Loss-of-function germline GATA2 mutations in patients with MDS/AML or MonoMAC syndrome and primary lymphedema reveal a key role for GATA2 in the lymphatic vasculature

GATA2 is required for lymphatic vessel valve development and maintenance

Heterozygous germline mutations in the zinc finger transcription factor GATA2 have recently been shown to underlie a range of clinical phenotypes, including Emberger syndrome, a disorder characterized by lymphedema and predisposition to myelodysplastic syndrome/acute myeloid leukemia (MDS/AML). Despite well-defined roles in hematopoiesis, the functions of GATA2 in the lymphatic vasculature and the mechanisms by which GATA2 mutations result in lymphedema have not been characterized. Here, we have provided a molecular explanation for lymphedema predisposition in a subset of patients with germline GATA2 mutations. Specifically, we demonstrated that Emberger-associated GATA2 missense mutations result in complete loss of GATA2 function, with respect to the capacity to regulate the transcription of genes that are important for lymphatic vessel valve development. We identified a putative enhancer element upstream of the key lymphatic transcriptional regulator PROX1 that is bound by GATA2, and the transcription factors FOXC2 and NFATC1. Emberger GATA2 missense mutants had a profoundly reduced capacity to bind this element. Conditional Gata2 deletion in mice revealed that GATA2 is required for both development and maintenance of lymphovenous and lymphatic vessel valves. Together, our data unveil essential roles for GATA2 in the lymphatic vasculature and explain why a select catalogue of human GATA2 mutations results in lymphedema.

Host susceptibility to non-tuberculous mycobacterial infections

Non-tuberculous mycobacteria cause a broad range of clinical disorders, from cutaneous infections, such as cervical or intrathoracic lymphadenitis in children, to disseminated infections at all ages. Recognition of the underlying immune defect is crucial for rational treatment, preventive care, family screening, and, in some cases, transplantation. So far, at least seven autosomal mutations (in IL12B, IL12RB1, ISG15, IFNGR1, IFNGR2, STAT1, and IRF8) and two X-linked mutations (in IKBKG and CYBB), mostly presenting in childhood, have been reported to confer susceptibility to disseminated non-tuberculous mycobacterial infection. GATA2 deficiency and anti-interferon γ autoantibodies also give rise to disseminated infection, typically in late childhood or adulthood. Furthermore, isolated pulmonary non-tuberculous mycobacterial infection has been increasing in prevalence in people without recognised immune dysfunction. In this Review, we discuss how to detect and differentiate host susceptibility factors underlying localised and systemic non-tuberculous mycobacterial infections.

Low-level GATA2 overexpression promotes myeloid progenitor self-renewal and blocks lymphoid differentiation in mice

The transcription factor GATA2 is highly expressed in hematopoietic stem cells and is downregulated during lineage maturation. Gain of function mutations, loss of function mutations, and overexpression of GATA2 have been reported in acute myeloid leukemia. In previous studies, we and others showed that GATA2 overexpression at high levels, similar to that seen in hematopoietic stem cells, blocked differentiation of hematopoietic stem cells and progenitors. To better understand the effects of GATA2, we designed a Tamoxifen-inducible GATA2-estrogen receptor (ERT) vector. In the absence of Tamoxifen, small amounts of GATA2-ERT were still able to enter the nucleus in mouse bone marrow (BM) cells, providing us with a tool to test the effects of low-level GATA2 overexpression. We observed that this low-level GATA2 overexpression enhanced self-renewal of myeloid progenitors in vitro and resulted in immortalization of BM cells to myeloid cell lines. Continuous GATA2-ERT expression was required for the proliferation of these immortalized lines. Myeloid expansion and a block in T and B lineage differentiation were observed in mice transplanted with GATA2-ERT-expressing BM cells. Myeloid expansion occurred after the granulocyte monocyte progenitor stage, and lymphoid block was distal to the common lymphoid progenitor in transgenic mice. GATA2 appeared to induce growth via downstream activation of Nmyc and Hoxa9. Our results demonstrate that GATA2 overexpression at low level confers self-renewal capacity to myeloid progenitors and is relevant to myeloid leukemia development.

Haematopoietic and immune defects associated with GATA2 mutation

Heterozygous familial or sporadic GATA2 mutations cause a multifaceted disorder, encompassing susceptibility to infection, pulmonary dysfunction, autoimmunity, lymphoedema and malignancy. Although often healthy in childhood, carriers of defective GATA2 alleles develop progressive loss of mononuclear cells (dendritic cells, monocytes, B and Natural Killer lymphocytes), elevated FLT3 ligand, and a 90% risk of clinical complications, including progression to myelodysplastic syndrome (MDS) by 60 years of age. Premature death may occur from childhood due to infection, pulmonary dysfunction, solid malignancy and MDS/acute myeloid leukaemia. GATA2 mutations include frameshifts, amino acid substitutions, insertions and deletions scattered throughout the gene but concentrated in the region encoding the two zinc finger domains. Mutations appear to cause haplo-insufficiency, which is known to impair haematopoietic stem cell survival in animal models. Management includes genetic counselling, prevention of infection, cancer surveillance, haematopoietic monitoring and, ultimately, stem cell transplantation upon the development of MDS or another life-threatening complication.

Germline ETV6 mutations in familial thrombocytopenia and hematologic malignancy

We report germline missense mutations in ETV6 segregating with the dominant transmission of thrombocytopenia and hematologic malignancy in three unrelated kindreds, defining a new hereditary syndrome featuring thrombocytopenia with susceptibility to diverse hematologic neoplasms. Two variants, p.Arg369Gln and p.Arg399Cys, reside in the highly conserved ETS DNA-binding domain. The third variant, p.Pro214Leu, lies within the internal linker domain, which regulates DNA binding. These three amino acid sites correspond to hotspots for recurrent somatic mutation in malignancies. Functional studies show that the mutations abrogate DNA binding, alter subcellular localization, decrease transcriptional repression in a dominant-negative fashion and impair hematopoiesis. These familial genetic studies identify a central role for ETV6 in hematopoiesis and malignant transformation. The identification of germline predisposition to cytopenias and cancer informs the diagnosis and medical management of at-risk individuals.

GATA2 deficiency

PURPOSE OF REVIEW

GATA2 deficiency is a germline disease that causes a wide spectrum of phenotypes including viral and bacterial infections, cytopenias, myelodysplasia, myeloid leukemias, pulmonary alveolar proteinosis and lymphedema. The age of clinical presentation ranges from early childhood to late adulthood, with most occurring in adolescence to early adulthood. We review the expanding GATA2-deficient phenotype, molecular genetics of disease and developments in treatment.

RECENT FINDINGS

GATA2 mutations have been found in up to 10% of those with congenital neutropenia and/or aplastic anemia. Heterozygous mutations appear to cause haploinsufficiency due to either protein dysfunction or uniallelic reduced transcription. Disease-associated mutations in intronic regulatory elements or variations within the 5' leader exons indicate that regulation of GATA2 is critical. Those with GATA2 mutations are at high risk for myelodysplasia, cytogenetic abnormalities, acute myeloid leukemia or chronic myelomonocytic leukemia. Bone marrow transplantation has been successful for both hematopoietic and pulmonary alveolar proteinosis repair.

SUMMARY

GATA2 is a zinc finger transcription factor essential for embryonic and definitive hematopoiesis as well as lymphatic angiogenesis. GATA2 deficiency is caused by a variety of mutations in the GATA2 gene and can have variable presentation, onset and outcome. Patients are susceptible to mycobacterial, viral and fungal infections and can develop myelodysplasia, acute or chronic leukemias, lymphedema and pulmonary alveolar proteinosis. Hematopoietic stem cell transplantation reverses most of the clinical phenotype with good long-term outcomes.

Spectrum of myeloid neoplasms and immune deficiency associated with germline GATA2 mutations

Guanine-adenine-thymine-adenine 2 (GATA2) mutated disorders include the recently described MonoMAC syndrome (Monocytopenia and Mycobacterium avium complex infections), DCML (dendritic cell, monocyte, and lymphocyte deficiency), familial MDS/AML (myelodysplastic syndrome/acute myeloid leukemia) (myeloid neoplasms), congenital neutropenia, congenital lymphedema (Emberger's syndrome), sensorineural deafness, viral warts, and a spectrum of aggressive infections seen across all age groups. While considerable efforts have been made to identify the mutations that characterize this disorder, pathogenesis remains a work in progress with less than 100 patients described in current literature. Varying clinical presentations offer diagnostic challenges. Allogeneic stem cell transplant remains the treatment of choice. Morbidity, mortality, and social costs due to the familial nature of the disease are considerable. We describe our experience with the disorder in three affected families and a comprehensive review of current literature.

A woman with warts, leg swelling, and deafness

KEY TEACHING POINTS • We describe a 45-year-old woman with GATA2 deficiency associated with verrucae, lymphedema, immunodeficiency, and a history of infections and skin cancer. • GATA2 deficiency has variable clinical expressivity with differing presentations, including infection, hematopoietic abnormalities, immunodeficiency, lymphedema, and cancer. • Cutaneous manifestations include verruca vulgaris, soft tissue infections, lymphedema, and panniculitis. • Patients may have verrucae that can progress to squamous cell carcinomas; dermatologists therefore play an important role in managing these patients as members of a multidisciplinary team.

Generalized verrucosis in a patient with GATA2 deficiency

Generalized verrucosis is a characteristic of several genetic and immunodeficiency disorders including epidermodysplasia verruciformis; warts, hypogammaglobulinaemia, infections and myelokathexis (WHIM) syndrome; warts, immunodeficiency, lymphoedema and anogenital dysplasia (WILD) syndrome; severe combined immune deficiency and HIV, among others. In recent years, it has been consistently recognized in patients with GATA2 deficiency, a novel immunodeficiency syndrome characterized by monocytopenia, B-cell and natural killer-cell lymphopenia, and a tendency to develop myeloid leukaemias and disseminated mycobacterial, human papillomavirus (HPV) and opportunistic fungal infections. Mutations in GATA2 cause haploinsufficiency and track in families as an autosomal dominant immunodeficiency. GATA2 is a transcription factor involved in early haematopoietic differentiation and lymphatic and vascular development. We describe a case of generalized verrucosis with HPV type 57 presenting in a young man with GATA2 deficiency. GATA2 deficiency is a novel dominant immunodeficiency that is often recognized later in life and should be considered in the differential diagnosis of patients with generalized verrucosis.

Tie1 is required for lymphatic valve and collecting vessel development

Tie1 is a receptor tyrosine kinase with broad expression in embryonic endothelium. Reduction of Tie1 levels in mouse embryos with a hypomorphic Tie1 allele resulted in abnormal lymphatic patterning and architecture, decreased lymphatic draining efficiency, and ultimately, embryonic demise. Here we report that Tie1 is present uniformly throughout the lymphatics and from late embryonic/early postnatal stages, becomes more restricted to lymphatic valve regions. To investigate later events of lymphatic development, we employed Cre-loxP recombination utilizing a floxed Tie1 allele and an Nfatc1Cre line, to provide loxP excision predominantly in lymphatic endothelium and developing valves. Interestingly, unlike the early prenatal defects previously described by ubiquitous endothelial deletion, excision of Tie1 with Nfatc1Cre resulted in abnormal lymphatic defects in postnatal mice and was characterized by agenesis of lymphatic valves and a deficiency of collecting lymphatic vessels. Attenuation of Tie1 signaling in lymphatic endothelium prevented initiation of lymphatic valve specification by Prox1 high expression lymphatic endothelial cells that is associated with the onset of turbulent flow in the lymphatic circulation. Our findings reveal a fundamental role for Tie1 signaling during lymphatic vessel remodeling and valve morphogenesis and implicate it as a candidate gene involved in primary lymphedema.

Genetics of hemangiomas, vascular malformations, and primary lymphedema

With improved genetic testing and genomic sequencing, abnormalities are increasingly being identified in affected or germline tissues in DNA of patients with vascular tumors, vascular malformations, and lymphedema. Recognition of the genetics of vascular anomalies should help clinicians make more specific diagnoses, anticipate diagnosis-specific morbidities, provide better genetic counseling, and have a better understanding of the pathogenesis of these anomalies. Growing pharmacologic options, including therapies targeted to specific mutations, with obvious parallels to cancer treatment now allow the pediatric hematologist-oncologist to assume a more prominent role in clinical care and research for patients with these diagnoses. We summarize genes and genetic loci that have been associated with vascular anomalies and offer guidelines for patient evaluations.

GATA2 deficiency-associated bone marrow disorder differs from idiopathic aplastic anemia

Germ-line GATA2 gene mutations, leading to haploinsufficiency, have been identified in patients with familial myelodysplastic syndrome/acute myeloid leukemia, monocytopenia and mycobacterial infections, Emberger syndrome, and dendritic cell, monocyte, B-, and NK-cell deficiency. GATA2 mutations have also been reported in a minority of patients with congenital neutropenia and aplastic anemia (AA). The bone marrow (BM) from patients with GATA2 deficiency is typically hypocellular, with varying degrees of dysplasia. Distinguishing GATA2 patients from those with AA is critical for selecting appropriate therapy. We compared the BM flow cytometric, morphologic, and cytogenetic features of 28 GATA2 patients with those of 32 patients being evaluated for idiopathic AA. The marrow of GATA2 patients had severely reduced monocytes, B cells, and NK cells; absent hematogones; and inverted CD4:CD8 ratios. Atypical megakaryocytes and abnormal cytogenetics were more common in GATA2 marrows. CD34(+) cells were comparably reduced in GATA2 and AA. Using these criteria, we prospectively identified 4 of 32 patients with suspected AA who had features suspicious for GATA2 mutations, later confirmed by DNA sequencing. Our results show that routine BM flow cytometry, morphology, and cytogenetics in patients who present with cytopenia(s) can identify patients for whom GATA2 sequencing is indicated.

Genomic analysis of bone marrow failure and myelodysplastic syndromes reveals phenotypic and diagnostic complexity

Accurate and timely diagnosis of inherited bone marrow failure and inherited myelodysplastic syndromes is essential to guide clinical management. Distinguishing inherited from acquired bone marrow failure/myelodysplastic syndrome poses a significant clinical challenge. At present, diagnostic genetic testing for inherited bone marrow failure/myelodysplastic syndrome is performed gene-by-gene, guided by clinical and laboratory evaluation. We hypothesized that standard clinically-directed genetic testing misses patients with cryptic or atypical presentations of inherited bone marrow failure/myelodysplastic syndrome. In order to screen simultaneously for mutations of all classes in bone marrow failure/myelodysplastic syndrome genes, we developed and validated a panel of 85 genes for targeted capture and multiplexed massively parallel sequencing. In patients with clinical diagnoses of Fanconi anemia, genomic analysis resolved subtype assignment, including those of patients with inconclusive complementation test results. Eight out of 71 patients with idiopathic bone marrow failure or myelodysplastic syndrome were found to harbor damaging germline mutations in GATA2, RUNX1, DKC1, or LIG4. All 8 of these patients lacked classical clinical stigmata or laboratory findings of these syndromes and only 4 had a family history suggestive of inherited disease. These results reflect the extensive genetic heterogeneity and phenotypic complexity of bone marrow failure/myelodysplastic syndrome phenotypes. This study supports the integration of broad unbiased genetic screening into the diagnostic workup of children and young adults with bone marrow failure and myelodysplastic syndromes.

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.

Genetics of vascular malformations

Vascular anomalies are developmental defects of the vasculature and encompass a variety of disorders. The majority of these occur sporadically, yet a few are reported to be familial. The identification of genes mutated in the different malformations provides insight into their etiopathogenic mechanisms and the specific roles the associated proteins play in vascular development and maintenance. It is becoming evident that somatic mosaicism plays a major role in the formation of vascular lesions. The importance of utilizing Next-Generating Sequencing (NGS) for high-throughput and "deep" screening of both blood and lesional DNA and RNA is thus emphasized, as the somatic changes are present in low quantities. There are several examples where NGS has already accomplished discovering these changes. The identification of all the causative genes and unraveling of a holistic overview of the pathogenic mechanisms should enable generation of in vitro and in vivo models and lead to development of more effective treatments, not only targeted on symptoms.

Primary and secondary lymphatic valve development: molecular, functional and mechanical insights

Fluid homeostasis in vertebrates critically relies on the lymphatic system forming a hierarchical network of lymphatic capillaries and collecting lymphatics, for the efficient drainage and transport of extravasated fluid back to the cardiovascular system. Blind-ended lymphatic capillaries employ specialized junctions and anchoring filaments to encourage a unidirectional flow of the interstitial fluid into the initial lymphatic vessels, whereas collecting lymphatics are responsible for the active propulsion of the lymph to the venous circulation via the combined action of lymphatic muscle cells and intraluminal valves. Here we describe recent findings on molecular and physical factors regulating the development and maturation of these two types of valves and examine their role in tissue-fluid homeostasis.

Lymphatic collecting vessel maturation and valve morphogenesis

The lymphatic vasculature plays an essential role in the maintenance of tissue interstitial fluid balance and in the immune response. After capture of fluids, proteins and antigens by lymphatic capillaries, lymphatic collecting vessels ensure lymph transport. An important component to avoid lymph backflow and to allow a unidirectional flow is the presence of intraluminal valves. Defects in the function of collecting vessels lead to lymphedema. Several important factors and signaling pathways involved in lymphatic collecting vessel maturation and valve morphogenesis have now been discovered. The present review summarizes the current knowledge about the key steps of lymphatic collecting vessel development and maturation and focuses on the regulatory mechanisms involved in lymphatic valve formation.

Allergic diseases and risk of hematopoietic malignancies in a cohort of postmenopausal women: a report from the Iowa Women's Health Study

BACKGROUND

Allergic diseases signify immune dysregulation attributable to underlying genetics and environmental exposures. Associations between various allergies and hematopoietic cancers have been observed, albeit inconsistently; however, few prospective studies have examined the risk, and even fewer among older adults.

METHODS

We examined risk of incident hematopoietic cancers in those reporting allergic diseases in a population-based cohort of 22,601 older women (Iowa Women's Health Study). Self-reported allergic status, including asthma, hay fever, eczema, and/or other allergies, was determined via questionnaire in 1997 (mean age, 72 years; range, 63-81 years). Incident cancers were ascertained by linkage with the Iowa Cancer Registry from 1997 to 2011. Cox proportional hazards regression was performed to estimate multivariate-adjusted HR and 95% confidence intervals (CI) for myeloid (N = 177) and lymphoid (N = 437) malignancies, respectively.

RESULTS

Allergic diseases were not associated with risk of myeloid (HR, 1.00; 95% CI, 0.72-1.37) or lymphoid (HR, 0.99; 95% CI, 0.81-1.22) malignancies overall, or for most allergic and malignant subtypes examined. Self-reported asthma was positively associated with development of myelodysplastic syndrome (MDS; HR, 2.00; 95% CI, 0.93-4.32). In addition, there was a 30% to 40% decrease in risk of both lymphoid and myeloid cancers in those reporting rural residences but no association in those reporting urban residences; the interaction between residence and allergy was statistically significant for lymphoid malignancies (Pinteraction = 0.05).

CONCLUSIONS AND IMPACT

These results suggest that asthma may contribute to the pathogenesis of MDS, a finding consistent with the chronic antigen stimulation hypothesis. Susceptibility differences by location of residence are concordant with the hygiene hypothesis and merit additional exploration.

Molecular and cellular mechanisms of lymphatic vascular maturation

Lymphatic vasculature is necessary for maintaining fluid homeostasis in vertebrates. During embryogenesis lymphatic endothelial cells originate from the veins as a homogeneous population. These cells undergo a series of changes at the morphological and molecular levels to become mature lymphatic vasculature that consists of lymphatic capillaries, collecting lymphatic vessels and valves. In this article we summarize our current knowledge about these steps and highlight some black boxes that require further clarification.

The challenging world of cytopenias: distinguishing myelodysplastic syndromes from other disorders of marrow failure

Over the past decade, our understanding of bone marrow failure has advanced considerably. Marrow failure encompasses multiple overlapping diseases, and there is increasing availability of diagnostic tools to distinguish among the subtypes. Identification of genetic alterations that underlie marrow failure has also greatly expanded, especially for myelodysplastic syndromes. Molecular markers are increasingly used to guide the management of myelodysplasia and may distinguish this diagnosis from other marrow failure disorders. This review summarizes the current state of distinguishing among causes of marrow failure and discusses the potential uses of multiple diagnostic and prognostic indicators in the management of myelodysplastic syndromes and other bone marrow failure disorders.

Inborn errors of the development of human natural killer cells

PURPOSE OF REVIEW

Inborn errors of human natural killer (NK) cells may affect the development of these cells, their function, or both. There are two broad categories of genetic defects of NK cell development, depending on whether the deficiency is apparently specific to NK cells or clearly affects multiple hematopoietic lineages. We review here recent progress in the genetic dissection of these NK deficiencies (NKDs).

RECENT FINDINGS

Patients with severe combined immunodeficiencies bearing mutations of adenosine deaminase, adenylate kinase 2, interleukin-2 receptor gamma chain, and Janus kinase 3 genes present NKDs and are prone to a broad range of infections. Patients with GATA binding protein 2 deficiency are susceptible to both mycobacterial and viral infections, and display NKDs and a lack of monocytes. Rare patients with mini chromosomal maintenance 4 deficiency display an apparently selective NKD associated with viral infections, but they also display various nonhematopoietic phenotypes, including adrenal insufficiency and growth retardation.

SUMMARY

These studies have initiated a genetic dissection of the development of human NK cells. Further studies are warranted, including the search for genetic causes of NKD in particular. This research may lead to the discovery of molecules specifically controlling the development of NK cells and to improvements in our understanding of the hitherto elusive function of these cells in humans.

Genetic Dissection of Tie Pathway in Mouse Lymphatic Maturation and Valve Development

Objective—

The genetic program underlying lymphatic development is still incompletely understood. This study aims to dissect the role of receptor tyrosine kinase with immunoglobulin-like and EGF (epidermal growth factor)-like domains 1 (Tie1) and Tie2 in lymphatic formation using genetically modified mouse models.

Approach and Results—

We generated conditional knockout mouse models targeting Tie1, Tie2, and angiopoietin-2 in this study. Tie1 Δ ICD /Δ ICD mice, with its intracellular domain targeted, appeared normal at E10.5 but displayed subcutaneous edema by E13.5. Lymph sac formation occurred in Tie1 Δ ICD /Δ ICD mice, but they had defects with the remodeling of primary lymphatic network to form collecting vessels and valvulogenesis. Consistently, induced deletion of Tie1-ICD postnatally using a ubiquitous Cre deleter led to abnormal lymphangiogenesis and valve formation in Tie1-ICD iUCKO/ − mice. In comparison with the lymphatic phenotype of Tie1 mutants, we found that the diameter of lymphatic capillaries was significantly less in mice deficient of angiopoietin-2, besides the disruption of collecting lymphatic vessel formation as previously reported. There was also no lymphedema observed in Ang2 −/− mice during embryonic development, which differs from that of Tie1 Δ ICD /Δ ICD mice. We further investigated whether Tie1 exerted its function via Tie2 during lymphatic development. To our surprise, genetic deletion of Tie2 ( Tie2 iUCKO/ − ) in neonate mice did not affect lymphatic vessel growth and maturation.

Conclusions—

In contrast to the important role of Tie2 in the regulation of blood vascular development, Tie1 is crucial in the process of lymphatic remodeling and maturation, which is independent of Tie2.

Heritable GATA2 mutations associated with familial AML-MDS: a case report and review of literature

A 50-year-old woman was diagnosed with acute myeloid leukemia (AML). She has history of thrombocytopenia for 25 years and a significant family history of thrombocytopenia, affecting her mother, siblings and their children, as well as her own children. Both her mother and maternal aunt died from myelodysplastic syndrome (MDS). Additional genetic analysis was performed and identified two heterozygous missence mutations in the second zinc finger domain of GATA2 gene (p.Thr358Lys, and p.Leu359Val), occurring in cis on the same allele. Given the patient’s family history and clinical manifestation, this was interpreted as an acute myeloid leukemia with heritable GATA2 mutations associated with familial AML-MDS. Germline GATA2 mutations are involved in a group of complex syndromes with overlapping clinical features of immune deficiency, lymphedema and propensity to acute myeloid leukemia or myelodysplastic syndrome (AML-MDS). Here we reported a case of familial AML-MDS with two novel GATA2 mutations. This case illustrates the importance of recognizing the clinical features for this rare category of AML-MDS and performing the appropriate molecular testing. The diagnosis of heritable gene mutations associated familial AML-MDS has significant clinical implication for the patients and affected families. Clinical trials are available to further investigate the role of allogeneic hematopoietic stem cell transplant in managing these patients.

Genetics of lymphatic anomalies

Lymphatic anomalies include a variety of developmental and/or functional defects affecting the lymphatic vessels: sporadic and familial forms of primary lymphedema, secondary lymphedema, chylothorax and chylous ascites, lymphatic malformations, and overgrowth syndromes with a lymphatic component. Germline mutations have been identified in at least 20 genes that encode proteins acting around VEGFR-3 signaling but also downstream of other tyrosine kinase receptors. These mutations exert their effects via the RAS/MAPK and the PI3K/AKT pathways and explain more than a quarter of the incidence of primary lymphedema, mostly of inherited forms. More common forms may also result from multigenic effects or post-zygotic mutations. Most of the corresponding murine knockouts are homozygous lethal, while heterozygotes are healthy, which suggests differences in human and murine physiology and the influence of other factors.

Development of the mammalian lymphatic vasculature

The two vascular systems of our body are the blood and lymphatic vasculature. Our understanding of the cellular and molecular processes controlling the development of the lymphatic vasculature has progressed significantly in the last decade. In mammals, this is a stepwise process that starts in the embryonic veins, where lymphatic EC (LEC) progenitors are initially specified. The differentiation and maturation of these progenitors continues as they bud from the veins to produce scattered primitive lymph sacs, from which most of the lymphatic vasculature is derived. Here, we summarize our current understanding of the key steps leading to the formation of a functional lymphatic vasculature.

Familial myelodysplastic syndrome/acute leukemia syndromes: a review and utility for translational investigations

The familial myelodysplastic (MDS)/acute leukemia (AL) predisposition syndromes are inherited disorders that lead to significantly increased lifetime risks of MDS and AL development. At present, four recognized syndromes have Clinical Laboratory Improvement Amendments--certified testing for their respective germ-line mutations: telomere biology disorders due to mutation of TERC or TERT, familial acute myeloid leukemia (AML) with mutated CEBPA, familial MDS/AML with mutated GATA2, and familial platelet disorder with propensity to myeloid malignancy. These disorders are heterogeneous with regard to their causative genetic mutations, clinical presentation, and progression to MDS/AL. However, as a group, they all share the unique requirement for a high index of clinical suspicion to allow appropriate genetic counseling, genetic testing, and mutation-specific clinical management. In addition, translational investigations of individuals and families with these syndromes provide a rare opportunity to understand key pathways underlying susceptibility and progression to MDS/AL and allow the possibility of novel strategies for the prevention and treatment of both familial and sporadic forms of MDS/AL.

Transcriptional control of lymphatic endothelial cell type specification

The lymphatic vasculature is the "sewer system" of our body as it plays an important role in transporting tissue fluids and extravasated plasma proteins back to the blood circulation and absorbs lipids from the intestinal tract. Malfunction of the lymphatic vasculature can result in lymphedema and obesity. The lymphatic system is also important for the immune response and is one of the main routes for the spreading of metastatic tumor cells. The development of the mammalian lymphatic vasculature is a stepwise process that requires the specification of lymphatic endothelial cell (LEC) progenitors in the embryonic veins, and the subsequent budding of those LEC progenitors from the embryonic veins to give rise to the primitive lymph sacs from which the entire lymphatic vasculature will eventually be derived. This process was first proposed by Florence Sabin over a century ago and was recently confirmed by several studies using lineage tracing and gene manipulation. Over the last decade, significant advances have been made in understanding the transcriptional control of lymphatic endothelial cell type differentiation. Here we summarize our current knowledge about the key transcription factors that are necessary to regulate several aspects of lymphatic endothelial specification and differentiation.

Interplay of mechanotransduction, FOXC2, connexins, and calcineurin signaling in lymphatic valve formation

The directional flow of lymph is maintained by hundreds of intraluminal lymphatic valves. Lymphatic valves are crucial to prevent lymphedema, accumulation of fluid in the tissues, and to ensure immune surveillance; yet, the mechanisms of valve formation are only beginning to be elucidated. In this chapter, we will discuss the main steps of lymphatic valve morphogenesis, the important role of mechanotransduction in this process, and the genetic program regulated by the transcription factor Foxc2, which is indispensable for all steps of valve development. Failure to form mature collecting lymphatic vessels and valves causes the majority of postsurgical lymphedema, e.g., in breast cancer patients. Therefore, this knowledge will be useful for diagnostics and development of better treatments of secondary lymphedema.

Cellular stress pathways in pediatric bone marrow failure syndromes: many roads lead to neutropenia

The inherited bone marrow failure syndromes, like severe congenital neutropenia (SCN) and Shwachman-Diamond syndrome (SDS), provide unique insights into normal and impaired myelopoiesis. The inherited neutropenias are heterogeneous in both clinical presentation and genetic associations, and their causative mechanisms are not well established. SCN, for example, is a genetically heterogeneous syndrome associated with mutations of ELANE, HAX1, GFI1, WAS, G6PC3, or CSF3R. The genetic diversity in SCN, along with congenital neutropenias associated with other genetically defined bone marrow failure syndromes (e.g., SDS), suggests that various pathways may be involved in their pathogenesis. Alternatively, all may lead to a final common pathway of enhanced apoptosis. The pursuit for a more complete understanding of the molecular mechanisms that drive inherited neutropenias remains at the forefront of pediatric translational and basic science investigation. Advances in our understanding of these disorders have greatly increased over the last 10 years concomitant with identification of their genetic lesions. Emerging themes include induction of the unfolded protein response (UPR), defective ribosome assembly, and p53-dependent apoptosis. Additionally, defects in metabolism, disruption of mitochondrial membrane potential, and mislocalization have been found. When perturbed, each of these lead to an intracellular stress that triggers apoptosis in the vulnerable granulocytic precursor.

The evolution of cellular deficiency in GATA2 mutation

Constitutive heterozygous GATA2 mutation is associated with deafness, lymphedema, mononuclear cytopenias, infection, myelodysplasia (MDS), and acute myeloid leukemia. In this study, we describe a cross-sectional analysis of 24 patients and 6 relatives with 14 different frameshift or substitution mutations of GATA2. A pattern of dendritic cell, monocyte, B, and natural killer (NK) lymphoid deficiency (DCML deficiency) with elevated Fms-like tyrosine kinase 3 ligand (Flt3L) was observed in all 20 patients phenotyped, including patients with Emberger syndrome, monocytopenia with Mycobacterium avium complex (MonoMAC), and MDS. Four unaffected relatives had a normal phenotype indicating that cellular deficiency may evolve over time or is incompletely penetrant, while 2 developed subclinical cytopenias or elevated Flt3L. Patients with GATA2 mutation maintained higher hemoglobin, neutrophils, and platelets and were younger than controls with acquired MDS and wild-type GATA2. Frameshift mutations were associated with earlier age of clinical presentation than substitution mutations. Elevated Flt3L, loss of bone marrow progenitors, and clonal myelopoiesis were early signs of disease evolution. Clinical progression was associated with increasingly elevated Flt3L, depletion of transitional B cells, CD56(bright) NK cells, naïve T cells, and accumulation of terminally differentiated NK and CD8(+) memory T cells. These studies provide a framework for clinical and laboratory monitoring of patients with GATA2 mutation and may inform therapeutic decision-making.

GATA2 deficiency: a protean disorder of hematopoiesis, lymphatics, and immunity

Haploinsufficiency of the hematopoietic transcription factor GATA2 underlies monocytopenia and mycobacterial infections; dendritic cell, monocyte, B, and natural killer (NK) lymphoid deficiency; familial myelodysplastic syndromes (MDS)/acute myeloid leukemia (AML); and Emberger syndrome (primary lymphedema with MDS). A comprehensive examination of the clinical features of GATA2 deficiency is currently lacking. We reviewed the medical records of 57 patients with GATA2 deficiency evaluated at the National Institutes of Health from January 1, 1992, to March 1, 2013, and categorized mutations as missense, null, or regulatory to identify genotype-phenotype associations. We identified a broad spectrum of disease: hematologic (MDS 84%, AML 14%, chronic myelomonocytic leukemia 8%), infectious (severe viral 70%, disseminated mycobacterial 53%, and invasive fungal infections 16%), pulmonary (diffusion 79% and ventilatory defects 63%, pulmonary alveolar proteinosis 18%, pulmonary arterial hypertension 9%), dermatologic (warts 53%, panniculitis 30%), neoplastic (human papillomavirus+ tumors 35%, Epstein-Barr virus+ tumors 4%), vascular/lymphatic (venous thrombosis 25%, lymphedema 11%), sensorineural hearing loss 76%, miscarriage 33%, and hypothyroidism 14%. Viral infections and lymphedema were more common in individuals with null mutations (P = .038 and P = .006, respectively). Monocytopenia, B, NK, and CD4 lymphocytopenia correlated with the presence of disease (P < .001). GATA2 deficiency unites susceptibility to MDS/AML, immunodeficiency, pulmonary disease, and vascular/lymphatic dysfunction. Early genetic diagnosis is critical to direct clinical management, preventive care, and family screening.

Acquired ASXL1 mutations are common in patients with inherited GATA2 mutations and correlate with myeloid transformation

Inherited or sporadic heterozygous mutations in the transcription factor GATA2 lead to a clinical syndrome characterized by non-tuberculous mycobacterial and other opportunistic infections, a severe deficiency in monocytes, B cells and natural killer cells, and progression from a hypocellular myelodysplastic syndrome to myeloid leukemias. To identify acquired somatic mutations associated with myeloid transformation in patients with GATA2 mutations, we sequenced the region of the ASXL1 gene previously associated with transformation from myelodysplasia to myeloid leukemia. Somatic, heterozygous ASXL1 mutations were identified in 14/48 (29%) of patients with GATA2 deficiency, including four out of five patients who developed a proliferative chronic myelomonocytic leukemia. Although patients with GATA2 mutations had a similarly high incidence of myeloid transformation when compared to previously described patients with ASXL1 mutations, GATA2 deficiency patients with acquired ASXL1 mutation were considerably younger, almost exclusively female, and had a high incidence of transformation to a proliferative chronic myelomonocytic leukemia. These patients may benefit from allogeneic hematopoietic stem cell transplantation before the development of acute myeloid leukemia or chronic myelomonocytic leukemia. (ClinicalTrials.gov identifier NCT00018044, NCT00404560, NCT00001467, NCT00923364.).

Applications of high-throughput DNA sequencing to benign hematology

The development of novel technologies for high-throughput DNA sequencing is having a major impact on our ability to measure and define normal and pathologic variation in humans. This review discusses advances in DNA sequencing that have been applied to benign hematologic disorders, including those affecting the red blood cell, the neutrophil, and other white blood cell lineages. Relevant examples of how these approaches have been used for disease diagnosis, gene discovery, and studying complex traits are provided. High-throughput DNA sequencing technology holds significant promise for impacting clinical care. This includes development of improved disease detection and diagnosis, better understanding of disease progression and stratification of risk of disease-specific complications, and development of improved therapeutic strategies, particularly patient-specific pharmacogenomics-based therapy, with monitoring of therapy by genomic biomarkers.

Mutations in the VEGFR3 signaling pathway explain 36% of familial lymphedema

Lymphedema is caused by dysfunction of lymphatic vessels, leading to disabling swelling that occurs mostly on the extremities. Lymphedema can be either primary (congenital) or secondary (acquired). Familial primary lymphedema commonly segregates in an autosomal dominant or recessive manner. It can also occur in combination with other clinical features. Nine mutated genes have been identified in different isolated or syndromic forms of lymphedema. However, the prevalence of primary lymphedema that can be explained by these genetic alterations is unknown. In this study, we investigated 7 of these putative genes. We screened 78 index patients from families with inherited lymphedema for mutations in FLT4, GJC2, FOXC2, SOX18, GATA2, CCBE1, and PTPN14. Altogether, we discovered 28 mutations explaining 36% of the cases. Additionally, 149 patients with sporadic primary lymphedema were screened for FLT4, FOXC2, SOX18, CCBE1, and PTPN14. Twelve mutations were found that explain 8% of the cases. Still unidentified is the genetic cause of primary lymphedema in 64% of patients with a family history and 92% of sporadic cases. Identification of those genes is important for understanding of etiopathogenesis, stratification of treatments and generation of disease models. Interestingly, most of the proteins that are encoded by the genes mutated in primary lymphedema seem to act in a single functional pathway involving VEGFR3 signaling. This underscores the important role this pathway plays in lymphatic development and function and suggests that the unknown genes also have a role.

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.

Genetic predispositions to childhood leukemia

While the majority of leukemia cases occur in the absence of any known predisposing factor, there are germline mutations that significantly increase the risk of developing hematopoietic malignancies in childhood. In this review article, we describe a number of these mutations and their clinical features. These predispositions can be broadly classified as those leading to bone marrow failure, those involving tumor suppressor genes, DNA repair defects, immunodeficiencies or other congenital syndromes associated with transient myeloid disorders. While leukemia can develop as a secondary event in the aforementioned syndromes, there are also several syndromes that specifically lead to the development of leukemia as their primary phenotype. Many of the genes discussed in this review can also be somatically mutated in other cancers, highlighting the importance of understanding shared alterations and mechanisms underpinning syndromic and sporadic leukemia.

GATA2 and Lmo2 control angiogenesis and lymphangiogenesis via direct transcriptional regulation of neuropilin-2

GATA-binding protein 2 (GATA2) and LIM domain only 2 (Lmo2) form common transcription complexes during hematopoietic differentiation. Here we show that these two transcription factors also play a key role in endothelial cells (EC) and lymphatic EC (LEC) function. Primary EC and tumor-associated blood vessels expressed GATA2 and Lmo2. VEGF-induced sprouting angiogenesis in both differentiating embryonic stem cells (embryoid bodies) and primary EC increased GATA2 and Lmo2 levels. Conversely, silencing of GATA2 and Lmo2 expression in primary EC inhibited VEGF-induced angiogenic activity, including EC migration and sprouting in vitro, two key steps of angiogenesis in vivo. This inhibition of EC function was associated with downregulated expression of neuropilin-2 (NRP2), a co-receptor of VEGFRs for VEGF, at the protein, mRNA and promoter levels. NRP2 overexpression partially rescued the impaired angiogenic sprouting in the GATA2/Lmo2 knockdown EC, confirming that GATA2 and Lmo2 mediated EC function, at least in part, by directly regulating NRP2 gene expression. Furthermore, it was found that primary LEC expressed GATA2 and Lmo2 as well. Silencing of GATA2 and Lmo2 expression in LEC inhibited VEGF-induced LEC sprouting, also in a NRP2-dependent manner. In conclusion, our results demonstrate that GATA2 and Lmo2 cooperatively regulate VEGF-induced angiogenesis and lymphangiogenesis via NRP2.

The cup runneth over: lessons from the ever-expanding pool of primary immunodeficiency diseases

A recent surge in newly described primary immunodeficiencies (PIDs) has highlighted new physiological and pathophysiological pathways that affect the immune system. Furthermore, the study of individuals with PIDs has substantially improved our understanding of basic cellular and signalling pathways in host defence and immune regulation. Single-gene defects can lead to disease manifestations that range from extremely narrow infectious phenotypes to remarkably broad multisystem effects. Hypomorphic or hypermorphic gene mutations often occur in human diseases; when coupled with the fact that humans are exposed to naturally encountered antigens and pathogens, this helps to make the case that the study of immunological diseases in humans should be at the forefront of basic immunological research.

The classification and diagnostic algorithm for primary lymphatic dysplasia: an update from 2010 to include molecular findings

Historically, primary lymphoedema was classified into just three categories depending on the age of onset of swelling; congenital, praecox and tarda. Developments in clinical phenotyping and identification of the genetic cause of some of these conditions have demonstrated that primary lymphoedema is highly heterogenous. In 2010, we introduced a new classification and diagnostic pathway as a clinical and research tool. This algorithm has been used to delineate specific primary lymphoedema phenotypes, facilitating the discovery of new causative genes. This article reviews the latest molecular findings and provides an updated version of the classification and diagnostic pathway based on this new knowledge.

MonoMAC syndrome in a patient with a GATA2 mutation: case report and review of the literature

We report a case of MonoMAC syndrome in a patient with a GATA2 mutation and discuss the manifestations, diagnosis, and treatment of this novel immunodeficiency disorder.

Getting out and about: the emergence and morphogenesis of the vertebrate lymphatic vasculature

The lymphatic vascular system develops from the pre-existing blood vasculature of the vertebrate embryo. New insights into lymphatic vascular development have recently been achieved with the use of alternative model systems, new molecular tools, novel imaging technologies and growing interest in the role of lymphatic vessels in human disorders. The signals and cellular mechanisms that facilitate the emergence of lymphatic endothelial cells from veins, guide migration through the embryonic environment, mediate interactions with neighbouring tissues and control vessel maturation are beginning to emerge. Here, we review the most recent advances in lymphatic vascular development, with a major focus on mouse and zebrafish model systems.

Mutations in GATA2 cause human NK cell deficiency with specific loss of the CD56(bright) subset

Mutations in the transcription factor GATA2 underlie the syndrome of monocytopenia and B- and natural killer (NK)-cell lymphopenia associated with opportunistic infections and cancers. In addition, patients have recurrent and severe viral infections. NK cells play a critical role in mediating antiviral immunity. Human NK cells are thought to mature in a linear fashion, with the CD56(bright) stage preceding terminal maturation to the CD56(dim) stage, considered the most enabled for cytotoxicity. Here we report an NK cell functional defect in GATA2-deficient patients and extend this genetic lesion to what is considered to be the original NK cell-deficient patient. In most cases, GATA2 deficiency is accompanied by a severe reduction in peripheral blood NK cells and marked functional impairment. The NK cells detected in peripheral blood of some GATA2-deficient patients are exclusively of the CD56(dim) subset, which is recapitulated on in vitro NK cell differentiation. In vivo, interferon α treatment increased NK cell number and partially restored function but did not correct the paucity of CD56(bright) cells. Thus, GATA2 is required for the maturation of human NK cells and the maintenance of the CD56(bright) pool in the periphery. Defects in GATA2 are a novel cause of profound NK cell dysfunction.

GATA2 haploinsufficiency caused by mutations in a conserved intronic element leads to MonoMAC syndrome

Previous reports of GATA2 mutations have focused on the coding region of the gene or full gene deletions. We recently identified 2 patients with novel insertion/deletion mutations predicted to result in mRNA nonsense-mediated decay, suggesting haploinsufficiency as the mechanism of GATA2 deficient disease. We therefore screened patients without identified exonic lesions for mutations within conserved noncoding and intronic regions. We discovered 1 patient with an intronic deletion mutation, 4 patients with point mutations within a conserved intronic element, and 3 patients with reduced or absent transcription from 1 allele. All mutations affected GATA2 transcription. Full-length cDNA analysis provided evidence for decreased expression of the mutant alleles. The intronic deletion and point mutations considerably reduced the enhancer activity of the intron 5 enhancer. Analysis of 512 immune system genes revealed similar expression profiles in all clinically affected patients and reduced GATA2 transcript levels. These mutations strongly support the haploinsufficient nature of GATA2 deficiency and identify transcriptional mechanisms and targets that lead to MonoMAC syndrome.