Lymphatic dysfunction, not aplasia, underlies Milroy disease

TRPS1 expression in breast angiosarcoma

Angiosarcoma (AS) of the breast, a rare mesenchymal neoplasm, exhibits distinct forms based on etiological and genetic features. While cases with typical clinical presentation and morphology allow for a straightforward diagnosis, challenges arise when clinical data are scarce, diagnostic material is limited, or morphological characteristics overlap with other tumors, including undifferentiated carcinomas. The trichorhinophalangeal syndrome protein 1 (TRPS1), once regarded as highly specific for breast carcinomas, now faces doubts regarding its reliability. This study explores TRPS1 expression in breast AS. Our investigation revealed that 60% of AS cases displayed TRPS1 labeling, contrasting with the 40% lacking expression. Scoring by four independent readers established a consensus, designating 12/35 ASs as unequivocally TRPS1-positive. However, uncertainty surrounded nine further cases due to a lack of reader agreement (being substantial as reflected by a kappa value of 0.76). These findings challenge the perceived specificity of TRPS1, shedding light on its presence in a noteworthy proportion of breast ASs. Consequently, the study underscores the importance of a comprehensive approach in evaluating breast ASs and expands the range of entities within the differential diagnosis associated with TRPS1 labeling.

Edema and lymphatic clearance: molecular mechanisms and ongoing challenges

Resolution of edema remains a significant clinical challenge. Conditions such as traumatic shock, sepsis, or diabetes often involve microvascular hyperpermeability, which leads to tissue and organ dysfunction. Lymphatic insufficiency due to genetic causes, surgical removal of lymph nodes, or infections, leads to varying degrees of tissue swelling that impair mobility and immune defenses. Treatment options are limited to management of edema as there are no specific therapeutics that have demonstrated significant success for ameliorating microvascular leakage or impaired lymphatic function. This review examines current knowledge about the physiological, cellular, and molecular mechanisms that control microvascular permeability and lymphatic clearance, the respective processes for interstitial fluid formation and removal. Clinical conditions featuring edema, along with potential future directions are discussed.

VEGFR3 is required for button junction formation in lymphatic vessels

Lymphatic capillaries develop discontinuous cell-cell junctions that permit the absorption of large macromolecules, chylomicrons, and fluid from the interstitium. While excessive vascular endothelial growth factor 2 (VEGFR2) signaling can remodel and seal these junctions, whether and how VEGFR3 can alter lymphatic junctions remains incompletely understood. Here, we use lymphatic-specific Flt4 knockout mice to investigate VEGFR3 signaling in lymphatic junctions. We show that loss of Flt4 prevents specialized button junction formation in multiple tissues and impairs interstitial absorption. Knockdown of FLT4 in human lymphatic endothelial cells results in impaired NOTCH1 expression and activation, and overexpression of the NOTCH1 intracellular domain in Flt4 knockout vessels rescues the formation of button junctions and absorption of interstitial molecules. Together, our data reveal a requirement for VEGFR3 and NOTCH1 signaling in the development of button junctions during postnatal development and may hold clinical relevance to lymphatic diseases with impaired VEGFR3 signaling.

Current Concepts in the Management of Primary Lymphedema

Primary lymphedema is a heterogeneous group of conditions encompassing all lymphatic anomalies that result in lymphatic swelling. Primary lymphedema can be difficult to diagnose, and diagnosis is often delayed. As opposed to secondary lymphedema, primary lymphedema has an unpredictable disease course, often progressing more slowly. Primary lymphedema can be associated with various genetic syndromes or can be idiopathic. Diagnosis is often clinical, although imaging can be a helpful adjunct. The literature on treating primary lymphedema is limited, and treatment algorithms are largely based on practice patterns for secondary lymphedema. The mainstay of treatment focuses on complete decongestive therapy, including manual lymphatic drainage and compression therapy. For those who fail conservative treatment, surgical treatment can be an option. Microsurgical techniques have shown promise in primary lymphedema, with both lymphovenous bypass and vascularized lymph node transfers demonstrating improved clinical outcomes in a few studies.

Two novel variations p.(Ser1275Thr) and p.(Ser1275Arg) in FLT4 causing prenatal hereditary lymphedema type 1

BACKGROUND

Hereditary lymphedema 1 is a rare congenital condition, characterized by the development of chronic swelling in body parts. It is highly variable in expression and age of onset with different presentations: from feet edema to hydrops fetalis. This affection is genetically heterogeneous with autosomal dominant inheritance and incomplete penetrance due to a mutation in the FLT4 gene in most cases.

CASES

In our study, we report on two fetuses harboring congenital lymphedema with FLT4 variation and review the prenatal confirmed ones of the literatures. Our cases were selected within fetuses explored by exome sequencing in a diagnosis setting. Prenatal ultrasonography showed hydrops fetalis in one case and an increased nuchal translucency with hydrothorax in the other. Comparative genomic hybridization array on amniocentesis was normal in both cases. Exome sequencing identified a variation p.(Ser1275Thr) and p.(Ser1275Arg) in fetus 1 and fetus 2 in the FLT4 gene, respectively. A de novo mutation at the same codon was reported in prenatal literature suggesting possible genotype phenotype correlation.

CONCLUSION

Cystic hygroma/hydrops fetalis are possible manifestations of several disorders. This study illustrates how the integration of exome sequencing in prenatal clinical practice can facilitate the diagnosis and genetic counseling of heterogeneous developmental affections.

How we approach lymphedema in the pediatric population

Lymphedema in children is rare; however, it is usually a progressive and chronic condition. Accurate diagnosis of lymphedema in the pediatric population often takes several months and sometimes is delayed for years. Lymphedema can be isolated or associated with genetic syndromes, thus it is very important to identify the correct diagnosis, to select carefully which patients to refer for genetic testing, and to initiate appropriate treatment in a timely fashion. In this article, we review key information about diagnosis of lymphedema, associated conditions and syndromes, and current treatment modalities.

How we approach lymphedema in the pediatric population

Lymphedema in children is rare; however, it is usually a progressive and chronic condition. Accurate diagnosis of lymphedema in the pediatric population often takes several months and sometimes is delayed for years. Lymphedema can be isolated or associated with genetic syndromes, thus it is very important to identify the correct diagnosis, to select carefully which patients to refer for genetic testing, and to initiate appropriate treatment in a timely fashion. In this article, we review key information about diagnosis of lymphedema, associated conditions and syndromes, and current treatment modalities.

Current Understanding of Pathological Mechanisms of Lymphedema

Significance: Lymphedema is a common disease that affects hundreds of millions of people worldwide with significant financial and social burdens. Despite increasing prevalence and associated morbidities, the mainstay treatment of lymphedema is largely palliative without an effective cure due to incomplete understanding of the disease. Recent Advances: Recent studies have described key histological and pathological processes that contribute to the progression of lymphedema, including lymphatic stasis, inflammation, adipose tissue deposition, and fibrosis. This review aims to highlight cellular and molecular mechanisms involved in each of these pathological processes. Critical Issues: Despite recent advances in the understanding of the pathophysiology of lymphedema, cellular and molecular mechanisms underlying the disease remains elusive due to its complex nature. Future Directions: Additional research is needed to gain a better insight into the cellular and molecular mechanisms underlying the pathophysiology of lymphedema, which will guide the development of therapeutic strategies that target specific pathology of the disease.

Preparation of the Biodegradable Lymphatic Targeting Imaging Agent Based on the Indocyanine Green Mesoporous Silicon System

The lymphatic system plays a crucial role in the immune system’s recognition and response to disease. Therefore, the imaging of the lymphatic system, especially lymphatic vessels, has emerged as a valuable tool for the diagnosis of metastasis. FDA-approved small-molecule dyes, namely, indocyanine green (ICG), have been widely applied to lymphatic vessels imaging. However, due to the small physical size, such molecule-based agents show no selectivity, and rapid clearance from lymph nodes. Herein, a biodegradable lymphatic targeting imaging agent based on the ICG-mesoporous silicon system (ICG@HMONs-HA) was obtained, which not only could target lymph vessels but also had a long residence time. The reported work provides a practical way for lymph vessel fluorescence imaging and paves the way for clinical translation of nanomaterial-based tracers.

Angiopoietin-2-induced lymphatic endothelial cell migration drives lymphangiogenesis via the β1 integrin-RhoA-formin axis

Lymphangiogenesis is an essential physiological process but also a determining factor in vascular-related pathological conditions. Angiopoietin-2 (Ang2) plays an important role in lymphatic vascular development and function and its upregulation has been reported in several vascular-related diseases, including cancer. Given the established role of the small GTPase RhoA on cytoskeleton-dependent endothelial functions, we investigated the relationship between RhoA and Ang2-induced cellular activities. This study shows that Ang2-driven human dermal lymphatic endothelial cell migration depends on RhoA. We demonstrate that Ang2-induced migration is independent of the Tie receptors, but dependent on β1 integrin-mediated RhoA activation with knockdown, pharmacological approaches, and protein sequencing experiments. Although the key proteins downstream of RhoA, Rho kinase (ROCK) and myosin light chain, were activated, blockade of ROCK did not abrogate the Ang2-driven migratory effect. However, formins, an alternative target of RhoA, were identified as key players, and especially FHOD1. The Ang2-RhoA relationship was explored in vivo, where lymphatic endothelial RhoA deficiency blocked Ang2-induced lymphangiogenesis, highlighting RhoA as an important target for anti-lymphangiogenic treatments.

The bright future of nanotechnology in lymphatic system imaging and imaging-guided surgery

Lymphatic system is identified the second vascular system after the blood circulation in mammalian species, however the research on lymphatic system has long been hampered by the lack of comprehensive imaging modality. Nanomaterials have shown the potential to enhance the quality of lymphatic imaging due to the unparalleled advantages such as the specific passive targeting and efficient co-delivery of cocktail to peripheral lymphatic system, ease molecular engineering for precise active targeting and prolonged retention in the lymphatic system of interest. Multimodal lymphatic imaging based on nanotechnology provides a complementary means to understand the kinetics of lymphoid tissues and quantify its function. In this review, we introduce the established approaches of lymphatic imaging used in clinic and summarize their strengths and weaknesses, and list the critical influence factors on lymphatic imaging. Meanwhile, the recent developments in the field of pre-clinical lymphatic imaging are discussed to shed new lights on the design of new imaging agents, the improvement of delivery methods and imaging-guided surgery strategies.

FLT4 Mutations Are Associated with Segmental Lymphatic Dysfunction and Initial Lymphatic Aplasia in Patients with Milroy Disease

This study explored mutations in the Fms-related tyrosine kinase 4/vascular endothelial growth factor receptor 3 gene (FLT4) and lymphatic defects in patients with Milroy disease (MD). Twenty-nine patients with lower limb lymphedema were enrolled. Sixteen patients had a familial history of MD, while 13 patients exhibited sporadic MD. Clinical signs, FLT4 mutations, indocyanine green (ICG) lymphography findings, and skin tissue immunohistochemical staining results were evaluated. Twenty-eight variants in FLT4 were identified. Twelve of these have previously been reported, while 16 are novel. Of the 28 variants, 26 are missense mutations, and the remaining two comprise a splicing mutation and a non-frame shift mutation. Twenty-five variants are located in the intracellular protein tyrosine kinase domain; three are located in the extracellular immunoglobulin domain. Substantially delayed contrast-enhanced tortuous lymphatic vessels were visualized to the ankle or knee level in 15 of 23 patients who underwent ICG lymphography. No initial lymphatic vessels were visualized in skin specimens from four patients who did not exhibit lymphatic vessels during imaging analyses. No specific variant was identified in relation to the unique clinical phenotype. Segmental dysfunction of lymphatic vessels and initial lymphatic aplasia are present in MD patients with FLT4 mutations.

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.

A family with Milroy disease caused by the FLT4/VEGFR3 gene variant c.2774 T > A

Background

Milroy disease (MD) is a rare, autosomal-dominant disorder. Variants in the Fms-related tyrosine kinase 4 (FLT4/VEGFR3) gene cause the symptoms of this disease. In this report, we investigated the variant in a large Chinese family with MD.

Methods

We conducted Sanger sequencing of exons 17–26 of FLT4/VEGFR3 (NM_182925.4). We assessed its pathogenicity based on the ACMG criteria and predicted it with an in silico program.

Results

A heterozygous substitution (NM_182925.4 (FLT4/VEGFR3):c.2774 T>A, p. (Val925Glu)) was detected in all patients with MD but not in any healthy controls. The variant was evaluated as pathogenic according to the ACMG criteria and was predicted to be pathogenic using an in silico program.

Conclusions

In this report, we described a large family with MD caused by a missense variant in FLT4/VEGFR3 (NM_182925.4 (FLT4/VEGFR3_v001):c.2774 T>A, p. (Val925Glu)). There are phenotypic heterogeneities among family members, and further research should be conducted to explore the possible reasons.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12920-021-00997-w.

Imaging technology of the lymphatic system

The lymphatic system plays critical roles in tissue fluid homeostasis and immunity and has been implicated in the development of many different pathologies, ranging from lymphedema, the spread of cancer to chronic inflammation. In this review, we first summarize the state-of-the-art of lymphatic imaging in the clinic and the advantages and disadvantages of these existing techniques. We then detail recent progress on imaging technology, including advancements in tracer design and injection methods, that have allowed visualization of lymphatic vessels with excellent spatial and temporal resolution in preclinical models. Finally, we describe the different approaches to quantifying lymphatic function that are being developed and discuss some emerging topics for lymphatic imaging in the clinic. Continued advancements in lymphatic imaging technology will be critical for the optimization of diagnostic methods for lymphatic disorders and the evaluation of novel therapies targeting the lymphatic system.

Lymphatic Tissue Engineering: A Further Step for Successful Lymphedema Treatment

BACKGROUND

 Secondary lymphedema, caused by oncologic surgery, radiation, and chemotherapy, is one of the most relevant, nononcological complications affecting cancer survivors. Severe functional deficits can result in impairing quality of life and a societal burden related to increased treatment costs. Often, conservative treatments are not sufficient to alleviate lymphedema or to prevent stage progression of the disease, as they do not address the underlying etiology that is the disruption of lymphatic pathways. In recent years, lymphatic surgery approaches were revolutionized by advances in microsurgical technique. Currently, lymphedema can effectively be treated by procedures such as lymphovenous anastomosis (LVA) and lymph node transfer (LNT). However, not all patients have suitable lymphatic vessels, and lymph node harvesting is associated with risks. In addition, some data have revealed nonresponders to the microsurgical techniques.

METHODS

 A literature review was performed to evaluate the value of lymphatic tissue engineering for plastic surgeons and to give an overview of the achievements, challenges, and goals of the field.

RESULTS

 While certain challenges exist, including cell harvesting, nutrient supply, biocompatibility, and hydrostatic properties, it is possible and desirable to engineer lymph nodes and lymphatic vessels. The path toward clinical translation is considered more complex for LNTs secondary to the complex microarchitecture and pending final mechanistic clarification, while LVA is more straight forward.

CONCLUSION

 Lymphatic tissue engineering has the potential to be the next step for microsurgical treatment of secondary lymphedema. Current and future researches are necessary to optimize this clinical paradigm shift for improved surgical treatment of lymphedema.

YAP and TAZ maintain PROX1 expression in the developing lymphatic and lymphovenous valves in response to VEGF-C signaling

Lymphatic vasculature is an integral part of digestive, immune and circulatory systems. The homeobox transcription factor PROX1 is necessary for the development of lymphatic vessels, lymphatic valves (LVs) and lymphovenous valves (LVVs). We and others previously reported a feedback loop between PROX1 and vascular endothelial growth factor-C (VEGF-C) signaling. PROX1 promotes the expression of the VEGF-C receptor VEGFR3 in lymphatic endothelial cells (LECs). In turn, VEGF-C signaling maintains PROX1 expression in LECs. However, the mechanisms of PROX1/VEGF-C feedback loop remain poorly understood. Whether VEGF-C signaling is necessary for LV and LVV development is also unknown. Here, we report for the first time that VEGF-C signaling is necessary for valve morphogenesis. We have also discovered that the transcriptional co-activators YAP and TAZ are required to maintain PROX1 expression in LVs and LVVs in response to VEGF-C signaling. Deletion of Yap and Taz in the lymphatic vasculature of mouse embryos did not affect the formation of LVs or LVVs, but resulted in the degeneration of these structures. Our results have identified VEGF-C, YAP and TAZ as a crucial molecular pathway in valve development.

Immunohistochemical Evaluation of Histological Change in a Chinese Milroy Disease Family With Venous and Skin Abnormities

Background: Milroy disease (MD) is rare and autosomal dominant resulting from mutations of the vascular endothelial growth factor receptor-3 (VEGFR-3 or FLT4), which leads to dysgenesis of the lymphatic system.

Methods: Here we report a Chinese MD family with 2 affected members of two generations. We identified the mutation of c.3075G>A in one allele of FLT4 in Chinese population firstly. The father and child presented lymphedema under knees both. Unfortunately, the child was premature delivered for a car accident of the mother and then died of asphyxia. Then we gathered the tissue of the lower-limb from the child with permission from the parents and ethic committee. We stained the tissue with lymphatic marker D2-40 and hematoxylin-eosin to explore the histological changes. Afterwards, we compared the results with a normal child who unfortunately died of premature delivery also.

Results: It is firstly identified the mutation of FLT4: c.3075G>A in Chinese population, and the mutation Inherited in the lineage. The histological evaluation indicated: (1) The number of lymphatic vessels decreased; (2) The morphology and structure of lymphatic vessels was abnormal. And what is added to our knowledge: (1) Capillary hyperemia and phlebectasia is severe; (2) Vascular malformations; (3) The number of vascular endothelial cells and vascular smooth muscle cells decreased; (4) Large sheets of epidermis desquamated; (5) The numbers of cutaneous appendages reduced in MD.

Conclusions: Based on the new findings, we assume that mutation of FLT4 not only affect the lymphogenesis, but also the angiogenesis, and epidermis structure.

Lymphatic Vessel Network Structure and Physiology

The lymphatic system is comprised of a network of vessels interrelated with lymphoid tissue, which has the holistic function to maintain the local physiologic environment for every cell in all tissues of the body. The lymphatic system maintains extracellular fluid homeostasis favorable for optimal tissue function, removing substances that arise due to metabolism or cell death, and optimizing immunity against bacteria, viruses, parasites, and other antigens. This article provides a comprehensive review of important findings over the past century along with recent advances in the understanding of the anatomy and physiology of lymphatic vessels, including tissue/organ specificity, development, mechanisms of lymph formation and transport, lymphangiogenesis, and the roles of lymphatics in disease. © 2019 American Physiological Society. Compr Physiol 9:207-299, 2019.

Cutaneous Manifestations of Chronic Vascular Disease

In the contemporary era of medical diagnosis via sophisticated radiographic imaging and/or comprehensive serological testing, a focused physical examination remains paramount in recognizing the cutaneous manifestations of chronic vascular disease. Recognition of the unique cutaneous signs of lymphatic and venous hypertension assists in the diagnosis as well as the staging and classification of both lymphedema and chronic venous insufficiency. Awareness of explicit dermatologic vasomotor manifestations aids not only in the identification of acrocyanosis, Raynaud phenomenon, pernio, and erythromelalgia but also mitigates confusion related to their clinical overlap. Although the clinical signs of peripheral artery disease are not necessarily specific or sensitive, a knowledge of suggestive dermatologic findings is helpful in recognition of severe limb ischemia. A brief review of the epidemiology, etiology, pathogenesis, and therapy of cutaneous related chronic vascular disease follows including an emphasis on characteristic clinical features supported by illustrative photographs.

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.

Lymphedema: Pathophysiology and clinical manifestations

Lymphedema is a localized form of tissue swelling resulting from excessive retention of lymphatic fluid in the interstitial compartment and caused by impaired lymphatic drainage. Lymphedema is classified as primary or secondary. Primary lymphedema is caused by developmental lymphatic vascular anomalies. Secondary lymphedema is acquired and arises as a result of an underlying systemic disease, trauma, or surgery. We performed PubMed and Google Scholar searches of the English-language literature (1966-2017) using the terms lymphedema, cancer-related lymphedema, and lymphatic complications. Relevant publications were manually reviewed for additional resources. This progressive chronic disease has serious implications on patients' quality of life. It is often misdiagnosed because it mimics other conditions of extremity swelling. There is no definitive cure for lymphedema. However, with proper diagnosis and management, its progression and potential complications may be limited.

Endothelial Cell Responses to Biomechanical Forces in Lymphatic Vessels

SIGNIFICANCE

Lymphatic vessels are important components of the cardiovascular and immune systems. They contribute both to the maintenance of normal homeostasis and to many pathological conditions, such as cancer and inflammation. The lymphatic vasculature is subjected to a variety of biomechanical forces, including fluid shear stress and vessel circumferential stretch.

RECENT ADVANCES

This review will discuss recent advances in our understanding of biomechanical forces in lymphatic vessels and their role in mammalian lymphatic vascular development and function.

CRITICAL ISSUES

We will highlight the importance of fluid shear stress generated by lymph flow in organizing the lymphatic vascular network. We will also describe how mutations in mechanosensitive genes lead to lymphatic vascular dysfunction.

FUTURE DIRECTIONS

Better understanding of how biomechanical and biochemical stimuli are perceived and interpreted by lymphatic endothelial cells is important for targeting regulation of lymphatic function in health and disease. Important remaining critical issues and future directions in the field will be discussed in this review. Antioxid. Redox Signal. 25, 451-465.

Quantitative Imaging In Vivo of Functioning Lymphatic Vessels Around Human Melanoma and Benign Nevi

OBJECTIVES

The density of functioning human lymphatics in vivo and of immunohistochemically defined lymphatics was quantified around melanomas, benign nevi, and matched normal skin, to assess the current lymphangiogenesis paradigm. We investigated whether histological and functioning density increased around melanomas compared with benign nevi or matched skin; whether functioning and histological density increased similarly; and whether larger increases occurred around metastatic melanomas.

METHODS

Functioning density was quantified in vivo as the total amount of human dermal microlymphatics taking up fluorescent marker injected at the lesion margin. After tissue excision, perilesion histological density was quantified using podoplanin marker D2-40.

RESULTS

Histological density was raised similarly around metastasising and non-metastasising melanomas compared with normal skin (+71%, p < 0.0001, n = 32); but was also raised significantly around benign nevi (+17%, p = 0.03, n = 20). In contrast, functioning lymphatic density was substantially reduced around the margins of melanomas (both metastasising and non-metastasising) compared with benign nevi (by 65%, p = 0.02) or normal skin (by 53%, p = 0.0014).

CONCLUSIONS

Raised perilesion histological lymphatic density is not unique to melanoma but occurs also around benign nevi. The findings indicated that the number of functioning lateral lymphatics around human melanomas in vivo but not benign nevi is reduced, despite histologically increased numbers of lymphatics.

The lymphatic phenotype in Turner syndrome: an evaluation of nineteen patients and literature review

Turner syndrome is a complex disorder caused by an absent or abnormal sex chromosome. It affects 1/2000-1/3000 live-born females. Congenital lymphoedema of the hands, feet and neck region (present in over 60% of patients) is a common and key diagnostic indicator, although is poorly described in the literature. The aim of this study was to analyse the medical records of a cohort of 19 Turner syndrome patients attending three specialist primary lymphoedema clinics, to elucidate the key features of the lymphatic phenotype and provide vital insights into its diagnosis, natural history and management. The majority of patients presented at birth with four-limb lymphoedema, which often resolved in early childhood, but frequently recurred in later life. The swelling was confined to the legs and hands with no facial or genital swelling. There was only one case of suspected systemic involvement (intestinal lymphangiectasia). The lymphoscintigraphy results suggest that the lymphatic phenotype of Turner syndrome may be due to a failure of initial lymphatic (capillary) function.

The lymphatic phenotype in Turner syndrome: an evaluation of nineteen patients and literature review

Turner syndrome is a complex disorder caused by an absent or abnormal sex chromosome. It affects 1/2000-1/3000 live-born females. Congenital lymphoedema of the hands, feet and neck region (present in over 60% of patients) is a common and key diagnostic indicator, although is poorly described in the literature. The aim of this study was to analyse the medical records of a cohort of 19 Turner syndrome patients attending three specialist primary lymphoedema clinics, to elucidate the key features of the lymphatic phenotype and provide vital insights into its diagnosis, natural history and management. The majority of patients presented at birth with four-limb lymphoedema, which often resolved in early childhood, but frequently recurred in later life. The swelling was confined to the legs and hands with no facial or genital swelling. There was only one case of suspected systemic involvement (intestinal lymphangiectasia). The lymphoscintigraphy results suggest that the lymphatic phenotype of Turner syndrome may be due to a failure of initial lymphatic (capillary) function.

A novel stop mutation in the vascular endothelial growth factor-C gene (VEGFC) results in Milroy-like disease

BACKGROUND

Milroy and Milroy-like disease are rare disorders characterised by congenital lymphoedema caused by dysfunctional lymphatic vessel formation. Loss of extracellular response mediated by vascular endothelial growth factor receptor 3 (VEGFR-3) is associated with Milroy disease, and VEGFR-3 gene is mutated in around 70% of the cases diagnosed. The only genetic alteration known to be associated with Milroy-like disease was recently identified in a family with a frameshift mutation in vascular endothelial growth factor C (VEGFC) gene, which encodes a VEGFR3 ligand.

METHODS AND RESULTS

We report a newborn patient with an external phenotype consistent with Milroy disease and a truncating mutation (p.R210X) in the VEGFC gene detected by exome sequence analysis. Subsequent analysis, by lymphoscintigraphic scan, performed for research purposes, allowed us to correct the diagnosis, confirming patient's disease as Milroy-like. The mutation segregates with the phenotype in the family according to a dominant model with full penetrance.

CONCLUSIONS

The clinical presentation, similar to Milroy disease, indicates an overlapping of the external phenotype of both diseases, suggesting that genetic analysis of VEGFC would be useful in diagnosing patients that present with Milroy features but have no mutation in VEGFR-3. Establishing a well-defined genetic pattern would help with differential diagnosis.

New developments in clinical aspects of lymphatic disease

The lymphatic system is fundamentally important to cardiovascular disease, infection and immunity, cancer, and probably obesity--the four major challenges in healthcare in the 21st century. This Review will consider the manner in which new knowledge of lymphatic genes and molecular mechanisms has demonstrated that lymphatic dysfunction should no longer be considered a passive bystander in disease but rather an active player in many pathological processes and, therefore, a genuine target for future therapeutic developments. The specific roles of the lymphatic system in edema, genetic aspects of primary lymphedema, infection (cellulitis/erysipelas), Crohn's disease, obesity, cancer, and cancer-related lymphedema are highlighted.

Significance of popliteal lymph nodes visualization during radionuclide lymphoscintigraphy for lower limb lymphedema

Purpose:

To examine the frequency and significance of visualization of popliteal nodes during lymphoscintigraphy for the investigation of lower extremity swelling.

Materials and Methods:

Technetium-99m-labeled nanocolloid was injected subcutaneously in the first web spaces of both feet of 90 patients (24 males, 66 females; age range, 4-70 years) who had clinical evidence of lower limb lymphedema and were referred for routine lymphoscintigraphy; imaging was performed 5, and 90 minutes after injection without any vigorous exercise between the injection and imaging.

Results:

According to the scan findings, patients were divided into two groups; group I included 63 patients without popliteal nodes visualization on scanning, and group II included 27 patients with positive popliteal nodes uptake. None of patients with primary lymphedema (N = 22) due to agenesis or hypoplasia showed popliteal node uptake, whereas, patients with secondary lymphedema (N = 68) had either severe (N = 23) or partial (N = 45) lymphatic obstruction. A high positive association of popliteal node uptake with the severity of lymphatic obstruction was noted. Popliteal nodes were visualized in 26 of 57 patients with dermal back flow (46%), and in only 1 of 33 patients without dermal back flow (3%). There was a strong association between skin rerouting and popliteal node visualization (P < 0.01). Skin changes were detected in 24 patients (38%) with positive popliteal node uptake.

Conclusion:

Popliteal lymph nodes uptake during lymphoscintigraphy for clinical lymphedema of the lower limb indicates lymph rerouting through the deep system and raises a diagnosis of higher severity and longer duration of lymphatic dysfunction.

[Enigmatic lymphatic diseases involving the lung]

Lymphedema associated with other developmental malformations (Milroy syndrome, Hennekam syndrome, Noonan syndrome, Gorham-Stout syndrome, yellow nail syndrome) are unfrequent disease, but explorations led to the identification of genetic mutations that have then been validated in mouse models. However, lymphatic vessels complexity and its proximity with the venous system suggest the need for further researches, especially in the comprehension of pulmonary symptoms.

Plant viral elongated nanoparticles modified for log-increases of foreign peptide immunogenicity and specific antibody detection

Elongated and flexuous recombinant nanoparticles were derived from Turnip mosaic virus to be used as bioscaffolds for increased peptide immunogenicity and peptide-specific antibody sensing. For this purpose, a 20-amino acid peptide derived from human vascular endothelial growth factor receptor 3 (VEGFR-3) was fused to the N-terminal region of Turnip mosaic virus coat protein (CP) by genetic insertion. The insertion was between codons corresponding to the first and second amino acids of the CP in two versions of a previously reported virus-derived vector. Systemic infections of two genetic constructs were achieved in two different plant hosts. The construct proved stable upon successive passages and generated virus nanoparticles identifiable under the electron microscope. The chimeric structures held the VEGFR-3 peptide. Purified VER3 nanoparticles were used to immunize mice, whose sera showed log increases of antibodies against the VEGFR-3 peptide when compared with mice immunized with peptide alone, thus providing the first quantitative data on the potential of elongated flexuous viruses for peptide immunogenicity increases. Purified VER3 nanoparticles also showed log increases in their ability to detect VER3 antibodies in sera, when used as reagents in ELISA assays, an application also used here for the first time.

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.

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.

Normal dendritic cell mobilization to lymph nodes under conditions of severe lymphatic hypoplasia

To address the requirement for lymphatic capillaries in dendritic cell (DC) mobilization from skin to lymph nodes (LNs), we used mice bearing one inactivated allele of vascular endothelial growth factor receptor 3 (VEGFR3) where skin lymphatic capillaries are reported absent. Unexpectedly, DC mobilization from the back skin to draining LNs was similar in magnitude, and kinetics to control mice and humoral immunity appeared intact. By contrast, DC migration from body extremities, including ear and forepaws, was ablated. An evaluation in different regions of skin revealed rare patches of lymphatic capillaries only in body trunk areas where migration was intact. That is, whereas the ear skin was totally devoid of lymphatic capillaries, residual capillaries in the back skin were present though retained only at ∼10% normal density. This reduction in density markedly reduced the clearance of soluble tracers, indicating that normal cell migration was spared under conditions when lymphatic transport function was poor. Residual lymphatic capillaries expressed slightly higher levels of CCL21 and migration of skin DCs to LNs remained dependent on CCR7 in Chy mice. DC migration from the ear could be rescued by the introduction of a limited number of lymphatic capillaries through skin transplantation. Thus, the development of lymphatic capillaries in the skin of body extremities was more severely impacted by a mutant copy of VEGFR3 than trunk skin, but lymphatic transport function was markedly reduced throughout the skin, demonstrating that even under conditions when a marked loss in lymphatic capillary density reduces lymph transport, DC migration from skin to LNs remains normal.

FLT4/VEGFR3 and Milroy disease: novel mutations, a review of published variants and database update

Milroy disease (MD) is an autosomal dominantly inherited primary lymphedema. In 1998, the gene locus for MD was mapped to 5q35.3 and variants in the VEGFR3 (FLT4) gene, encoding vascular endothelial growth factor receptor 3 (VEGFR3), were identified as being responsible for the majority of MD cases. Several reports have since been published detailing pathogenic FLT4 mutations. To date, a total of 58 different variants in FLT4, 20 of which are unpublished, have been observed in 95 families with MD. A review of published mutations is presented in this update. Furthermore, the unpublished variants are presented including clinical data. Comparison of clinical features in patients and their families with the same mutations reveals incomplete penetrance and variable expression, making genotype-phenotype correlations difficult. Most mutations are missense, but a few deletions and one splicing variant have also been reported. Several animal models have confirmed the role of VEGFR3 in lymphangiogenesis and studies show mutant VEGFR3 receptors are not phosphorylated. Here, an MD patient with the same p.Ile1053Phe change as seen in the Chy mouse is presented for the first time. This finding confirms that this mouse lineage is an excellent model for MD. All the data reviewed here has been submitted to a database based on the Leiden Open (source) Variation Database (LOVD) and is accessible online at www.lovd.nl/flt4.

Flow control in our vessels: vascular valves make sure there is no way back

The efficient transport of blood and lymph relies on competent intraluminal valves that ensure unidirectional fluid flow through the vessels. In the lymphatic vessels, lack of luminal valves causes reflux of lymph and can lead to lymphedema, while dysfunction of venous valves is associated with venous hypertension, varicose veins, and thrombosis that can lead to edema and ulcerations. Despite their clinical importance, the mechanisms that regulate valve formation are poorly understood and have only recently begun to be characterized. Here, we discuss new findings regarding the development of venous and lymphatic valves that indicate the involvement of common molecular mechanisms in regulating valve formation in different vascular beds.

Popliteal node visualization during standard pedal lymphoscintigraphy for a swollen limb indicates impaired lymph drainage

OBJECTIVE

The objective of our study was to examine the frequency and significance of visualization of popliteal nodes during lymphoscintigraphy for the investigation of lower extremity swelling.

MATERIALS AND METHODS

Technetium-99m-labeled nanocolloid was injected subcutaneously in the first web spaces of both feet of 204 consecutive patients (69 males, 135 females; age range, 11-79 years) undergoing routine, clinically indicated lymphoscintigraphy; imaging was performed 5, 45, and 150 minutes after injection. The patients were asked not to undertake any vigorous exercise between the injection and completion of imaging.

RESULTS

No popliteal nodes were visualized in 29 patients in whom there was no evidence of lymphedema on clinical or lymphoscintigraphic examination (group 1). Unilateral or bilateral popliteal nodes were visualized in 10 of 39 patients (25.6%) with clinical evidence of lymphedema but normal lymphoscintigraphy findings (group 2) (p < 0.005 vs group 1). In 136 patients with clinical evidence of lymphedema and abnormal lymphoscintigraphy findings (group 3), unilateral or bilateral popliteal nodes were visualized in 59 (43.4%) (p < 0.0001 vs group 1). Popliteal nodes were visualized in 40 of 73 limbs with "dermal backflow" (54.8%) and 42 of 335 limbs without dermal backflow (12.5%) (p < 0.0001).

CONCLUSION

Popliteal node visualization after subcutaneous foot web space injection is an important sign of abnormal lymphatic function in patients with clinical lymphedema of the lower extremities.