis in sickle cell disease

OBJECTIVE

The association of vascular endothelial growth factor (VEGFA) variants and VEGF secretion with sickle cell disease (SCD) vasoocclusive crisis (VOC) was investigated in 210 VOC patients and 114 pain-free control patients.

METHODS

VEGFA -2578C/A (rs699947), -460T/C (rs833061), -1154G/A (rs15703060), -634G/C (rs2010963), 398G/A (rs833068), 497G/A (rs833070), -583T/C (rs3025020), and 936C/T (rs3025039) were carried out by real-time PCR.

RESULTS

Higher frequency of rs2010963 C-allele, rs833068 A-allele, and rs3025020 C-allele and significant differences in rs2010963, rs833068, and rs3025020 genotype distribution were seen in VOC than steady-state patients. Increased VOC risk was seen with rs2010963 as heterozygous and more as homozygous, and in rs833068 and rs3025020 homozygous carriers. While there were no differences in VEGF levels between VOC and steady-state controls, there was a progressive decline in serum VEGF in rs2010963 and rs833068 heterozygous and homozygous genotypes, but an opposite trend was seen in VOC patients. Haploview analysis revealed high LD between rs699947, rs833061, rs1570360, rs2010963, rs833068, and rs833070, but weak or no LD between rs3025020 and rs3025039 and other SNPs. Six-locus (rs699947/rs833061/rs1570360/rs2010963/rs833068/rs833070) VEGFA haplotype analysis identified haplotype 111111 to be negatively (OR = 0.68) and haplotype 111222 to be positively (OR = 1.89) associated with VOC. rs2010963, rs833068, and rs3025020 were correlated with VOC type, while rs3025020 was correlated with hospitalization, VOC treatment, and duration.

CONCLUSION

Specific VEGFA variants contribute to the pathogenesis of SCD VOC.

β-thalassemia intermedia: a clinical perspective

Our understanding of the molecular and pathophysiological mechanisms underlying the disease process in patients with β-thalassemia intermedia has substantially increased over the past decade. Earlier studies observed that patients with β-thalassemia intermedia experience a clinical-complications profile that is different from that in patients with β-thalassemia major. In this article, a variety of clinical morbidities are explored, and their associations with the underlying disease pathophysiology and risk factors are examined. These involve several organs and organ systems including the vasculature, heart, liver, endocrine glands, bone, and the extramedullary hematopoietic system. The effects of some therapeutic interventions on the development of clinical complications are also discussed.