OBJECTIVE: Rare, deleterious genetic variants in FLT4 are associated with Tetralogy of Fallot (TOF), the most common cyanotic congenital heart disease (CHD). Distinct genetic variants in FLT4 are also an established cause of Milroy disease, the most prevalent form of primary hereditary lymphoedema. Phenotypic features of these two conditions are non-overlapping, implying pleiotropic cellular mechanisms during development.
RESULTS: Here, we show that FLT4 variants identified in TOF patients, when expressed in primary human endothelial cells, cause aggregation of FLT4 protein in the perinuclear endoplasmic reticulum, activating proteostatic and metabolic signalling, whereas lymphoedema-associated FLT4 variants and wildtype FLT4 do not. FLT4 TOF variants display characteristic gene expression profiles in key developmental signalling pathways, revealing a role for FLT4 in cardiogenesis distinct from its role in lymphatic development. Inhibition of proteostatic signalling abrogates these effects, identifying potential avenues for therapeutic intervention. Depletion of flt4 in zebrafish caused cardiac phenotypes of reduced heart size and altered heart looping. These phenotypes were rescued with coinjection of wildtype human FLT4 mRNA, but incompletely or not at all by mRNA harbouring FLT4 TOF variants.
CONCLUSIONS: Taken together, we identify a pathogenic mechanism for FLT4 variants predisposing to TOF that is distinct from the known dominant negative mechanism of Milroy-causative variants. FLT4 variants give rise to conditions of the two circulatory subdivisions of the vascular system via distinct developmental pleiotropic molecular mechanisms.
UNASSIGNED: Proteostatic dysfunction, if confirmed as a mechanism of CHD pathogenesis for other predisposing genes, may identify pathways to therapeutic interventions. Distinguishing mechanistically how variants in FLT4 give rise to CHD may have potential to individualise genetic counselling in affected families.

Developmental and functional defects in the lymphatic system are responsible for primary lymphoedema (PL). PL is a chronic debilitating disease caused by increased accumulation of interstitial fluid, predisposing to inflammation, infections and fibrosis. There is no cure, only symptomatic treatment is available. Thirty-two genes or loci have been linked to PL, and another 22 are suggested, including Hepatocyte Growth Factor (HGF). We searched for HGF variants in 770 index patients from the Brussels PL cohort. We identified ten variants predicted to cause HGF loss-of-function (six nonsense, two frameshifts, and two splice-site changes; 1.3% of our cohort), and 14 missense variants predicted to be pathogenic in 17 families (2.21%). We studied co-segregation within families, mRNA stability for non-sense variants, and in vitro functional effects of the missense variants. Analyses of the mRNA of patient cells revealed degradation of the nonsense mutant allele. Reduced protein secretion was detected for nine of the 14 missense variants expressed in COS-7 cells. Stimulation of lymphatic endothelial cells with these 14 HGF variant proteins resulted in decreased activation of the downstream targets AKT and ERK1/2 for three of them. Clinically, HGF-associated PL was diverse, but predominantly bilateral in the lower limbs with onset varying from early childhood to adulthood. Finally, aggregation study in a second independent cohort underscored that rare likely pathogenic variants in HGF explain about 2% of PL. Therefore, HGF signalling seems crucial for lymphatic development and/or maintenance in human beings and HGF should be included in diagnostic genetic screens for PL.

Primary lymphoedema, axillary web syndrome (AWS) and yellow nail syndrome may be related. Mr B is a 66-year-old gentleman with genital lymphoedema and lymphoedema of all four extremities. In 2023, he was diagnosed with non-Hodgkin lymphoma and also underwent cardiac surgery. In November 2023, he completed an inpatient rehabilitation at the Földi clinic in Germany, where he received intensive treatment for his lymphoedema and was also diagnosed with bilateral AWS. The presence of AWS in a patient with primary lymphoedema and no history of axillary surgery is unique. Although AWS typically presents after axillary surgery, this case highlights that it can also occur in patients without lymph node surgery. While the precise cause of this presentation of AWS is not known, it may be connected to yellow nail syndrome or potentially the recent chemotherapy treatment. This article will describe the clinical case, highlighting the need for further research on AWS present in primary lymphoedema.

This case study describes the successful management of a patient with primary lymphoedema, who was experiencing lymphorrhoea and epidermolysis, using a multidisciplinary approach. The patient had Klippel-Trenaunay syndrome. The multidisciplinary team, in an outpatient clinic in Japan, included a certified lymphoedema therapist, plastic surgeons, and a wound, ostomy and continence nurse. The team performed complex physical therapy and lymphaticovenular anastomosis, which promoted the resolution of the lymphorrhoea. This resulted in improvements in skin condition, the prevention of recurrent cellulitis, and no increase in limb circumferences during the 1-year follow-up period. This report highlights the importance of a multidisciplinary approach to lymphoedema management, including lymphorrhoea control that fitted in with the patient\'s daily life. It is hoped that this article will contribute to the improvement of the quality of life of patients with lymphoedema.

Coumarin is an effective treatment for primary lymphoedema, as well as lymphoedema related to breast cancer radiotherapy or surgery. However, its clinical use is limited in several countries due to the possible occurrence of hepatotoxicity, mainly in the form of mild to moderate transaminase elevation. It is worth noting that only a few cases of severe hepatotoxicity have been described in the literature, with no reported cases of liver failure. Data available on coumarin absorption, distribution, metabolism, and excretion have been reviewed, focusing on hepatotoxicity studies carried out in vitro and in vivo. Finally, safety and tolerability data from clinical trials have been thoroughly discussed. Based on these data, coumarin-induced hepatotoxicity is restricted to a small subset of patients, probably due to the activation in these individuals of alternative metabolic pathways involving specific CYP450s isoforms. The aim of this work is to stimulate research to clearly identify patients at risk of developing hepatotoxicity following coumarin treatment. Early identification of this subset of patients could open the possibility of more safely exploiting the therapeutical properties of coumarin, allowing patients suffering from lymphoedema to benefit from the anti-oedematous activity of the treatment.

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.

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.

OBJECTIVE: Primary lymphoedema is rare and in most cases develops in the lower extremities. In some cases, conservative treatment is insufficient and can be supported by surgical procedure. The aim of this case study was to show the difference in the effectiveness of a compression wrap device and compression stockings in the treatment of primary lymphoedema.
METHODS: Before and after liposuction the patient was treated on an outpatient basis every day for three weeks. This consisted of complex decongestive therapy (CDT) including manual lymph drainage, tailored exercises, skin and nail care, compression therapy and intermittent pneumatic compression. After CDT, the patient was provided with a flat-knit compression garment. Measurements were taken at one week and at three months of wearing the compression garment. The oedema severity was measured by summary calculation method. For both healthy and swollen limbs, the sum of circumferences taken at nine fixed measuring points was determined. The difference between these sums expressed in percents was presented as a relative metric coefficient of leg lymphoedema (RMCL).
RESULTS: At the start of therapy, the difference in circumference between the healthy and swollen limb was 21.85%. After CDT (RMCL: 13.46%), the patient was provided with a flat-knit compression stocking (class 3). After one week, the RMCL was 15.92%, while after three months RCML was 20.84%. Because fluid retention was observed the patient was again treated with CDT (RMCL: 13.89%). The patient was provided with compression stocking (class 4). After one week of wearing, the RMCL was 15.77%, while after three months RMCL was 20.26%. As the results proved unsatisfactory, the patient was treated with CDT (RMCL: 13.60%) and a combination of two class 4 compression stockings was used. After one week, RMCL was 14.91%, while after three months RMCL was 19.25%. As the effects of oedema reduction were insufficient, the patient was treated again with CDT (RMCL: 13.89%) and advised to replace one of the stockings with a CirAid device (adjustable compression wrap). After one week, RMCL was 14.18% and after three months RMCL was 14.76%. The patient then qualified for liposuction (RMCL: 7.81%). At three months after surgery, the compression stocking was replaced by an adjustable compression wrap, to reduce the difference in circumference between healthy and swollen limbs (from 21.85 % to 8.68%).
CONCLUSIONS: This case study shows that in primary oedema one class of compression garment is not always sufficient, nor is the combination of two garments with varying degrees of compression. In some cases, the situation requires the use of non-elastic leg binders such as a CircAid device which, thanks to its greater stiffness, helps improve clinical outcomes.

Background: The International Lymphedema Framework developed an international study, Lymphedema Impact and Prevalence International (LIMPRINT), to estimate the prevalence and impact of chronic edema (CO) in heterogeneous populations. Methods and Results: A validation study using the LIMPRINT methodology was undertaken in Denmark. Participants with CO were identified from inpatient services and compared with those identified within a specialist lymphedema service and three primary care settings. Of 452 inpatients available for screening, CO was present in 177 (39%) and absent in 275 (61%). In addition, 723 participants were found from specialist and primary care services (LPCSs). Inpatients were significantly older and more likely to be underweight or normal weight. They were more likely to suffer from heart failure/ischaemic heart disease (44.6% vs. 23.4%, p < 0.001) and have neurological problems (18.1% vs. 10.9% p = 0.009). Patients in the inpatient group were nearly all suffering from secondary lymphedema and were less likely to have a cancer or venous diagnosis, but more likely to have immobility as the cause of CO (44.0% vs. 17.7%, p < 0.001). No inpatients had midline CO compared with 30 within LPCSs. Fewer in the inpatient group had standard CO treatment (17.1% vs. 73.5%, p < 0.001) and subjective control of swelling was worse (19.9% vs. 66.7%, p < 0.001). While the inpatient group experienced fewer acute infections, when they did so, they were more likely to be admitted to hospital for this (78.6% vs. 51.0%, p = 0.049). Conclusion: The prevalence of CO in inpatient facilities is high and those with CO have multiple comorbidities that vary according to setting. The feasibility study showed that the methodology could be adapted for use in different health systems.

Lymphoedema is the build-up of lymphatic fluid leading to swelling in the tissues. Most commonly it affects the peripheries. Diagnosis is based on clinical assessment and imaging with lymphoscintigraphy. Treatment is supportive with compression garments, massage, good skin hygiene and prompt use of antibiotics to avoid the complication of cellulitis. Most commonly, lymphoedema occurs as a result of damage to the lymphatic system following surgery, trauma, radiation or infection. However, it can be primary, often associated with a genetic defect that causes disruption to the development of the lymphatic system. Common genetic conditions associated with lymphoedema include Turner syndrome and Noonan syndrome; however, there are numerous others that can be classified based on their clinical presentation and associated features. Herein we discuss how to diagnose and classify the known primary lymphoedema conditions and how best to investigate and manage this group of patients.