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.

Self-care treatment for lymphoedema of lymphatic filariasis using integrative medicine.

BACKGROUND: Lymphatic filariasis (LF) is a neglected tropical disease presenting mainly as lymphoedema (elephantiasis). At present, LF is not effectively treated. Integrative medicine (IM) treatment for lymphoedema uses a combination of Indian traditional medicine, Ayurveda, alongside yoga exercises, compression therapy, antibiotics and antifungal treatments, providing a useful combination where resources are limited and different practices are in use. OBJECTIVES: To assess the effectiveness of the IM in the existing clinical practice of lower-limb lymphoedema management and to determine whether the treatment outcomes align with the World Health Organization (WHO) global goal of LF management. METHODS: Institutional data from electronic medical records of all 1698 patients with LF between 2010 and 2019 were retrospectively analysed using pre- and post-treatment comparisons and the National Institute for Health and Care Excellence guidelines for clinical audit. The primary treatment outcomes evaluated were limb volume, bacterial entry points (BEEPs), episodes of cellulitis, and health-related quality of life (HRQoL). Secondary outcomes included the influence of the patient's sex, duration of illness, education and employment status on volume reduction. Multiple regression analysis, t-test, χ2-test, analysis of variance, Mann-Whitney U-test and the Kruskal-Wallis test were used to assess the association between IM and patients' treatment outcomes. RESULTS: Limb volume reduced by 24.5% [95% confidence interval (CI) 22.47-26.61; n = 1660] following an intensive supervised care period (mean 14.84 days, n = 1660). Limb volume further reduced by 1.42% (95% CI 0.76-2.07; n = 1259) at the first follow-up visit (mean 81.45 days), and by 2.3% between the first and second follow-up visits (mean 231.32 days) (95% CI 1.26-3.34; n = 796). BEEPs were reduced upon follow-up; excoriations (78.4%) and intertrigo (26.7%) were reduced at discharge and further improvements was achieved at the follow-up visits. In total, 4% of patients exhibited new BEEPs at the first follow-up [eczema (3.9%), folliculitis (6.5%), excoriations (11.9%) and intertrigo (15.4%); 4 of 7 BEEPs were recorded]. HRQoL, measured using the disease-specific Lymphatic Filariasis Specific Quality of Life Questionnaire, showed an average score of 73.9 on admission, which increased by 17.8 at the first follow-up and 18.6 at the second follow-up. No patients developed new cellulitis episodes at the first follow-up, and only five patients (5.3%) developed new episodes of cellulitis at the second follow-up. CONCLUSIONS: IM for lower-limb lymphoedema successfully reduces limb volume and episodes of cellulitis, and also reduces BEEPs, leading to improved HRQoL. IM aligns with the LF treatment goals of the WHO and is a low-cost, predominantly self-care management protocol. IM has the potential to change care models and improve the lives of patients with lymphoedema.

Janus-faced EPHB4-associated disorders: novel pathogenic variants and unreported intrafamilial overlapping phenotypes.

PURPOSE: Several clinical phenotypes including fetal hydrops, central conducting lymphatic anomaly or capillary malformations with arteriovenous malformations 2 (CM-AVM2) have been associated with EPHB4 (Ephrin type B receptor 4) variants, demanding new approaches for deciphering pathogenesis of novel variants of uncertain significance (VUS) identified in EPHB4, and for the identification of differentiated disease mechanisms at the molecular level. METHODS: Ten index cases with various phenotypes, either fetal hydrops, CM-AVM2, or peripheral lower limb lymphedema, whose distinct clinical phenotypes are described in detail in this study, presented with a variant in EPHB4. In vitro functional studies were performed to confirm pathogenicity. RESULTS: Pathogenicity was demonstrated for six of the seven novel EPHB4 VUS investigated. A heterogeneity of molecular disease mechanisms was identified, from loss of protein production or aberrant subcellular localization to total reduction of the phosphorylation capability of the receptor. There was some phenotype-genotype correlation; however, previously unreported intrafamilial overlapping phenotypes such as lymphatic-related fetal hydrops (LRFH) and CM-AVM2 in the same family were observed. CONCLUSION: This study highlights the usefulness of protein expression and subcellular localization studies to predict EPHB4 variant pathogenesis. Our accurate clinical phenotyping expands our interpretation of the Janus-faced spectrum of EPHB4-related disorders, introducing the discovery of cases with overlapping phenotypes.

Systematic Review of Magnetic Resonance Lymphangiography From a Technical Perspective.

BACKGROUND: Clinical examination and lymphoscintigraphy are the current standard for investigating lymphatic function. Magnetic resonance imaging (MRI) facilitates three-dimensional (3D), nonionizing imaging of the lymphatic vasculature, including functional assessments of lymphatic flow, and may improve diagnosis and treatment planning in disease states such as lymphedema. PURPOSE: To summarize the role of MRI as a noninvasive technique to assess lymphatic drainage and highlight areas in need of further study. STUDY TYPE: Systematic review. POPULATION: In October 2019, a systematic literature search (PubMed) was performed to identify articles on magnetic resonance lymphangiography (MRL). FIELD STRENGTH/SEQUENCE: No field strength or sequence restrictions. ASSESSMENT: Article quality assessment was conducted using a bespoke protocol, designed with heavy reliance on the National Institutes of Health quality assessment tool for case series studies and Downs and Blacks quality checklist for health care intervention studies. STATISTICAL TESTS: The results of the original research articles are summarized. RESULTS: From 612 identified articles, 43 articles were included and their protocols and results summarized. Field strength was 1.5 or 3.0 T in all studies, with 25/43 (58%) employing 3.0 T imaging. Most commonly, imaging of the peripheries, upper and lower limbs including the pelvis (32/43, 74%), and the trunk (10/43, 23%) is performed, including two studies covering both regions. Imaging protocols were heterogenous; however, T2 -weighted and contrast-enhanced T1 -weighted images are routinely acquired and demonstrate the lymphatic vasculature. Edema, vessel, quantity and morphology, and contrast uptake characteristics are commonly reported indicators of lymphatic dysfunction. DATA CONCLUSION: MRL is uniquely placed to yield large field of view, qualitative and quantitative, 3D imaging of the lymphatic vasculature. Despite study heterogeneity, consensus is emerging regarding MRL protocol design. MRL has the potential to dramatically improve understanding of the lymphatics and detect disease, but further optimization, and research into the influence of study protocol differences, is required before this is fully realized. LEVEL OF EVIDENCE: 2 TECHNICAL EFFICACY: Stage 2.

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.

Penicillin to prevent recurrent leg cellulitis.

BACKGROUND: Cellulitis of the leg is a common bacterial infection of the skin and underlying tissue. We compared prophylactic low-dose penicillin with placebo for the prevention of recurrent cellulitis. METHODS: We conducted a double-blind, randomized, controlled trial involving patients with two or more episodes of cellulitis of the leg who were recruited in 28 hospitals in the United Kingdom and Ireland. Randomization was performed according to a computer-generated code, and study medications (penicillin [250 mg twice a day] or placebo for 12 months) were dispensed by a central pharmacy. The primary outcome was the time to a first recurrence. Participants were followed for up to 3 years. Because the risk of recurrence was not constant over the 3-year period, the primary hypothesis was tested during prophylaxis only. RESULTS: A total of 274 patients were recruited. Baseline characteristics were similar in the two groups. The median time to a first recurrence of cellulitis was 626 days in the penicillin group and 532 days in the placebo group. During the prophylaxis phase, 30 of 136 participants in the penicillin group (22%) had a recurrence, as compared with 51 of 138 participants in the placebo group (37%) (hazard ratio, 0.55; 95% confidence interval [CI], 0.35 to 0.86; P=0.01), yielding a number needed to treat to prevent one recurrent cellulitis episode of 5 (95% CI, 4 to 9). During the no-intervention follow-up period, there was no difference between groups in the rate of a first recurrence (27% in both groups). Overall, participants in the penicillin group had fewer repeat episodes than those in the placebo group (119 vs. 164, P=0.02 for trend). There was no significant between-group difference in the number of participants with adverse events (37 in the penicillin group and 48 in the placebo group, P=0.50). CONCLUSIONS: In patients with recurrent cellulitis of the leg, penicillin was effective in preventing subsequent attacks during prophylaxis, but the protective effect diminished progressively once drug therapy was stopped. (Funded by Action Medical Research; PATCH I Controlled-Trials.com number, ISRCTN34716921.).

Mutations in KIF11 cause autosomal-dominant microcephaly variably associated with congenital lymphedema and chorioretinopathy.

We have identified KIF11 mutations in individuals with syndromic autosomal-dominant microcephaly associated with lymphedema and/or chorioretinopathy. Initial whole-exome sequencing revealed heterozygous KIF11 mutations in three individuals with a combination of microcephaly and lymphedema from a microcephaly-lymphedema-chorioretinal-dysplasia cohort. Subsequent Sanger sequencing of KIF11 in a further 15 unrelated microcephalic probands with lymphedema and/or chorioretinopathy identified additional heterozygous mutations in 12 of them. KIF11 encodes EG5, a homotetramer kinesin motor. The variety of mutations we have found (two nonsense, two splice site, four missense, and six indels causing frameshifts) are all predicted to have an impact on protein function. EG5 has previously been shown to play a role in spindle assembly and function, and these findings highlight the critical role of proteins necessary for spindle formation in CNS development. Moreover, identification of KIF11 mutations in patients with chorioretinopathy and lymphedema suggests that EG5 is involved in the development and maintenance of retinal and lymphatic structures.

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.

Mutation in vascular endothelial growth factor-C, a ligand for vascular endothelial growth factor receptor-3, is associated with autosomal dominant milroy-like primary lymphedema.

RATIONALE: Mutations in vascular endothelial growth factor (VEGF) receptor-3 (VEGFR3 or FLT4) cause Milroy disease, an autosomal dominant condition that presents with congenital lymphedema. Mutations in VEGFR3 are identified in only 70% of patients with classic Milroy disease, suggesting genetic heterogeneity. OBJECTIVE: To investigate the underlying cause in patients with clinical signs resembling Milroy disease in whom sequencing of the coding region of VEGFR3 did not reveal any pathogenic variation. METHODS AND RESULTS: Exome sequencing of 5 such patients was performed, and a novel frameshift variant, c.571_572insTT in VEGFC, a ligand for VEGFR3, was identified in 1 proband. The variant cosegregated with the affected status in the family. An assay to assess the biological function of VEGFC activity in vivo, by expressing human VEGFC in the zebrafish floorplate was established. Forced expression of wild-type human VEGFC in the floorplate of zebrafish embryos leads to excessive sprouting in neighboring vessels. However, when overexpressing the human c.571_572insTT variant in the floorplate, no sprouting of vessels was observed, indicating that the base changes have a marked effect on the activity of VEGFC. CONCLUSIONS: We propose that the mutation in VEGFC is causative for the Milroy disease-like phenotype seen in this family. This is the first time a mutation in one of the ligands of VEGFR3 has been reported to cause primary lymphedema.

LymphActiv: A Digital Physical Activity Behavior Intervention for the Treatment of Lymphedema and Lipedema.

Background: Lymphedema and lipedema are debilitating conditions with no proven drug or surgical therapy. Effective treatment requires self-management through movement and compression to reduce limb volume and the incidence of cellulitis. The addition of personalized everyday physical activity (PA) could be transformative, increasing the therapy window to include all waking hours per week and enabling an increased dose of PA. Aim: This service evaluation aimed to determine the feasibility of LymphActiv as a treatment option for lymphedema and lipedema patients. Methods: This service evaluation followed an open observational cohort design, including 55 patients who participated in LymphActiv over 24 weeks. Patients wore an objective PA monitor and interacted with their data in an online dashboard, alongside remote mentor support. Primary outcomes were changes to PA, body weight, limb volume and quality of life. Clinical assessments occurred at baseline and after the 24-week program. Noncompleters were used as a quasi-control group for comparison. Results: Thirty-seven patients completed, of which 81% improved PA. On average, completers reduced their right and left lower limb volumes by -1.8% and -2.1%, respectively. Completers also experienced small average weight losses of -1.2 kg. Noncompleters experienced small average increases in each of these outcome measures. Discussion: These results establish the value of LymphActiv, providing benefit to patients who might otherwise have deteriorated. For services, this could lead to substantial cost-savings through reduced admissions, greater patient independence, and less need for community health care input. The next step is to undertake a randomized, controlled trial comparing the intervention with standard care.

Magnetic resonance lymphangiography: Establishing normal.

BACKGROUND: Despite an increased interest in visualizing the lymphatic vessels with magnetic resonance lymphangiography (MRL), little literature is available describing their appearance in nonlymphedematous individuals. To determine lymphatic abnormalities, an understanding of how healthy lymphatic vessels appear and behave needs to be established. Therefore, in this study, MRL of individuals without a history of lymphatic disease was performed. METHODS: A total of 25 individuals (15 women) underwent MRL of their lower limbs using a 3.0 T Philips magnetic resonance imaging scanner (Philips Medical Systems). The first nine participants were recruited to establish the concentration of gadolinium-based contrast agent (GBCA) to administer, with the remainder imaged before and after interdigital forefoot GBCA injections at the optimized dose. Outcomes, including lymphatic vessel diameter, tortuosity, and frequency of drainage via particular drainage routes, were recorded. RESULTS: Healthy lymphatic vessels following the anteromedial pathway were routinely observed in post-contrast T1-weighted images (average tortuosity, 1.09 ± 0.03), with an average of 2.16 ± 0.93 lymphatic vessels with a diameter of 2.47 ± 0.50 mm crossing the anterior ankle. In six limbs, vessels following the anterolateral pathways were observed. No vessels traversing the posterior of the legs were seen. In a subset of 10 vessels, the lymphatic signal, measured at the ankle, peaked 29 minutes, 50 seconds ± 9 minutes, 29 seconds after GBCA administration. No lymphatic vessels were observed in T2-weighted images. CONCLUSIONS: Contrast-enhanced MRL reliably depicts the lymphatic vessels in the legs of healthy controls. Following interdigital contrast injection, anteromedial drainage appears dominant. Quantitative measures related to lymphatic vessel size, tortuosity, and drainage rate are readily obtainable and could be beneficial for detecting even subtle lymphatic impairment.

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.

Intralymphatic granulomas in lymphoedema secondary to anogenital granulomatosis.

The granulomatous inflammation seen in filariasis, orofacial granulomatosis (OFG), rosacea and sarcoidosis can be associated with lymphoedema. In the setting of OFG, the finding of intralymphatic granulomas has been reported as a possible mechanism for lymphoedema. Anogenital granulomatosis (AGG) is a similar chronic inflammatory condition of unknown pathogenesis. It presents as granulomatous genital or anoperineal inflammation and associated lymphoedema, with histological findings of non-caseating granulomas and a perivascular infiltrate. We report a case of AGG and lymphoedema with intralymphatic granulomas seen on biopsy. This finding is unique and we propose that the intralymphatic granulomatous inflammation causes a partial or complete occlusion of lymphatic drainage, thus resulting in the clinical situation of lymphoedema.

Erythematous capillary-lymphatic malformations mimicking blood vascular anomalies.

Superficial erythematous cutaneous vascular malformations are assumed to be blood vascular in origin, but cutaneous lymphatic malformations can contain blood and appear red. Management may be different and so an accurate diagnosis is important. Cutaneous malformations were investigated through 2D histology and 3D whole-mount histology. Two lesions were clinically considered as port-wine birthmarks and another 3 lesions as erythematous telangiectasias. The aims were (i) to demonstrate that cutaneous erythematous malformations including telangiectasia can represent a lymphatic phenotype, (ii) to determine if lesions represent expanded but otherwise normal or malformed lymphatics, and (iii) to determine if the presence of erythrocytes explained the red color. Microscopy revealed all lesions as lymphatic structures. Port-wine birthmarks proved to be cystic lesions, with nonuniform lymphatic marker expression and a disconnected lymphatic network suggesting a lymphatic malformation. Erythematous telangiectasias represented expanded but nonmalformed lymphatics. Blood within lymphatics appeared to explain the color. Blood-lymphatic shunts could be detected in the erythematous telangiectasia. In conclusion, erythematous cutaneous capillary lesions may be lymphatic in origin but clinically indistinguishable from blood vascular malformations. Biopsy is advised for correct phenotyping and management. Erythrocytes are the likely explanation for color accessing lymphatics through lympho-venous shunts.

Rapid identification of mutations in GJC2 in primary lymphoedema using whole exome sequencing combined with linkage analysis with delineation of the phenotype.

BACKGROUND: Primary lymphoedema describes a chronic, frequently progressive, failure of lymphatic drainage. This disorder is frequently genetic in origin, and a multigenerational family in which eight individuals developed postnatal lymphoedema of all four limbs was ascertained from the joint Lymphoedema/Genetic clinic at St George's Hospital. METHODS: Linkage analysis was used to determine a locus, and exome sequencing was employed to look for causative variants. RESULTS: Linkage analysis revealed cosegregation of a 16.1 Mb haplotype on chromosome 1q42 that contained 173 known or predicted genes. Whole exome sequencing in a single affected individual was undertaken, and the search for the causative variant was focused to within the linkage interval. This approach revealed two novel non-synonymous single nucleotide substitutions within the chromosome 1 locus, in NVL and GJC2. NVL and GJC2 were sequenced in an additional cohort of individuals with a similar phenotype and non-synonymous variants were found in GJC2 in four additional families. CONCLUSION: This report demonstrates the power of exome sequencing efficiently applied to a traditional positional cloning pipeline in disease gene discovery, and suggests that the phenotype produced by GJC2 mutations is predominantly one of 4 limb lymphoedema.

Case Report: Progressive central conducting lymphatic abnormalities in the RASopathies. Two case reports, including successful treatment by MEK inhibition.

The RASopathies are a group of genetic conditions resulting from mutations within the RAS/mitogen-activated protein kinase (RAS-MAPK) pathway. Lymphatic abnormalities are commonly associated with these conditions, however central conducting lymphatic abnormalities (CCLA) have only recently been described. CCLAs may be progressive and can result in devastating systemic sequelae, such as recurrent chylothoraces, chylopericardium and chylous ascites which can cause significant morbidity and even mortality. Improvements in imaging modalities of the central lymphatics have enhanced our understanding of these complex abnormalities. Management is challenging and have mainly consisted of diuretics and invasive mechanical drainages. We describe two adult males with Noonan syndrome with a severe and progressive CCLA. In one patient we report the therapeutic role of targeted molecular therapy with the MEK inhibitor 'Trametinib', which has resulted in dramatic, and sustained, clinical improvement. The successful use of MEK inhibition highlights the importance of understanding the molecular cause of lymphatic abnormalities and utilising targeted therapies to improve quality of life and potentially life expectancy.

Image registration and subtraction in dynamic magnetic resonance lymphangiography (MRL) of the legs.

Dynamic contrast-enhanced magnetic resonance lymphangiography (DCE-MRL) is regularly reported as unable to depict lymphatic vessels in healthy limbs. In this study, we aim to improve lymph vessel conspicuity with appropriate registration and subtraction of a reference baseline image. Five unaffected individuals and a single unilateral primary lymphoedema patient were recruited to undergo fat suppressed 3D T 1 weighted spoiled gradient echo imaging of the lower limbs at 3.0 T. Images were quality assessed by two physicians and a medical physicist following registration via one of six registration pipelines, and subtraction of the first post-contrast dynamic image (PC1). Wilcoxon non-parametric testing was performed to compare image quality ranking vs the unregistered images and inter-rater reliability estimated using intraclass correlation coefficient. Signal enhancement curves were also computed in lymphatic vessels for two participants. Subtraction images were considered to improve lymphatic visibility, and three registration pipelines significantly (p < 0.05) outranked those without registration. Those registered to PC1 with an affine and elastic approach were rated best quality (p = 0.006). Moderate inter-rater reliability was observed (intraclass correlation coefficient = 0.71) and signal enhancement behaviour appears affected by registration when motion is evident across the DCE-MRL series. We therefore conclude that lymphatic vessel visibility in DCE-MRL images can be improved with registration and baseline subtraction.

Investigation of clinical characteristics and genome associations in the 'UK Lipoedema' cohort.

Lipoedema is a chronic adipose tissue disorder mainly affecting women, causing excess subcutaneous fat deposition on the lower limbs with pain and tenderness. There is often a family history of lipoedema, suggesting a genetic origin, but the contribution of genetics is currently unclear. A tightly phenotyped cohort of 200 lipoedema patients was recruited from two UK specialist clinics. Objective clinical characteristics and measures of quality of life data were obtained. In an attempt to understand the genetic architecture of the disease better, genome-wide single nucleotide polymorphism (SNP) genotype data were obtained, and a genome wide association study (GWAS) was performed on 130 of the recruits. The analysis revealed genetic loci suggestively associated with the lipoedema phenotype, with further support provided by an independent cohort taken from the 100,000 Genomes Project. The top SNP rs1409440 (ORmeta ≈ 2.01, Pmeta ≈ 4 x 10-6) is located upstream of LHFPL6, which is thought to be involved with lipoma formation. Exactly how this relates to lipoedema is not yet understood. This first GWAS of a UK lipoedema cohort has identified genetic regions of suggestive association with the disease. Further replication of these findings in different populations is warranted.