Analysis of the coding regions of VEGFR3 and VEGFC in Milroy disease and other primary lymphoedemas

ADAMTS3 and FLT4 gene mutations result in congenital lymphangiectasia in newborns: A case report

BACKGROUND

Congenital lymphangiectasia is a rare disease characterized by dilated interstitial lymphatic vessels and cystic expansion of the lymphatic vessels. Congenital lymphangiectasia can affect various organ systems; however, it frequently occurs in the lungs accompanied with unexplained pleural effusion. Further, it might not be diagnosed during prenatal examination owing to the absence of pronounced abnormalities. However, after birth the newborn rapidly develops respiratory distress that quickly deteriorates. Genetic variations in proteins controlling the development of lymphatic vessels contribute to the pathophysiology of this disease. We report a rare case of heterozygous mutation of ADAMTS3 and FLT4 genes, which have not been reported previously.

CASE SUMMARY

We analysed the case of a neonate who had presented with only pleural effusion at a late gestational age and eventually died due to its inability to establish spontaneous breathing after birth. An autopsy revealed lymphangiectasia of the organ systems. Further, whole exome sequencing revealed heterozygous mutations of the lymphangiogenesis-controlling genes, ADAMTS3 and FLT4, and Sanger verification revealed similar lesions in the mother with no symptoms.

CONCLUSION

Considering the presented case, obstetricians should observe unexplained foetal pleural effusion, and perform pathology analysis and whole exome sequencing for a conclusive diagnosis and prompt treatment.

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.

Case Report: The compound heterozygotes variants in FLT4 causes autosomal recessive hereditary lymphedema in a Chinese family

Background: Lymphedema is a local form of tissue swelling, which is caused by excessive retention of lymph fluid in interstitial compartment caused by impaired lymphatic drainage damage. Primary lymphedema is caused by developmental lymphatic vascular abnormalities. Most cases are inherited as autosomal dominant, with incomplete penetrance and variable expression. Here we report compound heterozygotes variants in FLT4 of a Chinese family associated with primary lymphedema display autosomal recessive inheritance. Case presentation: Trio-whole-exome sequencing (Trio-WES) was performanced to analyse the underlying genetic cause of a proband with primary lymphedema in a Chinese family. Sanger sequencing was used to validate the variants in proband with primary lymphedema and members of the family with no clinical signs and symptoms. We reported compound heterozygotes for the Fms Related Receptor Tyrosine Kinase 4 (FLT4) gene detected in the proband, who carrying two different point variants. One was a missense variant (NM_182925.5; c.1504G>A, p.Glu502Lys), and the other was a recurrent variant (NM_182925.5; c.3323_3325del, p.Phe1108del). The missense variant c.1504G>A was detected in the proband, unaffected father, and unaffected paternal grandmother but not detected in unaffected paternal grandfather. The recurrent variant c.3323_3325del was detected in the proband, unaffected mother, and unaffected maternal grandfather but not detected in unaffected maternal grandmother. Our results suggests the possibility of an autosomal recessive inherited form of primary lymphedema resulting from variants of FLT4 encoding the vascular endothelial growth factor receptor-3. Conclusion: The results of the present study identifed compound heterozygotes FLT4 variants in a family with primary lymphedema which provides more information for autosomal recessive primary lymphedema caused by FLT4.

Heterozygous deletion of the VEGFC gene in 4q34.3 is associated with Milroy-like lymphedema: First prenatal case report

Deleterious variants in the vascular endothelial growth factor C (VEGFC) gene have been recently associated with Milroy-like primary lymphedema, an autosomal dominant disorder, characterized mainly by swelling of the lower limbs due to functional impairment of the lymphatic vessels. To date, only 26 patients with congenital lymphedema harboring VEGFC pathogenic variants were documented. Here, we describe the first prenatal case of a fetus with Milroy-like disease. Fetal ultrasound showed bilateral foot swelling. Chromosomal microarray analysis revealed a 137-kb copy number loss in 4q34.3 including only VEGFC gene in the propositus fetus. Segregation analysis showed that the deletion was inherited from the affected mother and grandmother. Taken together, our study highlights the important role of microarray analysis to detect subtle chromosomal imbalances in the prenatal setting and contributes to delineate the fetal phenotype of VEGFC-related primary congenital lymphedema.

The impact of VEGF on cancer metastasis and systemic disease

Metastasis is the leading cause of cancer-associated mortality and the underlying mechanisms of cancer metastasis remain elusive. Both blood and lymphatic vasculatures are essential structures for mediating distal metastasis. The vasculature plays multiple functions, including accelerating tumor growth, sustaining the tumor microenvironment, supplying growth and invasive signals, promoting metastasis, and causing cancer-associated systemic disease. VEGF is one of the key angiogenic factors in tumors and participates in the initial stage of tumor development, progression and metastasis. Consequently, VEGF and its receptor-mediated signaling pathways have become one of the most important therapeutic targets for treating various cancers. Today, anti-VEGF-based antiangiogenic drugs (AADs) are widely used in the clinic for treating different types of cancer in human patients. Despite nearly 20-year clinical experience with AADs, the impact of these drugs on cancer metastasis and systemic disease remains largely unknown. In this review article, we focus our discussion on tumor VEGF in cancer metastasis and systemic disease and mechanisms underlying AADs in clinical benefits.

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.

The physiological and pathological functions of VEGFR3 in cardiac and lymphatic development and related diseases

Vascular endothelial growth factor receptors (VEGFRs) are part of the evolutionarily conserved VEGF signalling pathways that regulate the development and maintenance of the body's cardiovascular and lymphovascular systems. VEGFR3, encoded by the FLT4 gene, has an indispensable and well-characterized function in development and establishment of the lymphatic system. Autosomal dominant VEGFR3 mutations, that prevent the receptor functioning as a homodimer, cause one of the major forms of hereditary primary lymphoedema; Milroy disease. Recently, we and others have shown that FLT4 variants, distinct to those observed in Milroy disease cases, predispose individuals to Tetralogy of Fallot, the most common cyanotic congenital heart disease, demonstrating a novel function for VEGFR3 in early cardiac development. Here, we examine the familiar and emerging roles of VEGFR3 in the development of both lymphovascular and cardiovascular systems, respectively, compare how distinct genetic variants in FLT4 lead to two disparate human conditions, and highlight the research still required to fully understand this multifaceted receptor.

Development and aging of the lymphatic vascular system

The lymphatic vasculature has a pivotal role in regulating body fluid homeostasis, immune surveillance and dietary fat absorption. The increasing number of in vitro and in vivo studies in the last decades has shed light on the processes of lymphatic vascular development and function. Here, we will discuss the current progress in lymphatic vascular biology such as the mechanisms of lymphangiogenesis, lymphatic vascular maturation and maintenance and the emerging mechanisms of lymphatic vascular aging.

Segregation Analysis of Rare NRP1 and NRP2 Variants in Families with Lymphedema

Neuropilins are transmembrane coreceptors expressed by endothelial cells and neurons. NRP1 and NRP2 bind a variety of ligands, by which they trigger cell signaling, and are important in the development of lymphatic valves and lymphatic capillaries, respectively. This study focuses on identifying rare variants in the NRP1 and NRP2 genes that could be linked to the development of lymphatic malformations in patients diagnosed with lymphedema. Two hundred and thirty-five Italian lymphedema patients, who tested negative for variants in known lymphedema genes, were screened for variants in NRP1 and NRP2. Two probands carried variants in NRP1 and four in NRP2. The variants of both genes segregated with lymphedema in familial cases. Although further functional and biochemical studies are needed to clarify their involvement with lymphedema and to associate NRP1 and NRP2 with lymphedema, we suggest that it is worthwhile also screening lymphedema patients for these two new candidate genes.

Lymphedema (Seminars in pediatric surgery)

Lymphedema is the chronic, progressive swelling of tissue due to inadequate lymphatic function. Over time, protein-rich fluid accumulates in the tissue causing it to enlarge. Lymphedema is a specific disease and should not be used as a generic term for an enlarged extremity. The diagnosis is made by history and physical examination, and confirmed with lymphoscintigraphy. Intervention includes patient education, compression, and rarely, surgery. Patients are advised to exercise, maintain a normal body mass index, and moisturize / protect the diseased limb from incidental trauma. Conservative management consists of compression regimens. Operative interventions either attempt to address the underlying lymphatic anomaly or the excess tissue. Lymphatic-venous anastomosis and lymph node transfer attempt to create new lymphatic connections to improve lymph flow. Suction-assisted lipectomy and cutaneous excision reduce the size of the area by removing fibroadipose hypertrophy.

A dual role for Tbx1 in cardiac lymphangiogenesis through genetic interaction with Vegfr3

The transcription factor TBX1 is the major gene implicated in 22q11.2 deletion syndrome (22q11.2DS). The complex clinical phenotype includes vascular anomalies and a recent report presented new cases of primary lymphedema in 22q11.2DS patients. We have previously shown that TBX1 is required for systemic lymphatic vessel development in prenatal mice and it is critical for their survival postnatally. Using loss-of-function genetics and transgenesis in the mouse, we show here a strong genetic interaction between Tbx1 and Vegfr3 in cardiac lymphangiogenesis. Intriguingly, we found that different aspects of the cardiac lymphatic phenotype in Tbx1-Vegfr3 compound heterozygotes were regulated independently by the two genes, with Tbx1 primarily regulating vessel numbers and Vegfr3 vessel morphology. Consistent with this observation, Tbx1^Cre -activated expression of a Vegfr3 transgene rescued partially the cardiac lymphatic abnormalities in compound heterozygotes. Through time-controlled genetic experiments, we show that Tbx1 is activated and required in cardiac lymphatic endothelial cell (LEC) progenitors between E10.5 and E11.5. Furthermore, we found that it is also required later in development for the growth of the cardiac lymphatics. Finally, our study revealed a differential sensitivity between ventral and dorsal cardiac lymphatics to the effects of altered Tbx1 and Vegfr3 gene dosage, and we show that this likely results from an earlier requirement for Tbx1 in ventral cardiac LEC progenitors.

Investigation on the role of biallelic variants in VEGF-C found in a patient affected by Milroy-like lymphedema

Background

Milroy‐like disease is the diagnostic definition used for patients with phenotypes that resemble classic Milroy disease (MD) but are negative to genetic testing for FLT4. In this study, we aimed at performing a genetic characterization and biochemical analysis of VEGF‐C variations found in a female proband born with congenital edema consistent with Milroy‐like disease.

Methods

The proband underwent next‐generation sequencing‐based genetic testing for a panel of genes associated with known forms of hereditary lymphedema. Segregation analysis was performed on family members by direct sequencing. In vitro studies were performed to evaluate the role of a novel identified variant.

Results

Two VEGF‐C variations were found in the proband, a novel p.(Ser65Arg) and a pathogenic c.148‐3_148‐2delCA, of paternal and maternal origin, respectively. Functional characterization of the p.(Ser65Arg) variation in vitro showed alterations in VEGF‐C processing.

Conclusions

Our findings reveal an interesting case in which biallelic variants in VEGF‐C are found in a patient with Milroy‐like lymphedema. These data expand our understanding of the etiology of congenital Milroy‐like lymphedema.

Update and audit of the St George's classification algorithm of primary lymphatic anomalies: a clinical and molecular approach to diagnosis

Primary lymphatic anomalies may present in a myriad of ways and are highly heterogenous. Careful consideration of the presentation can lead to an accurate clinical and/or molecular diagnosis which will assist with management. The most common presentation is lymphoedema, swelling resulting from failure of the peripheral lymphatic system. However, there may be internal lymphatic dysfunction, for example, chylous reflux, or lymphatic malformations, including the thorax or abdomen. A number of causal germline or postzygotic gene mutations have been discovered. Some through careful phenotyping and categorisation of the patients based on the St George’s classification pathway/algorithm. The St George’s classification algorithm is aimed at providing an accurate diagnosis for patients with lymphoedema based on age of onset, areas affected by swelling and associated clinical features. This has enabled the identification of new causative genes. This update brings the classification of primary lymphatic disorders in line with the International Society for the Study of Vascular Anomalies 2018 classification for vascular anomalies. The St George’s algorithm considers combined vascular malformations and primary lymphatic anomalies. It divides the types of primary lymphatic anomalies into lymphatic malformations and primary lymphoedema. It further divides the primary lymphoedema into syndromic, generalised lymphatic dysplasia with internal/systemic involvement, congenital-onset lymphoedema and late-onset lymphoedema. An audit and update of the algorithm has revealed where new genes have been discovered and that a molecular diagnosis was possible in 26% of all patients overall and 41% of those tested.

The Lymphatic System in Obesity, Insulin Resistance, and Cardiovascular Diseases

Obesity, insulin resistance, dyslipidemia, and hypertension are fundamental clinical manifestations of the metabolic syndrome. Studies over the last few decades have implicated chronic inflammation and microvascular remodeling in the development of obesity and insulin resistance. Newer observations, however, suggest that dysregulation of the lymphatic system underlies the development of the metabolic syndrome. This review summarizes recent advances in the field, discussing how lymphatic abnormality promotes obesity and insulin resistance, and, conversely, how the metabolic syndrome impairs lymphatic function. We also discuss lymphatic biology in metabolically dysregulated diseases, including type 2 diabetes, atherosclerosis, and myocardial infarction.

Application of microscale culture technologies for studying lymphatic vessel biology

Immense progress in microscale engineering technologies has significantly expanded the capabilities of in vitro cell culture systems for reconstituting physiological microenvironments that are mediated by biomolecular gradients, fluid transport, and mechanical forces. Here, we examine the innovative approaches based on microfabricated vessels for studying lymphatic biology. To help understand the necessary design requirements for microfluidic models, we first summarize lymphatic vessel structure and function. Next, we provide an overview of the molecular and biomechanical mediators of lymphatic vessel function. Then we discuss the past achievements and new opportunities for microfluidic culture models to a broad range of applications pertaining to lymphatic vessel physiology. We emphasize the unique attributes of microfluidic systems that enable the recapitulation of multiple physicochemical cues in vitro for studying lymphatic pathophysiology. Current challenges and future outlooks of microscale technology for studying lymphatics are also discussed. Collectively, we make the assertion that further progress in the development of microscale models will continue to enrich our mechanistic understanding of lymphatic biology and physiology to help realize the promise of the lymphatic vasculature as a therapeutic target for a broad spectrum of diseases.

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.

Outcomes of Vascularized Lymph Node Transfer and Lymphovenous Anastomosis for Treatment of Primary Lymphedema

BACKGROUND

Primary lymphedema is a debilitating disease. This study was to investigate the outcomes between vascularized lymph node transfer (VLNT) and lymphovenous anastomosis (LVA) for treating primary lymphedema.

METHODS

Between January 2010 and December 2016, 17 patients with mean age of 31.5 ± 15.5 (ranged, 2-57) years diagnosed with 19 primary limb lymphedema were recruited. Patients with patent lymphatic ducts on indocyanine green lymphography were indicated for LVA, whereas those without patent lymphatic ducts were indicated for VLNT. Circumferential limb measurements, body weight, episodes of cellulitis and Lymphedema Quality-of-Life (LYMQoL) questionnaire were compared between preoperatively and postoperatively.

RESULTS

Fifteen lymphedematous limbs underwent VLNT (79%) and 4 underwent LVA (21%). All VLNT flaps survived. At a mean follow-up of 19.7 ± 8.5 months, mean reduction of limb circumference, body weight, and episodes of cellulitis were 3.7 ± 2.9 cm and 1.9 ± 2.9 cm (P = 0.2); 6.6 ± 5.9 kg and 1.7 ± 0.6 kg (P < 0.05); 5.1 ± 2.8 times/y and 4.2 ± 0.5 times/y in VLNT and LVA groups, respectively (P = 0.7). Improvements in overall score (from 3.9 ± 1.2 to 6.4 ± 1.1, P < 0.05) of the LYMQoL in VLNT group had statistical significant difference than that (from 3.0 ± 1.4 to 5.0 ± 2.4, P = 0.07) in LVA group.

CONCLUSIONS

Both VLNT and LVA can effectively treat primary lymphedema patients. The reduction of above-knee circumference, body weight, episodes of cellulitis, and the improvement of LYMQoL was significantly greater in LVNT compared with LVA.

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.

A Novel Splice-Site Mutation in VEGFC Is Associated with Congenital Primary Lymphoedema of Gordon

Lymphedema is characterized by chronic swelling of any body part caused by malfunctioning or obstruction in the lymphatic system. Primary lymphedema is often considered genetic in origin. VEGFC, which is a gene encoding the ligand for the vascular endothelial growth factor receptor 3 (VEGFR3/FLT4) and important for lymph vessel development during lymphangiogenesis, has been associated with a specific subtype of primary lymphedema. Through Sanger sequencing of a proband with bilateral congenital pedal edema resembling Milroy disease, we identified a novel mutation (NM_005429.2; c.361+5G>A) in VEGFC. The mutation induced skipping of exon 2 of VEGFC resulting in a frameshift and the introduction of a premature stop codon (p.Ala50ValfsTer18). The mutation leads to a loss of the entire VEGF-homology domain and the C-terminus. Expression of this Vegfc variant in the zebrafish floorplate showed that the splice-site variant significantly reduces the biological activity of the protein. Our findings confirm that the splice-site variant, c.361+5G>A, causes the primary lymphedema phenotype in the proband. We examine the mutations and clinical phenotypes of the previously reported cases to review the current knowledge in this area.

A novel mutation in the conserved sequence of vascular endothelial growth factor receptor 3 leads to primary lymphoedema

Objective

To investigate whether lymphoedema in a Chinese family showed the hereditary and clinical characteristics of Milroy disease, an autosomal dominant form of congenital lymphoedema, typically characterized by chronic lower limb tissue swelling due to abnormal lymphatic vasculature development, and to perform mutational analyses of vascular endothelial growth factor receptor (VEGFR)3.

Methods

Individuals from a three-generation family affected by congenital lymphoedema were clinically assessed for Milroy disease. Mutation analysis of VEGFR3 was performed using DNA from family members and healthy controls.

Results

Out of 20 family members, eight were diagnosed with hereditary lymphoedema. Mutation analyses revealed a novel mutation site for c.3163 G>A, resulting in a p.1055D>N mutation in the second tyrosine kinase domain of VEGFR3, which was present in affected individuals only (absent in all unaffected family members and 130 healthy controls). Computed functional analyses showed the mutation may lead to structural alterations with a probability of 0.99999 of being disease causing.

Conclusion

A novel mutation associated with Milroy disease was identified in a Chinese family, expanding our knowledge of VEGFR3 gene function and providing a potential molecular target for treating hereditary lymphoedema.

From fish embryos to human patients: lymphangiogenesis in development and disease

The lymphatic vasculature plays vital roles in immune surveillance, fluid homeostasis and fat absorption in the body. Lined by endothelial cells, the lymphatic system is functionally distinct from the blood vasculature, and fulfills different physiological functions. In recent years, insight from zebrafish, mice and human patients have improved our understanding of lymphatics, and the interplay between zebrafish genetics, studies in mice and GWAS analysis in human patients have identified genes that, when mutated, will lead to lymphedema formation. Here, we focus on components of the Vegfr3 pathway, and how they are connected to Milroy disease and Hennekam syndrome.

Vegfd modulates both angiogenesis and lymphangiogenesis during zebrafish embryonic development

Vascular endothelial growth factors (VEGFs) control angiogenesis and lymphangiogenesis during development and in pathological conditions. In the zebrafish trunk, Vegfa controls the formation of intersegmental arteries by primary angiogenesis and Vegfc is essential for secondary angiogenesis, giving rise to veins and lymphatics. Vegfd has been largely thought of as dispensable for vascular development in vertebrates. Here, we generated a zebrafish vegfd mutant by genome editing. vegfd mutants display significant defects in facial lymphangiogenesis independent of vegfc function. Strikingly, we find that vegfc and vegfd cooperatively control lymphangiogenesis throughout the embryo, including during the formation of the trunk lymphatic vasculature. Interestingly, we find that vegfd and vegfc also redundantly drive artery hyperbranching phenotypes observed upon depletion of Flt1 or Dll4. Epistasis and biochemical binding assays suggest that, during primary angiogenesis, Vegfd influences these phenotypes through Kdr (Vegfr2) rather than Flt4 (Vegfr3). These data demonstrate that, rather than being dispensable during development, Vegfd plays context-specific indispensable and also compensatory roles during both blood vessel angiogenesis and lymphangiogenesis.

Adipose-derived stem cell transplantation for therapeutic lymphangiogenesis in a mouse secondary lymphedema model

AIM

Secondary lymphedema is observed in common after postmalignancy treatment of the breast and the gynecologic organs but effective therapies are not established. Adipose-derived stem cells (ADSCs), which are pluripotent, regenerative in local injection, are tested for murine hindlimb secondary lymphedema by regenerative method.

METHODS & RESULTS

Mice were divided into four groups: no ADSCs, 1 × 10(6) ADSCs, 1 × 10(5) ADSCs and 1 × 10(4) ADSCs (each group, n = 20) in a stringent surgical resection and irradiation. Circumferential measurement, lymphatic flow assessment and quantification of lymphatic vessels were performed.

RESULTS

The numbers of lymphatic vessels by LYVE-1 immunohistochemistry, and VEGF-C- or VEGFR3-expressing cells were significantly increased in transplanted groups (p < 0.05).

CONCLUSION

ADSCs can restore the lymphatic vascular network in secondary lymphedema with increased collecting vessels.

Pediatric lymphatic malformations: evolving understanding and therapeutic options

Multimodal treatment of lymphatic malformations continues to expand as new information about the biology and genetics of these lesions is discovered, along with knowledge gained from clinical practice. A patient-centered approach, ideally provided by a multidisciplinary medical and surgical team, should guide timing and modality of treatment. Current treatment options include observation, surgery, sclerotherapy, radiofrequency ablation, and laser therapy. New medical and surgical therapies are emerging, and include sildenafil, propranolol, sirolimus, and vascularized lymph node transfer. The primary focus of management is to support and optimize these patients' quality of life. Researchers continue to study lymphatic malformations with the goal of increasing therapeutic options and developing effective clinical pathways for these complicated lesions.

Primary Intestinal Lymphangiectasia Manifested as Unusual Edemas and Effusions: A Case Report

Primary intestinal lymphangiectasia (PIL) is a rare disorder of unknown etiology characterized by diffuse or localized dilation and eventual rupture of the enteric lymphatic vessels in mucosa, submucosa, and/or subserosa. Lymph, rich in all kinds of proteins and lymphocytes, leaks into the gastrointestinal tract via the affected lymphatic vessels causing hypoproteinemia and lymphopenia. The main symptom is variable degrees of pitting edemas of bilateral lower limbs. But edemas of any other parts of body, and mild serous effusions may also occur sometimes. PIL occurs in conjunction with a right hemifacial edema, a right upper limb lymphedema, asymmetric bilateral calves edemas, and a unilateral massive pleural effusion seems never to be reported before. In addition, increased enteric protein loss that may cause severe hypoproteinemia usually get overlooked, and the lymphatic system disorders always put the diagnoses in a dilemma.We described a case of a 17-year-old Chinese girl with a history of gradually progressive swellings of right-sided face, right upper limb, and bilateral calves since 3 to 4 months of age. A right-sided massive pleural effusion, a moderate pericardial effusion, and a mild ascites have been proved unchanged by a series of computerized tomography (CT) scans since 5 years ago. The diagnosis of PIL was finally confirmed by severe hypoproteinemia, endoscopic changes, and histology of jejunum biopsy. Further lymphoscintigraphy and lymphangiography also identified lymph leakage in her bowel and several abnormal lymphatic vessels. A high-protein, low-fat diet supplemented with medium-chain triglycerides (MCT) showed some benefit.This case suggested that PIL was a rare but important etiology of hypoproteinemia, effusions, and edemas. PIL, effusions, and lymphedema can be the features of multisegmental generalized lymphatic dysplasia. In addition, both lymphoscintigraphy and intranodal lymphangiography could be considered when lymphatic system disorders are suspected.

A Novel Missense Mutation in FLT4 Causes Autosomal Recessive Hereditary Lymphedema

BACKGROUND

Primary lymphedema covers around 10% of all lymphedema cases. Most cases segregate as an autosomal dominant trait and rarely manifest autosomal recessive inheritance. Our research aimed to map and ultimately to hunt the mutation that causes hereditary lymphedema in an extended consanguineous Muslim family consisting of several affected individuals.

METHODS AND RESULTS

We attempted molecular diagnosis by applying homozygosity mapping and whole genome linkage analysis. A candidate locus of 2.3 Mb located on chromosome 5q35.3 was identified, yielding an overall LOD score of 3.18. This locus has been previously linked to congenital lymphedema, namely by the FLT4 gene. Mutations in FLT4 that were previously described in Muslim-Israeli families were discarded as culprit using sequence analysis. Sanger sequencing the gene revealed a novel missense variant in exon 28 (NM_182925.4: c.3704C>G; p.Ser1235Cys). This variant has perfect segregation within the extended family and was not previously reported in either common or pathogenic variants databases.

CONCLUSIONS

Our mutation is the first reported pathogenic variant located outside the tyrosine kinase domains of the VEGFR3 receptor, and the second to portray autosomal recessive inheritance. The homozygous substitution of serine by cysteine at position 1235 affects protein tyrosine kinase activity, possibly through a null effect mechanism rather than a negative dominant effect. Our variant is associated with a mild phenotype, possibly reflecting some residual receptor activity, most probably attributed to the variant's location beyond the TK domains.

Isolation of human lymphatic endothelial cells by multi-parameter fluorescence-activated cell sorting

Lymphatic system disorders such as primary lymphedema, lymphatic malformations and lymphatic tumors are rare conditions that cause significant morbidity but little is known about their biology. Isolating highly pure human lymphatic endothelial cells (LECs) from diseased and healthy tissue would facilitate studies of the lymphatic endothelium at genetic, molecular and cellular levels. It is anticipated that these investigations may reveal targets for new therapies that may change the clinical management of these conditions. A protocol describing the isolation of human foreskin LECs and lymphatic malformation lymphatic endothelial cells (LM LECs) is presented. To obtain a single cell suspension tissue was minced and enzymatically treated using dispase II and collagenase II. The resulting single cell suspension was then labelled with antibodies to cluster of differentiation (CD) markers CD34, CD31, Vascular Endothelial Growth Factor-3 (VEGFR-3) and PODOPLANIN. Stained viable cells were sorted on a fluorescently activated cell sorter (FACS) to separate the CD34(Low)CD31(Pos)VEGFR-3(Pos)PODOPLANIN(Pos) LM LEC population from other endothelial and non-endothelial cells. The sorted LM LECs were cultured and expanded on fibronectin-coated flasks for further experimental use.

Self-care status, symptom burden, and reported infections in individuals with lower-extremity primary lymphedema

PURPOSE

The purposes of this study were (a) to evaluate self-care, symptom burden, and reported infections among individuals with lower-extremity primary lymphedema; (b) to examine the differences in self-care, symptom burden, and reported infections between individuals with unilateral and those with bilateral lower-extremity primary lymphedema; and (c) to examine the associations among self-care status, symptom burden, and reported infections in individuals with lower-extremity primary lymphedema.

DESIGN

A secondary data analysis was used. Data were collected from a cross-sectional survey study supported by the National Lymphedema Network from March 2006 through January 2010. The surveys were available both online and in hard copy in order to increase accessibility.

METHODS

Descriptive statistics were conducted and associations between variables were assessed using Mann-Whitney tests and chi-square tests of independence. Multiple logistic regression was used to test for associations while controlling for potentially confounding variables.

FINDINGS

A total of 803 participants reported having lower-extremity primary lymphedema. The majority of the participants were female (82.9%), White (74.2%), and from the United States (90.7%). Approximately two thirds of the respondents conducted some home daily lymphedema self-care. Over half of the respondents reported experiencing symptom burden and 44.8% reported at least one episode of infection. Compared to individuals with unilateral lower-extremity primary lymphedema, individuals with bilateral lower-extremity lymphedema were more likely to conduct skin care (p = .004), use alternative medications (p = .005), more frequently reported symptoms (p < .05), and more likely to report at least one episode of infection (p = .002). Respondents who reported use of compression garments also were less likely to have self-reported pain (p = .002), poor range of motion (p = .026), and numbness (p = .001). Participants who reported exercising also were less likely to have self-reported pain (p = .003). Participants who reported at least one episode of infection also reported experiencing more symptoms (p < .001).

CONCLUSIONS

Individuals with lower-extremity primary lymphedema experienced substantial symptom burden and infection episodes. Significant associations were identified among self-care, symptom burden, and reported infections.

CLINICAL RELEVANCE

The findings support the need for clinicians to educate patients with lower-extremity primary lymphedema regarding the importance of self-care, symptom management, and infection control. It is critically important for clinicians to evaluate symptom burden and reduce infections in individuals with lower-extremity primary lymphedema.

Lymphedema

Lymphedema is the chronic, progressive swelling of tissue due to inadequate lymphatic function. Over time, protein-rich fluid accumulates in the tissue, causing it to enlarge. Lymphedema is a specific disease and should not be used as a generic term for an enlarged extremity. The diagnosis is made by evaluating the history and physical examination, and can be confirmed with lymphoscintigraphy. Intervention includes patient education, compression, and, rarely, surgery. Patients are advised to exercise, maintain a normal body mass index, and moisturize/protect the diseased limb from incidental trauma. Conservative management consists of compression regimens. Operative interventions either attempt to address the underlying lymphatic anomaly or the excess tissue. Lymphatic-venous anastomosis and lymph node transfer attempt to create new lymphatic connections to correct the defect. Suction-assisted lipectomy and staged cutaneous/subcutaneous excision reduce the size of the area by removing extra tissues.

The link between lymphedema, breast reconstruction and microsurgery

SUMMARY 

This management perspective will explore the relationship between lymphedema and breast reconstruction surgery. Little data exist, but early reports suggest breast reconstruction may be associated with a lower risk of lymphedema. Theories surrounding this relationship, as well as available data on lymphatic repair theories, will be discussed. In addition, the emerging role of lymphatic surgery to prevent or reverse lymphedema will be discussed. The refinement of advanced microsurgical techniques has resulted in a renewed interest in lymphatic surgery to cure lymphedema. However, efficacy, validation of surgical results, and surgery's ability to eliminate from patients the need for daily compression garments and therapy need further study.

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.

Transcription of the vascular endothelial growth factor receptor-3 (VEGFR3) gene is regulated by the zinc finger proteins Sp1 and Sp3 and is under epigenetic control: transcription of vascular endothelial growth factor receptor 3

BACKGROUND

In the past, the vascular endothelial growth factor receptor-3 (VEGFR-3) has been linked to the regulation of lymphangiogenesis and the lymphatic spread of solid malignancies. The molecular mechanisms controlling VEGFR3 gene expression have, however, remained poorly understood. Here, we aimed at assessing these mechanisms through VEGFR3 gene promoter analysis and the identification of transcription factors binding to it. In addition, we focussed on epigenetic modifications underlying VEGFR3 transcription regulation.

METHODS

5' Deletion analyses for the identification of functional promoter elements, electrophoretic mobility shift assays, chromatin immunoprecipitations, methylation-specific PCRs, and Trichostatin A (TSA) and 5-Aza desoxycytidine (5-Aza dC) treatments were performed in this study.

RESULTS

Following the isolation of a 2 kb stretch of 5'-flanking DNA of VEGFR3, we identified a novel GC-rich element (GRE) spanning -101/-66 sufficient for VEGFR3 transcription and activated by Sp1 and Sp3, respectively. Histone de-acetylase inhibition by TSA led to the accumulation of acetylated histones H3/H4 at the VEGFR3 gene promoter, up-regulation of its mRNA levels, and transactivation of promoter reporter constructs in endothelial cell lines. Similarly, methylation inhibition by 5-Aza dC triggered up-regulation of VEGFR3 mRNA levels and increased promoter activity. TSA and 5-Aza-dC did not influence Sp1/Sp3 binding, but increased the transactivating capacity of both transcription factors, suggesting epigenetic modification as an underlying mechanism.

CONCLUSIONS

Here we describe the identification of regulatory elements controlling human VEGFR3 gene expression and show that histone acetylation and CpG methylation are important determinants of VEGFR3 transcription regulation. These findings may facilitate the development of intervention strategies aimed at targeting VEGFR3-based tumor lymphangiogenesis and/or lymphatic tumor spread.

[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.

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.

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.

The new era of the lymphatic system: no longer secondary to the blood vascular system

The blood and lymphatic systems are the two major circulatory systems in our body. Although the blood system has been studied extensively, the lymphatic system has received much less scientific and medical attention because of its elusive morphology and mysterious pathophysiology. However, a series of landmark discoveries made in the past decade has begun to change the previous misconception of the lymphatic system to be secondary to the more essential blood vascular system. In this article, we review the current understanding of the development and pathology of the lymphatic system. We hope to convince readers that the lymphatic system is no less essential than the blood circulatory system for human health and well-being.

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.