Dyskeratosis congenita: advances in the understanding of the telomerase defect and the role of stem cell transplantation

Research progress of RNA pseudouridine modification in nervous system

Recent advances of pseudouridine (Ψ, 5-ribosyluracil) modification highlight its crucial role as a post-transcriptional regulator in gene expression and its impact on various RNA processes. Ψ synthase (PUS), a category of RNA-modifying enzymes, orchestrates the pseudouridylation reaction. It can specifically recognize conserved sequences or structural motifs within substrates, thereby regulating the biological function of various RNA molecules accurately. Our comprehensive review underscored the close association of PUS1, PUS3, PUS7, PUS10, and dyskerin PUS1 with various nervous system disorders, including neurodevelopmental disorders, nervous system tumors, mitochondrial myopathy, lactic acidosis and sideroblastic anaemia (MLASA) syndrome, peripheral nervous system disorders, and type II myotonic dystrophy. In light of these findings, this study elucidated how Ψ strengthened RNA structures and contributed to RNA function, thereby providing valuable insights into the intricate molecular mechanisms underlying nervous system diseases. However, the detailed effects and mechanisms of PUS on neuron remain elusive. This lack of mechanistic understanding poses a substantial obstacle to the development of therapeutic approaches for various neurological disorders based on Ψ modification.

Clinical considerations at the intersection of hematopoietic cell transplantation and hereditary hematopoietic malignancy

In recent years, advances in genetics and the integration of clinical-grade next-generation sequencing (NGS) assays into patient care have facilitated broader recognition of hereditary hematopoietic malignancy (HHM) among clinicians, in addition to the identification and characterization of novel HHM syndromes. Studies on genetic risk distribution within affected families and unique considerations of HHM biology represent exciting areas of translational research. More recently, data are now emerging pertaining to unique aspects of clinical management of malignancies arising in the context of pathogenic germline mutations, with particular emphasis on chemotherapy responsiveness. In this article, we explore considerations surrounding allogeneic transplantation in the context of HHMs. We review pre- and post-transplant patient implications, including genetic testing donor selection and donor-derived malignancies. Additionally, we consider the limited data that exist regarding the use of transplantation in HHMs and safeguards that might be pursued to mitigate transplant-related toxicities.

Germline Predisposition to Myelodysplastic Syndromes

ABSTRACT

While germline predisposition to myelodysplastic syndromes is well-established, knowledge has advanced rapidly resulting in more cases of inherited hematologic malignancies being identified. Understanding the biological features and main clinical manifestations of hereditary hematologic malignancies is essential to recognizing and referring patients with myelodysplastic syndrome, who may underlie inherited predisposition, for appropriate genetic evaluation. Importance lies in individualized genetic counseling along with informed treatment decisions, especially with regard to hematopoietic stem cell transplant-related donor selection. Future studies will improve comprehension of these disorders, enabling better management of affected patients and their families.

The biology and management of dyskeratosis congenita and related disorders of telomeres

BACKGROUND

Dyskeratosis congenita (DC) is a multisystem syndrome characterized by mucocutaneous abnormalities, bone marrow failure, and predisposition to cancer. Studies over the last 25 years have led to the identification of 18 disease genes. These have a principal role in telomere maintenance, and patients usually have very short/abnormal telomeres. The advances have also led to the unification of DC with a number of other diseases, now collectively referred to as the telomeropathies or telomere biology disorders.

WHAT IS COVERED

Clinical features, genetics, and biology of the different subtypes. Expert view on diagnosis, treatment of the hematological complications and future.

EXPERT VIEW

As these are very pleotropic disorders affecting multiple organs, a high index of suspicion is necessary to make the diagnosis. Telomere length measurement and genetic analysis of the disease genes have become useful diagnostic tools. Although hematological defects can respond to danazol/oxymetholone, the only current curative treatment for these is hematopoietic stem cell transplantation (HSCT) using fludarabine-based conditioning protocols. New therapies are needed where danazol/oxymetholone is ineffective and HSCT is not feasible.

Bilateral cytomegalovirus retinitis as the presenting feature of Dyskeratosis Congenita

PURPOSE

To describe a young male with bilateral sequential Cytomegalovirus retinitis (CMVR) as the presenting feature of Dyskeratosis Congenita.

CASE REPORT

A 25-year-old human immunodeficiency virus (HIV) negative male developed CMVR in his left eye, while on a three week course of oral valganciclovir therapy for CMV retinitis in his right eye. Systemic examination revealed reticular hypopigmentation of the forearms, dystrophic nails, oral leukoplakia and complete blood counts showed pancytopenia. A diagnosis of Dyskeratosis Congenita was confirmed with genetic testing.

CONCLUSION

CMVR in non-HIV individuals should be considered as a harbinger of systemic immunosuppressive conditions. Ophthalmologists may be the first ones to suspect and diagnose congenital immunosuppressive disorders like Dyskeratosis Congenita in these patients.

Extrahematopoietic manifestations of the short telomere syndromes

The short telomere syndromes encompass a spectrum of clinical manifestations that present from infancy to late adulthood. They are caused by mutations in telomerase and other telomere maintenance genes and have a predominantly degenerative phenotype characterized by organ failure across multiple systems. They are collectively one of the most common inherited bone marrow failure syndromes; however, their most prevalent presentations are extrahematopoietic. This review focuses on these common nonhematologic complications, including pulmonary fibrosis, liver pathology, and immunodeficiency. The short telomere syndrome diagnosis informs clinical care, especially in guiding diagnostic evaluations as well as in the solid organ transplant setting. Early recognition allows an individualized approach to screening and management. This review illustrates a myriad of extrahematopoietic presentations of short telomere syndromes and how they impact clinical decisions.

The complex genetic landscape of familial MDS and AML reveals pathogenic germline variants

The inclusion of familial myeloid malignancies as a separate disease entity in the revised WHO classification has renewed efforts to improve the recognition and management of this group of at risk individuals. Here we report a cohort of 86 acute myeloid leukemia (AML) and myelodysplastic syndrome (MDS) families with 49 harboring germline variants in 16 previously defined loci (57%). Whole exome sequencing in a further 37 uncharacterized families (43%) allowed us to rationalize 65 new candidate loci, including genes mutated in rare hematological syndromes (ADA, GP6, IL17RA, PRF1 and SEC23B), reported in prior MDS/AML or inherited bone marrow failure series (DNAH9, NAPRT1 and SH2B3) or variants at novel loci (DHX34) that appear specific to inherited forms of myeloid malignancies. Altogether, our series of MDS/AML families offer novel insights into the etiology of myeloid malignancies and provide a framework to prioritize variants for inclusion into routine diagnostics and patient management.

The Role of Ubiquitination and SUMOylation in Telomere Biology

Telomeres are a unique structure of DNA repeats covered by proteins at the ends of the chromosomes that protect the coding regions of the genome and function as a biological clock. They require a tight regulation of the factors covering and protecting their structure, as they are shortened with each cell division to limit the ability of cells to replicate uncontrollably. Additionally, they protect the chromosome ends from DNA damage responses and thereby, prevent genomic instability. Telomere dysfunction can lead to chromosomal abnormalities and cancer. Therefore, dysregulation of any of the factors that regulate the integrity of the telomeres will have implications to chromosomal stability, replicative lifespan and may lead to cell transformation. This review will cover the main factors participating in the normal function of the telomeres and how these are regulated by the ubiquitin and SUMO systems. Accumulating evidence indicate that the ubiquitin and SUMO pathways are significant regulators of the shelterin complex and other chromatin modifiers, which are important for telomere structure integrity. Furthermore, the crosstalk between these two pathways has been reported in telomeric DNA repair. A better understanding of the factors contributing to telomere biology, and how they are regulated, is important for the design of new strategies for cancer therapies and regenerative medicine.

Evaluation and Management of Hematopoietic Failure in Dyskeratosis Congenita

Dyskeratosis congenita (DC) is a rare, inherited bone marrow failure (BMF) syndrome characterized by variable manifestations and ages of onset, and predisposition to cancer. DC is one of a spectrum of diseases caused by mutations in genes regulating telomere maintenance, collectively referred to as telomere biology disorders (TBDs). Hematologic disease is common in children with DC/TBD. Timely diagnosis of underlying TBD in patients with BMF affects treatment and has been facilitated by increased awareness and availability of diagnostic tests in recent years. This article summarizes the pathophysiology, evaluation, and management of hematopoietic failure in patients with DC and other TBDs.

Current Perspectives of Telomerase Structure and Function in Eukaryotes with Emerging Views on Telomerase in Human Parasites

Replicative capacity of a cell is strongly correlated with telomere length regulation. Aberrant lengthening or reduction in the length of telomeres can lead to health anomalies, such as cancer or premature aging. Telomerase is a master regulator for maintaining replicative potential in most eukaryotic cells. It does so by controlling telomere length at chromosome ends. Akin to cancer cells, most single-cell eukaryotic pathogens are highly proliferative and require persistent telomerase activity to maintain constant length of telomere and propagation within their host. Although telomerase is key to unlimited cellular proliferation in both cases, not much was known about the role of telomerase in human parasites (malaria, Trypanosoma, etc.) until recently. Since telomerase regulation is mediated via its own structural components, interactions with catalytic reverse transcriptase and several factors that can recruit and assemble telomerase to telomeres in a cell cycle-dependent manner, we compare and discuss here recent findings in telomerase biology in cancer, aging and parasitic diseases to give a broader perspective of telomerase function in human diseases.

Insights from human genetic studies of lung and organ fibrosis

Genetic investigations of fibrotic diseases, including those of late onset, often yield unanticipated insights into disease pathogenesis. This Review focuses on pathways underlying lung fibrosis that are generalizable to other organs. Herein, we discuss genetic variants subdivided into those that shorten telomeres, activate the DNA damage response, change resident protein expression or function, or affect organelle activity. Genetic studies provide a window into the downstream cascade of maladaptive responses and pathways that lead to tissue fibrosis. In addition, these studies reveal interactions between genetic variants, environmental factors, and age that influence the phenotypic spectrum of disease. The discovery of forces counterbalancing inherited risk alleles identifies potential therapeutic targets, thus providing hope for future prevention or reversal of fibrosis.

Familial myelodysplastic syndrome/acute myeloid leukemia

A growing number of inherited genetic loci that contribute to myelodysplastic syndrome/acute myeloid leukemia (MDS/AML) development in both children as well as adults are rapidly being identified. In recognition of the clinical impact of this emerging field, the World Health Organization, National Comprehensive Cancer Network, and European LeukemiaNet have all added consideration of inherited predisposition to MDS/AML classification and management. Study of these disorders is providing unique insight into the biology of both sporadic and familial MDS/AML. International collaborative efforts to store germline tissue, document family histories, and pool data are essential to progress in diagnosing and treating both hereditary and sporadic forms of MDS/AML.

Recommendations for Childhood Cancer Screening and Surveillance in DNA Repair Disorders

DNA repair syndromes are heterogeneous disorders caused by pathogenic variants in genes encoding proteins key in DNA replication and/or the cellular response to DNA damage. The majority of these syndromes are inherited in an autosomal-recessive manner, but autosomal-dominant and X-linked recessive disorders also exist. The clinical features of patients with DNA repair syndromes are highly varied and dependent on the underlying genetic cause. Notably, all patients have elevated risks of syndrome-associated cancers, and many of these cancers present in childhood. Although it is clear that the risk of cancer is increased, there are limited data defining the true incidence of cancer and almost no evidence-based approaches to cancer surveillance in patients with DNA repair disorders. This article is the product of the October 2016 AACR Childhood Cancer Predisposition Workshop, which brought together experts from around the world to discuss and develop cancer surveillance guidelines for children with cancer-prone disorders. Herein, we focus on the more common of the rare DNA repair disorders: ataxia telangiectasia, Bloom syndrome, Fanconi anemia, dyskeratosis congenita, Nijmegen breakage syndrome, Rothmund-Thomson syndrome, and Xeroderma pigmentosum. Dedicated syndrome registries and a combination of basic science and clinical research have led to important insights into the underlying biology of these disorders. Given the rarity of these disorders, it is recommended that centralized centers of excellence be involved directly or through consultation in caring for patients with heritable DNA repair syndromes. Clin Cancer Res; 23(11); e23-e31. ©2017 AACRSee all articles in the online-only CCR Pediatric Oncology Series.

How I diagnose and manage individuals at risk for inherited myeloid malignancies

Although inherited hematopoietic malignancies have been reported clinically since the early twentieth century, the molecular basis for these diseases has only recently begun to be elucidated. Growing utilization of next-generation sequencing technologies has facilitated the rapid discovery of an increasing number of recognizable heritable hematopoietic malignancy syndromes while also deepening the field's understanding of the molecular mechanisms that underlie these syndromes. Because individuals with inherited hematopoietic malignancies continue to be underdiagnosed and are increasingly likely to be encountered in clinical practice, clinicians need to have a high index of suspicion and be aware of the described syndromes. Here, we present the methods we use to identify, test, and manage individuals and families suspected of having a hereditary myeloid malignancy syndrome. Finally, we address the areas of ongoing research in the field and encourage clinicians and researchers to contribute and collaborate.

Hereditary Predispositions to Myelodysplastic Syndrome

Myelodysplastic syndromes (MDS) are heterogeneous clonal hematopoietic disorders characterized by ineffective hematopoiesis, bone marrow dysplasia, and peripheral cytopenias. Familial forms of MDS have traditionally been considered rare, especially in adults; however, the increasing availability of somatic and germline genetic analyses has identified multiple susceptibility loci. Bone marrow failure syndromes have been well-described in the pediatric setting, e.g., Fanconi anemia (FA), dyskeratosis congenita (DC), Diamond-Blackfan anemia (DBA), and Shwachman-Diamond syndrome (SBS), hallmarked by clinically-recognizable phenotypes (e.g., radial ray anomalies in FA) and significantly increased risks for MDS and/or acute myeloid leukemia (AML) in the setting of bone marrow failure. However, additional families with multiple cases of MDS or AML have long been reported in the medical literature with little known regarding potential hereditary etiologies. Over the last decade, genomic investigation of such families has revealed multiple genes conferring inherited risks for MDS and/or AML as the primary malignancy, including RUNX1, ANKRD26, DDX41, ETV6, GATA2, and SRP72. As these syndromes are increasingly appreciated in even apparently de novo presentations of MDS, it is important for hematologists/oncologists to become familiar with these newly-described syndromes. Herein, we provide a review of familial MDS syndromes and practical aspects of management in patients with predisposition syndromes.

Allogeneic hematopoietic stem cell transplantation for inherited bone marrow failure syndromes

Inherited bone marrow failure (IBMF) syndromes are a heterogeneous group of rare hematological disorders characterized by the impairment of hematopoiesis, which harbor specific clinical presentations and pathogenic mechanisms. Some of these syndromes may progress through clonal evolution, myelodysplastic syndrome (MDS) and acute myeloid leukemia (AML). Most prominent are failures of DNA repair such as Fanconi Anemia and much rarer failure of ribosomal apparatus, e.g., Diamond Blackfan Anemia or of telomere elongation such as dyskeratosis congenita. In these congenital disorders, hematopoietic stem cell transplantation (HSCT) is often a consideration. However, HSCT will not correct the underlying disease and possible co-existing extra-medullary (multi)-organ defects, but will improve BMF. Indications as well as transplantation characteristics are most of the time controversial in this setting because of the rarity of reported cases. The present paper proposes a short overview of current practices.

A Reduced-Intensity Conditioning Regimen for Patients with Dyskeratosis Congenita Undergoing Hematopoietic Stem Cell Transplantation

Allogeneic hematopoietic stem cell transplantation (HSCT) is the only curative option for progressive marrow failure, myelodysplastic syndrome, or leukemia associated with dyskeratosis congenita (DC). HSCT for DC is limited by a high incidence of treatment-related mortality, thought to be related to underlying chromosomal instability and sensitivity to chemotherapy and radiation. We report our experience in 7 patients with DC who underwent allogeneic transplantation using a reduced-intensity conditioning (RIC) preparative regimen that contained chemotherapy only (no radiation). This RIC regimen, designed specifically for patients with DC, contained alemtuzumab, fludarabine, and melphalan (with melphalan at 50% reduced dosing), with the goal of decreasing toxicity and improving outcome. All 7 patients engrafted, with none developing mixed chimerism or rejection. Two patients experienced acute graft-versus-host disease (GVHD) and 1 went on to develop limited chronic GVHD of the skin. Five patients remain alive and well at a median follow-up of 44 months (range, 14 to 57 months). We conclude that a radiation-free RIC regimen results in durable engraftment, acceptable toxicity, and improved overall survival in patients with DC undergoing allogeneic HSCT.

The short and long telomere syndromes: paired paradigms for molecular medicine

Recent advances have defined a role for abnormally short telomeres in a broad spectrum of genetic disorders. They include rare conditions such as dyskeratosis congenita as well pulmonary fibrosis and emphysema. Now, there is new evidence that some familial cancers, such as melanoma, are caused by mutations that lengthen telomeres. Here, we examine the significance of these short and long telomere length extremes for understanding the molecular basis of age-related disease and cancer.

Therapeutic effect of androgen therapy in a mouse model of aplastic anemia produced by short telomeres

Aplastic anemia is a rare but life-threatening disorder characterized by cytopenia in at least two of the three blood lineages. A frequent feature of patients with aplastic anemia is that they have shorter telomeres than those of age-matched controls. Testosterone has been used for over half a century in the treatment of aplastic anemia. However, although remissions are frequent following hormone therapy, the molecular mechanism underlying the response to treatment has remained unknown. Here we explored the possibility that the recently described regulation of telomerase activity by sex hormones may be the mechanism responsible. To this end, we used a mouse model of aplastic anemia induced by short telomeres in the bone marrow compartment. We found that testosterone therapy results in telomerase up-regulation, improved blood counts, and a significant extension of life-span of these mice. Importantly, longitudinal follow-up studies revealed longer telomeres in peripheral blood in mice subjected to hormone treatment. Our results demonstrate that testosterone-mediated telomerase activation can attenuate or reverse aplastic anemia disease progression associated with the presence of short telomeres.

Successful T-cell-depleted haploidentical hematopoietic stem cell transplantation in a child with dyskeratosis congenita after a fludarabine-based conditioning regimen

Allogeneic hematopoietic stem cell transplantation (HSCT) is the only cure for marrow failure associated with dyskeratosis congenita (DC). Data on transplants from alternative donors are limited. We describe a boy with DC and severe aplastic anemia who underwent haploidentical T-cell depleted HSCT using a reduced-intensity conditioning regimen. He underwent engraftment without toxicity or GVHD. His posttransplant course was complicated by EBV reactivation, treated with rituximab and EBV-specific T lymphocytes. After 26 months, he is in complete chimerism, with normal blood count and no sign of GVHD or pulmonary dysfunction. To the best of our knowledge, this is the first report of DC successfully treated with allogeneic HSCT from a haploidentical family donor.

Telomere dysfunction causes alveolar stem cell failure

Telomere syndromes have their most common manifestation in lung disease that is recognized as idiopathic pulmonary fibrosis and emphysema. In both conditions, there is loss of alveolar integrity, but the underlying mechanisms are not known. We tested the capacity of alveolar epithelial and stromal cells from mice with short telomeres to support alveolar organoid colony formation and found that type 2 alveolar epithelial cells (AEC2s), the stem cell-containing population, were limiting. When telomere dysfunction was induced in adult AEC2s by conditional deletion of the shelterin component telomeric repeat-binding factor 2, cells survived but remained dormant and showed all the hallmarks of cellular senescence. Telomere dysfunction in AEC2s triggered an immune response, and this was associated with AEC2-derived up-regulation of cytokine signaling pathways that are known to provoke inflammation in the lung. Mice uniformly died after challenge with bleomycin, underscoring an essential role for telomere function in AEC2s for alveolar repair. Our data show that alveoloar progenitor senescence is sufficient to recapitulate the regenerative defects, inflammatory responses, and susceptibility to injury that are characteristic of telomere-mediated lung disease. They suggest alveolar stem cell failure is a driver of telomere-mediated lung disease and that efforts to reverse it may be clinically beneficial.

Telomere-regulating genes and the telomere interactome in familial cancers

Telomeres are repetitive sequence structures at the ends of linear chromosomes that consist of double-stranded DNA repeats followed by a short single-stranded DNA protrusion. Telomeres need to be replicated in each cell cycle and protected from DNA-processing enzymes, tasks that cells execute using specialized protein complexes such as telomerase (that includes TERT), which aids in telomere maintenance and replication, and the shelterin complex, which protects chromosome ends. These complexes are also able to interact with a variety of other proteins, referred to as the telomere interactome, to fulfill their biological functions and control signaling cascades originating from telomeres. Given their essential role in genomic maintenance and cell-cycle control, germline mutations in telomere-regulating proteins and their interacting partners have been found to underlie a variety of diseases and cancer-predisposition syndromes. These syndromes can be characterized by progressively shortening telomeres, in which carriers can present with organ failure due to stem cell senescence among other characteristics, or can also present with long or unprotected telomeres, providing an alternative route for cancer formation. This review summarizes the critical roles that telomere-regulating proteins play in cell-cycle control and cell fate and explores the current knowledge on different cancer-predisposing conditions that have been linked to germline defects in these proteins and their interacting partners.

Bone marrow failure and the telomeropathies

Our understanding of the pathophysiology of aplastic anemia is undergoing significant revision, with implications for diagnosis and treatment. Constitutional and acquired disease is poorly delineated, as lesions in some genetic pathways cause stereotypical childhood syndromes and also act as risk factors for clinical manifestations in adult life. Telomere diseases are a prominent example of this relationship. Accelerated telomere attrition is the result of mutations in telomere repair genes and genes encoding components of the shelterin complex and related proteins. Genotype-phenotype correlations show genes responsible for X-linked (DKC1) and severe recessive childhood dyskeratosis congenita, typically with associated mucocutaneous features, and others (TERC and TERT) for more subtle presentation as telomeropathy in adults, in which multiorgan failure may be prominent. Telomerase mutations also are etiologic in familial pulmonary fibrosis and cryptic liver disease. Detection of a telomere disease requires awareness in the clinic, appropriate laboratory testing of telomere content, and genetic sequencing. In treatment decisions, genetic screening of related donors for hematopoietic stem cell transplantation is critical, and androgen therapy may be helpful. Telomeres shorten normally with aging, as well as under environmental circumstances, with regenerative stress and oxidative damage. Telomere biology is complexly related to oncogenesis: telomere attrition is protective by enforcing senescence or apoptosis in cells with a long mitotic history, but telomere loss also can destabilize the genome by chromosome rearrangement and aneuploidy.

Inherited predisposition to acute myeloid leukemia

Germline testing for familial predisposition to myeloid malignancies is becoming more common with the recognition of multiple familial syndromes. Currently, Clinical Laboratory Improvement Amendments-approved testing exists for the following: familial platelet disorder with propensity to acute myeloid leukemia, caused by mutations in RUNX1; familial myelodysplastic syndrome/acute myeloid leukemia with mutated GATA2; familial acute myeloid leukemia with mutated CEBPA; and the inherited bone marrow failure syndromes, including dyskeratosis congenita, a disease of abnormal telomere maintenance. With the recognition of additional families with a genetic component to their myeloid diseases, new predisposition alleles are likely to be identified. Awareness of the existence of these syndromes will facilitate proper genetic counseling, appropriate testing, and clinical management of these cases.

Telomere and telomerase in chronic liver disease and hepatocarcinoma

The pathogenesis of liver cirrhosis is not completely elucidated. Although in the majority of patients, the risk factors may be identified in B and C viral hepatitis, alcohol intake, drugs or fatty liver disease, there is a small percentage of patients with no apparent risk factors. In addition, the evolution of chronic liver disease is highly heterogeneous from one patient to another. Among patient with identical risk factors, some rapidly progress to cirrhosis and hepatocellular carcinoma (HCC) whereas others have a benign course. Therefore, a genetic predisposition may contribute to the development of cirrhosis and HCC. Evidence supporting the role of genetic factors as a risk for cirrhosis has been accumulating during the past years. In addition to the results from epidemiological studies, polymorphisms studies and data on twins, the concept of telomere shortening as a genetic risk factor for chronic liver disease and HCC has been proposed. Here we review the literature on telomerase mutations, telomere shortening and liver disease including hepatocellular carcinoma.

Lung transplantation in telomerase mutation carriers with pulmonary fibrosis

Lung transplantation is the only intervention that prolongs survival in idiopathic pulmonary fibrosis (IPF). Telomerase mutations are the most common identifiable genetic cause of IPF, and at times, the telomere defect manifests in extrapulmonary disease such as bone marrow failure. The relevance of this genetic diagnosis for lung transplant management has not been examined.

We gathered an international series of telomerase mutation carriers who underwent lung transplant in the USA, Australia and Sweden.

The median age at transplant was 52 years. Seven recipients are alive with a median follow-up of 1.9 years (range 6 months to 9 years); one died at 10 months. The most common complications were haematological, with recipients requiring platelet transfusion support (88%) and adjustment of immunosuppressives (100%). Four recipients (50%) required dialysis for tubular injury and calcineurin inhibitor toxicity. These complications occurred at significantly higher rates relative to historic series (p<0.0001).

Our observations support the feasibility of lung transplantation in telomerase mutation carriers; however, severe post-transplant complications reflecting the syndromic nature of their disease appear to occur at higher rates. While these findings need to be expanded to other cohorts, caution should be exercised when approaching the transplant evaluation and management of this subset of pulmonary fibrosis patients.

Telomerase mutation carriers with IPF may be prone to complications from their underlying telomere syndrome after LTxhttp://ow.ly/wmy6P

Dyskeratosis congenita complicated by hepatic fibrosis with hepatic vein thrombosis

We describe the case of 2 male siblings with dyskeratosis congenita (DC). Extensive genetic analysis failed to identify a causative genetic abnormality. The elder brother developed hepatic fibrosis accompanied with hepatic vein thrombosis at the age of 9 years. Recent studies have found that patients with DC sometimes develop hepatic complications, including cirrhosis. However, little is known about hepatic complications in patients with DC who lack these mutations. Further genetic studies are required to understand the relationship between DC and hepatic complications. In addition, although danazol can sometimes be effective for treating bone marrow failure, hepatotoxicity can be a major complication. Therefore, when danazol is administered to patients with DC, careful monitoring for hepatic complications is important.

Human telomeres and telomere biology disorders

Telomeres consist of long nucleotide repeats and a protein complex at chromosome ends essential for chromosome stability. Telomeres shorten with each cell division and thus are markers of cellular age. Dyskeratosis congenita (DC) is a cancer-prone inherited bone marrow failure syndrome caused by germ-line mutations in key telomere biology genes that result in extremely short telomeres. The triad of nail dysplasia, abnormal skin pigmentation, and oral leukoplakia is diagnostic of DC but highly variable. Patients with DC may also have but numerous other medical problems, including pulmonary fibrosis, liver abnormalities, avascular necrosis of the hips, and stenosis of the esophagus, lacrimal ducts, and/or urethra. All modes of inheritance have been reported in DC and de novo mutations are common. Broad phenotypic heterogeneity occurs within DC. Clinically severe variants of DC are Hoyeraal-Hreidarsson syndrome and Revesz syndrome. Coats plus syndrome joined the spectrum of DC with the discovery that it is caused by mutations in a telomere-capping gene. Less clinically severe variants, such as subsets of apparently isolated aplastic anemia or pulmonary fibrosis, have also been recognized. These patients may not have the DC-associated mucocutaneous triad or complicated medical features, but they do have the same underlying genetic etiology. This has led to the use of the descriptive term telomere biology disorder (TBD). This chapter will review the connection between telomere biology and human disease through the examples of DC and its related TBDs.

Telomere dysfunction and hematologic disorders

Aplastic anemia is a disease in which the hematopoietic stem cell fails to adequately produce peripheral blood cells, causing pancytopenia. In some cases of acquired aplastic anemia and in inherited type of aplastic anemia, dyskeratosis congenita, telomere biology gene mutations and telomere shortening are etiologic. Telomere erosion hampers the ability of hematopoietic stem and progenitor cells to adequately replicate, clinically resulting in bone marrow failure. Additionally, telomerase mutations and short telomeres are genetic risk factors for the development of some hematologic cancers, including myelodysplastic syndrome, acute myeloid leukemia, and chronic lymphocytic leukemia.

Updates on the biology and management of dyskeratosis congenita and related telomere biology disorders

Dyskeratosis congenita (DC) is a cancer-prone inherited bone marrow failure syndrome caused by aberrant telomere biology. The mucocutaneous triad of nail dysplasia, abnormal skin pigmentation and oral leukoplakia is diagnostic, but is not always present; DC can also be diagnosed by the presence of very short leukocyte telomeres. Patients with DC are at high risk of bone marrow failure, pulmonary fibrosis, liver disease, cancer and other medical problems. Germline mutations in one of nine genes associated with telomere maintenance are present in approximately 60% of patients. DC is one among the group of clinically and biologically related telomere biology disorders, including Hoyeraal-Hreidarsson syndrome, Revesz syndrome, Coats plus (also known as cranioretinal microangiopathy with calcifications and cysts) and subsets of aplastic anemia, pulmonary fibrosis, nonalcoholic and noninfectious liver disease and leukemia. The authors review the pathobiology that connects DC and the related telomere biology disorders, methods of diagnosis and management modalities.

Dyskerin localizes to the mitotic apparatus and is required for orderly mitosis in human cells

Dyskerin is a highly conserved, nucleolar RNA-binding protein with established roles in small nuclear ribonucleoprotein biogenesis, telomerase and telomere maintenance and precursor rRNA processing. Telomerase is functional during S phase and the bulk of rRNA maturation occurs during G₁ and S phases; both processes are inactivated during mitosis. Yet, we show that during the course of cell cycle progression, human dyskerin expression peaks during G₂/M in parallel with the upregulation of pro-mitotic factors. Dyskerin redistributed from the nucleolus in interphase cells to the perichromosomal region during prometaphase, metaphase and anaphase. With continued anaphase progression, dyskerin also localized to the cytoplasm within the mid-pole region. Loss of dyskerin function via siRNA-mediated depletion promoted G₂/M accumulation and this was accompanied by an increased mitotic index and activation of the spindle assembly checkpoint. Live cell imaging further revealed an array of mitotic defects including delayed prometaphase progression, a significantly increased incidence of multi-polar spindles, and anaphase bridges culminating in micronucleus formation. Together, these findings suggest that dyskerin is a highly dynamic protein throughout the cell cycle and increases the repertoire of fundamental cellular processes that are disrupted by absence of its normal function.

Bone marrow transplantation in Schimke immuno-osseous dysplasia

Schimke immuno-osseous dysplasia (SIOD, OMIM 242900) is a rare autosomal recessive multisystem childhood disorder characterized by short stature, renal failure, T-cell immunodeficiency, and hypersensitivity to genotoxic agents. SIOD is associated with biallelic mutations in SMARCAL1 (SWI/SNF-related matrix-associated actin-dependent regulator of chromatin, subfamily a-like 1), which encodes a DNA stress response enzyme with annealing helicase activity. Two features of SIOD causing much morbidity and mortality are bone marrow failure and T-cell deficiency with the consequent opportunistic infections. To address the safety and efficacy of bone marrow transplantation (BMT) in SIOD, we reviewed the outcomes of the only five SIOD patients known to us in whom bone marrow or hematopoietic stem cell transplantation has been attempted. We find that only one patient survived the transplantation procedure and that the existing indicators of a good prognosis for bone marrow transplantation were not predictive in this small cohort. Given these observations, we also discuss some considerations for the poor outcomes.

Recognizing familial myeloid leukemia in adults

Germline testing for familial cases of myeloid leukemia in adults is becoming more common with the recognition of multiple genetic syndromes predisposing people to bone marrow disease. Currently, Clinical Laboratory Improvement Amendments approved testing exists for several myeloid leukemia predisposition syndromes: familial platelet disorder with propensity to acute myeloid leukemia (FPD/AML), caused by mutations in RUNX1; familial AML with mutated CEBPA; familial myelodysplastic syndrome and acute leukemia with mutated GATA2; and the inherited bone marrow failure syndromes, including dyskeratosis congenita, a disease of abnormal telomere maintenance. With the recognition of additional families with a genetic component to their leukemia, new predisposition alleles will likely be identified. We highlight how to recognize and manage these cases as well as outline the characteristics of the major known syndromes. We look forward to future research increasing our understanding of the scope of inherited myeloid leukemia syndromes.

Outcomes of allogeneic hematopoietic cell transplantation in patients with dyskeratosis congenita

We describe outcomes after allogeneic transplantation in 34 patients with dyskeratosis congenita who underwent transplantation between 1981 and 2009. The median age at transplantation was 13 years (range, 2 to 35). Approximately 50% of transplantations were from related donors. Bone marrow was the predominant source of stem cells (24 of 34). The day-28 probability of neutrophil recovery was 73% and the day-100 platelet recovery was 72%. The day-100 probability of grade II to IV acute GVHD and the 3-year probability of chronic graft-versus-host disease were 24% and 37%, respectively. The 10-year probability of survival was 30%; 14 patients were alive at last follow-up. Ten deaths occurred within 4 months from transplantation because of graft failure (n = 6) or other transplantation-related complications; 9 of these patients had undergone transplantation from mismatched related or from unrelated donors. Another 10 deaths occurred after 4 months; 6 of them occurred more than 5 years after transplantation, and 4 of these were attributed to pulmonary failure. Transplantation regimen intensity and transplantations from mismatched related or unrelated donors were associated with early mortality. Transplantation of grafts from HLA-matched siblings with cyclophosphamide-containing nonradiation regimens was associated with early low toxicity. Late mortality was attributed mainly to pulmonary complications and likely related to the underlying disease.

Dyskeratosis congenita mutations in dyskerin SUMOylation consensus sites lead to impaired telomerase RNA accumulation and telomere defects

Mutations in the dyskerin gene (DKC1) cause X-linked dyskeratosis congenita (DC), a rare and fatal premature aging syndrome characterized by defective telomere maintenance. Dyskerin is a highly conserved nucleolar protein, and a component of the human telomerase complex that is essential for human telomerase RNA (hTR) stability. However, its regulation remains poorly understood. Here, we report that dyskerin can be modified by small ubiquitin-like modifiers (SUMOs). We find that human DC-causing mutations in highly conserved dyskerin SUMOylation consensus sites lead to impaired hTR accumulation, telomerase activity and telomere maintenance. Finally, we show that modification of dyskerin by SUMOylation is required for its stability. Our findings provide the first evidence that dyskerin stability is regulated by SUMOylation and that mutations altering dyskerin SUMOylation can lead to defects in telomere maintenance that are characteristics of DC.

Irreversible leukoencephalopathy after reduced-intensity stem cell transplantation in a dyskeratosis congenita patient with TINF2 mutation

Hematopoietic stem cell transplantation (HSCT) for dyskeratosis congenita (DC) is challenging due to severe treatment-related adverse effects. Development of pulmonary fibrosis or veno-occlusive disease is well described in DC. However, neurological complication after HSCT has not been reported. A 9-year-old Japanese male with DC harboring the TINF2 mutation received reduced-intensity HSCT. Unfortunately, patient developed posterior reversible encephalopathy syndrome-like symptoms plausibly result by combination of thrombotic microangiopathy, graft-versus-host disease, and persistent hypertension and has been persisted mental retardation. Therefore, to decrease risk in DC cases after HSCT, strict control of hypertension, graft-versus-host disease, and thrombotic microangiopathy is required.

Reduced intensity conditioning is effective for hematopoietic SCT in dyskeratosis congenita-related BM failure

BM failure (BMF) is a major and frequent complication of dyskeratosis congenita (DKC). Allogeneic hematopoietic SCT (allo-HSCT) represents the only curative treatment for BMF associated with this condition. Transplant-related morbidity/mortality is common especially after myeloablative conditioning regimens. Herein, we report nine cases of patients with DKC who received an allo-SCT at five different member centers within the Eastern Mediterranean Blood and Marrow Transplantation Registry. Between October 1992 and February 2011, nine DKC patients (male, 7 and female, 2), with a median age at transplantation of 19.1 (4.9-31.1) years, underwent an allo-HSCT from HLA-matched, morphologically normal-related donors (100%). Preparative regimens varied according to different centers, but was reduced intensity conditioning (RIC) in eight patients. Graft source was unstimulated BM in five cases (56%) and G-CSF-mobilized PBSCs in four (44%) cases. The median stem cell dose was 6.79 (2.06-12.4) × 10(6) cells/kg body weight. GVHD prophylaxis consisted of CsA in all nine cases; MTX or mycophenolate mofetil were added in five (56%) and two (22%) cases, respectively. Anti-thymocyte globulin was administered at various doses and scheduled in four (44%) cases. Median time-to-neutrophil engraftment was 21 (17-27) days. In one case, late graft failure was noted at 10.4 months post allo-HSCT. Only one patient developed grade II acute GVHD (11%). Extensive chronic GVHD was reported in one case, whereas limited chronic GVHD occurred in another four cases. At a median follow-up of 61 (0.8-212) months, seven (78%) patients were still alive and transfusion independent. One patient died of metastatic gastric adenocarcinoma and graft failure was the cause of death in another patient. This study suggests that RIC preparative regimens are successful in inducing hematopoietic cell engraftment in patients with BMF from DKC. Owing to the limited sample size, the use of registry data and heterogeneity of preparative as well as GVHD prophylaxis regimens reported in this series, we are unable to recommend a particular regimen to be considered as the standard for patients with this disease.

Telomeres and age-related disease: how telomere biology informs clinical paradigms

Telomere length shortens with age and predicts the onset of replicative senescence. Recently, short telomeres have been linked to the etiology of degenerative diseases such as idiopathic pulmonary fibrosis, bone marrow failure, and cryptogenic liver cirrhosis. These disorders have recognizable clinical manifestations, and the telomere defect explains their genetics and informs the approach to their treatment. Here, I review how telomere biology has become intimately connected to clinical paradigms both for understanding pathophysiology and for individualizing therapy decisions. I also critically examine nuances of interpreting telomere length measurement in clinical studies.

[Dyskeratosis congenita: an update]

Dyskeratosis congenita is a rare inherited bone marrow failure characterized by excessively short telomeres in highly proliferative tissues. These abnormalities are due to disturbance of the telomere maintenance machinery. The clinical presentation is characterized by skin pigmentation, nail dystrophy, and mucosal leukoplakia. All these mucocutaneous features are rare in childhood: they usually appear between 5 and 10 years of age. In young children, the initial presentation can associate bone marrow failure and neurological or ocular problems: Hoyeraal-Hreidarsson and Revesz syndromes, respectively. Clinical progression of the disease can lead to aplastic anemia (86% of all patients) and to pulmonary or hepatic complications. These patients also have an increased risk of cancer. Diagnosis is often suspected on bone marrow failure with no clinical or biological abnormalities compatible with Fanconi anemia diagnosis. The telomere length study can be helpful for diagnosis in case of aplastic anemia in children before studying gene mutations. Until now, 6 genes (DKC1, TERT, TERC, NOLA2, NOLA3, TINF2) have been identified in dyskeratosis congenita. Transmission of the disease can be autosomal recessive, autosomal dominant, or X-linked. In half of the cases, the genetic abnormality is unknown. Treatment of DC has to be adapted to each patient, from symptomatic or androgenic treatment to hematopoietic stem cell transplantation.

Inherited bone marrow failure syndromes in 2012

Inherited bone marrow failure syndromes (CBMFS) are a heterogeneous group of genetic disorders characterized by bone marrow failure, congenital anomalies, and an increased risk of malignant disease. The representative diseases with trilineage involvement are Fanconi anemia and dyskeratosis congenita, while the disease with the single lineage cytopenia is Diamond-Blackfan anemia. Recent advances in our understanding of these diseases have come from the identification of genetic lesions responsible for the disease and their pathways. Although recent studies have identified many causative genes, mutations of these genes have only been found in less than half of the patients. Next-generation sequencing technologies may reveal new causative genes in these patients. Also, induced pluripotent stem cells derived from patients with CBMFS will be useful to study the pathophysiology of the diseases. The only long-term curative treatment for bone marrow failure in patients with inherited bone marrow failure syndromes is allogeneic hematopoietic stem cell transplantation, although this procedure has a risk of severe adverse effects. Multicenter prospective studies are warranted to establish appropriate conditioning regimens aimed at reducing transplant-related mortality.

Posttransplant Lymphoproliferative Disorder Complicating Hematopoietic Stem Cell Transplantation in a Patient With Dyskeratosis Congenita

Dyskeratosis congenita (DC) is a rare inherited disorder characterized by bone marrow failure and cancer predisposition. We present a case of a 28-year-old woman with DC who was admitted for hematopoietic stem cell transplantation (HSCT) for aplastic anemia and who developed acute myeloid leukemia with complex genetic karyotype abnormalities including the MLL (11q23) gene, 1q25, and chromosome 8. After transplantation, a monomorphic Epstein–Barr virus (EBV) negative posttransplant-associated lymphoproliferative disorder (PTLD) diffuse large B-cell lymphoma was discovered involving the liver, omental tissue, and peritoneal fluid samples showing additional MLL (11q23) gene abnormalities by fluorescence in situ hybridization. Despite treatment, the patient died of complications associated with transplantation and invasive fungal infection. This case represents the first bona fide documented case of EBV-negative monomorphic PTLD host derived, with MLL gene abnormalities in a patient with DC, and shows another possible mechanism for the development of a therapy-related lymphoid neoplasm after transplantation.

The telomere syndromes

There has been mounting evidence of a causal role for telomere dysfunction in a number of degenerative disorders. Their manifestations encompass common disease states such as idiopathic pulmonary fibrosis and bone marrow failure. Although these disorders seem to be clinically diverse, collectively they comprise a single syndrome spectrum defined by the short telomere defect. Here we review the manifestations and unique genetics of telomere syndromes. We also discuss their underlying molecular mechanisms and significance for understanding common age-related disease processes.