CCBE1 mutation in two siblings, one manifesting lymphedema-cholestasis syndrome, and the other, fetal hydrops

The role of key biomarkers in lymphatic malformation: An updated review

The lymphatic system, crucial for tissue fluid balance and immune surveillance, can be severely impacted by disorders that hinder its activities. Lymphatic malformations (LMs) are caused by fluid accumulation in tissues owing to defects in lymphatic channel formation, the obstruction of lymphatic vessels or injury to lymphatic tissues. Somatic mutations, varying in symptoms based on lesions' location and size, provide insights into their molecular pathogenesis by identifying LMs' genetic causes. In this review, we collected the most recent findings about the role of genetic and inflammatory biomarkers in LMs that control the formation of these malformations. A thorough evaluation of the literature from 2000 to the present was conducted using the PubMed and Google Scholar databases. Although it is obvious that the vascular endothelial growth factor receptor 3 mutation accounts for a significant proportion of LM patients, several mutations in other genes thought to be linked to LM have also been discovered. Also, inflammatory mediators like interleukin-6, interleukin-8, tumor necrosis factor-alpha and mammalian target of rapamycin are the most commonly associated biomarkers with LM. Understanding the mutations and genes expression responsible for the abnormalities in lymphatic endothelial cells could lead to novel therapeutic strategies based on molecular pathways.

Pathophysiology of Slow-Flow Vascular Malformations: Current Understanding and Unanswered Questions

Background

Slow-flow vascular malformations include venous, lymphatic, and lymphaticovenous malformations. Recent studies have linked genetic variants hyperactivating either the PI3K/AKT/mTOR and/or RAS/RAF/MAPK signaling pathways with slow-flow vascular malformation development, leading to the use of pharmacotherapies such as sirolimus and alpelisib. It is important that clinicians understand basic and translational research advances in slow-flow vascular malformations.

Methods

A literature review of basic science publications in slow-flow vascular malformations was performed on Pubmed, using search terms "venous malformation," "lymphatic malformation," "lymphaticovenous malformation," "genetic variant," "genetic mutation," "endothelial cells," and "animal model." Relevant publications were reviewed and summarized.

Results

The study of patient tissues and the use of primary pathogenic endothelial cells from vascular malformations shed light on their pathological behaviors, such as endothelial cell hyperproliferation and disruptions in vessel architecture. The use of xenograft and transgenic animal models confirmed the pathogenicity of genetic variants and allowed for preclinical testing of potential therapies. These discoveries underscore the importance of basic and translational research in understanding the pathophysiology of vascular malformations, which will allow for the development of improved biologically targeted treatments.

Conclusion

Despite basic and translation advances, a cure for slow-flow vascular malformations remains elusive. Many questions remain unanswered, including how genotype variants result in phenotypes, and genotype-phenotype heterogeneity. Continued research into venous and lymphatic malformation pathobiology is critical in understanding the mechanisms by which genetic variants contribute to vascular malformation phenotypic features.

Primary Lymphedema: Update on Genetic Basis and Management

Significance: Primary lymphedema is a chronic condition without a cure. The lower extremities are more commonly affected than the arms or genitalia. The disease can be syndromic. Morbidity includes decreased self-esteem, infections, and reduced function of the area. Recent Advances: Several mutations can cause lymphedema, and new variants continue to be elucidated. A critical determinant that predicts the natural history and morbidity of lymphedema is the patient's body mass index (BMI). Individuals who maintain an active lifestyle with a normal BMI generally have less severe disease compared to subjects who are obese. Because other causes of lower extremity enlargement can be confused with lymphedema, definitive diagnosis requires lymphoscintigraphy. Critical Issues: Most patients with primary lymphedema are satisfactorily managed with compression regimens, exercise, and maintenance of a normal body weight. Suction-assisted lipectomy is our preferred operative intervention for symptomatic patients who have failed conservative therapy. Suction-assisted lipectomy effectively removes excess subcutaneous fibro-adipose tissue and can improve underlying lymphatic function. Future Directions: Many patients with primary lymphedema do not have an identifiable mutation and thus novel variants will be identified. The mechanisms by which mutations cause lymphedema continue to be studied. In the future, drug therapy for the disease may be developed.

Hepatic lymphatic vascular system in health and disease

In recent years, significant advances have been made in the study of lymphatic vessels with the identification of their specific markers and the development of research tools that have accelerated our understanding of their role in tissue homeostasis and disease pathogenesis in many organs. Compared to other organs, the lymphatic system in the liver is understudied despite its obvious importance for hepatic physiology and pathophysiology. In this review, we describe fundamental aspects of the hepatic lymphatic system and its role in a range of liver-related pathological conditions such as portal hypertension, ascites formation, malignant tumours, liver transplantation, congenital liver diseases, non-alcoholic fatty liver disease, and hepatic encephalopathy. The article concludes with a discussion regarding the modulation of lymphangiogenesis as a potential therapeutic strategy for liver diseases.

CCBE1 in Cardiac Development and Disease

The collagen- and calcium-binding EGF-like domains 1 (CCBE1) is a secreted protein extensively described as indispensable for lymphangiogenesis during development enhancing VEGF-C signaling. In human patients, mutations in CCBE1 have been found to cause Hennekam syndrome, an inherited disease characterized by malformation of the lymphatic system that presents a wide variety of symptoms such as primary lymphedema, lymphangiectasia, and heart defects. Importantly, over the last decade, an essential role for CCBE1 during heart development is being uncovered. In mice, Ccbe1 expression was initially detected in distinct cardiac progenitors such as first and second heart field, and the proepicardium. More recently, Ccbe1 expression was identified in the epicardium and sinus venosus (SV) myocardium at E11.5–E13.5, the stage when SV endocardium–derived (VEGF-C dependent) coronary vessels start to form. Concordantly, CCBE1 is required for the correct formation of the coronary vessels and the coronary artery stem in the mouse. Additionally, Ccbe1 was found to be enriched in mouse embryonic stem cells (ESC) and revealed as a new essential gene for the differentiation of ESC-derived early cardiac precursor cell lineages. Here, we bring an up-to-date review on the role of CCBE1 in cardiac development, function, and human disease implications. Finally, we envisage the potential of this molecule’s functions from a regenerative medicine perspective, particularly novel therapeutic strategies for heart disease.

Development and physiological functions of the lymphatic system: insights from human genetic studies of primary lymphedema

Primary lymphedema is a long-term (chronic) condition characterized by tissue lymph retention and swelling that can affect any part of the body, although it usually develops in the arms or legs. Due to the relevant contribution of the lymphatic system to human physiology, while this review mainly focuses on the clinical and physiological aspects related to the regulation of fluid homeostasis and edema, clinicians need to know that the impact of lymphatic dysfunction with a genetic origin can be wide ranging. Lymphatic dysfunction can affect immune function so leading to infection; it can influence cancer development and spread, and it can determine fat transport so impacting on nutrition and obesity. Genetic studies and the development of imaging techniques for the assessment of lymphatic function have enabled the recognition of primary lymphedema as a heterogenic condition in terms of genetic causes and disease mechanisms. In this review, the known biological functions of several genes crucial to the development and function of the lymphatic system are used as a basis for understanding normal lymphatic biology. The disease conditions originating from mutations in these genes are discussed together with a detailed clinical description of the phenotype and the up-to-date knowledge in terms of disease mechanisms acquired from in vitro and in vivo research models.

Predicting the Most Deleterious Missense Nonsynonymous Single-Nucleotide Polymorphisms of Hennekam Syndrome-Causing CCBE1 Gene, In Silico Analysis

Hennekam lymphangiectasia-lymphedema syndrome has been linked to single-nucleotide polymorphisms in the CCBE1 (collagen and calcium-binding EGF domains 1) gene. Several bioinformatics methods were used to find the most dangerous nsSNPs that could affect CCBE1 structure and function. Using state-of-the-art in silico tools, this study examined the most pathogenic nonsynonymous single-nucleotide polymorphisms (nsSNPs) that disrupt the CCBE1 protein and extracellular matrix remodeling and migration. Our results indicate that seven nsSNPs, rs115982879, rs149792489, rs374941368, rs121908254, rs149531418, rs121908251, and rs372499913, are deleterious in the CCBE1 gene, four (G330E, C102S, C174R, and G107D) of which are the highly deleterious, two of them (G330E and G107D) have never been seen reported in the context of Hennekam syndrome. Twelve missense SNPs, rs199902030, rs267605221, rs37517418, rs80008675, rs116596858, rs116675104, rs121908252, rs147974432, rs147681552, rs192224843, rs139059968, and rs148498685, are found to revert into stop codons. Structural homology-based methods and sequence homology-based tools revealed that 8.8% of the nsSNPs are pathogenic. SIFT, PolyPhen2, M-CAP, CADD, FATHMM-MKL, DANN, PANTHER, Mutation Taster, LRT, and SNAP2 had a significant score for identifying deleterious nsSNPs. The importance of rs374941368 and rs200149541 in the prediction of post-translation changes was highlighted because it impacts a possible phosphorylation site. Gene-gene interactions revealed CCBE1's association with other genes, showing its role in a number of pathways and coexpressions. The top 16 deleterious nsSNPs found in this research should be investigated further in the future while researching diseases caused CCBE1 gene specifically HS. The FT web server predicted amino acid residues involved in the ligand-binding site of the CCBE1 protein, and two of the substitutions (R167W and T153N) were found to be involved. These highly deleterious nsSNPs can be used as marker pathogenic variants in the mutational diagnosis of the HS syndrome, and this research also offers potential insights that will aid in the development of precision medicines. CCBE1 proteins from Hennekam syndrome patients should be tested in animal models for this purpose.

A system-based approach to the genetic etiologies of non-immune hydrops fetalis

A wide spectrum of genetic causes may lead to nonimmune hydrops fetalis (NIHF), and a thorough phenotypic and genetic evaluation are essential to determine the underlying etiology, optimally manage these pregnancies, and inform discussions about anticipated prognosis. In this review, we outline the known genetic etiologies of NIHF by fetal organ system affected, and provide a systematic approach to the evaluation of NIHF. Some of the underlying genetic disorders are associated with characteristic phenotypic features that may be seen on prenatal ultrasound, such as hepatomegaly with lysosomal storage disorders, hyperechoic kidneys with congenital nephrosis, or pulmonary valve stenosis with RASopathies. However, this is not always the case, and the approach to evaluation must include prenatal ultrasound findings as well as genetic testing and many other factors. Genetic testing that has been utilized for NIHF ranges from standard chromosomal microarray or karyotype to gene panels and broad approaches such as whole exome sequencing. Family and obstetric history, as well as pathology examination, can yield additional clues that are helpful in establishing a diagnosis. A systematic approach to evaluation can guide a more targeted approach to genetic evaluation, diagnosis, and management of NIHF.

Establishment and maintenance of blood-lymph separation

Hippocratic Corpus, a collection of Greek medical literature, described the functional anatomy of the lymphatic system in the fifth century B.C. Subsequent studies in cadavers and surgical patients firmly established that lymphatic vessels drain extravasated interstitial fluid, also known as lymph, into the venous system at the bilateral lymphovenous junctions. Recent advances revealed that lymphovenous valves and platelet-mediated hemostasis at the lymphovenous junctions maintain life-long separation of the blood and lymphatic vascular systems. Here, we review murine models that exhibit failure of blood-lymph separation to highlight the novel mechanisms and molecular targets for the modulation of lymphatic disorders. Specifically, we focus on the transcription factors, cofactors, and signaling pathways that regulate lymphovenous valve development and platelet-mediated lymphovenous hemostasis, which cooperate to maintain blood-lymph separation.

CCBE1 is required for coronary vessel development and proper coronary artery stem formation in the mouse heart

BACKGROUND

Proper coronary vasculature development is essential for late-embryonic and adult heart function. The developmental regulation of coronary embryogenesis is complex and includes the coordinated activity of multiple signaling pathways. CCBE1 plays an important role during lymphangiogenesis, enhancing VEGF-C signaling, which is also required for coronary vasculature formation. However, whether CCBE1 plays a similar role during coronary vasculature development is still unknown. Here, we investigate the coronary vasculature development in Ccbe1 mutant embryos.

RESULTS

We show that Ccbe1 is expressed in the epicardium, like Vegf-c, and also in the sinus venosus (SV) at the stages of its contribution to coronary vasculature formation. We also report that absence of CCBE1 in cardiac tissue inhibited coronary growth that sprouts from the SV endocardium at the dorsal cardiac wall. This disruption of coronary formation correlates with abnormal processing of VEGF-C propeptides, suggesting VEGF-C-dependent signaling alteration. Moreover, Ccbe1 loss-of-function leads to the development of defective dorsal and ventral intramyocardial vessels. We also demonstrate that Ccbe1 mutants display delayed and mispatterned coronary artery (CA) stem formation.

CONCLUSIONS

CCBE1 is essential for coronary vessel formation, independent of their embryonic origin, and is also necessary for peritruncal vessel growth and proper CA stem patterning. Developmental Dynamics 247:1135-1145, 2018. © 2018 Wiley Periodicals, Inc.

Novel mutation in CCBE 1 as a cause of recurrent hydrops fetalis from Hennekam lymphangiectasia-lymphedema syndrome-1

Whole exome sequencing (WES) was used to determine the etiology of recurrent hydrops fetalis in this case of Hennekam lymphangiectasia-lymphedema syndrome-1. WES is a useful approach for diagnosing rare single-gene conditions with nonspecific phenotypes and should be considered early in the diagnostic process of investigating fetal abnormalities.

Mechanisms of Connexin-Related Lymphedema

RATIONALE

Mutations in GJC2 and GJA1, encoding Cxs (connexins) 47 and 43, respectively, are linked to lymphedema, but the underlying mechanisms are unknown. Because efficient lymph transport relies on the coordinated contractions of lymphatic muscle cells (LMCs) and their electrical coupling through Cxs, Cx-related lymphedema is proposed to result from dyssynchronous contractions of lymphatic vessels.

OBJECTIVE

To determine which Cx isoforms in LMCs and lymphatic endothelial cells are required for the entrainment of lymphatic contraction waves and efficient lymph transport.

METHODS AND RESULTS

We developed novel methods to quantify the spatiotemporal entrainment of lymphatic contraction waves and used optogenetic techniques to analyze calcium signaling within and between the LMC and the lymphatic endothelial cell layers. Genetic deletion of the major lymphatic endothelial cell Cxs (Cx43, Cx47, or Cx37) revealed that none were necessary for the synchronization of the global calcium events that triggered propagating contraction waves. We identified Cx45 in human and mouse LMCs as the critical Cx mediating the conduction of pacemaking signals and entrained contractions. Smooth muscle-specific Cx45 deficiency resulted in 10- to 18-fold reduction in conduction speed, partial-to-severe loss of contractile coordination, and impaired lymph pump function ex vivo and in vivo. Cx45 deficiency resulted in profound inhibition of lymph transport in vivo, but only under an imposed gravitational load.

CONCLUSIONS

Our results (1) identify Cx45 as the Cx isoform mediating the entrainment of the contraction waves in LMCs; (2) show that major endothelial Cxs are dispensable for the entrainment of contractions; (3) reveal a lack of coupling between lymphatic endothelial cells and LMCs, in contrast to arterioles; (4) point to lymphatic valve defects, rather than contraction dyssynchrony, as the mechanism underlying GJC2- or GJA1-related lymphedema; and (5) show that a gravitational load exacerbates lymphatic contractile defects in the intact mouse hindlimb, which is likely critical for the development of lymphedema in the adult mouse.

Genetic testing for Hennekam syndrome

Hennekam Syndrome (HS) is a combination of congenital lymphatic malformation, lymphangiectasia and other disorders. It is a very rare disorder with autosomal recessive inheritance. We developed the test protocol “Hennekam Syndrome” on the basis of the latest research findings and diagnostic protocols on lymphatic malformation in HS. The genetic test is useful for confirming diagnosis, as well as for differential diagnosis, couple risk assessment and access to clinical trials.

Lymphatics in the liver

The liver is the largest lymph producing organ. A significant increase in the number of hepatic lymphatic vessels, or lymphangiogenesis, has been reported in various liver diseases, including, but not limited to, cirrhosis, viral hepatitis and hepatocellular carcinoma. Despite its apparent relevance in healthy and diseased livers as these and other observations indicate, the hepatic lymphatic system has been poorly studied. With knowledge of the lymphatic system in other organs and tissues incorporated, this review article addresses the current knowledge of the hepatic lymphatic system and the potential role of lymphatic endothelial cells in the health and the disease of the liver and concludes with a brief description on future directions of the study of the hepatic lymphatic system.

Biology of Vascular Endothelial Growth Factor C in the Morphogenesis of Lymphatic Vessels

Because virtually all tissues contain blood vessels, the importance of hemevascularization has been long recognized in regenerative medicine and tissue engineering. However, the lymphatic vasculature has only recently become a subject of interest. Central to the task of growing a lymphatic network are lymphatic endothelial cells (LECs), which constitute the innermost layer of all lymphatic vessels. The central molecule that directs proliferation and migration of LECs during embryogenesis is vascular endothelial growth factor C (VEGF-C). VEGF-C is therefore an important ingredient for LEC culture and attempts to (re)generate lymphatic vessels and networks. During its biosynthesis VEGF-C undergoes a stepwise proteolytic processing, during which its properties and affinities for its interaction partners change. Many of these fundamental aspects of VEGF-C biosynthesis have only recently been uncovered. So far, most—if not all—applications of VEGF-C do not discriminate between different forms of VEGF-C. However, for lymphatic regeneration and engineering purposes, it appears mandatory to understand these differences, since they relate, e.g., to important aspects such as biodistribution and receptor activation potential. In this review, we discuss the molecular biology of VEGF-C as it relates to the growth of LECs and lymphatic vessels. However, the properties of VEGF-C are similarly relevant for the cardiovascular system, since both old and recent data show that VEGF-C can have a profound effect on the blood vasculature.

Genetic tests in lymphatic vascular malformations and lymphedema

Syndromes with lymphatic malformations show phenotypic variability within the same entity, clinical features that overlap between different conditions and allelic as well as locus heterogeneity. The aim of this review is to provide a comprehensive clinical genetic description of lymphatic malformations and the techniques used for their diagnosis, and to propose a flowchart for genetic testing. Literature and database searches were performed to find conditions characterised by lymphatic malformations or the predisposition to lymphedema after surgery, to identify the associated genes and to find the guidelines and genetic tests currently used for the molecular diagnosis of these disorders. This search allowed us to identify several syndromes with lymphatic malformations that are characterised by a great heterogeneity of phenotypes, alleles and loci, and a high frequency of sporadic cases, which may be associated with somatic mutations. For these disorders, we found many diagnostic tests, an absence of harmonic guidelines for molecular diagnosis and well-established clinical guidelines. Targeted sequencing is the preferred method for the molecular diagnosis of lymphatic malformations. These techniques are easy to implement and have a good diagnostic success rates. In addition, they are relatively inexpensive and permit parallel analysis of all known disease-associated genes. The targeted sequencing approach has improved the diagnostic process, giving patients access to better treatment and, potentially, to therapy personalised to their genetic profiles. These new techniques will also facilitate the prenatal and early postnatal diagnosis of congenital lymphatic conditions and the possibility of early intervention.

Clinical significance of CCBE1 expression in lung cancer

Lymph node metastasis (LNM) is one of the major causes of cancer-associated morbidity and mortality in patients with lung cancer following radical pulmonary carcinoma resection. The present study aimed to investigate the relationship between the expression of collagen and calcium-binding epidermal growth factor domain-containing protein 1 (CCBE1) and lymphatic vessel endothelial hyaluronan receptor 1 (LYVE1) in tumor tissue with the clinical prognosis of lung cancer. The present study included 40 patients with lung cancer that underwent pulmonary carcinoma resection, including 10 patients with LNM, and 10 control patients who underwent pulmonary bullae resection. CCBE1 and LYVE1 expression was assessed in samples from normal and tumor tissue using polymerase chain reaction, western blot analysis and immunohistochemistry. CCBE1 expression appeared to be decreased in lung tumor tissue and further downregulated in samples from patients with LNM, and was revealed to be correlated with poor clinical outcome. Conversely, LYVE1 expression appeared to be upregulated in lung cancer tissue. In conclusion, the present results suggested that CCBE1 and LYVE1 may have potential as biomarkers for the identification of lung cancer patients at a high risk of LNM.

CCBE1 mutation causing sclerosing cholangitis: Expanding the spectrum of lymphedema-cholestasis syndrome

A 52-year old patient presented with lymphedema, protein loosing enteropathy, and sclerosing cholangitis and was diagnosed with lymphedema cholestasis syndrome (LCS). Cholangioscopy revealed dilated lymphatic vessels obstructing the bile duct and compound heterozygosity for collagen and calcium-binding epidermal growth factor domain-containing protein 1 (CCBE1) mutations was identified defining a novel type of LCS. (Hepatology 2017;66:286-288).

Angioid streaks in aagenaes syndrome

Aagenaes syndrome, also called lymphoedema cholestasis syndrome 1 (LSC1), is characterized by neonatal intrahepatic cholestasis, often lessening and becoming intermittent with age and severe chronic lymphoedema, mainly affecting the lower extremities. The condition is autosomal recessively inherited, and the gene is located on chromosome 15q. The locus, LCS1, was mapped to a 6.6 cM region on chromosome 15. Angioid streaks are visible irregular crack-like dehiscences in bruch's membrane that are associated with atrophic degeneration of the overlying retinal pigment epithelium. Angioid streaks have been described to be associated with pseudoxanthoma elasticum, paget's disease, sickle-cell anaemia, acromegaly, Ehlers-Danlos syndrome, and diabetes mellitus, but also appear in patients without any systemic diseases. Patients with angioid streaks are generally asymptomatic, unless the lesions extend towards the foveola or develop complications such as traumatic bruch's membrane rupture or macular choroidal neovascularization.

A Multiplex Kindred with Hennekam Syndrome due to Homozygosity for a CCBE1 Mutation that does not Prevent Protein Expression

Collagen and calcium-binding EGF domain-containing protein 1 (CCBE1) bi-allelic mutations have been associated with syndromes of widespread congenital lymphatic dysplasia, including Hennekam Syndrome (HS). HS is characterized by lymphedema, lymphangiectasia, and intellectual disability. CCBE1 encodes a putative extracellular matrix protein but the HS-causing mutations have not been studied biochemically. We report two HS siblings, born to consanguineous parents of Turkish ancestry, whose clinical phenotype also includes protein losing enteropathy, painful relapsing chylous ascites, and hypogammaglobulinemia. We identified by whole exome and Sanger sequencing the homozygous CCBE1 C174Y mutation in both siblings. This mutation had been previously reported in another HS kindred from the Netherlands. In over-expression studies, we found increased intracellular expression of all forms (monomers, dimers, trimers) of the CCBE1 C174Y mutant protein, by Western blot, despite mutant mRNA levels similar to wild-type (WT). In addition, we detected increased secretion of the mutant CCBE1 protein by ELISA. We further found the mutant and WT proteins to be evenly distributed in the cytoplasm, by immunofluorescence and confocal microscopy. Finally, we found a strong decrease of lymphatic vessels, with a corresponding diminished expression of CCBE1, by immunohistochemistry of the patients' intestinal biopsies. In contrast, mucosal blood vessels and muscularis mucosae showed normal CCBE1 staining. Our findings show that the mutant CCBE1 C174Y protein is not loss-of-function by loss-of-expression.

A novel CCBE1 mutation leading to a mild form of hennekam syndrome: case report and review of the literature

Background

Mutations in CCBE1 have been found to be responsible for a subset of families with autosomal recessive Hennekam syndrome. Hennekam syndrome is defined as the combination of generalized lymphatic dysplasia (ie. lymphedema and lymphangiectasia), variable intellectual disability and characteristic dysmorphic features. The patient we describe here has a lymphatic dysplasia without intellectual disability or dysmorphism caused by mutation in CCBE1, highlighting the phenotypic variability that can be seen with abnormalities in this gene.

Case presentation

Our patient is a 5 week old child of Pakistani descent who presented to our center with generalized edema, ascites, and hypoalbuminemia. She was diagnosed with a protein losing enteropathy secondary to segmental primary intestinal lymphangiectasia. As the generalized edema resolved, it became clear that she had mild persistent lymphedema in her hands and feet. No other abnormalities were noted on examination and development was unremarkable at 27 months of age. Given the suspected genetic etiology and the consanguinity in the family, we used a combination of SNP genotyping and exome sequencing to identify the underlying cause of her disease. We identified several large stretches of homozygosity in the patient that allowed us to sort the variants found in the patient’s exome to identify p.C98W in CCBE1 as the likely pathogenic variant.

Conclusions

CCBE1 mutation analysis should be considered in all patients with unexplained lymphatic dysplasia even without the other features of classic Hennekam syndrome.

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.

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.