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

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.

Primary lymphoedema

Lymphoedema is the swelling of one or several parts of the body owing to lymph accumulation in the extracellular space. It is often chronic, worsens if untreated, predisposes to infections and causes an important reduction in quality of life. Primary lymphoedema (PLE) is thought to result from abnormal development and/or functioning of the lymphatic system, can present in isolation or as part of a syndrome, and can be present at birth or develop later in life. Mutations in numerous genes involved in the initial formation of lymphatic vessels (including valves) as well as in the growth and expansion of the lymphatic system and associated pathways have been identified in syndromic and non-syndromic forms of PLE. Thus, the current hypothesis is that most cases of PLE have a genetic origin, although a causative mutation is identified in only about one-third of affected individuals. Diagnosis relies on clinical presentation, imaging of the structure and functionality of the lymphatics, and in genetic analyses. Management aims at reducing or preventing swelling by compression therapy (with manual drainage, exercise and compressive garments) and, in carefully selected cases, by various surgical techniques. Individuals with PLE often have a reduced quality of life owing to the psychosocial and lifelong management burden associated with their chronic condition. Improved understanding of the underlying genetic origins of PLE will translate into more accurate diagnosis and prognosis and personalized treatment.

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.

Advances in Lymphedema

Lymphedema is a common, complex, and inexplicably underappreciated human disease. Despite a history of relative neglect by health care providers and by governmental health care agencies, the last decade has seen an explosive growth of insights into, and approaches to, the problem of human lymphedema. The current review highlights the significant advances that have occurred in the investigative and clinical approaches to lymphedema, particularly over the last decade. This review summarizes the progress that has been attained in the realms of genetics, lymphatic imaging, and lymphatic surgery. Newer molecular insights are explored, along with their relationship to future molecular therapeutics. Growing insights into the relationships among lymphedema, obesity, and other comorbidities are important to consider in current and future responses to patients with lymphedema.

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.

Cellular Origins of the Lymphatic Endothelium: Implications for Cancer Lymphangiogenesis

The lymphatic system plays important roles in physiological and pathological conditions. During cancer progression in particular, lymphangiogenesis can exert both positive and negative effects. While the formation of tumor associated lymphatic vessels correlates with metastatic dissemination, increased severity and poor patient prognosis, the presence of functional lymphatics is regarded as beneficial for anti-tumor immunity and cancer immunotherapy delivery. Therefore, a profound understanding of the cellular origins of tumor lymphatics and the molecular mechanisms controlling their formation is required in order to improve current strategies to control malignant spread. Data accumulated over the last decades have led to a controversy regarding the cellular sources of tumor-associated lymphatic vessels and the putative contribution of non-endothelial cells to this process. Although it is widely accepted that lymphatic endothelial cells (LECs) arise mainly from pre-existing lymphatic vessels, additional contribution from bone marrow-derived cells, myeloid precursors and terminally differentiated macrophages, has also been claimed. Here, we review recent findings describing new origins of LECs during embryonic development and discuss their relevance to cancer lymphangiogenesis.

Functional, structural, and molecular identification of lymphatic outflow from subconjunctival blebs

The purpose of this study is to evaluate outflow pathways from subconjunctival blebs and to identify their identity. Post-mortem porcine (n = 20), human (n = 1), and bovine (n = 1) eyes were acquired, and tracers (fluorescein, indocyanine green, or fixable/fluorescent dextrans) were injected into the subconjunctival space to create raised blebs where outflow pathways were visualized qualitatively and quantitatively. Rodents with fluorescent reporter transgenes were imaged for structural comparison. Concurrent optical coherence tomography (OCT) was obtained to study the structural nature of these pathways. Using fixable/fluorescent dextrans, tracers were trapped to the bleb outflow pathway lumen walls for histological visualization and molecular identification using immunofluorescence against lymphatic and blood vessel markers. Bleb outflow pathways could be observed using all tracers in all species. Quantitative analysis showed that the nasal quadrant had more bleb-related outflow pathways compared to the temporal quadrant (nasal: 1.9±0.3 pathways vs. temporal: 0.7±0.2 pathways; p = 0.003). However, not all blebs resulted in an outflow pathway (0-pathways = 18.2%; 1-pathway = 36.4%; 2-pathways = 38.6%; and 3-pathways = 6.8%). Outflow signal was validated as true luminal pathways using optical coherence tomography and histology. Bicuspid valves were identified in the direction of flow in porcine eyes. Immunofluorescence of labeled pathways demonstrated a lymphatic (Prox-1 and podoplanin) but not a blood vessel (CD31) identity. Therefore, subconjunctival bleb outflow occurs in discrete luminal pathways. They are lymphatic as assessed by structural identification of valves and molecular identification of lymphatic markers. Better understanding of lymphatic outflow may lead to improved eye care for glaucoma surgery and ocular drug delivery.

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.