Pia Ostergaard

Mutations in GATA2 cause primary lymphedema associated with a predisposition to acute myeloid leukemia (Emberger syndrome)

We report an allelic series of eight mutations in GATA2 underlying Emberger syndrome, an autosomal dominant primary lymphedema associated with a predisposition to acute myeloid leukemia. GATA2 is a transcription factor that plays an essential role in gene regulation during vascular development and hematopoietic differentiation. Our findings indicate that haploinsufficiency of GATA2 underlies primary lymphedema and predisposes to acute myeloid leukemia in this syndrome.

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.

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.Rationale: Mutations in VEGFR3 (FLT4) cause Milroy Disease (MD), an autosomal dominant condition that presents with congenital lymphedema. Mutations in VEGFR3 are identified in only 70% of patients with classic MD, suggesting genetic heterogeneity. Objective: To investigate the underlying cause in patients with clinical signs resembling MD in whom sequencing of the coding region of VEGFR3 did not reveal any pathogenic variation. Methods and Results: Exome sequencing of five such patients was performed and a novel frameshift variant, c.571\_572insTT in VEGFC , a ligand for VEGFR3, was identified in one proband. The variant co-segregated 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 wildtype human VEGFC in the floorplate of zebrafish embryos leads to excessive sprouting in neighbouring 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 MD-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.

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.

Novel mutations in PIEZO1 cause an autosomal recessive generalized lymphatic dysplasia with non-immune hydrops fetalis.

Generalized lymphatic dysplasia (GLD) is a rare form of primary lymphoedema characterized by a uniform, widespread lymphoedema affecting all segments of the body, with systemic involvement such as intestinal and/or pulmonary lymphangiectasia, pleural effusions, chylothoraces and/or pericardial effusions. This may present prenatally as non-immune hydrops. Here we report homozygous and compound heterozygous mutations in PIEZO1, resulting in an autosomal recessive form of GLD with a high incidence of non-immune hydrops fetalis and childhood onset of facial and four limb lymphoedema. Mutations in PIEZO1, which encodes a mechanically activated ion channel, have been reported with autosomal dominant dehydrated hereditary stomatocytosis and non-immune hydrops of unknown aetiology. Besides its role in red blood cells, our findings indicate that PIEZO1 is also involved in the development of lymphatic structures.

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

Milroy disease (hereditary lymphoedema type I, MIM 153100) is a congenital onset primary lymphoedema with autosomal dominant inheritance. Mutations in the gene, vascular endothelial growth factor receptor 3, VEGFR3 (FLT4), are known to cause Milroy disease, but there is uncertainty about the prevalence of VEGFR3 mutations in patients with primary lymphoedema and more specifically in those with a phenotype that resembles Milroy disease. This study aims to address this issue and thereby delineate the Milroy disease phenotype. Fifty-two patients with primary lymphoedema were analysed for mutations in the coding regions of VEGFR3. Patients were divided into four groups: Typical Milroy disease with family history (group I), typical Milroy disease with no family history (group II), atypical Milroy disease (group III), and complex primary lymphoedema (group IV). Results demonstrated that with rigorous phenotyping the likelihood of detecting VEGFR3 mutations is optimised. Mutation prevalence is 75% in typical Milroy patients with a family history (group I) and 68% if positive family history is not a diagnostic criterion. A positive family history is not essential in Milroy disease. The likelihood of detecting VEGFR3 mutations in patients who have a phenotype which is not typical of Milroy disease is very small (<5%). For the 22 mutation positive patients, 14 novel VEGFR3 mutations were identified, two of which were in exon 22 and one in exon 17, confirming that these exons should be included in VEGFR3 analysis. No mutations were found outside the kinase domains, showing that analysis of this part of the gene is not useful for Milroy disease patients. VEGFC, which encodes the ligand for VEGFR3, was sequenced in all patients with typical Milroy disease (groups I and II) and no mutations were identified.

Lipedema: An Inherited Condition

Lipedema is a condition characterized by swelling and enlargement of the lower limbs due to abnormal deposition of subcutaneous fat. Lipedema is an under‐recognized condition, often misdiagnosed as lymphedema or dismissed as simple obesity. We present a series of pedigrees and propose that lipedema is a genetic condition with either X‐linked dominant inheritance or more likely, autosomal dominant inheritance with sex limitation. Lipedema appears to be a condition almost exclusively affecting females, presumably estrogen‐requiring as it usually manifests at puberty. Lipedema is an entity distinct from obesity, but may be wrongly diagnosed as primary obesity, due to clinical overlap. The phenotype suggests a condition distinct from obesity and associated with pain, tenderness, and easy bruising in affected areas.

Emberger syndrome—Primary lymphedema with myelodysplasia: Report of seven new cases

Four reports have been published on an association between acute myeloid leukaemia (AML) and primary lymphedema, with or without congenital deafness. We report seven new cases, including one extended family, confirming this entity as a genetic syndrome. The lymphedema typically presents in one or both lower limbs, before the hematological abnormalities, with onset between infancy and puberty and frequently affecting the genitalia. The AML is often preceded by pancytopenia or myelodysplasia with a high incidence of monosomy 7 in the bone marrow (five propositi and two relatives). Associated anomalies included hypotelorism, epicanthic folds, long tapering fingers and/or neck webbing (four patients), recurrent cellulitis in the affected limb (four patients), generalized warts (two patients), and congenital, high frequency sensorineural deafness (one patient). Children with lower limb and genital lymphedema should be screened for hematological abnormalities and immunodeficiency.

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.

Three children with Milroy disease and de novo mutations in VEGFR3

To the Editor: Milroy disease (MD) is a form of primary lymphoedema with congenital onset and autosomal dominant inheritance. The location of a gene responsible for at least some cases of the disorder was discovered on chromosome 5q 35.3 (1, 2), and the mutated gene identified as coding for vascular endothelial growth factor receptor 3 (VEGFR3) (1, 3, 4). There are few associated features with MD, other than large calibre leg veins (23%) and hydrocele in men (37%) (5); so, any parameters that aid in delineating it from other, similar, forms of primary lymphoedema are helpful. Congenital onset of the swelling is one such sign, and a family history of the disease has always been considered a strong indicator in making the correct diagnosis (5, 6). Milroy himself included it as a prerequisite (6). Although new mutations in a dominantly inherited disorder are not unexpected, there has only been one reported to date (7). We present three cases of children with congenital onset of lymphoedema but no family history, all of whom have mutations in VEGFR3 which are not present in either parent, confirming that a family history of MD is not necessary for a diagnosis. All patients (two boys, one girl) were ascertained via a joint specialist (dermatology and genetics) primary lymphoedema clinic. All the patients and their parents were examined by at least two of the authors (G. B., S. M. or P. M.).