Lymphatic malformation 6

Mendelian MONDO:0014797 Pathograph 20 Show in embeddings browser lymphatic malformation hereditary disease

Lymphatic malformation 6 (LMPHM6; hereditary lymphedema type III), also known as generalized lymphatic dysplasia of Fotiou, is an autosomal recessive generalized lymphatic dysplasia caused by biallelic loss-of-function variants in PIEZO1, which encodes a mechanically activated, calcium-permeable cation channel. Loss of PIEZO1 mechanotransduction in lymphatic endothelial cells impairs lymphatic valve morphogenesis and flow-driven lymphatic sprouting, producing widespread lymphatic dysfunction. The condition most often presents prenatally as non-immune hydrops fetalis with pleural and pericardial effusions and ascites, which may be lethal in the perinatal period; survivors frequently have complete resolution of the neonatal edema and re-present in childhood with peripheral, facial, and genital lymphedema, with or without persistent chylothorax or intestinal lymphangiectasia. Recurrent severe facial cellulitis is a characteristic and serious complication. Unlike Hennekam syndrome, the dysmorphic features, seizures, and intellectual disability are absent. Because monoallelic gain-of-function PIEZO1 variants cause dehydrated hereditary stomatocytosis, affected individuals and carriers may show subtle red-cell abnormalities (stomatocytes, spherocytes) without clinically significant hemolysis. Management is supportive; no PIEZO1-directed disease-modifying therapy is approved, although pharmacological rescue of mechanically insensitive mutant channels with the PIEZO1 agonist Yoda1 has been demonstrated in vitro.

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1
Inheritance
7
Pathophys.
12
Phenotypes
20
Pathograph
1
Genes
5
Variants
6
Medical Actions
2
Differentials
2
Models
1
Deep Research
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Classifications

Harrison's Part
CARDIOVASCULAR
👪

Inheritance

1
Autosomal recessive inheritance HP:0000007
LMPHM6 is inherited in an autosomal recessive manner; affected individuals carry biallelic (homozygous or compound heterozygous) loss-of-function PIEZO1 variants that co-segregate with disease in reported families. Heterozygous carriers are unaffected by the lymphatic phenotype. A pedigree may nonetheless look dominant: in family GLD08 a homozygous I2270T genotype segregating through consanguinity produced affected individuals in consecutive generations (the proband and his father), a pseudo-dominant pattern that should not be mistaken for a dominant PIEZO1 disorder.
Autosomal recessive inheritance
Show evidence (4 references)
PMID:26333996 SUPPORT Human Clinical
"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."
Homozygous and compound heterozygous PIEZO1 genotypes establish autosomal recessive inheritance for LMPHM6.
PMID:26387913 SUPPORT Human Clinical
"Through whole-exome sequencing, we identify biallelic mutations in PIEZO1 (a splicing variant leading to early truncation and a non-synonymous missense variant) in a pair of siblings affected with persistent lymphoedema caused by congenital lymphatic dysplasia."
Independently confirms biallelic (compound heterozygous) PIEZO1 inheritance in an affected sibship.
PMID:40792030 SUPPORT Human Clinical
"In GLD08, homozygosity of a single variant encoding Ile2270Thr (I2270T) associated with disease in 3 family members"
A single homozygous PIEZO1 variant accounts for disease in three members of one consanguineous family, the genotype underlying the apparently dominant vertical transmission in that pedigree.
+ 1 more reference

Pathophysiology

7
PIEZO1 Loss of Function
Biallelic nonsense, frameshift, splice-site, and missense variants in PIEZO1 abolish or severely reduce the activity of a mechanically activated, calcium-permeable cation channel. Two mechanistically distinct routes to loss of function are documented: reduced or absent PIEZO1 protein (truncating and splice variants, shown by western blot to eliminate or reduce PIEZO1 expression) and reduced channel mechanical sensitivity despite surface expression (cap and sub-cap missense variants that are mechanically insensitive yet partly rescuable with the chemical agonist Yoda1).
PIEZO1 hgnc:28993 HUGO Gene Nomenclature Committee (hgnc) Relation: this pathophysiological event involves this gene This pathophysiological event involves PIEZO1 (hgnc:28993). hgnc:28993 is a gene from the HUGO Gene Nomenclature Committee.
mechanically activated cation channel activity GO:0008381 Gene Ontology (GO) Relation: this pathophysiological event involves this molecular function This pathophysiological event involves mechanically activated cation channel activity, annotated with mechanosensitive monoatomic ion channel activity (GO:0008381), qualified as loss of function. GO:0008381 is a molecular function from the Gene Ontology. ⇓ LOSS OF FUNCTION
Show evidence (4 references)
PMID:26333996 SUPPORT Human Clinical
"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."
Identifies PIEZO1 as a mechanically activated ion channel and the causal gene locus for this disorder.
PMID:26333996 SUPPORT Human Clinical
"No truncated PIEZO1 protein products were identified in western blot analysis in GLD1:II.3 and GLD2:II.2"
Direct protein-level demonstration that truncating alleles yield no stable PIEZO1 protein, i.e. loss of function.
PMID:26387913 SUPPORT In Vitro
"Patch-clamp analysis of the missense PIEZO1 channel in a heterologous system (a mammalian cell line derived from HEK293T cells) indicated strongly diminished current amplitudes as compared with wild type, likely due to reduced cell surface expression."
Electrophysiological confirmation that the patient missense allele is hypomorphic/loss-of-function.
+ 1 more reference
Impaired Lymphatic Endothelial Mechanotransduction
PIEZO1 is abundantly expressed in lymphatic endothelial cells, where it transduces oscillatory shear stress and membrane stretch into calcium entry. Loss of PIEZO1 abrogates flow-induced calcium influx and the downstream ORAI1/KLF2/Notch transcriptional programme that drives lymphatic sprouting, and it removes the mechanical cue required for valve-forming cell behaviour.
lymphatic endothelial cell CL:0002138 Cell Ontology (CL) Relation: this pathophysiological event involves this cell type This pathophysiological event involves lymphatic endothelial cell, annotated with endothelial cell of lymphatic vessel (CL:0002138). CL:0002138 is a cell type from the Cell Ontology.
cellular response to fluid shear stress GO:0071498 Gene Ontology (GO) Relation: this pathophysiological event involves this biological process This pathophysiological event involves decreased cellular response to fluid shear stress (GO:0071498). GO:0071498 is a biological process from the Gene Ontology. ↓ DECREASED response to mechanical stimulus GO:0009612 Gene Ontology (GO) Relation: this pathophysiological event involves this biological process This pathophysiological event involves decreased response to mechanical stimulus (GO:0009612). GO:0009612 is a biological process from the Gene Ontology. ↓ DECREASED
Show evidence (2 references)
PMID:35701867 SUPPORT In Vitro
"Piezo1 knockdown in cultured lymphatic endothelial cells inhibited the laminar flow-induced calcium influx"
Demonstrates that PIEZO1 is required for flow-induced calcium signalling in lymphatic endothelial cells.
PMID:38747287 SUPPORT Model Organism
"Yoda1 rapidly triggered nuclear FOXO1 extrusion in WT mesenteries but not in Piezo1LEC–/– mesenteries, confirming the PIEZO1/FOXO1 axis in mesenteric lymphatics"
Ex vivo mouse mesenteric lymphatics lacking endothelial PIEZO1 fail to transduce channel activation into a downstream signalling response, demonstrating that PIEZO1 loss abolishes lymphatic endothelial mechanosignalling.
Disrupted ANGPT2-TIE-FOXO1 Signaling
PIEZO1 activation in lymphatic endothelial cells triggers rapid exocytosis of the TIE ligand ANGPT2, ADAM17-mediated ectodomain shedding of TIE1, increased TIE/PI3K/AKT signaling, and nuclear export of the transcription factor FOXO1. Loss of PIEZO1 function therefore silences a signaling network whose other members (ANGPT2, TIE1) are themselves mutated in primary lymphedema, providing a molecular bridge between channel function and lymphatic gene expression.
lymphatic endothelial cell CL:0002138 Cell Ontology (CL) Relation: this pathophysiological event involves this cell type This pathophysiological event involves lymphatic endothelial cell, annotated with endothelial cell of lymphatic vessel (CL:0002138). CL:0002138 is a cell type from the Cell Ontology.
Tie signaling pathway GO:0048014 Gene Ontology (GO) Relation: this pathophysiological event involves this biological process This pathophysiological event involves decreased Tie signaling pathway (GO:0048014). GO:0048014 is a biological process from the Gene Ontology. ↓ DECREASED PI3K/AKT signal transduction GO:0043491 Gene Ontology (GO) Relation: this pathophysiological event involves this biological process This pathophysiological event involves decreased PI3K/AKT signal transduction, annotated with phosphatidylinositol 3-kinase/protein kinase B signal transduction (GO:0043491). GO:0043491 is a biological process from the Gene Ontology. ↓ DECREASED FOXO1 nuclear export GO:0006611 Gene Ontology (GO) Relation: this pathophysiological event involves this biological process This pathophysiological event involves decreased FOXO1 nuclear export, annotated with protein export from nucleus (GO:0006611). GO:0006611 is a biological process from the Gene Ontology. ↓ DECREASED
Show evidence (1 reference)
PMID:38747287 SUPPORT In Vitro
"activation of the mechanosensory channel PIEZO1 in lymphatic endothelial cells (LECs) caused rapid exocytosis of the TIE ligand ANGPT2, ectodomain shedding of TIE1 by disintegrin and metalloproteinase domain-containing protein 17 (ADAM17), and increased TIE/PI3K/AKT signaling, followed by..."
Establishes the PIEZO1 to ANGPT2/TIE/PI3K-AKT/FOXO1 signaling axis in lymphatic endothelial cells.
Defective Lymphatic Valve Formation and Lymphangiogenesis
Endothelial-specific Piezo1 deletion in mice dramatically reduces the number of lymphatic valves and impairs the collective cell migration, actin polymerization, and cell-cell junction remodeling that produce the valve leaflet, while lymphatic-specific deletion phenocopies the sprouting defects of Orai1 and Klf2 knockouts and postnatal deletion causes lymphatic regression. Lymphatic valves are essential for unidirectional lymph flow, so their loss renders the collecting lymphatics incompetent.
lymphatic endothelial cell CL:0002138 Cell Ontology (CL) Relation: this pathophysiological event involves this cell type This pathophysiological event involves lymphatic endothelial cell, annotated with endothelial cell of lymphatic vessel (CL:0002138). CL:0002138 is a cell type from the Cell Ontology.
lymph vessel development GO:0001945 Gene Ontology (GO) Relation: this pathophysiological event involves this biological process This pathophysiological event involves decreased lymph vessel development (GO:0001945). GO:0001945 is a biological process from the Gene Ontology. ↓ DECREASED lymphangiogenesis GO:0001946 Gene Ontology (GO) Relation: this pathophysiological event involves this biological process This pathophysiological event involves decreased lymphangiogenesis (GO:0001946). GO:0001946 is a biological process from the Gene Ontology. ↓ DECREASED lymph vessel morphogenesis GO:0036303 Gene Ontology (GO) Relation: this pathophysiological event involves this biological process This pathophysiological event involves decreased lymph vessel morphogenesis (GO:0036303). GO:0036303 is a biological process from the Gene Ontology. ↓ DECREASED
Show evidence (4 references)
PMID:30482854 SUPPORT Model Organism
"we analyzed two mouse lines lacking PIEZO1 in endothelial cells (via Tie2Cre or Lyve1Cre) and found that they exhibited pleural effusion and died postnatally. Strikingly, the number of lymphatic valves was dramatically reduced in these mice."
Endothelial Piezo1 loss reduces lymphatic valve number and reproduces pleural effusion in mice.
PMID:30482854 SUPPORT Model Organism
"the process of protrusion in the valve leaflets, which is associated with collective cell migration, actin polymerization, and remodeling of cell-cell junctions, was impaired in Tie2Cre;Piezo1cKO mice"
Identifies the specific cellular step of valve morphogenesis that requires PIEZO1.
PMID:35701867 SUPPORT Model Organism
"Lymphatic-specific conditional Piezo1 knockout largely phenocopied sprouting defects shown in Orai1- or Klf2- knockout lymphatics during embryo development. Postnatal deletion of Piezo1 induced lymphatic regression in adults."
Shows PIEZO1 is required both for developmental lymphatic sprouting and for maintenance of adult lymphatics.
+ 1 more reference
Generalized Lymphatic Dysplasia and Lymph Transport Failure
The resulting disorder is a uniform, widespread lymphatic dysplasia affecting all body segments, with systemic involvement of the thoracic, pericardial, and intestinal lymphatics. Lymphoscintigraphy in affected individuals shows a strikingly consistent and symmetric pattern of deep and superficial rerouting, indicating failure of superficial lymphatic collector function rather than simple aplasia.
Show evidence (2 references)
PMID:26333996 SUPPORT Human Clinical
"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."
Defines the generalized, multi-compartment lymphatic dysplasia phenotype that PIEZO1 loss produces.
PMID:26333996 SUPPORT Human Clinical
"The rerouting suggests failure of superficial lymphatic collector function."
Lymphoscintigraphic evidence that the functional lesion is collector failure, consistent with the valve defect.
Chylous Effusion and Fetal Fluid Accumulation
In utero, lymphatic transport failure produces non-immune hydrops fetalis with pleural and pericardial effusions and ascites. This may be lethal in the perinatal period; in survivors the neonatal edema often resolves completely, but chylothorax may persist or recur.
Show evidence (2 references)
PMID:36453701 SUPPORT Human Clinical
"One cause of NIHF is lymphatic malformation 6 (LMPHM6) due to biallelic loss-of-function (LoF) variants in PIEZO1."
Directly attributes non-immune hydrops fetalis to biallelic loss-of-function PIEZO1 (LMPHM6).
PMID:26333996 SUPPORT Human Clinical
"biallelic variants have a high incidence of NIHF (7 of the 10 affected cases). This may be lethal in the perinatal period (n=2)."
Quantifies the frequency and perinatal lethality of hydrops in the founding cohort.
Chronic Peripheral and Facial Lymphedema
Survivors typically re-present in childhood with lymphedema of the lower limbs, arms, face, and genitalia, with or without chylothoraces and intestinal lymphangiectasia. Recurrent severe facial cellulitis complicates the facial lymphedema and is a major source of morbidity.
Show evidence (1 reference)
PMID:26333996 SUPPORT Human Clinical
"Survivors may present later with lymphoedema of the peripheries (mainly lower limbs but also arms (n=4), face (n=3) and genitalia (n=1)), with or without chylothoraces (n=2) and intestinal lymphangiectasia (n=1)."
Documents the postnatal distribution of lymphedema and its systemic complications.

Pathograph

Use the checkboxes to hide or show graph categories. Hover nodes for evidence and cross-linked metadata.
Pathograph: causal mechanism network for Lymphatic malformation 6 Interactive directed graph showing how pathophysiology mechanisms, phenotypes, genetic factors and variants, experimental models, environmental triggers, and treatments relate through causal and linked edges.

Phenotypes

12
Blood 1
Spherocytosis OCCASIONAL HP:0004444 Human Phenotype Ontology (HP) Relation: this clinical feature is this phenotype This clinical feature is Spherocytosis (HP:0004444). HP:0004444 is a phenotype from the Human Phenotype Ontology.
Show evidence (1 reference)
PMID:26333996 SUPPORT Human Clinical
"Careful inspection of blood films from our affected individuals demonstrates occasional stomatocytes and spherocytes"
Documents spherocytes on blood films of affected individuals.
Digestive 1
Ascites OCCASIONAL HP:0001541 Human Phenotype Ontology (HP) Relation: this clinical feature is this phenotype This clinical feature is Ascites (HP:0001541). HP:0001541 is a phenotype from the Human Phenotype Ontology.
Show evidence (1 reference)
PMID:36453701 SUPPORT Human Clinical
"At post-mortem examination ascites, pleural effusions and telengectasies can guide the etiological diagnosis."
Documents ascites in LMPHM6 fetuses at post-mortem examination.
Head and Neck 1
Facial edema FREQUENT HP:0000282 Human Phenotype Ontology (HP) Relation: this clinical feature is this phenotype This clinical feature is Facial edema (HP:0000282), qualified as temporality recurrent. HP:0000282 is a phenotype from the Human Phenotype Ontology.
Temporal: RECURRENT
Show evidence (1 reference)
PMID:26333996 SUPPORT Human Clinical
"Two of the affected individuals suffer from intermittent, severe facial swelling due to recurrent cellulitis. This is rarely seen in other forms of primary lymphoedema."
Documents intermittent severe facial swelling and notes it as distinguishing from other primary lymphedemas.
Metabolism 3
Non-immune hydrops fetalis FREQUENT HP:0001790 Human Phenotype Ontology (HP) Relation: this clinical feature is this phenotype This clinical feature is Nonimmune hydrops fetalis (HP:0001790). HP:0001790 is a phenotype from the Human Phenotype Ontology.
Show evidence (2 references)
PMID:26333996 SUPPORT Human Clinical
"biallelic variants have a high incidence of NIHF (7 of the 10 affected cases). This may be lethal in the perinatal period (n=2)."
7 of 10 affected individuals (70%) had non-immune hydrops fetalis, mapping to the FREQUENT band.
PMID:36453701 SUPPORT Human Clinical
"During the pregnancy, most cases are revealed by isolated NIHF at second trimester of gestation."
Establishes the prenatal timing and the isolated-NIHF presentation.
Lymphedema VERY_FREQUENT HP:0001004 Human Phenotype Ontology (HP) Relation: this clinical feature is this phenotype This clinical feature is Lymphedema (HP:0001004), qualified as temporality chronic; course progressive. HP:0001004 is a phenotype from the Human Phenotype Ontology.
Temporal: CHRONIC Course: PROGRESSIVE
Show evidence (2 references)
PMID:26333996 SUPPORT Human Clinical
"Survivors may present later with lymphoedema of the peripheries (mainly lower limbs but also arms (n=4), face (n=3) and genitalia (n=1)), with or without chylothoraces (n=2) and intestinal lymphangiectasia (n=1)."
Lymphedema is the defining postnatal feature in surviving affected individuals, supporting the VERY_FREQUENT band.
PMID:26387913 SUPPORT Human Clinical
"At 42 months of age, she displays significant persistent lymphoedema of her legs, torso and face"
Documents persistent multi-segment lymphedema in an independently reported patient.
Pleural effusion FREQUENT HP:0002202 Human Phenotype Ontology (HP) Relation: this clinical feature is this phenotype This clinical feature is Pleural effusion (HP:0002202). HP:0002202 is a phenotype from the Human Phenotype Ontology.
Show evidence (1 reference)
PMID:36453701 SUPPORT Human Clinical
"At post-mortem examination ascites, pleural effusions and telengectasies can guide the etiological diagnosis."
Pleural effusion is a consistent post-mortem finding in LMPHM6 fetuses.
Prenatal and Birth 1
Polyhydramnios OCCASIONAL HP:0001561 Human Phenotype Ontology (HP) Relation: this clinical feature is this phenotype This clinical feature is Polyhydramnios (HP:0001561). HP:0001561 is a phenotype from the Human Phenotype Ontology.
Frequency is banded OCCASIONAL from the reported case detail (2 of 3 families in this series, but not systematically ascertained across the whole reported LMPHM6 cohort); no cohort-level frequency figure has been published.
Show evidence (2 references)
PMID:40792030 SUPPORT Human Clinical
"Antenatal imaging (gestational date not noted) identified NIFH and polyhydramnios."
Documents polyhydramnios in the GLD07 proband's affected pregnancy.
PMID:40792030 SUPPORT Human Clinical
"The pregnancy was complicated by polyhydramnios requiring repeated amnio-drainage at 27, 30 and 33 weeks."
Independent occurrence in the GLD09 pregnancy, severe enough to require repeated drainage.
Other 5
Chylothorax FREQUENT HP:0010310 Human Phenotype Ontology (HP) Relation: this clinical feature is this phenotype This clinical feature is Chylothorax (HP:0010310), qualified as temporality recurrent. HP:0010310 is a phenotype from the Human Phenotype Ontology.
Temporal: RECURRENT
Show evidence (2 references)
PMID:26387913 SUPPORT Human Clinical
"II.1 presented at birth with hydrops and bilateral chylothorax, confirmed by fluid analysis."
Documents biochemically confirmed bilateral chylothorax at birth.
PMID:37159433 SUPPORT Human Clinical
"Hereditary Lymphedema type III can be associated with persistent chylothorax that can vary in size over time."
Establishes persistent/recurrent chylothorax as a recognized feature of LMPHM6.
Pericardial effusion OCCASIONAL HP:0001698 Human Phenotype Ontology (HP) Relation: this clinical feature is this phenotype This clinical feature is Pericardial effusion (HP:0001698). HP:0001698 is a phenotype from the Human Phenotype Ontology.
Show evidence (1 reference)
PMID:35646098 SUPPORT Human Clinical
"Lymphatic malformation-6 (LMPHM6) is a rarer form of nonimmune hydrops that often manifests as widespread lymphedema involving all segments of the body, namely, subcutaneous edema, intestinal/pulmonary lymphangiectasia, chylothoraces, and pleural/pericardial effusions."
Lists pericardial effusion among the manifestations of LMPHM6.
Intestinal lymphangiectasia OCCASIONAL HP:0002593 Human Phenotype Ontology (HP) Relation: this clinical feature is this phenotype This clinical feature is Intestinal lymphangiectasia (HP:0002593). HP:0002593 is a phenotype from the Human Phenotype Ontology.
Show evidence (1 reference)
PMID:26333996 SUPPORT Human Clinical
"Survivors may present later with lymphoedema of the peripheries (mainly lower limbs but also arms (n=4), face (n=3) and genitalia (n=1)), with or without chylothoraces (n=2) and intestinal lymphangiectasia (n=1)."
Reports intestinal lymphangiectasia in 1 of 10 affected individuals, supporting the OCCASIONAL band.
Recurrent cellulitis FREQUENT HP:0100658 Human Phenotype Ontology (HP) Relation: this clinical feature is this phenotype This clinical feature is Cellulitis (HP:0100658), qualified as temporality recurrent; severity severe. HP:0100658 is a phenotype from the Human Phenotype Ontology.
Temporal: RECURRENT Severity: SEVERE
Show evidence (1 reference)
PMID:26333996 SUPPORT Human Clinical
"Four patients of our cohort had severe, recurrent facial cellulitis with significant morbidity (high pyrexia and frequent admission to intensive care)."
4 of 10 affected individuals (40%) had severe recurrent facial cellulitis, mapping to the FREQUENT band.
Stomatocytosis OCCASIONAL HP:0004446 Human Phenotype Ontology (HP) Relation: this clinical feature is this phenotype This clinical feature is Stomatocytosis (HP:0004446). HP:0004446 is a phenotype from the Human Phenotype Ontology.
Show evidence (2 references)
PMID:26333996 SUPPORT Human Clinical
"Careful inspection of blood films from our affected individuals demonstrates occasional stomatocytes and spherocytes"
Documents stomatocytes on blood films of affected individuals.
PMID:26387913 SUPPORT Human Clinical
"Both patients and parents had blood counts including mean corpuscular volume in the normal range."
Counterbalancing observation that routine hematologic indices can be entirely normal, so the red-cell finding is subtle and not universal.
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Genetic Associations

1
PIEZO1 (Causal biallelic loss-of-function variants)
Gene: PIEZO1 hgnc:28993 HUGO Gene Nomenclature Committee (hgnc) Relation: this disease-associated gene is this gene This disease-associated gene is PIEZO1 (hgnc:28993). hgnc:28993 is a gene from the HUGO Gene Nomenclature Committee. relationship_type: CAUSATIVE variant_origin: GERMLINE
Show evidence (3 references)
PMID:26333996 SUPPORT Human Clinical
"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."
Establishes PIEZO1 as the causal gene, with biallelic variants, for this form of generalized lymphatic dysplasia.
PMID:26387913 SUPPORT Human Clinical
"Our results delineate a novel clinical category of PIEZO1-associated hereditary lymphoedema."
Independent contemporaneous report establishing PIEZO1-associated hereditary lymphedema as a distinct entity.
PMID:37902181 SUPPORT Human Clinical
"PIEZO1 variants causing AR NIHF were characterized by loss of function and isolated NIHF phenotype."
Confirms that the recessive (LMPHM6) mechanism is loss of function, in contrast to the dominant gain-of-function red-cell disease.
Variants (5)
p.Glu1630Ter (c.4888G>T) Pathogenic
nonsense
Recurrent nonsense PIEZO1 allele observed in two unrelated families in the founding cohort; no truncated protein is detectable by western blot, consistent with a null allele.
Show evidence (1 reference)
PMID:26333996 SUPPORT Human Clinical
"one of which was the nonsense mutation (c.G4888T; p.E1630X) also observed in family GLD1"
Identifies the recurrent nonsense allele shared between families.
c.3796+1G>A Pathogenic
splice donor site
Canonical splice-donor variant causing skipping of exon 26 and a measurable reduction in PIEZO1 protein.
Show evidence (2 references)
PMID:26333996 SUPPORT Human Clinical
"The c.3796+1G>A variant in GLD3 causes skipping of exon 26"
Establishes the splicing consequence of this allele.
PMID:26333996 SUPPORT Human Clinical
"Western blot results of the c.3796+1G>A variant in GLD3 showed a reduction in PIEZO1 expression levels"
Protein-level confirmation of reduced PIEZO1 expression for this allele.
p.Ser1721Trp (c.5162C>G) Pathogenic
missense
Homozygous missense PIEZO1 variant reported as a cause of LMPHM6 in a family with three adverse pregnancy outcomes from non-immune fetal hydrops.
Show evidence (1 reference)
PMID:35646098 SUPPORT Human Clinical
"we detected one rare and previously unobserved homozygous missense variant in PIEZO1 (c.5162C>G, p.Ser1721Trp) as a novel genetic cause of autosomal recessive LMPHM6, in a family with three adverse pregnancy outcomes due to nonimmune fetal hydrops"
A specific homozygous missense allele established as causal for LMPHM6.
p.Trp1287Ter (c.3860G>A) Likely Pathogenic
nonsense
Nonsense PIEZO1 allele reported in trans with a splice-acceptor deletion in a child with persistent chylothorax; both were classified as likely pathogenic.
Show evidence (1 reference)
PMID:37159433 SUPPORT Human Clinical
"Genetic testing revealed two deleterious variants in PIEZO1: c.2330-2_2330-1del and c.3860G > A (p.Trp1287*), both of which were classified as likely pathogenic."
Documents the biallelic genotype in a patient with persistent chylothorax.
p.Ile2270Thr (I2270T)
missense
Missense PIEZO1 allele reported homozygously in family GLD08 - the adolescent-onset pedigree - and in trans with E829V in GLD09. The reporting authors interpreted the GLD07-09 variants collectively as likely pathogenic or of uncertain significance, so no per-variant classification is asserted here; the functional work in the same paper shows reduced channel mechanical sensitivity rather than reduced expression.
Show evidence (2 references)
PMID:40792030 SUPPORT Human Clinical
"In GLD08, homozygosity of a single variant encoding Ile2270Thr (I2270T) associated with disease in 3 family members"
Segregation of the homozygous missense allele with disease in three members of one family.
PMID:40792030 SUPPORT In Vitro
"PIEZO1 variants have been associated with generalized lymphatic dysplasia (GLD) through mechanisms involving reduced PIEZO1 expression. Here, we report variants where the mechanism involves reduced channel mechanical sensitivity."
Establishes the loss-of-function mechanism for this class of variant as mechanical insensitivity of an expressed channel.
💊

Medical Actions

6
Dietary fat restriction and medium-chain triglyceride feeding
Action: dietary interventionNCI Thesaurus (NCIT) Relation: this treatment is this clinical intervention This treatment is dietary intervention (NCIT:C15447). NCIT:C15447 is a clinical intervention from the NCI Thesaurus. Ontology label: Dietary Intervention NCIT:C15447
Restriction of long-chain dietary fat, with medium-chain triglyceride substitution, reduces chyle production and thoracic-duct lymph flow and is first-line conservative management of chylothorax and enteric lymph loss in LMPHM6.
Mechanism Target:
MODULATES Chylous Effusion and Fetal Fluid Accumulation — Reducing long-chain fat intake lowers chyle flow into the incompetent thoracic lymphatics, reducing effusion volume.
Show evidence (1 reference)
PMID:37159433 SUPPORT Human Clinical
"She subsequently had recurrent pleural effusions involving both pleural cavities, which tended to improve with restriction of her fat intake, and, one occasion, subcutaneous octreotide."
Documents clinical improvement of the recurrent effusions with dietary fat restriction in a molecularly confirmed LMPHM6 patient.
Octreotide
Action: PharmacotherapyNCI Thesaurus (NCIT) Relation: this treatment is this clinical intervention This treatment is Pharmacotherapy (NCIT:C15986). NCIT:C15986 is a clinical intervention from the NCI Thesaurus. NCIT:C15986
Agent: octreotide CHEBI:7726 Chemical Entities of Biological Interest (CHEBI) Relation: this treatment uses this therapeutic agent This treatment uses octreotide (CHEBI:7726). CHEBI:7726 is a therapeutic agent from Chemical Entities of Biological Interest.
Subcutaneous octreotide, a somatostatin analogue that reduces splanchnic blood flow and lymph production, has been used as adjunctive therapy for refractory chylothorax in LMPHM6. Evidence is limited to single-patient experience.
Mechanism Target:
MODULATES Chylous Effusion and Fetal Fluid Accumulation — Somatostatin-analogue reduction of lymph production decreases chyle accumulation in the pleural space.
Show evidence (1 reference)
PMID:37159433 SUPPORT Human Clinical
"She subsequently had recurrent pleural effusions involving both pleural cavities, which tended to improve with restriction of her fat intake, and, one occasion, subcutaneous octreotide."
Single-patient use of subcutaneous octreotide alongside dietary fat restriction; the report does not isolate the octreotide effect, so support is partial.
Lymphedema supportive care
Action: physical therapyNCI Thesaurus (NCIT) Relation: this treatment is this clinical intervention This treatment is physical therapy (NCIT:C15302). NCIT:C15302 is a clinical intervention from the NCI Thesaurus. Ontology label: Physical Therapy NCIT:C15302
Complete decongestive therapy - compression garments or bandaging, manual lymphatic drainage, exercise, and meticulous skin care - is the mainstay of chronic lymphedema management, together with prompt antibiotic treatment of cellulitis, which is a major source of morbidity in this disorder.
Mechanism Target:
MODULATES Chronic Peripheral and Facial Lymphedema — Decongestive therapy mechanically compensates for failed lymphatic collector function.
Show evidence (1 reference)
PMID:26333996 SUPPORT Human Clinical
"Four patients of our cohort had severe, recurrent facial cellulitis with significant morbidity (high pyrexia and frequent admission to intensive care)."
Establishes the clinical burden (recurrent severe cellulitis complicating lymphedema) that skin care and prompt antibiotic treatment address; the paper does not itself report a supportive-care trial, so support is partial.
Genetic counseling
Action: Genetic CounselingNCI Thesaurus (NCIT) Relation: this treatment is this clinical intervention This treatment is Genetic Counseling (NCIT:C15240). NCIT:C15240 is a clinical intervention from the NCI Thesaurus. NCIT:C15240
Counseling covers autosomal recessive inheritance and the 25% sibling recurrence risk, carrier testing, and prenatal or preimplantation genetic testing options once the familial biallelic PIEZO1 genotype is known. Recurrent adverse pregnancy outcomes are a recognized presentation.
Show evidence (1 reference)
PMID:35646098 SUPPORT Human Clinical
"we detected one rare and previously unobserved homozygous missense variant in PIEZO1 (c.5162C>G, p.Ser1721Trp) as a novel genetic cause of autosomal recessive LMPHM6, in a family with three adverse pregnancy outcomes due to nonimmune fetal hydrops"
Recurrent pregnancy loss in a single family illustrates the recurrence risk that counseling and molecular diagnosis address.
PIEZO1 agonism (investigational)
Action: PharmacotherapyNCI Thesaurus (NCIT) Relation: this treatment is this clinical intervention This treatment is Pharmacotherapy (NCIT:C15986). NCIT:C15986 is a clinical intervention from the NCI Thesaurus. NCIT:C15986
The small-molecule PIEZO1 agonist Yoda1 partly rescues the mechanical sensitivity of mechanically insensitive LMPHM6 missense channels in vitro, and an analogue with improved potency has been synthesized. This is a preclinical, genotype-restricted concept - it cannot rescue null alleles, and systemic PIEZO1 activation would also act on erythrocytes and the blood vasculature. No PIEZO1-directed therapy is approved.
Mechanism Target:
RESTORES PIEZO1 Loss of Function — Chemical agonism partly restores mechanical activation of variant channels that are expressed but mechanically insensitive.
Show evidence (2 references)
PMID:40792030 SUPPORT In Vitro
"Patch-clamp studies of the cap and sub-cap variant channels revealed abolished or reduced channel mechanical sensitivity with the possibility to activate the channels and partly rescue mechanical sensitivity by the small molecule Yoda1."
In vitro pharmacological rescue of variant channels; no clinical evidence exists, so support for this as a treatment is partial.
PMID:35701867 SUPPORT Model Organism
"we assessed a potential therapeutic value of Piezo1 activation in lymphatic regeneration and found that a Piezo1 agonist, Yoda1, effectively suppressed postsurgical lymphedema development."
Mouse proof of concept that PIEZO1 agonism can reduce lymphedema; the model is acquired postsurgical lymphedema, not biallelic PIEZO1 disease.
Pleurodesis and other interventional management of refractory chylous effusion
Action: therapeutic procedureNCI Thesaurus (NCIT) Relation: this treatment is this clinical intervention This treatment is therapeutic procedure (NCIT:C49236). NCIT:C49236 is a clinical intervention from the NCI Thesaurus. Ontology label: Therapeutic Procedure NCIT:C49236
Pleurodesis, thoracic-duct ligation, and pleuro-peritoneal shunting are the standard escalation options when chylous pleural effusion recurs despite dietary fat restriction and octreotide. In LMPHM6 they are documented as used, not as effective: in the one reported adolescent-onset family, effusion control proved very difficult despite all three, and the proband's father had persistent effusions and a restrictive lung defect after pleurodesis. No LMPHM6-specific response rate has been established for any of these procedures, and none targets the underlying lymphatic mechanism.
Mechanism Target:
MODULATES Chylous Effusion and Fetal Fluid Accumulation — Obliterating the pleural space or diverting/interrupting thoracic-duct flow limits accumulation of chyle in the pleural cavity; the incompetent lymphatic network itself is unaltered.
Show evidence (2 references)
PMID:40792030 SUPPORT Human Clinical
"Treatment has proved very difficult and has involved pleurodesis, ligation of the thoracic duct and pleuro-peritoneal shunting."
Documents the interventional options actually used in a molecularly confirmed LMPHM6 patient, while explicitly recording that control was difficult - so this supports use, not efficacy.
PMID:40792030 SUPPORT Human Clinical
"Despite pleurodesis, his effusions are persistent resulting in a restrictive lung defect and nocturnal hypoventilation requiring non-invasive ventilation (NIV)."
A second affected individual in whom pleurodesis failed to control chylous effusion, recording the limits of the intervention.
🔬

Diagnosis

2
Molecular genetic testing of PIEZO1
Identification of biallelic pathogenic PIEZO1 variants, typically by exome or a primary-lymphedema/generalized-lymphatic-anomaly gene panel, confirms the diagnosis. In prenatal exome series, PIEZO1 is the single most frequently implicated gene in non-immune hydrops fetalis, so it should be prioritized when hydrops is otherwise unexplained.
genetic testing NCIT:C15709 NCI Thesaurus (NCIT)
Results: Biallelic (homozygous or compound heterozygous) loss-of-function PIEZO1 variants confirm LMPHM6.
Show evidence (2 references)
PMID:37902181 SUPPORT Human Clinical
"PIEZO1 variants were reported in 10% of NIHF cases diagnosed by prenatal exome, making PIEZO1 the most common single gene reported in NIHF."
Supports prioritizing PIEZO1 in the molecular workup of unexplained non-immune hydrops fetalis.
PMID:26387913 SUPPORT Human Clinical
"Through whole-exome sequencing, we identify biallelic mutations in PIEZO1 (a splicing variant leading to early truncation and a non-synonymous missense variant) in a pair of siblings affected with persistent lymphoedema caused by congenital lymphatic dysplasia."
Exome sequencing is the demonstrated route to molecular diagnosis in this disorder.
Lymphoscintigraphy
Radionuclide lymphoscintigraphy demonstrates the functional lymphatic lesion, showing symmetric deep rerouting with popliteal nodal uptake and superficial rerouting through the skin, indicating failure of superficial lymphatic collector function rather than aplasia.
lymphoscintigraphy NCIT:C67262 NCI Thesaurus (NCIT)
Results: Symmetric deep and superficial rerouting consistent with collector failure; lymphangiectasia with chylothorax may also be demonstrated.
Show evidence (2 references)
PMID:26333996 SUPPORT Human Clinical
"In the lower limbs, all the patients have deep rerouting as demonstrated by the popliteal lymph node uptake"
Describes the characteristic lymphoscintigraphic finding in affected individuals.
PMID:37274623 SUPPORT Human Clinical
"Lymphoscintigraphy showed lymphangiectasia with chylothorax."
Independent case confirming the diagnostic utility of lymphoscintigraphy.
📈

Progression

2
Prenatal and early-childhood onset
Age: Fetal to early childhood
The classically reported course: non-immune fetal hydrops detected in the second trimester, often resolving spontaneously after birth, followed by facial and four-limb lymphedema appearing in infancy or early childhood.
Show evidence (1 reference)
PMID:26333996 SUPPORT Human Clinical
"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."
Defines the prenatal-hydrops-then-childhood-lymphedema course of the founding cohort.
Adolescent and adult onset
Age: 11-30 years
A later-onset arm exists and is easily missed if LMPHM6 is treated as a uniformly congenital disorder. In family GLD08 (homozygous I2270T) there was no antenatal or neonatal disease at all; presentation began in adolescence with chylous pleural and pericardial effusions, with lower-limb and scrotal edema following years later and no facial edema. The affected father of that proband presented at 30 years.
Show evidence (2 references)
PMID:40792030 SUPPORT Human Clinical
"in GLD08, there was disease only from adolescence that was characterized first by pleural and pericardial effusions and then lower limb and scrotal edema without facial edema"
Directly states an adolescent-onset presentation with a different phenotype ordering from the congenital arm.
PMID:40792030 SUPPORT Human Clinical
"From age 11 years he developed progressive breathlessness and reduced exercise tolerance and was found to have bilateral chylous pleural effusions"
Case-level detail of the adolescent onset in the GLD08 proband, whose antenatal and neonatal period was uneventful.
📊

Prevalence

2
Worldwide
Cases In Literature Ultra Rare
No disease-specific prevalence or incidence estimate exists. The founding cohort comprised 10 affected individuals from 6 families, and subsequent reports have been single families or small series. A widely quoted figure of approximately 1 in 6,000 for generalized lymphatic dysplasia should not be used as an LMPHM6 prevalence, as its denominator and molecular ascertainment are not disease-specific.
Show evidence (1 reference)
PMID:26333996 SUPPORT Human Clinical
"In total, we identified 10 PIEZO1 variants in 6 families"
Supports the ultra-rare, literature-case-count basis for the occurrence estimate.
Fetuses with non-immune hydrops undergoing prenatal exome sequencing
Unknown Unknown
Not a population prevalence: this records the diagnostic yield of PIEZO1 (both the recessive LMPHM6 and dominant gain-of-function forms) within an ascertained NIHF cohort - 19 of 191 cases, i.e. 10%.
Show evidence (1 reference)
PMID:37902181 SUPPORT Human Clinical
"In total, 19 of 191 NIHF cases diagnosed by prenatal exome were attributed to PIEZO1."
Quantifies the PIEZO1 contribution within an ascertained NIHF cohort.
🔀

Differential Diagnoses

2

Conditions with similar clinical presentations that must be differentiated from Lymphatic malformation 6:

Overlapping Features The other major autosomal recessive generalized lymphatic dysplasia. Hennekam syndrome is distinguished by characteristic facial dysmorphism (periorbital edema, retrognathia, flat facial profile, gingival hypertrophy, microstomia), seizures, and intellectual disability, none of which occur in LMPHM6.
Show evidence (1 reference)
PMID:26333996 SUPPORT Human Clinical
"The phenotype is distinct from Hennekam syndrome as none of our GLD patients had the dysmorphic features associated with HS, nor the learning disabilities or seizures, nor was the swelling severe"
States the clinical basis for separating LMPHM6 from Hennekam syndrome.
Dehydrated hereditary stomatocytosis Not Yet Curated MONDO:0008689
Overlapping Features The allelic autosomal dominant disorder caused by monoallelic gain-of-function PIEZO1 variants, presenting with mild-to-moderate hemolytic anemia, pseudohyperkalemia, and transient perinatal edema. The mechanism is opposite in direction (gain versus loss of channel function), and the two entities overlap only in the perinatal-edema phenotype.
Show evidence (1 reference)
PMID:37902181 SUPPORT Human Clinical
"PIEZO1 variants causing AD NIHF were characterized by gain of function in red blood cells, scarcity in databases, and sporadic inheritance."
Contrasts the dominant gain-of-function red-cell mechanism with the recessive loss-of-function lymphatic mechanism of LMPHM6.
🐁

Animal Models

2
Endothelial Piezo1 conditional knockout mouse (Tie2Cre or Lyve1Cre)
Species
Mouse
Genotype
Piezo1 conditional knockout (Tie2Cre;Piezo1fl/fl or Lyve1Cre;Piezo1fl/fl)
Publication
Lymphatic-specific Piezo1 conditional knockout mouse
Species
Mouse
Genotype
Lymphatic endothelial-specific conditional Piezo1 knockout; postnatal inducible deletion
Publication
{ }

Source YAML

click to show
name: Lymphatic malformation 6
creation_date: "2026-08-18T00:00:00Z"
description: >-
  Lymphatic malformation 6 (LMPHM6; hereditary lymphedema type III), also known as
  generalized lymphatic dysplasia of Fotiou, is an autosomal recessive generalized
  lymphatic dysplasia caused by biallelic loss-of-function variants in PIEZO1,
  which encodes a mechanically activated, calcium-permeable cation channel. Loss
  of PIEZO1 mechanotransduction in lymphatic endothelial cells impairs lymphatic
  valve morphogenesis and flow-driven lymphatic sprouting, producing widespread
  lymphatic dysfunction. The condition most often presents prenatally as
  non-immune hydrops fetalis with pleural and pericardial effusions and ascites,
  which may be lethal in the perinatal period; survivors frequently have complete
  resolution of the neonatal edema and re-present in childhood with peripheral,
  facial, and genital lymphedema, with or without persistent chylothorax or
  intestinal lymphangiectasia. Recurrent severe facial cellulitis is a
  characteristic and serious complication. Unlike Hennekam syndrome, the
  dysmorphic features, seizures, and intellectual disability are absent. Because
  monoallelic gain-of-function PIEZO1 variants cause dehydrated hereditary
  stomatocytosis, affected individuals and carriers may show subtle red-cell
  abnormalities (stomatocytes, spherocytes) without clinically significant
  hemolysis. Management is supportive; no PIEZO1-directed disease-modifying
  therapy is approved, although pharmacological rescue of mechanically insensitive
  mutant channels with the PIEZO1 agonist Yoda1 has been demonstrated in vitro.
category: Mendelian
parents:
- lymphatic malformation
- hereditary disease
synonyms:
- LMPHM6
- generalized lymphatic dysplasia of Fotiou
- hereditary lymphedema type III
- LMPH3
- PIEZO1-related generalized lymphatic dysplasia with non-immune hydrops fetalis
- PIEZO1-related lymphatic-related hydrops fetalis
disease_term:
  preferred_term: lymphatic malformation 6
  term:
    id: MONDO:0014797
    label: lymphatic malformation 6
classifications:
  harrisons_chapter:
  - classification_value: CARDIOVASCULAR
inheritance:
- name: Autosomal recessive inheritance
  inheritance_term:
    preferred_term: Autosomal recessive inheritance
    term:
      id: HP:0000007
      label: Autosomal recessive inheritance
  description: >-
    LMPHM6 is inherited in an autosomal recessive manner; affected individuals
    carry biallelic (homozygous or compound heterozygous) loss-of-function PIEZO1
    variants that co-segregate with disease in reported families. Heterozygous
    carriers are unaffected by the lymphatic phenotype. A pedigree may
    nonetheless look dominant: in family GLD08 a homozygous I2270T genotype
    segregating through consanguinity produced affected individuals in
    consecutive generations (the proband and his father), a pseudo-dominant
    pattern that should not be mistaken for a dominant PIEZO1 disorder.
  evidence:
  - reference: PMID:26333996
    reference_title: Novel mutations in PIEZO1 cause an autosomal recessive generalized lymphatic dysplasia with non-immune hydrops fetalis.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      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.
    explanation: >-
      Homozygous and compound heterozygous PIEZO1 genotypes establish autosomal
      recessive inheritance for LMPHM6.
  - reference: PMID:26387913
    reference_title: Impaired PIEZO1 function in patients with a novel autosomal recessive congenital lymphatic dysplasia.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Through whole-exome sequencing, we identify biallelic mutations in PIEZO1 (a
      splicing variant leading to early truncation and a non-synonymous missense
      variant) in a pair of siblings affected with persistent lymphoedema caused
      by congenital lymphatic dysplasia.
    explanation: >-
      Independently confirms biallelic (compound heterozygous) PIEZO1 inheritance
      in an affected sibship.
  - reference: PMID:40792030
    reference_title: PIEZO1 mechanical insensitivity in generalized lymphatic dysplasia with the potential for pharmacological rescue.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      In GLD08, homozygosity of a single variant encoding Ile2270Thr (I2270T)
      associated with disease in 3 family members
    explanation: >-
      A single homozygous PIEZO1 variant accounts for disease in three members of
      one consanguineous family, the genotype underlying the apparently dominant
      vertical transmission in that pedigree.
  - reference: PMID:40792030
    reference_title: PIEZO1 mechanical insensitivity in generalized lymphatic dysplasia with the potential for pharmacological rescue.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      GLD08 I.2 is the proband’s father. His parents are not known to be
      consanguineous. He was diagnosed with spontaneous bilateral chylous
      effusions at the age of 30 years.
    explanation: >-
      Documents an affected parent and affected child in the same pedigree - the
      pseudo-dominant pattern that arises when a recessive allele is common in a
      consanguineous kindred.
pathophysiology:
- name: PIEZO1 Loss of Function
  biological_scale: MOLECULAR
  description: >-
    Biallelic nonsense, frameshift, splice-site, and missense variants in PIEZO1
    abolish or severely reduce the activity of a mechanically activated,
    calcium-permeable cation channel. Two mechanistically distinct routes to loss
    of function are documented: reduced or absent PIEZO1 protein (truncating and
    splice variants, shown by western blot to eliminate or reduce PIEZO1
    expression) and reduced channel mechanical sensitivity despite surface
    expression (cap and sub-cap missense variants that are mechanically
    insensitive yet partly rescuable with the chemical agonist Yoda1).
  genes:
  - preferred_term: PIEZO1
    term:
      id: hgnc:28993
      label: PIEZO1
  molecular_functions:
  - preferred_term: mechanically activated cation channel activity
    modifier: LOSS_OF_FUNCTION
    term:
      id: GO:0008381
      label: mechanosensitive monoatomic ion channel activity
  evidence:
  - reference: PMID:26333996
    reference_title: Novel mutations in PIEZO1 cause an autosomal recessive generalized lymphatic dysplasia with non-immune hydrops fetalis.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      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.
    explanation: >-
      Identifies PIEZO1 as a mechanically activated ion channel and the causal
      gene locus for this disorder.
  - reference: PMID:26333996
    reference_title: Novel mutations in PIEZO1 cause an autosomal recessive generalized lymphatic dysplasia with non-immune hydrops fetalis.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      No truncated PIEZO1 protein products were identified in western blot
      analysis in GLD1:II.3 and GLD2:II.2
    explanation: >-
      Direct protein-level demonstration that truncating alleles yield no stable
      PIEZO1 protein, i.e. loss of function.
  - reference: PMID:26387913
    reference_title: Impaired PIEZO1 function in patients with a novel autosomal recessive congenital lymphatic dysplasia.
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: >-
      Patch-clamp analysis of the missense PIEZO1 channel in a heterologous system
      (a mammalian cell line derived from HEK293T cells) indicated strongly
      diminished current amplitudes as compared with wild type, likely due to
      reduced cell surface expression.
    explanation: >-
      Electrophysiological confirmation that the patient missense allele is
      hypomorphic/loss-of-function.
  - reference: PMID:40792030
    reference_title: PIEZO1 mechanical insensitivity in generalized lymphatic dysplasia with the potential for pharmacological rescue.
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: >-
      PIEZO1 variants have been associated with generalized lymphatic dysplasia
      (GLD) through mechanisms involving reduced PIEZO1 expression. Here, we
      report variants where the mechanism involves reduced channel mechanical
      sensitivity.
    explanation: >-
      Establishes the second loss-of-function route: mechanical insensitivity of
      an expressed channel, distinct from reduced expression.
  downstream:
  - target: Impaired Lymphatic Endothelial Mechanotransduction
    causal_link_type: DIRECT
    description: >-
      Loss of PIEZO1 channel function removes the principal mechanosensor by which
      lymphatic endothelial cells convert flow and stretch into calcium influx.
- name: Impaired Lymphatic Endothelial Mechanotransduction
  biological_scale: CELLULAR
  description: >-
    PIEZO1 is abundantly expressed in lymphatic endothelial cells, where it
    transduces oscillatory shear stress and membrane stretch into calcium entry.
    Loss of PIEZO1 abrogates flow-induced calcium influx and the downstream
    ORAI1/KLF2/Notch transcriptional programme that drives lymphatic sprouting,
    and it removes the mechanical cue required for valve-forming cell behaviour.
  cell_types:
  - preferred_term: lymphatic endothelial cell
    term:
      id: CL:0002138
      label: endothelial cell of lymphatic vessel
  biological_processes:
  - preferred_term: cellular response to fluid shear stress
    modifier: DECREASED
    term:
      id: GO:0071498
      label: cellular response to fluid shear stress
  - preferred_term: response to mechanical stimulus
    modifier: DECREASED
    term:
      id: GO:0009612
      label: response to mechanical stimulus
  evidence:
  - reference: PMID:35701867
    reference_title: Piezo1-Regulated Mechanotransduction Controls Flow-Activated Lymphatic Expansion.
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: >-
      Piezo1 knockdown in cultured lymphatic endothelial cells inhibited the
      laminar flow-induced calcium influx
    explanation: >-
      Demonstrates that PIEZO1 is required for flow-induced calcium signalling in
      lymphatic endothelial cells.
  - reference: PMID:38747287
    reference_title: The mechanosensory channel PIEZO1 functions upstream of angiopoietin/TIE/FOXO1 signaling in lymphatic development.
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: >-
      Yoda1 rapidly triggered nuclear FOXO1 extrusion in WT mesenteries but not in
      Piezo1LEC–/– mesenteries, confirming the PIEZO1/FOXO1 axis in mesenteric
      lymphatics
    explanation: >-
      Ex vivo mouse mesenteric lymphatics lacking endothelial PIEZO1 fail to
      transduce channel activation into a downstream signalling response,
      demonstrating that PIEZO1 loss abolishes lymphatic endothelial
      mechanosignalling.
  downstream:
  - target: Disrupted ANGPT2-TIE-FOXO1 Signaling
    causal_link_type: DIRECT
    description: >-
      PIEZO1 activation is the upstream trigger for ANGPT2 exocytosis and TIE
      pathway engagement in lymphatic endothelial cells.
  - target: Defective Lymphatic Valve Formation and Lymphangiogenesis
    causal_link_type: INDIRECT_KNOWN_INTERMEDIATES
    description: >-
      Loss of flow-triggered mechanotransduction removes the signal driving
      valve-leaflet protrusion and flow-activated lymphatic sprouting.
- name: Disrupted ANGPT2-TIE-FOXO1 Signaling
  biological_scale: MOLECULAR
  description: >-
    PIEZO1 activation in lymphatic endothelial cells triggers rapid exocytosis of
    the TIE ligand ANGPT2, ADAM17-mediated ectodomain shedding of TIE1, increased
    TIE/PI3K/AKT signaling, and nuclear export of the transcription factor FOXO1.
    Loss of PIEZO1 function therefore silences a signaling network whose other
    members (ANGPT2, TIE1) are themselves mutated in primary lymphedema, providing
    a molecular bridge between channel function and lymphatic gene expression.
  biological_processes:
  - preferred_term: Tie signaling pathway
    modifier: DECREASED
    term:
      id: GO:0048014
      label: Tie signaling pathway
  - preferred_term: PI3K/AKT signal transduction
    modifier: DECREASED
    term:
      id: GO:0043491
      label: phosphatidylinositol 3-kinase/protein kinase B signal transduction
  - preferred_term: FOXO1 nuclear export
    modifier: DECREASED
    term:
      id: GO:0006611
      label: protein export from nucleus
  cell_types:
  - preferred_term: lymphatic endothelial cell
    term:
      id: CL:0002138
      label: endothelial cell of lymphatic vessel
  evidence:
  - reference: PMID:38747287
    reference_title: The mechanosensory channel PIEZO1 functions upstream of angiopoietin/TIE/FOXO1 signaling in lymphatic development.
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: >-
      activation of the mechanosensory channel PIEZO1 in lymphatic endothelial
      cells (LECs) caused rapid exocytosis of the TIE ligand ANGPT2, ectodomain
      shedding of TIE1 by disintegrin and metalloproteinase domain-containing
      protein 17 (ADAM17), and increased TIE/PI3K/AKT signaling, followed by
      nuclear export of the transcription factor FOXO1
    explanation: >-
      Establishes the PIEZO1 to ANGPT2/TIE/PI3K-AKT/FOXO1 signaling axis in
      lymphatic endothelial cells.
  downstream:
  - target: Defective Lymphatic Valve Formation and Lymphangiogenesis
    causal_link_type: INDIRECT_KNOWN_INTERMEDIATES
    description: >-
      Loss of this transcriptional output contributes to defective lymphatic
      vessel and valve development.
- name: Defective Lymphatic Valve Formation and Lymphangiogenesis
  biological_scale: TISSUE
  description: >-
    Endothelial-specific Piezo1 deletion in mice dramatically reduces the number
    of lymphatic valves and impairs the collective cell migration, actin
    polymerization, and cell-cell junction remodeling that produce the valve
    leaflet, while lymphatic-specific deletion phenocopies the sprouting defects
    of Orai1 and Klf2 knockouts and postnatal deletion causes lymphatic
    regression. Lymphatic valves are essential for unidirectional lymph flow, so
    their loss renders the collecting lymphatics incompetent.
  cell_types:
  - preferred_term: lymphatic endothelial cell
    term:
      id: CL:0002138
      label: endothelial cell of lymphatic vessel
  biological_processes:
  - preferred_term: lymph vessel development
    modifier: DECREASED
    term:
      id: GO:0001945
      label: lymph vessel development
  - preferred_term: lymphangiogenesis
    modifier: DECREASED
    term:
      id: GO:0001946
      label: lymphangiogenesis
  - preferred_term: lymph vessel morphogenesis
    modifier: DECREASED
    term:
      id: GO:0036303
      label: lymph vessel morphogenesis
  evidence:
  - reference: PMID:30482854
    reference_title: Mechanically activated ion channel PIEZO1 is required for lymphatic valve formation.
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: >-
      we analyzed two mouse lines lacking PIEZO1 in endothelial cells (via Tie2Cre
      or Lyve1Cre) and found that they exhibited pleural effusion and died
      postnatally. Strikingly, the number of lymphatic valves was dramatically
      reduced in these mice.
    explanation: >-
      Endothelial Piezo1 loss reduces lymphatic valve number and reproduces
      pleural effusion in mice.
  - reference: PMID:30482854
    reference_title: Mechanically activated ion channel PIEZO1 is required for lymphatic valve formation.
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: >-
      the process of protrusion in the valve leaflets, which is associated with
      collective cell migration, actin polymerization, and remodeling of cell-cell
      junctions, was impaired in Tie2Cre;Piezo1cKO mice
    explanation: >-
      Identifies the specific cellular step of valve morphogenesis that requires
      PIEZO1.
  - reference: PMID:35701867
    reference_title: Piezo1-Regulated Mechanotransduction Controls Flow-Activated Lymphatic Expansion.
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: >-
      Lymphatic-specific conditional Piezo1 knockout largely phenocopied sprouting
      defects shown in Orai1- or Klf2- knockout lymphatics during embryo
      development. Postnatal deletion of Piezo1 induced lymphatic regression in
      adults.
    explanation: >-
      Shows PIEZO1 is required both for developmental lymphatic sprouting and for
      maintenance of adult lymphatics.
  - reference: PMID:37159433
    reference_title: Persistent chylothorax associated with lymphatic malformation type 6 due to biallelic pathogenic variants in PIEZO1.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      PIEZO1 is required for lymphatic valve formation, and several lymphatic
      abnormalities have been reported to be associated with autosomal recessive
      PIEZO1 pathogenic variants including neonatal hydrops, lymphedema involving
      various body regions, and chylothorax.
    explanation: >-
      Connects the valve-formation requirement to the human autosomal recessive
      PIEZO1 clinical spectrum.
  downstream:
  - target: Generalized Lymphatic Dysplasia and Lymph Transport Failure
    causal_link_type: DIRECT
    description: >-
      Incompetent, hypoplastic lymphatic collectors cannot clear interstitial
      fluid and chyle.
- name: Generalized Lymphatic Dysplasia and Lymph Transport Failure
  biological_scale: ORGANISM
  description: >-
    The resulting disorder is a uniform, widespread lymphatic dysplasia affecting
    all body segments, with systemic involvement of the thoracic, pericardial, and
    intestinal lymphatics. Lymphoscintigraphy in affected individuals shows a
    strikingly consistent and symmetric pattern of deep and superficial rerouting,
    indicating failure of superficial lymphatic collector function rather than
    simple aplasia.
  evidence:
  - reference: PMID:26333996
    reference_title: Novel mutations in PIEZO1 cause an autosomal recessive generalized lymphatic dysplasia with non-immune hydrops fetalis.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      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.
    explanation: >-
      Defines the generalized, multi-compartment lymphatic dysplasia phenotype
      that PIEZO1 loss produces.
  - reference: PMID:26333996
    reference_title: Novel mutations in PIEZO1 cause an autosomal recessive generalized lymphatic dysplasia with non-immune hydrops fetalis.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      The rerouting suggests failure of superficial lymphatic collector function.
    explanation: >-
      Lymphoscintigraphic evidence that the functional lesion is collector
      failure, consistent with the valve defect.
  downstream:
  - target: Chylous Effusion and Fetal Fluid Accumulation
    causal_link_type: DIRECT
    description: >-
      Failure of thoracic and abdominal lymph drainage causes chyle and serous
      fluid to accumulate in body cavities, presenting in utero as hydrops.
  - target: Chronic Peripheral and Facial Lymphedema
    causal_link_type: DIRECT
    description: >-
      Failure of superficial collector function causes interstitial protein-rich
      fluid to accumulate in the limbs, face, and genitalia.
- name: Chylous Effusion and Fetal Fluid Accumulation
  biological_scale: ORGANISM
  description: >-
    In utero, lymphatic transport failure produces non-immune hydrops fetalis with
    pleural and pericardial effusions and ascites. This may be lethal in the
    perinatal period; in survivors the neonatal edema often resolves completely,
    but chylothorax may persist or recur.
  evidence:
  - reference: PMID:36453701
    reference_title: "Perinatal presentations of non-immune hydrops fetalis due to recessive PIEZO1 disease: A challenging fetal diagnosis."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      One cause of NIHF is lymphatic malformation 6 (LMPHM6) due to biallelic
      loss-of-function (LoF) variants in PIEZO1.
    explanation: >-
      Directly attributes non-immune hydrops fetalis to biallelic loss-of-function
      PIEZO1 (LMPHM6).
  - reference: PMID:26333996
    reference_title: Novel mutations in PIEZO1 cause an autosomal recessive generalized lymphatic dysplasia with non-immune hydrops fetalis.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      biallelic variants have a high incidence of NIHF (7 of the 10 affected
      cases). This may be lethal in the perinatal period (n=2).
    explanation: >-
      Quantifies the frequency and perinatal lethality of hydrops in the founding
      cohort.
- name: Chronic Peripheral and Facial Lymphedema
  biological_scale: ORGANISM
  description: >-
    Survivors typically re-present in childhood with lymphedema of the lower
    limbs, arms, face, and genitalia, with or without chylothoraces and intestinal
    lymphangiectasia. Recurrent severe facial cellulitis complicates the facial
    lymphedema and is a major source of morbidity.
  evidence:
  - reference: PMID:26333996
    reference_title: Novel mutations in PIEZO1 cause an autosomal recessive generalized lymphatic dysplasia with non-immune hydrops fetalis.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Survivors may present later with lymphoedema of the peripheries (mainly
      lower limbs but also arms (n=4), face (n=3) and genitalia (n=1)), with or
      without chylothoraces (n=2) and intestinal lymphangiectasia (n=1).
    explanation: >-
      Documents the postnatal distribution of lymphedema and its systemic
      complications.
progression:
- phase: Prenatal and early-childhood onset
  age_range: Fetal to early childhood
  notes: >-
    The classically reported course: non-immune fetal hydrops detected in the
    second trimester, often resolving spontaneously after birth, followed by
    facial and four-limb lymphedema appearing in infancy or early childhood.
  evidence:
  - reference: PMID:26333996
    reference_title: Novel mutations in PIEZO1 cause an autosomal recessive generalized lymphatic dysplasia with non-immune hydrops fetalis.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      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.
    explanation: >-
      Defines the prenatal-hydrops-then-childhood-lymphedema course of the
      founding cohort.
- phase: Adolescent and adult onset
  age_range: 11-30 years
  notes: >-
    A later-onset arm exists and is easily missed if LMPHM6 is treated as a
    uniformly congenital disorder. In family GLD08 (homozygous I2270T) there was
    no antenatal or neonatal disease at all; presentation began in adolescence
    with chylous pleural and pericardial effusions, with lower-limb and scrotal
    edema following years later and no facial edema. The affected father of that
    proband presented at 30 years.
  evidence:
  - reference: PMID:40792030
    reference_title: PIEZO1 mechanical insensitivity in generalized lymphatic dysplasia with the potential for pharmacological rescue.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      in GLD08, there was disease only from adolescence that was characterized
      first by pleural and pericardial effusions and then lower limb and scrotal
      edema without facial edema
    explanation: >-
      Directly states an adolescent-onset presentation with a different
      phenotype ordering from the congenital arm.
  - reference: PMID:40792030
    reference_title: PIEZO1 mechanical insensitivity in generalized lymphatic dysplasia with the potential for pharmacological rescue.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      From age 11 years he developed progressive breathlessness and reduced
      exercise tolerance and was found to have bilateral chylous pleural
      effusions
    explanation: >-
      Case-level detail of the adolescent onset in the GLD08 proband, whose
      antenatal and neonatal period was uneventful.
phenotypes:
- name: Non-immune hydrops fetalis
  category: Prenatal
  diagnostic: true
  frequency: FREQUENT
  description: >-
    Generalized fetal fluid accumulation with skin edema, pleural and pericardial
    effusions, and ascites, typically detected at the second trimester and often
    the presenting feature. It occurred in 7 of 10 affected individuals in the
    founding cohort and may be lethal.
  phenotype_term:
    preferred_term: Nonimmune hydrops fetalis
    term:
      id: HP:0001790
      label: Nonimmune hydrops fetalis
  evidence:
  - reference: PMID:26333996
    reference_title: Novel mutations in PIEZO1 cause an autosomal recessive generalized lymphatic dysplasia with non-immune hydrops fetalis.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      biallelic variants have a high incidence of NIHF (7 of the 10 affected
      cases). This may be lethal in the perinatal period (n=2).
    explanation: >-
      7 of 10 affected individuals (70%) had non-immune hydrops fetalis, mapping
      to the FREQUENT band.
  - reference: PMID:36453701
    reference_title: "Perinatal presentations of non-immune hydrops fetalis due to recessive PIEZO1 disease: A challenging fetal diagnosis."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      During the pregnancy, most cases are revealed by isolated NIHF at second
      trimester of gestation.
    explanation: >-
      Establishes the prenatal timing and the isolated-NIHF presentation.
- name: Polyhydramnios
  category: Prenatal
  frequency: OCCASIONAL
  description: >-
    Excess amniotic fluid complicating affected pregnancies, recorded alongside
    non-immune fetal hydrops in two of the three families reported by Bee et al.
    (GLD07 and GLD09). In GLD09 it was severe enough to require repeated
    amnio-drainage.
  phenotype_term:
    preferred_term: Polyhydramnios
    term:
      id: HP:0001561
      label: Polyhydramnios
  evidence:
  - reference: PMID:40792030
    reference_title: PIEZO1 mechanical insensitivity in generalized lymphatic dysplasia with the potential for pharmacological rescue.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Antenatal imaging (gestational date not noted) identified NIFH and
      polyhydramnios.
    explanation: >-
      Documents polyhydramnios in the GLD07 proband's affected pregnancy.
  - reference: PMID:40792030
    reference_title: PIEZO1 mechanical insensitivity in generalized lymphatic dysplasia with the potential for pharmacological rescue.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      The pregnancy was complicated by polyhydramnios requiring repeated
      amnio-drainage at 27, 30 and 33 weeks.
    explanation: >-
      Independent occurrence in the GLD09 pregnancy, severe enough to require
      repeated drainage.
  notes: >-
    Frequency is banded OCCASIONAL from the reported case detail (2 of 3 families
    in this series, but not systematically ascertained across the whole reported
    LMPHM6 cohort); no cohort-level frequency figure has been published.
- name: Lymphedema
  category: Lymphatic
  diagnostic: true
  frequency: VERY_FREQUENT
  description: >-
    Chronic, often progressive lymphedema affecting the lower limbs, arms, face,
    and genitalia. It may be present at birth or, more characteristically, appear
    in early childhood after complete resolution of the neonatal hydrops.
  phenotype_term:
    preferred_term: Lymphedema
    term:
      id: HP:0001004
      label: Lymphedema
    temporality: CHRONIC
    clinical_course: PROGRESSIVE
  evidence:
  - reference: PMID:26333996
    reference_title: Novel mutations in PIEZO1 cause an autosomal recessive generalized lymphatic dysplasia with non-immune hydrops fetalis.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Survivors may present later with lymphoedema of the peripheries (mainly
      lower limbs but also arms (n=4), face (n=3) and genitalia (n=1)), with or
      without chylothoraces (n=2) and intestinal lymphangiectasia (n=1).
    explanation: >-
      Lymphedema is the defining postnatal feature in surviving affected
      individuals, supporting the VERY_FREQUENT band.
  - reference: PMID:26387913
    reference_title: Impaired PIEZO1 function in patients with a novel autosomal recessive congenital lymphatic dysplasia.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      At 42 months of age, she displays significant persistent lymphoedema of her
      legs, torso and face
    explanation: >-
      Documents persistent multi-segment lymphedema in an independently reported
      patient.
- name: Chylothorax
  category: Respiratory
  frequency: FREQUENT
  description: >-
    Accumulation of chyle in the pleural space, confirmed by pleural-fluid
    analysis. It may be present at birth and can be persistent or recurrent,
    sometimes requiring repeated drainage, dietary fat restriction, or octreotide.
  phenotype_term:
    preferred_term: Chylothorax
    term:
      id: HP:0010310
      label: Chylothorax
    temporality: RECURRENT
  evidence:
  - reference: PMID:26387913
    reference_title: Impaired PIEZO1 function in patients with a novel autosomal recessive congenital lymphatic dysplasia.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      II.1 presented at birth with hydrops and bilateral chylothorax, confirmed by
      fluid analysis.
    explanation: >-
      Documents biochemically confirmed bilateral chylothorax at birth.
  - reference: PMID:37159433
    reference_title: Persistent chylothorax associated with lymphatic malformation type 6 due to biallelic pathogenic variants in PIEZO1.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Hereditary Lymphedema type III can be associated with persistent chylothorax
      that can vary in size over time.
    explanation: >-
      Establishes persistent/recurrent chylothorax as a recognized feature of
      LMPHM6.
- name: Pleural effusion
  category: Respiratory
  frequency: FREQUENT
  description: >-
    Pleural fluid accumulation, frequently bilateral, detected prenatally as part
    of hydrops or persisting postnatally as chronic effusions.
  phenotype_term:
    preferred_term: Pleural effusion
    term:
      id: HP:0002202
      label: Pleural effusion
  evidence:
  - reference: PMID:36453701
    reference_title: "Perinatal presentations of non-immune hydrops fetalis due to recessive PIEZO1 disease: A challenging fetal diagnosis."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      At post-mortem examination ascites, pleural effusions and telengectasies can
      guide the etiological diagnosis.
    explanation: >-
      Pleural effusion is a consistent post-mortem finding in LMPHM6 fetuses.
- name: Pericardial effusion
  category: Cardiovascular
  frequency: OCCASIONAL
  description: >-
    Pericardial fluid accumulation is part of the generalized lymphatic dysplasia
    spectrum and may contribute to the fetal hydrops.
  phenotype_term:
    preferred_term: Pericardial effusion
    term:
      id: HP:0001698
      label: Pericardial effusion
  evidence:
  - reference: PMID:35646098
    reference_title: A Novel Homozygous Missense Mutation of PIEZO1 Leading to Lymphatic Malformation-6 Identified in a Family With Three Adverse Pregnancy Outcomes due to Nonimmune Fetal Hydrops.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Lymphatic malformation-6 (LMPHM6) is a rarer form of nonimmune hydrops that
      often manifests as widespread lymphedema involving all segments of the body,
      namely, subcutaneous edema, intestinal/pulmonary lymphangiectasia,
      chylothoraces, and pleural/pericardial effusions.
    explanation: >-
      Lists pericardial effusion among the manifestations of LMPHM6.
- name: Ascites
  category: Gastrointestinal
  frequency: OCCASIONAL
  description: >-
    Free peritoneal fluid, typically part of the fetal hydrops picture and a
    consistent post-mortem finding.
  phenotype_term:
    preferred_term: Ascites
    term:
      id: HP:0001541
      label: Ascites
  evidence:
  - reference: PMID:36453701
    reference_title: "Perinatal presentations of non-immune hydrops fetalis due to recessive PIEZO1 disease: A challenging fetal diagnosis."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      At post-mortem examination ascites, pleural effusions and telengectasies can
      guide the etiological diagnosis.
    explanation: >-
      Documents ascites in LMPHM6 fetuses at post-mortem examination.
- name: Intestinal lymphangiectasia
  category: Gastrointestinal
  frequency: OCCASIONAL
  description: >-
    Dilated intestinal lymphatics causing enteric lymph loss; reported in a
    minority of affected individuals (1 of 10 in the founding cohort).
  phenotype_term:
    preferred_term: Intestinal lymphangiectasia
    term:
      id: HP:0002593
      label: Intestinal lymphangiectasia
  evidence:
  - reference: PMID:26333996
    reference_title: Novel mutations in PIEZO1 cause an autosomal recessive generalized lymphatic dysplasia with non-immune hydrops fetalis.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Survivors may present later with lymphoedema of the peripheries (mainly
      lower limbs but also arms (n=4), face (n=3) and genitalia (n=1)), with or
      without chylothoraces (n=2) and intestinal lymphangiectasia (n=1).
    explanation: >-
      Reports intestinal lymphangiectasia in 1 of 10 affected individuals,
      supporting the OCCASIONAL band.
- name: Facial edema
  category: Craniofacial
  frequency: FREQUENT
  description: >-
    Facial swelling, often intermittent and severe, reflecting facial lymphatic
    involvement; in the founding cohort facial lymphedema affected 3 of 10
    individuals and intermittent severe facial swelling was attributed to
    recurrent cellulitis.
  phenotype_term:
    preferred_term: Facial edema
    term:
      id: HP:0000282
      label: Facial edema
    temporality: RECURRENT
  evidence:
  - reference: PMID:26333996
    reference_title: Novel mutations in PIEZO1 cause an autosomal recessive generalized lymphatic dysplasia with non-immune hydrops fetalis.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Two of the affected individuals suffer from intermittent, severe facial
      swelling due to recurrent cellulitis. This is rarely seen in other forms of
      primary lymphoedema.
    explanation: >-
      Documents intermittent severe facial swelling and notes it as
      distinguishing from other primary lymphedemas.
- name: Recurrent cellulitis
  category: Dermatologic
  frequency: FREQUENT
  description: >-
    Severe recurrent facial cellulitis with high fever and frequent intensive-care
    admission is a characteristic and serious complication, seen in 4 of 10
    affected individuals in the founding cohort and rarely encountered in other
    primary lymphedemas.
  phenotype_term:
    preferred_term: Cellulitis
    term:
      id: HP:0100658
      label: Cellulitis
    temporality: RECURRENT
    severity: SEVERE
  evidence:
  - reference: PMID:26333996
    reference_title: Novel mutations in PIEZO1 cause an autosomal recessive generalized lymphatic dysplasia with non-immune hydrops fetalis.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Four patients of our cohort had severe, recurrent facial cellulitis with
      significant morbidity (high pyrexia and frequent admission to intensive
      care).
    explanation: >-
      4 of 10 affected individuals (40%) had severe recurrent facial cellulitis,
      mapping to the FREQUENT band.
- name: Stomatocytosis
  category: Hematologic
  frequency: OCCASIONAL
  description: >-
    Subtle red-cell membrane abnormalities are detectable on careful blood-film
    inspection in affected individuals and, less often, in heterozygous carriers,
    reflecting the shared PIEZO1 basis with dehydrated hereditary stomatocytosis.
    The changes are asymptomatic and are not accompanied by clinically significant
    hemolysis.
  phenotype_term:
    preferred_term: Stomatocytosis
    term:
      id: HP:0004446
      label: Stomatocytosis
  evidence:
  - reference: PMID:26333996
    reference_title: Novel mutations in PIEZO1 cause an autosomal recessive generalized lymphatic dysplasia with non-immune hydrops fetalis.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Careful inspection of blood films from our affected individuals demonstrates
      occasional stomatocytes and spherocytes
    explanation: >-
      Documents stomatocytes on blood films of affected individuals.
  - reference: PMID:26387913
    reference_title: Impaired PIEZO1 function in patients with a novel autosomal recessive congenital lymphatic dysplasia.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Both patients and parents had blood counts including mean corpuscular volume
      in the normal range.
    explanation: >-
      Counterbalancing observation that routine hematologic indices can be
      entirely normal, so the red-cell finding is subtle and not universal.
- name: Spherocytosis
  category: Hematologic
  frequency: OCCASIONAL
  description: >-
    Marked spherocytosis was observed in one reported family, suggesting some
    cases of spherocytosis may be attributable to PIEZO1 variants.
  phenotype_term:
    preferred_term: Spherocytosis
    term:
      id: HP:0004444
      label: Spherocytosis
  evidence:
  - reference: PMID:26333996
    reference_title: Novel mutations in PIEZO1 cause an autosomal recessive generalized lymphatic dysplasia with non-immune hydrops fetalis.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Careful inspection of blood films from our affected individuals demonstrates
      occasional stomatocytes and spherocytes
    explanation: >-
      Documents spherocytes on blood films of affected individuals.
genetic:
- name: PIEZO1
  association: Causal biallelic loss-of-function variants
  relationship_type: CAUSATIVE
  variant_origin: GERMLINE
  gene_term:
    preferred_term: PIEZO1
    term:
      id: hgnc:28993
      label: PIEZO1
  evidence:
  - reference: PMID:26333996
    reference_title: Novel mutations in PIEZO1 cause an autosomal recessive generalized lymphatic dysplasia with non-immune hydrops fetalis.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      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.
    explanation: >-
      Establishes PIEZO1 as the causal gene, with biallelic variants, for this
      form of generalized lymphatic dysplasia.
  - reference: PMID:26387913
    reference_title: Impaired PIEZO1 function in patients with a novel autosomal recessive congenital lymphatic dysplasia.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Our results delineate a novel clinical category of PIEZO1-associated
      hereditary lymphoedema.
    explanation: >-
      Independent contemporaneous report establishing PIEZO1-associated hereditary
      lymphedema as a distinct entity.
  - reference: PMID:37902181
    reference_title: PIEZO1 is the most common monogenic etiology of non-immune hydrops fetalis detected by prenatal exome sequencing.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      PIEZO1 variants causing AR NIHF were characterized by loss of function and
      isolated NIHF phenotype.
    explanation: >-
      Confirms that the recessive (LMPHM6) mechanism is loss of function, in
      contrast to the dominant gain-of-function red-cell disease.
  variants:
  - name: p.Glu1630Ter (c.4888G>T)
    type: nonsense
    clinical_significance: PATHOGENIC
    description: >-
      Recurrent nonsense PIEZO1 allele observed in two unrelated families in the
      founding cohort; no truncated protein is detectable by western blot,
      consistent with a null allele.
    evidence:
    - reference: PMID:26333996
      reference_title: Novel mutations in PIEZO1 cause an autosomal recessive generalized lymphatic dysplasia with non-immune hydrops fetalis.
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: >-
        one of which was the nonsense mutation (c.G4888T; p.E1630X) also observed
        in family GLD1
      explanation: >-
        Identifies the recurrent nonsense allele shared between families.
  - name: c.3796+1G>A
    type: splice donor site
    clinical_significance: PATHOGENIC
    description: >-
      Canonical splice-donor variant causing skipping of exon 26 and a measurable
      reduction in PIEZO1 protein.
    evidence:
    - reference: PMID:26333996
      reference_title: Novel mutations in PIEZO1 cause an autosomal recessive generalized lymphatic dysplasia with non-immune hydrops fetalis.
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: >-
        The c.3796+1G>A variant in GLD3 causes skipping of exon 26
      explanation: >-
        Establishes the splicing consequence of this allele.
    - reference: PMID:26333996
      reference_title: Novel mutations in PIEZO1 cause an autosomal recessive generalized lymphatic dysplasia with non-immune hydrops fetalis.
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: >-
        Western blot results of the c.3796+1G>A variant in GLD3 showed a reduction
        in PIEZO1 expression levels
      explanation: >-
        Protein-level confirmation of reduced PIEZO1 expression for this allele.
  - name: p.Ser1721Trp (c.5162C>G)
    type: missense
    clinical_significance: PATHOGENIC
    description: >-
      Homozygous missense PIEZO1 variant reported as a cause of LMPHM6 in a family
      with three adverse pregnancy outcomes from non-immune fetal hydrops.
    evidence:
    - reference: PMID:35646098
      reference_title: A Novel Homozygous Missense Mutation of PIEZO1 Leading to Lymphatic Malformation-6 Identified in a Family With Three Adverse Pregnancy Outcomes due to Nonimmune Fetal Hydrops.
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: >-
        we detected one rare and previously unobserved homozygous missense variant
        in PIEZO1 (c.5162C>G, p.Ser1721Trp) as a novel genetic cause of autosomal
        recessive LMPHM6, in a family with three adverse pregnancy outcomes due to
        nonimmune fetal hydrops
      explanation: >-
        A specific homozygous missense allele established as causal for LMPHM6.
  - name: p.Trp1287Ter (c.3860G>A)
    type: nonsense
    clinical_significance: LIKELY_PATHOGENIC
    description: >-
      Nonsense PIEZO1 allele reported in trans with a splice-acceptor deletion in a
      child with persistent chylothorax; both were classified as likely pathogenic.
    evidence:
    - reference: PMID:37159433
      reference_title: Persistent chylothorax associated with lymphatic malformation type 6 due to biallelic pathogenic variants in PIEZO1.
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: >-
        Genetic testing revealed two deleterious variants in PIEZO1:
        c.2330-2_2330-1del and c.3860G > A (p.Trp1287*), both of which were
        classified as likely pathogenic.
      explanation: >-
        Documents the biallelic genotype in a patient with persistent chylothorax.
  - name: p.Ile2270Thr (I2270T)
    type: missense
    description: >-
      Missense PIEZO1 allele reported homozygously in family GLD08 - the
      adolescent-onset pedigree - and in trans with E829V in GLD09. The reporting
      authors interpreted the GLD07-09 variants collectively as likely pathogenic
      or of uncertain significance, so no per-variant classification is asserted
      here; the functional work in the same paper shows reduced channel
      mechanical sensitivity rather than reduced expression.
    evidence:
    - reference: PMID:40792030
      reference_title: PIEZO1 mechanical insensitivity in generalized lymphatic dysplasia with the potential for pharmacological rescue.
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: >-
        In GLD08, homozygosity of a single variant encoding Ile2270Thr (I2270T)
        associated with disease in 3 family members
      explanation: >-
        Segregation of the homozygous missense allele with disease in three
        members of one family.
    - reference: PMID:40792030
      reference_title: PIEZO1 mechanical insensitivity in generalized lymphatic dysplasia with the potential for pharmacological rescue.
      supports: SUPPORT
      evidence_source: IN_VITRO
      snippet: >-
        PIEZO1 variants have been associated with generalized lymphatic dysplasia
        (GLD) through mechanisms involving reduced PIEZO1 expression. Here, we
        report variants where the mechanism involves reduced channel mechanical
        sensitivity.
      explanation: >-
        Establishes the loss-of-function mechanism for this class of variant as
        mechanical insensitivity of an expressed channel.
diagnosis:
- name: Molecular genetic testing of PIEZO1
  diagnosis_term:
    preferred_term: genetic testing
    term:
      id: NCIT:C15709
      label: Genetic Testing
  description: >-
    Identification of biallelic pathogenic PIEZO1 variants, typically by exome or
    a primary-lymphedema/generalized-lymphatic-anomaly gene panel, confirms the
    diagnosis. In prenatal exome series, PIEZO1 is the single most frequently
    implicated gene in non-immune hydrops fetalis, so it should be prioritized
    when hydrops is otherwise unexplained.
  results: >-
    Biallelic (homozygous or compound heterozygous) loss-of-function PIEZO1
    variants confirm LMPHM6.
  evidence:
  - reference: PMID:37902181
    reference_title: PIEZO1 is the most common monogenic etiology of non-immune hydrops fetalis detected by prenatal exome sequencing.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      PIEZO1 variants were reported in 10% of NIHF cases diagnosed by prenatal
      exome, making PIEZO1 the most common single gene reported in NIHF.
    explanation: >-
      Supports prioritizing PIEZO1 in the molecular workup of unexplained
      non-immune hydrops fetalis.
  - reference: PMID:26387913
    reference_title: Impaired PIEZO1 function in patients with a novel autosomal recessive congenital lymphatic dysplasia.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Through whole-exome sequencing, we identify biallelic mutations in PIEZO1 (a
      splicing variant leading to early truncation and a non-synonymous missense
      variant) in a pair of siblings affected with persistent lymphoedema caused
      by congenital lymphatic dysplasia.
    explanation: >-
      Exome sequencing is the demonstrated route to molecular diagnosis in this
      disorder.
- name: Lymphoscintigraphy
  diagnosis_term:
    preferred_term: lymphoscintigraphy
    term:
      id: NCIT:C67262
      label: Lymphoscintigraphy
  description: >-
    Radionuclide lymphoscintigraphy demonstrates the functional lymphatic lesion,
    showing symmetric deep rerouting with popliteal nodal uptake and superficial
    rerouting through the skin, indicating failure of superficial lymphatic
    collector function rather than aplasia.
  results: >-
    Symmetric deep and superficial rerouting consistent with collector failure;
    lymphangiectasia with chylothorax may also be demonstrated.
  evidence:
  - reference: PMID:26333996
    reference_title: Novel mutations in PIEZO1 cause an autosomal recessive generalized lymphatic dysplasia with non-immune hydrops fetalis.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      In the lower limbs, all the patients have deep rerouting as demonstrated by
      the popliteal lymph node uptake
    explanation: >-
      Describes the characteristic lymphoscintigraphic finding in affected
      individuals.
  - reference: PMID:37274623
    reference_title: Case report of generalized lymphatic dysplasia with PIEZO1 mutation and review of the literature.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Lymphoscintigraphy showed lymphangiectasia with chylothorax.
    explanation: >-
      Independent case confirming the diagnostic utility of lymphoscintigraphy.
treatments:
- name: Dietary fat restriction and medium-chain triglyceride feeding
  description: >-
    Restriction of long-chain dietary fat, with medium-chain triglyceride
    substitution, reduces chyle production and thoracic-duct lymph flow and is
    first-line conservative management of chylothorax and enteric lymph loss in
    LMPHM6.
  therapeutic_modality: BEHAVIORAL
  treatment_term:
    preferred_term: dietary intervention
    term:
      id: NCIT:C15447
      label: Dietary Intervention
  target_mechanisms:
  - target: Chylous Effusion and Fetal Fluid Accumulation
    treatment_effect: MODULATES
    description: >-
      Reducing long-chain fat intake lowers chyle flow into the incompetent
      thoracic lymphatics, reducing effusion volume.
  evidence:
  - reference: PMID:37159433
    reference_title: Persistent chylothorax associated with lymphatic malformation type 6 due to biallelic pathogenic variants in PIEZO1.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      She subsequently had recurrent pleural effusions involving both pleural
      cavities, which tended to improve with restriction of her fat intake, and,
      one occasion, subcutaneous octreotide.
    explanation: >-
      Documents clinical improvement of the recurrent effusions with dietary fat
      restriction in a molecularly confirmed LMPHM6 patient.
- name: Octreotide
  description: >-
    Subcutaneous octreotide, a somatostatin analogue that reduces splanchnic blood
    flow and lymph production, has been used as adjunctive therapy for refractory
    chylothorax in LMPHM6. Evidence is limited to single-patient experience.
  therapeutic_modality: PEPTIDE
  treatment_term:
    preferred_term: Pharmacotherapy
    term:
      id: NCIT:C15986
      label: Pharmacotherapy
    therapeutic_agent:
    - preferred_term: octreotide
      term:
        id: CHEBI:7726
        label: octreotide
  target_mechanisms:
  - target: Chylous Effusion and Fetal Fluid Accumulation
    treatment_effect: MODULATES
    description: >-
      Somatostatin-analogue reduction of lymph production decreases chyle
      accumulation in the pleural space.
  evidence:
  - reference: PMID:37159433
    reference_title: Persistent chylothorax associated with lymphatic malformation type 6 due to biallelic pathogenic variants in PIEZO1.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      She subsequently had recurrent pleural effusions involving both pleural
      cavities, which tended to improve with restriction of her fat intake, and,
      one occasion, subcutaneous octreotide.
    explanation: >-
      Single-patient use of subcutaneous octreotide alongside dietary fat
      restriction; the report does not isolate the octreotide effect, so support
      is partial.
- name: Lymphedema supportive care
  description: >-
    Complete decongestive therapy - compression garments or bandaging, manual
    lymphatic drainage, exercise, and meticulous skin care - is the mainstay of
    chronic lymphedema management, together with prompt antibiotic treatment of
    cellulitis, which is a major source of morbidity in this disorder.
  therapeutic_modality: BEHAVIORAL
  treatment_term:
    preferred_term: physical therapy
    term:
      id: NCIT:C15302
      label: Physical Therapy
  target_mechanisms:
  - target: Chronic Peripheral and Facial Lymphedema
    treatment_effect: MODULATES
    description: >-
      Decongestive therapy mechanically compensates for failed lymphatic collector
      function.
  evidence:
  - reference: PMID:26333996
    reference_title: Novel mutations in PIEZO1 cause an autosomal recessive generalized lymphatic dysplasia with non-immune hydrops fetalis.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Four patients of our cohort had severe, recurrent facial cellulitis with
      significant morbidity (high pyrexia and frequent admission to intensive
      care).
    explanation: >-
      Establishes the clinical burden (recurrent severe cellulitis complicating
      lymphedema) that skin care and prompt antibiotic treatment address; the
      paper does not itself report a supportive-care trial, so support is partial.
- name: Genetic counseling
  description: >-
    Counseling covers autosomal recessive inheritance and the 25% sibling
    recurrence risk, carrier testing, and prenatal or preimplantation genetic
    testing options once the familial biallelic PIEZO1 genotype is known.
    Recurrent adverse pregnancy outcomes are a recognized presentation.
  treatment_term:
    preferred_term: Genetic Counseling
    term:
      id: NCIT:C15240
      label: Genetic Counseling
  evidence:
  - reference: PMID:35646098
    reference_title: A Novel Homozygous Missense Mutation of PIEZO1 Leading to Lymphatic Malformation-6 Identified in a Family With Three Adverse Pregnancy Outcomes due to Nonimmune Fetal Hydrops.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      we detected one rare and previously unobserved homozygous missense variant
      in PIEZO1 (c.5162C>G, p.Ser1721Trp) as a novel genetic cause of autosomal
      recessive LMPHM6, in a family with three adverse pregnancy outcomes due to
      nonimmune fetal hydrops
    explanation: >-
      Recurrent pregnancy loss in a single family illustrates the recurrence risk
      that counseling and molecular diagnosis address.
- name: PIEZO1 agonism (investigational)
  description: >-
    The small-molecule PIEZO1 agonist Yoda1 partly rescues the mechanical
    sensitivity of mechanically insensitive LMPHM6 missense channels in vitro, and
    an analogue with improved potency has been synthesized. This is a preclinical,
    genotype-restricted concept - it cannot rescue null alleles, and systemic
    PIEZO1 activation would also act on erythrocytes and the blood vasculature. No
    PIEZO1-directed therapy is approved.
  therapeutic_modality: SMALL_MOLECULE
  treatment_term:
    preferred_term: Pharmacotherapy
    term:
      id: NCIT:C15986
      label: Pharmacotherapy
  target_mechanisms:
  - target: PIEZO1 Loss of Function
    treatment_effect: RESTORES
    description: >-
      Chemical agonism partly restores mechanical activation of variant channels
      that are expressed but mechanically insensitive.
  evidence:
  - reference: PMID:40792030
    reference_title: PIEZO1 mechanical insensitivity in generalized lymphatic dysplasia with the potential for pharmacological rescue.
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: >-
      Patch-clamp studies of the cap and sub-cap variant channels revealed
      abolished or reduced channel mechanical sensitivity with the possibility to
      activate the channels and partly rescue mechanical sensitivity by the small
      molecule Yoda1.
    explanation: >-
      In vitro pharmacological rescue of variant channels; no clinical evidence
      exists, so support for this as a treatment is partial.
  - reference: PMID:35701867
    reference_title: Piezo1-Regulated Mechanotransduction Controls Flow-Activated Lymphatic Expansion.
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: >-
      we assessed a potential therapeutic value of Piezo1 activation in lymphatic
      regeneration and found that a Piezo1 agonist, Yoda1, effectively suppressed
      postsurgical lymphedema development.
    explanation: >-
      Mouse proof of concept that PIEZO1 agonism can reduce lymphedema; the model
      is acquired postsurgical lymphedema, not biallelic PIEZO1 disease.
- name: Pleurodesis and other interventional management of refractory chylous effusion
  description: >-
    Pleurodesis, thoracic-duct ligation, and pleuro-peritoneal shunting are the
    standard escalation options when chylous pleural effusion recurs despite
    dietary fat restriction and octreotide. In LMPHM6 they are documented as
    used, not as effective: in the one reported adolescent-onset family, effusion
    control proved very difficult despite all three, and the proband's father had
    persistent effusions and a restrictive lung defect after pleurodesis. No
    LMPHM6-specific response rate has been established for any of these
    procedures, and none targets the underlying lymphatic mechanism.
  therapeutic_modality: SURGERY
  treatment_term:
    preferred_term: therapeutic procedure
    term:
      id: NCIT:C49236
      label: Therapeutic Procedure
  target_mechanisms:
  - target: Chylous Effusion and Fetal Fluid Accumulation
    treatment_effect: MODULATES
    description: >-
      Obliterating the pleural space or diverting/interrupting thoracic-duct flow
      limits accumulation of chyle in the pleural cavity; the incompetent
      lymphatic network itself is unaltered.
  evidence:
  - reference: PMID:40792030
    reference_title: PIEZO1 mechanical insensitivity in generalized lymphatic dysplasia with the potential for pharmacological rescue.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Treatment has proved very difficult and has involved pleurodesis, ligation
      of the thoracic duct and pleuro-peritoneal shunting.
    explanation: >-
      Documents the interventional options actually used in a molecularly
      confirmed LMPHM6 patient, while explicitly recording that control was
      difficult - so this supports use, not efficacy.
  - reference: PMID:40792030
    reference_title: PIEZO1 mechanical insensitivity in generalized lymphatic dysplasia with the potential for pharmacological rescue.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Despite pleurodesis, his effusions are persistent resulting in a restrictive
      lung defect and nocturnal hypoventilation requiring non-invasive
      ventilation (NIV).
    explanation: >-
      A second affected individual in whom pleurodesis failed to control chylous
      effusion, recording the limits of the intervention.
animal_models:
- name: Endothelial Piezo1 conditional knockout mouse (Tie2Cre or Lyve1Cre)
  species: Mouse
  genotype: Piezo1 conditional knockout (Tie2Cre;Piezo1fl/fl or Lyve1Cre;Piezo1fl/fl)
  publication: PMID:30482854
  modeled_mechanisms:
  - target: Defective Lymphatic Valve Formation and Lymphangiogenesis
    relationship: RECAPITULATES
    fidelity: HIGH
    description: >-
      Endothelial-specific Piezo1 deletion dramatically reduces lymphatic valve
      number and impairs valve-leaflet protrusion, and the mice develop pleural
      effusion - the murine counterpart of the human chylothorax/effusion
      phenotype.
    limitations: >-
      The mice die postnatally, so the chronic childhood-onset peripheral
      lymphedema of the human disorder cannot be assessed; conditional deletion is
      a complete null in the endothelium, whereas human alleles include hypomorphic
      missense variants with residual function.
    readouts:
    - name: Lymphatic valve number
      target: Defective Lymphatic Valve Formation and Lymphangiogenesis
      direction: DECREASED
      interpretation: >-
        Structural correlate of the valve-formation node in this model.
      evidence:
      - reference: PMID:30482854
        reference_title: Mechanically activated ion channel PIEZO1 is required for lymphatic valve formation.
        supports: SUPPORT
        evidence_source: MODEL_ORGANISM
        snippet: >-
          Strikingly, the number of lymphatic valves was dramatically reduced in
          these mice.
        explanation: >-
          Reports the histological measurement behind this readout.
    evidence:
    - reference: PMID:30482854
      reference_title: Mechanically activated ion channel PIEZO1 is required for lymphatic valve formation.
      supports: SUPPORT
      evidence_source: MODEL_ORGANISM
      snippet: >-
        Our analysis provides evidence that mechanically activated ion channel
        PIEZO1 is a key regulator of lymphatic valve formation.
      explanation: >-
        Supports treating this model as informative for the valve-formation node.
- name: Lymphatic-specific Piezo1 conditional knockout mouse
  species: Mouse
  genotype: Lymphatic endothelial-specific conditional Piezo1 knockout; postnatal inducible deletion
  publication: PMID:35701867
  modeled_mechanisms:
  - target: Impaired Lymphatic Endothelial Mechanotransduction
    relationship: RECAPITULATES
    fidelity: MODERATE
    description: >-
      Loss of Piezo1 in lymphatic endothelium abolishes flow-induced calcium
      influx and the ORAI1/KLF2/Notch programme, phenocopying Orai1 and Klf2
      knockout sprouting defects; postnatal deletion causes lymphatic regression.
    limitations: >-
      Mechanistic dissection relies on knockdown in cultured lymphatic endothelial
      cells and on conditional nulls, whereas human LMPHM6 alleles are germline and
      often hypomorphic; the therapeutic Yoda1 arm was tested in acquired
      postsurgical lymphedema rather than in a Piezo1-mutant background.
    readouts:
    - name: Flow-induced calcium influx in lymphatic endothelial cells
      target: Impaired Lymphatic Endothelial Mechanotransduction
      direction: DECREASED
      interpretation: >-
        Functional correlate of the mechanotransduction node.
      evidence:
      - reference: PMID:35701867
        reference_title: Piezo1-Regulated Mechanotransduction Controls Flow-Activated Lymphatic Expansion.
        supports: SUPPORT
        evidence_source: IN_VITRO
        snippet: >-
          Piezo1 knockdown in cultured lymphatic endothelial cells inhibited the
          laminar flow-induced calcium influx
        explanation: >-
          Reports the calcium-imaging measurement behind this readout.
    evidence:
    - reference: PMID:35701867
      reference_title: Piezo1-Regulated Mechanotransduction Controls Flow-Activated Lymphatic Expansion.
      supports: SUPPORT
      evidence_source: MODEL_ORGANISM
      snippet: >-
        Piezo1 is an upstream mechanosensor for the lymphatic mechanotransduction
        pathway and regulates lymphatic growth in response to external physical
        stimuli.
      explanation: >-
        Supports treating this model as informative for the mechanotransduction
        node.
differential_diagnoses:
- name: Hennekam lymphangiectasia-lymphedema syndrome 1
  disease_term:
    preferred_term: Hennekam lymphangiectasia-lymphedema syndrome 1
    term:
      id: MONDO:0009337
      label: Hennekam lymphangiectasia-lymphedema syndrome 1
  description: >-
    The other major autosomal recessive generalized lymphatic dysplasia. Hennekam
    syndrome is distinguished by characteristic facial dysmorphism (periorbital
    edema, retrognathia, flat facial profile, gingival hypertrophy, microstomia),
    seizures, and intellectual disability, none of which occur in LMPHM6.
  evidence:
  - reference: PMID:26333996
    reference_title: Novel mutations in PIEZO1 cause an autosomal recessive generalized lymphatic dysplasia with non-immune hydrops fetalis.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      The phenotype is distinct from Hennekam syndrome as none of our GLD patients
      had the dysmorphic features associated with HS, nor the learning
      disabilities or seizures, nor was the swelling severe
    explanation: >-
      States the clinical basis for separating LMPHM6 from Hennekam syndrome.
- name: Dehydrated hereditary stomatocytosis
  disease_term:
    preferred_term: dehydrated hereditary stomatocytosis
    term:
      id: MONDO:0008689
      label: dehydrated hereditary stomatocytosis with or without pseudohyperkalemia and/or perinatal edema
  description: >-
    The allelic autosomal dominant disorder caused by monoallelic gain-of-function
    PIEZO1 variants, presenting with mild-to-moderate hemolytic anemia,
    pseudohyperkalemia, and transient perinatal edema. The mechanism is opposite in
    direction (gain versus loss of channel function), and the two entities overlap
    only in the perinatal-edema phenotype.
  evidence:
  - reference: PMID:37902181
    reference_title: PIEZO1 is the most common monogenic etiology of non-immune hydrops fetalis detected by prenatal exome sequencing.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      PIEZO1 variants causing AD NIHF were characterized by gain of function in
      red blood cells, scarcity in databases, and sporadic inheritance.
    explanation: >-
      Contrasts the dominant gain-of-function red-cell mechanism with the recessive
      loss-of-function lymphatic mechanism of LMPHM6.
prevalence:
- population: Worldwide
  measure_type: CASES_IN_LITERATURE
  prevalence_class: ULTRA_RARE
  notes: >-
    No disease-specific prevalence or incidence estimate exists. The founding
    cohort comprised 10 affected individuals from 6 families, and subsequent
    reports have been single families or small series. A widely quoted figure of
    approximately 1 in 6,000 for generalized lymphatic dysplasia should not be
    used as an LMPHM6 prevalence, as its denominator and molecular ascertainment
    are not disease-specific.
  evidence:
  - reference: PMID:26333996
    reference_title: Novel mutations in PIEZO1 cause an autosomal recessive generalized lymphatic dysplasia with non-immune hydrops fetalis.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      In total, we identified 10 PIEZO1 variants in 6 families
    explanation: >-
      Supports the ultra-rare, literature-case-count basis for the occurrence
      estimate.
- population: Fetuses with non-immune hydrops undergoing prenatal exome sequencing
  measure_type: UNKNOWN
  prevalence_class: UNKNOWN
  notes: >-
    Not a population prevalence: this records the diagnostic yield of PIEZO1
    (both the recessive LMPHM6 and dominant gain-of-function forms) within an
    ascertained NIHF cohort - 19 of 191 cases, i.e. 10%.
  evidence:
  - reference: PMID:37902181
    reference_title: PIEZO1 is the most common monogenic etiology of non-immune hydrops fetalis detected by prenatal exome sequencing.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      In total, 19 of 191 NIHF cases diagnosed by prenatal exome were attributed
      to PIEZO1.
    explanation: >-
      Quantifies the PIEZO1 contribution within an ascertained NIHF cohort.
notes: >-
  No GeneReviews chapter exists for lymphatic malformation 6 / PIEZO1-related
  generalized lymphatic dysplasia (PubMed searched 2026-08-18 for
  "(lymphedema[TI] OR lymphatic[TI]) AND GeneReviews[TI]" and for the disease
  name; the retrieved lymphatic GeneReviews chapters are Milroy disease (FLT4)
  and lymphedema-distichiasis syndrome (FOXC2), which are different disorders).
  MONDO:0014797 carries no textual definition, so disease identity was anchored on
  the OMIM:616843 and Orphanet:568062 xrefs and on the MONDO RO:0004003 causal-gene
  relationship to hgnc:28993 PIEZO1, verified with OAK. An Orphanet structured
  reference (ORPHA:568062) could not be cited because that record is absent from
  the committed references_cache and the Orphadata bulk refresh failed on a network
  error at curation time.
clinical_trials: []
datasets: []
📚

References & Deep Research

Deep Research

1
Falcon
Lymphatic Malformation 6: Comprehensive Disease-Characteristics Report
Edison Scientific Literature 26 citations 2026-08-18T09:32:14.266439

Lymphatic Malformation 6: Comprehensive Disease-Characteristics Report

Executive summary

Lymphatic malformation 6 (LM6) is a rare Mendelian disorder of lymphatic development caused principally by biallelic loss-of-function variants in PIEZO1, which encodes a mechanically activated, calcium-permeable cation channel. It is best understood clinically as PIEZO1-related generalized lymphatic dysplasia (GLD). The characteristic spectrum comprises prenatal nonimmune hydrops fetalis, pleural or pericardial effusions, chylothorax, ascites, pulmonary or intestinal lymphangiectasia, and congenital or later-onset generalized lymphedema. Disease severity is highly variable, ranging from fetal death to transient prenatal edema followed by childhood- or adult-onset lymphatic disease. Founding human studies were published independently in September 2015 by Fotiou et al. and Lukacs et al. (PMIDs indexed for the disease association include 26333996 and 26387913). (OpenTargets Search: lymphatic malformation 6, iyer2020lymphaticvalvesand pages 15-17, fotiou2015novelmutationsin pages 1-2)

The strongest recent mechanistic advance is the 2024 demonstration that PIEZO1 activation in lymphatic endothelial cells induces ANGPT2 exocytosis, ADAM17-mediated TIE1 shedding, TIE/PI3K/AKT activation, and FOXO1 nuclear export. This complements earlier evidence that PIEZO1 controls lymphatic-valve morphogenesis, lymphatic sprouting, and vessel maintenance. No approved PIEZO1-directed treatment exists; small-molecule PIEZO1 agonism with Yoda1 remains preclinical. (du2024themechanosensorychannel pages 1-2, choi2022piezo1regulatedmechanotransductioncontrols pages 1-3, ludlow2023smallmoleculefunctionalrescue pages 14-16)

The following table summarizes the principal evidence and ontology-ready annotations.

Domain Key finding Evidence type Quantitative detail Source / date / DOI / PMID Knowledge-base ontology suggestions
Disease identity / gene Lymphatic malformation 6 is linked to PIEZO1; disease-target association databases map LM6 to MONDO:0014797 and PIEZO1 as the only strong associated target Curated disease-resource + human genetics OpenTargets evidence size: 5 literature-backed links for PIEZO1–LM6 association OpenTargets disease-target association for “lymphatic malformation 6” (MONDO_0014797) (OpenTargets Search: lymphatic malformation 6) MONDO:0014797; HGNC:13866 PIEZO1; NCIT: C129043 Lymphatic Malformation
Founding human cohort Autosomal recessive generalized lymphatic dysplasia (GLD) due to homozygous/compound-heterozygous PIEZO1 variants; frequent non-immune hydrops fetalis (NIHF) and childhood facial/four-limb lymphedema Human clinical / human genetics 6 families, 10 PIEZO1 variants reported; high incidence of NIHF; onset of facial and four-limb lymphedema in childhood Fotiou et al., 2015-09, Nature Communications, DOI: https://doi.org/10.1038/ncomms9085 (PMID not available in context) (fotiou2015novelmutationsin pages 1-2) HP:0001789 Lymphedema; HP:0001561 Hydrops fetalis; HP:0000978 Facial edema; HP:0002202 Pleural effusion; HP:0001744 Ascites; HP:0001733 Lymphangiectasia
Founding human cohort details GLD phenotype includes widespread edema with systemic lymphatic involvement: intestinal/pulmonary lymphangiectasia, pleural/chylous/pericardial effusions; some prenatal demise, some postnatal hydrops resolution followed by later lymphedema Human clinical 5 patients across 4 families highlighted; hydrops in at least 2 families; one in utero demise at 34 weeks; postnatal lymphedema onset reported around 6–9 years in survivors Fotiou et al., 2015-09, DOI: https://doi.org/10.1038/ncomms9085 (fotiou2015novelmutationsin pages 2-3) HP:0003573 Congenital onset; HP:0001789 Lymphedema; HP:0010318 Chylothorax; HP:0001698 Pericardial effusion; UBERON:0005409 lymphatic vessel
Variant classes / function Disease-associated PIEZO1 variants include nonsense, splice-site, and missense alleles with segregation in affected families; evidence supports loss of protein and/or loss of function Human genetics + in vitro / ex vivo functional Examples in context include nonsense variants p.E1630X, p.E755X, p.Q2228X and splice variant c.3796+1G>A; reduced/absent protein on Western blot; subtle RBC abnormalities noted Fotiou et al., 2015-09, DOI: https://doi.org/10.1038/ncomms9085 (fotiou2015novelmutationsin pages 1-2, fotiou2015novelmutationsin pages 2-3) SO:0001587 nonsense_variant; SO:0001629 splice_donor_variant; GO:0006816 calcium ion transport; GO:0008308 voltage-gated ion channel activity
Independent founding family Biallelic PIEZO1 mutations identified in 2 siblings with persistent congenital lymphedema; affected alleles showed markedly reduced channel activity Human clinical + human genetics + heterologous functional assay 2 affected siblings; one splice/truncating allele plus one missense allele; channel function “greatly attenuated” Lukacs et al., 2015-09, Nature Communications, DOI: https://doi.org/10.1038/ncomms9329 (PMID not available in context) (iyer2020lymphaticvalvesand pages 15-17) HP:0001789 Lymphedema; HP:0003577 Congenital onset; MONDO:0014797; GO:0005262 calcium channel activity
Recent human variant interpretation Four novel GLD-associated missense variants can reach the cell surface as full-length protein but still show reduced or abolished mechanical channel function, supporting pathogenic LOF mechanisms beyond absent trafficking Human genetics + in vitro Variants in context: E829V, G1978D, I2270T, R2335Q; all rare/ultra-rare, with no homozygotes in gnomAD noted in context Ludlow et al., 2023-08, medRxiv preprint, DOI: https://doi.org/10.1101/2023.08.01.23292554 (ludlow2023smallmoleculefunctionalrescue pages 41-45, ludlow2023smallmoleculefunctionalrescue pages 5-8) SO:0001583 missense_variant; GO:0005516 mechanosensitive ion channel activity; ECO:0001565 cell-based functional assay evidence
Recent families / phenotype expansion Additional PIEZO1-GLD families show antenatal NIHF, polyhydramnios, congenital limb edema, chylothoraces and ascites; one family showed adult-onset bilateral chylothoraces in the 30s before later lymphedema Human clinical 3 families in context (GLD07-09); GLD09 hydrothoraces detected at 19 weeks gestation; pseudo-dominant appearance in one consanguineous family due to homozygous I2270T Ludlow et al., 2023-08, DOI: https://doi.org/10.1101/2023.08.01.23292554 (ludlow2023smallmoleculefunctionalrescue pages 8-10, ludlow2023smallmoleculefunctionalrescue pages 14-16) HP:0001561 Hydrops fetalis; HP:0002023 Polyhydramnios; HP:0002202 Pleural effusion; HP:0010318 Chylothorax; HP:0001744 Ascites; HP:0001789 Lymphedema
Preclinical rescue Yoda1 and analogues rescued function of some GLD-associated PIEZO1 missense channels in vitro; this is preclinical, not an approved genotype-specific therapy In vitro / preclinical Missense variants showed ~65–90% reduction in Ca2+ signaling vs WT in context; Yoda1 restored mechanically evoked responses in rescue assays Ludlow et al., 2023-08, DOI: https://doi.org/10.1101/2023.08.01.23292554 (preprint) (ludlow2023smallmoleculefunctionalrescue pages 8-10, ludlow2023smallmoleculefunctionalrescue pages 14-16) CHEBI: not established here for Yoda1; NCIT suggestion: Experimental Therapeutic Procedure; GO:0051480 regulation of cytosolic calcium ion concentration
Valve-development mechanism PIEZO1 is required for lymphatic valve formation; loss in endothelial/lymphatic endothelium reduces valve number and causes pleural effusion/postnatal lethality in mouse models Mouse + cultured LECs Endothelial-specific knockout mice showed dramatic reduction in lymphatic valves; pleural effusion and postnatal death reported Nonomura et al., 2018-11, PNAS, DOI: https://doi.org/10.1073/pnas.1817070115 (PMID not available in context) (iyer2020lymphaticvalvesand pages 15-17) GO:0001946 lymphangiogenesis; GO:0035239 tube morphogenesis; CL:0000115 endothelial cell; CL lymphatic endothelial cell; UBERON:0005409 lymphatic vessel
Valve development and maintenance PIEZO1 senses oscillating shear stress and drives the genetic program for lymphatic valve development and maintenance; adult deletion causes valve degeneration Mouse + in vitro LECs Newborn endothelial or lymphatic-specific deletion inhibited valve formation; adult deletion caused “substantial” valve degeneration Choi et al., 2019-05, JCI Insight, DOI: https://doi.org/10.1172/jci.insight.125068 (choi2019piezo1incorporatesmechanical pages 2-4, choi2019piezo1incorporatesmechanical pages 1-2) GO:0034405 response to fluid shear stress; GO:0001946 lymphangiogenesis; HP:0002564 Lymphatic vessel abnormality
Sprouting / regression mechanism PIEZO1 acts upstream of ORAI1 in flow-activated lymphatic expansion; deletion causes sprouting defects and adult lymphatic regression; activation enhances regeneration Mouse + in vitro LECs Lymphatic-specific conditional KO phenocopied sprouting defects; postnatal deletion induced regression; Yoda1 suppressed postsurgical lymphedema in mice Choi et al., 2022-07, Circulation Research, DOI: https://doi.org/10.1161/circresaha.121.320565 (choi2022piezo1regulatedmechanotransductioncontrols pages 10-12, choi2022piezo1regulatedmechanotransductioncontrols pages 1-3) GO:0001946 lymphangiogenesis; GO:0035556 intracellular signal transduction; NCIT: Preclinical Study
2024 pathway advance PIEZO1 functions upstream of ANGPT2/TIE/PI3K/AKT/FOXO1 signaling in lymphatic endothelial cells, linking mechanosensation to transcriptional regulation relevant to lymphedema biology Mouse + in vitro LECs PIEZO1 activation triggered rapid ANGPT2 exocytosis, TIE1 ectodomain shedding by ADAM17, increased TIE/PI3K/AKT, and FOXO1 nuclear export Du et al., 2024-05, J Clin Invest, DOI: https://doi.org/10.1172/jci176577 (du2024themechanosensorychannel pages 1-2) GO:0034405 response to fluid shear stress; GO:0014068 positive regulation of phosphatidylinositol 3-kinase signaling; GO:0001525 angiogenesis/lymphatic vascular development; CL:0000115 endothelial cell
Current understanding of pathophysiology Consensus model: biallelic PIEZO1 LOF impairs lymphatic endothelial mechanosensation, disrupting valve morphogenesis, sprouting, and maintenance, producing fetal effusions/hydrops and later systemic lymphedema Synthesis of human + in vitro + mouse evidence Supported across 2015–2024 human genetics and mechanistic studies Supported by Fotiou 2015, Lukacs 2015, Nonomura 2018, Choi 2019/2022, Du 2024 (du2024themechanosensorychannel pages 1-2, choi2019piezo1incorporatesmechanical pages 2-4, choi2022piezo1regulatedmechanotransductioncontrols pages 10-12, iyer2020lymphaticvalvesand pages 15-17, fotiou2015novelmutationsin pages 1-2) MONDO:0014797; GO:0001946 lymphangiogenesis; GO:0034405 response to fluid shear stress; CL: lymphatic endothelial cell
Diagnostics Most specific diagnostic evidence is molecular: exome sequencing/NGS identifying biallelic PIEZO1 variants, supported by segregation and functional testing when missense/VUS alleles are found Human clinical / molecular diagnostics WES identified causative variants in founding families and sibling pair; lymphoscintigraphy reported in Fotiou cohort; RBC film abnormalities can be supportive but nonspecific Fotiou et al., 2015-09; Lukacs et al., 2015-09 (fotiou2015novelmutationsin pages 2-3, iyer2020lymphaticvalvesand pages 15-17) NCIT: Whole Exome Sequencing; HP:0001789; LOINC/NCIT suggestions for lymphoscintigraphy not disease-specific
Prognosis / natural history Prenatal course can include NIHF and fetal demise; in survivors, edema may partially/fully resolve postnatally then recur as persistent or childhood-onset lymphedema with systemic complications Human clinical Context notes fetal demise, postnatal hydrops resolution, onset around 6–9 years in some survivors, and adult presentations in later families Fotiou 2015; Ludlow 2023 (fotiou2015novelmutationsin pages 2-3, ludlow2023smallmoleculefunctionalrescue pages 8-10, cheng2025piezo1variantimplications pages 3-4) HP:0003573 Congenital onset; HP:0001789 Lymphedema; HP:0002202 Pleural effusion
Epidemiology Disease-specific prevalence/incidence for LM6 is not established in retrieved sources; generalized lymphatic dysplasia is rare Human clinical / review-level statement No robust population rate found for LM6; one preprint excerpt mentioned GLD approx. 1 in 6000, but this appears to refer broadly and should be treated cautiously Ludlow et al., 2023-08 preprint (context summary only) (ludlow2023smallmoleculefunctionalrescue pages 5-8) MONDO:0014797; Orphan disease coding pending confirmation
Clinical treatment evidence No approved PIEZO1-genotype-specific therapy was found in retrieved evidence; management in published human LM6 reports is largely supportive and complication-directed Human clinical + evidence gap No controlled LM6 treatment trial identified in retrieved sources Evidence gap across retrieved LM6 literature (fotiou2015novelmutationsin pages 1-2, ludlow2023smallmoleculefunctionalrescue pages 8-10, fotiou2015novelmutationsin pages 2-3) NCIT: Supportive Care; NCIT: Lymphedema Therapy
Generic lymphatic-malformation trials Active LM/vascular-anomaly trials exist for sirolimus/rapamycin and alpelisib, but these are not PIEZO1-genotype-specific and should not be interpreted as LM6-targeted evidence Clinical trials, non-genotype-specific Examples: NCT06673290 recruiting, n=150; NCT03243019 recruiting, n=28; NCT06239480 active-not-recruiting, n=51; NCT05948943 recruiting, n=232; NCT00975819 completed, n=61 ClinicalTrials.gov results retrieved in tool output (current statuses as returned) (OpenTargets Search: lymphatic malformation 6) NCIT: Sirolimus; NCIT: Alpelisib; NCIT: Clinical Trial; note: not specific to MONDO:0014797
Prevention / environment No evidence supports environmental, infectious, lifestyle, or protective factors as causal for LM6; prevention is primarily genetic counseling/reproductive risk management in affected families Human genetics / evidence gap Autosomal recessive inheritance implies 25% recurrence risk for carrier-couple pregnancies, though exact counseling numbers were not directly quoted in retrieved contexts Inference from AR inheritance established by Fotiou/Lukacs (iyer2020lymphaticvalvesand pages 15-17, fotiou2015novelmutationsin pages 1-2) NCIT: Genetic Counseling; HP/GO not applicable
Model systems Best-supported disease models are endothelial or lymphatic-specific Piezo1 knockout mice and cultured lymphatic endothelial cells; these recapitulate valve/sprouting defects and enable pathway dissection Mouse + in vitro Multiple conditional models: Tie2Cre, Lyve1Cre, Prox1-CreERT2, Cdh5(PAC)-CreERT2 reported in context Nonomura 2018; Choi 2019; Choi 2022; Du 2024 (du2024themechanosensorychannel pages 1-2, choi2019piezo1incorporatesmechanical pages 2-4, choi2022piezo1regulatedmechanotransductioncontrols pages 10-12, iyer2020lymphaticvalvesand pages 15-17) CL: lymphatic endothelial cell; GO:0001946 lymphangiogenesis; NCIT: Disease Model

Table: This compact table organizes the key human, in vitro, mouse, and trial evidence for PIEZO1-related lymphatic malformation 6. It highlights the founding 2015 cohorts, recent mechanistic advances, and the important distinction between preclinical Yoda1 rescue and non-genotype-specific lymphatic-malformation trials.

1. Disease information

Definition and identifiers

  • Preferred name: Lymphatic malformation 6.
  • Core clinical designation: PIEZO1-related generalized lymphatic dysplasia.
  • MONDO: MONDO:0014797.
  • OMIM: 616843.
  • Causal gene: PIEZO1, Ensembl ENSG00000103335; approved name piezo type mechanosensitive ion channel component 1 (Er blood group). OpenTargets identifies PIEZO1 as the sole associated target, supported by five evidence records and multiple disease-defining publications. (OpenTargets Search: lymphatic malformation 6)
  • Common synonyms: generalized lymphatic dysplasia with nonimmune hydrops fetalis; PIEZO1-related generalized lymphatic dysplasia; congenital lymphatic dysplasia; hereditary lymphedema due to PIEZO1 deficiency; Fotiou generalized lymphatic dysplasia.
  • Classification: congenital primary lymphatic anomaly; autosomal-recessive Mendelian disease.

No unique disease-specific ICD-10, ICD-11, or MeSH code was established in the retrieved evidence. Coding therefore generally relies on broader categories for congenital lymphatic malformation, primary lymphedema, hydrops fetalis, or chylous effusion. The evidence summarized here is principally aggregated disease-level information derived from published families and experimental studies, not individual EHR data.

Defining abstract quotations

Fotiou et al. defined GLD as “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.” They further reported “homozygous and compound heterozygous mutations in PIEZO1, resulting in an autosomal recessive form of GLD with a high incidence of non-immune hydrops fetalis.” Published September 2015; DOI: https://doi.org/10.1038/ncomms9085; PMID 26333996. (OpenTargets Search: lymphatic malformation 6, fotiou2015novelmutationsin pages 1-2)

Lukacs et al. reported: “Through whole-exome sequencing, we identify biallelic mutations in PIEZO1 … in a pair of siblings affected with persistent lymphoedema caused by congenital lymphatic dysplasia.” Published September 2015; DOI: https://doi.org/10.1038/ncomms9329; PMID 26387913. (OpenTargets Search: lymphatic malformation 6, iyer2020lymphaticvalvesand pages 15-17)

2. Etiology

Causal factors and genetic risk

The established cause is biallelic pathogenic or likely pathogenic PIEZO1 variation, usually homozygous or compound heterozygous, producing absent protein, defective membrane trafficking, or impaired mechanically activated channel function. Reported classes include nonsense, canonical splice-site, frameshift/deletion, and missense variants. Ten variants were initially identified across six families; an independently reported sibling pair carried a splice/truncating allele and a missense allele. (iyer2020lymphaticvalvesand pages 15-17, fotiou2015novelmutationsin pages 1-2, cheng2025piezo1variantimplications pages 3-4)

Important genotype distinction:

  1. Biallelic PIEZO1 loss of function causes LM6/GLD.
  2. Heterozygous PIEZO1 gain-of-function variants more commonly cause autosomal-dominant dehydrated hereditary stomatocytosis, sometimes accompanied by perinatal edema or hydrops. These allelic disorders should not be conflated. (iyer2020lymphaticvalvesand pages 15-17, ludlow2023smallmoleculefunctionalrescue pages 5-8)

Family history, parental consanguinity, and carriage of a pathogenic allele in each parent increase reproductive risk. A pseudo-dominant pedigree can occur when an affected homozygous person and a heterozygous carrier have affected children, as reported for the I2270T allele in a consanguineous family. (ludlow2023smallmoleculefunctionalrescue pages 8-10, ludlow2023smallmoleculefunctionalrescue pages 14-16)

Environmental, infectious, and lifestyle factors

No reproducible toxin, radiation, infectious, dietary, smoking, alcohol, occupational, or other environmental cause has been demonstrated. There is likewise no established environmental protective factor or validated gene–environment interaction. Mechanical forces are essential physiological signals sensed by PIEZO1, but they are part of the molecular mechanism—not an avoidable environmental exposure.

No genetic protective allele has been validated for LM6. Variable residual PIEZO1 activity may modify severity, but this remains a genotype–function hypothesis rather than a clinically validated protective factor.

3. Phenotypes

The phenotype is multisystemic and markedly variable. Reliable disease-specific percentages are unavailable because published cohorts are small.

  • Nonimmune hydrops fetalis — HP:0001561: prenatal sign, often detected in the second or third trimester; ranges from transient to lethal. One founding-family fetus died at 34 weeks, whereas hydrops resolved after birth in some survivors. (fotiou2015novelmutationsin pages 1-2, fotiou2015novelmutationsin pages 2-3)
  • Pleural effusion — HP:0002202; chylothorax — HP:0010318: prenatal, neonatal, childhood, or adult manifestation; may be bilateral and persistent. In a recent family, bilateral hydrothoraces were detected at 19 weeks; another patient developed bilateral chylothoraces in the third decade. (ludlow2023smallmoleculefunctionalrescue pages 8-10, ludlow2023smallmoleculefunctionalrescue pages 41-45)
  • Pericardial effusion — HP:0001698: systemic lymphatic manifestation; CT documentation accompanied bilateral chylothorax in one recent proband. (ludlow2023smallmoleculefunctionalrescue pages 41-45)
  • Ascites — HP:0001744: prenatal or postnatal fluid accumulation resulting from defective lymphatic drainage. (ludlow2023smallmoleculefunctionalrescue pages 8-10, ludlow2023smallmoleculefunctionalrescue pages 5-8)
  • Generalized/peripheral lymphedema — HP:0001789: congenital or delayed onset, affecting all four limbs, face, and sometimes genitalia. Some founding-cohort survivors developed edema around 6–9 years, whereas recent families expand onset into adulthood. (ludlow2023smallmoleculefunctionalrescue pages 8-10, fotiou2015novelmutationsin pages 2-3, ludlow2023smallmoleculefunctionalrescue pages 5-8)
  • Facial edema/facial dysmorphism — suggested HP:0000978: secondary to chronic lymphatic swelling; may impair appearance, oral function, and psychosocial well-being. (fotiou2015novelmutationsin pages 1-2)
  • Lymphangiectasia — HP:0001733: intestinal or pulmonary; may lead to respiratory morbidity, protein loss, nutritional problems, and recurrent effusions. (choi2022piezo1regulatedmechanotransductioncontrols pages 10-12, fotiou2015novelmutationsin pages 1-2)
  • Polyhydramnios — HP:0002023: reported in antenatally affected pregnancies. (ludlow2023smallmoleculefunctionalrescue pages 8-10)
  • Recurrent cellulitis: two founding-cohort patients had severe recurrent facial cellulitis, a complication of chronic edema and impaired local barrier/immune function. (fotiou2015novelmutationsin pages 2-3)
  • Subtle erythrocyte abnormalities: stomatocytes or spherocytes were reported in some affected people and carriers, but these are inconsistent and are not diagnostic of LM6. (fotiou2015novelmutationsin pages 2-3)

Quality-of-life studies specific to LM6 were not retrieved. Expected burdens include chronic swelling, disfigurement, restricted mobility, recurrent infection, dyspnea from thoracic effusions, repeated drainage or hospitalization, and psychosocial effects. These impacts are clinically plausible but have not been quantified with EQ-5D, SF-36, or a disease-specific instrument in a sufficiently large LM6 cohort.

4. Genetic and molecular information

PIEZO1 encodes a large trimeric mechanosensitive ion channel that increases membrane permeability to calcium and other cations in response to membrane tension, stretch, and fluid shear. Disease-associated LM6 alleles generally reduce mechanosensitivity or channel abundance. (du2024themechanosensorychannel pages 1-2, iyer2020lymphaticvalvesand pages 15-17)

Reported variants in retrieved studies include truncating alleles p.E755X, p.E1630X, and p.Q2228X, splice donor c.3796+1G>A, and recent missense substitutions E829V, G1978D, I2270T, and R2335Q. The 2015 study also documented another splice-site allele, c.1669+1G>A. Exact transcript-dependent HGVS normalization should be verified against the current MANE transcript before database ingestion. (fotiou2015novelmutationsin pages 1-2, fotiou2015novelmutationsin pages 2-3, ludlow2023smallmoleculefunctionalrescue pages 41-45)

The early variants segregated with disease; most were absent from dbSNP, 1000 Genomes, and 900 controls, while two had reported minor-allele frequencies of approximately 0.0002. The four 2023 missense alleles were absent or ultra-rare in gnomAD, with no homozygotes reported. (fotiou2015novelmutationsin pages 1-2, ludlow2023smallmoleculefunctionalrescue pages 41-45)

Functional consequences include exon skipping or intron retention, premature truncation, reduced/absent protein, impaired surface trafficking, and channels that reach the membrane but have markedly reduced mechanosensitivity. In 2023 assays, the missense channels exhibited approximately 65–90% lower calcium signaling than wild type; I2270T produced no detectable stretch-activated current under the tested conditions. Yoda1 restored activity in several mutant channels. (ludlow2023smallmoleculefunctionalrescue pages 8-10, ludlow2023smallmoleculefunctionalrescue pages 14-16)

No validated modifier gene, disease-specific methylation signature, recurrent chromosomal abnormality, or somatic mosaic mechanism has been established. The disorder is primarily a germline single-gene disease.

5. Environmental information

Environmental toxins, pollution, radiation, infection, diet, exercise, smoking, and alcohol have no established etiological role. Infection can occur secondarily as cellulitis in chronically edematous tissue but is not the primary cause. Lifestyle measures may reduce secondary lymphedema complications but cannot correct PIEZO1 deficiency.

6. Mechanism and pathophysiology

Causal chain

Biallelic PIEZO1 loss of function → deficient lymphatic endothelial sensing of shear/stretch → reduced calcium-dependent mechanotransduction → disturbed valve-gene regulation, endothelial rearrangement, sprouting, and vessel maintenance → valve paucity/regression and malformed lymphatic networks → lymph reflux or failed drainage → fetal effusions/hydrops, lymphangiectasia, chylothorax, ascites, and chronic lymphedema. Human genetics establishes the upstream cause; cell and mouse studies establish the intervening mechanism. (du2024themechanosensorychannel pages 1-2, choi2019piezo1incorporatesmechanical pages 2-4, choi2022piezo1regulatedmechanotransductioncontrols pages 1-3, iyer2020lymphaticvalvesand pages 15-17, fotiou2015novelmutationsin pages 1-2)

Principal pathways

  1. Valve morphogenesis: Piezo1 detects oscillatory shear stress in lymphatic endothelial cells. Conditional deletion suppresses valve formation in newborn mice; adult deletion causes substantial valve degeneration. Knockdown prevents flow-induced expression of valve genes, whereas overexpression or Yoda1 activation promotes valve-gene expression. (choi2019piezo1incorporatesmechanical pages 2-4, choi2019piezo1incorporatesmechanical pages 1-2)
  2. Cytoskeletal and junctional remodeling: endothelial Piezo1 knockout impairs valve-leaflet protrusion, collective migration, actin polymerization, and remodeling of VE-cadherin-positive junctions. Knockout mice have markedly fewer lymphatic valves, pleural effusions, and postnatal death. (iyer2020lymphaticvalvesand pages 15-17)
  3. PIEZO1–ORAI1–KLF2/DTX/NOTCH axis: flow-activated PIEZO1 lies upstream of ORAI1-dependent calcium signaling and regulates KLF2, DTX1, DTX3L, and NOTCH1. Loss causes embryonic sprouting defects and adult lymphatic regression; Dtx3L expression can rescue aspects of the knockout phenotype. (choi2022piezo1regulatedmechanotransductioncontrols pages 10-12, choi2022piezo1regulatedmechanotransductioncontrols pages 1-3)
  4. 2024 ANGPT2/TIE/PI3K/AKT/FOXO1 advance: PIEZO1 activation triggers ANGPT2 exocytosis, ADAM17-dependent TIE1 ectodomain shedding, increased TIE/PI3K/AKT signaling, and FOXO1 nuclear export. It regulates lymphedema-associated valve genes including FOXC2, GATA2, GJA4, and ITGA9. Published May 2024; DOI: https://doi.org/10.1172/JCI176577. (du2024themechanosensorychannel pages 1-2)

Suggested annotations include GO:0034405 response to fluid shear stress, GO:0001946 lymphangiogenesis, calcium-ion transport/signaling, actin-cytoskeleton organization, cell–cell junction organization, and PI3K/AKT signaling. The principal cell is the lymphatic endothelial cell; use the current Cell Ontology identifier after release-specific validation. No robust LM6-specific metabolomic, lipidomic, proteomic, epigenomic, single-cell, spatial-transcriptomic, or multi-omic patient signature has been validated.

7. Anatomical structures affected

The primary lesion is distributed throughout the lymphatic vasculature, especially collecting vessels, intraluminal lymphatic valves, and lymphovenous drainage structures. Suggested anatomy annotations are UBERON:0005409 lymphatic vessel, lymphatic capillary, collecting lymphatic vessel, lymphatic valve, and lymphatic endothelium.

Secondary sites include subcutaneous connective tissue of all limbs and face; pleural and pericardial cavities; lungs; intestinal lymphatics; abdominal/peritoneal cavity; and occasionally genital tissue. Disease is typically generalized and often asymmetric in severity rather than strictly unilateral. At the subcellular level, PIEZO1 is a plasma-membrane channel, although intracellular channel pools were suggested by calcium-release experiments. (ludlow2023smallmoleculefunctionalrescue pages 8-10, ludlow2023smallmoleculefunctionalrescue pages 5-8)

8. Temporal development

Onset may be antenatal, congenital, childhood, or—less commonly—adult. Prenatal disease is chronic developmental rather than an acute acquired process. Hydrops may remit spontaneously around birth, but remission does not ensure cure: edema and systemic lymphatic complications can recur years later. Founding survivors developed lymphedema at approximately 6–9 years; a recent family included adult-onset bilateral chylothoraces in the 30s. (ludlow2023smallmoleculefunctionalrescue pages 8-10, fotiou2015novelmutationsin pages 2-3, cheng2025piezo1variantimplications pages 3-4)

There is no validated staging system. A pragmatic course is: prenatal effusions/hydrops; neonatal stabilization or death; latent/partially resolved interval in some survivors; then chronic lymphedema, lymphangiectasia, recurrent effusions, or infections. The disease is generally lifelong even if individual fluid collections resolve.

9. Inheritance and population

Inheritance is predominantly autosomal recessive, with variable expressivity and incompletely defined penetrance. For two confirmed carrier parents, standard Mendelian counseling predicts a 25% affected, 50% carrier, and 25% unaffected/noncarrier probability for each pregnancy. Pseudo-dominant inheritance can occur in consanguineous pedigrees. Germline mosaicism has not been established but cannot be excluded in apparently de novo recurrence. No founder allele, carrier frequency, ethnic enrichment, sex bias, anticipation, or geographic concentration is established. (fotiou2015novelmutationsin pages 1-2, ludlow2023smallmoleculefunctionalrescue pages 14-16)

Disease-specific prevalence and incidence are unknown. A broad estimate of approximately 1 in 6,000 was mentioned for generalized lymphatic dysplasia in a 2023 preprint, but it should not be used as an established LM6 prevalence because the denominator and molecular ascertainment were not disease-specific. (ludlow2023smallmoleculefunctionalrescue pages 5-8)

10. Diagnostics

Clinical and imaging assessment

Prenatal ultrasound should evaluate skin edema, ascites, pleural/pericardial effusions, hydrothorax, placental edema, and polyhydramnios. Postnatal assessment may include ultrasound, echocardiography, chest radiography/CT or MRI, lymphoscintigraphy, and—where available—dynamic contrast MR lymphangiography to define central lymphatic flow. Lymphoscintigraphy was consistently abnormal in four founding-cohort patients. (fotiou2015novelmutationsin pages 2-3)

Laboratory evaluation is mainly directed toward complications: CBC and blood film; hemolysis indices where stomatocytosis is suspected; albumin, total protein, immunoglobulins and lymphocyte counts for intestinal lymph loss; electrolytes; and pleural-fluid triglycerides/chylomicrons for chylothorax. No validated circulating LM6 biomarker exists.

Genetic testing algorithm

  1. Confirm a generalized congenital lymphatic phenotype and exclude immune, cardiac, chromosomal, infectious, hematologic, and structural causes of hydrops.
  2. Use a primary-lymphedema/generalized lymphatic-anomaly panel that includes PIEZO1 and relevant differential genes such as PIEZO2, EPHB4, RASA1, ANGPT2, TIE1, FLT4, CCBE1, FAT4, ADAMTS3, FOXC2, GATA2, PTPN14, and PIK3CA.
  3. If negative, perform trio WES or WGS; WGS is useful for deep intronic, structural, and poorly captured variants.
  4. Confirm candidate PIEZO1 variants by segregation analysis. For missense VUS, functional channel assays may be decisive because surface-localized protein can still lack mechanical activity. (iyer2020lymphaticvalvesand pages 15-17, ludlow2023smallmoleculefunctionalrescue pages 8-10, ludlow2023smallmoleculefunctionalrescue pages 41-45)

CMA or karyotyping is appropriate in fetal hydrops with multiple anomalies but does not specifically diagnose LM6. FISH, mitochondrial testing, and repeat-expansion testing are not routine LM6 investigations.

Differential diagnoses include PIK3CA-related lymphatic malformations, Hennekam lymphangiectasia-lymphedema syndrome, hereditary lymphedema caused by FLT4 or FOXC2, EPHB4-related lymphatic-related hydrops, RASopathies, Turner syndrome, congenital infection, fetal anemia, cardiac disease, and heterozygous PIEZO1-associated dehydrated hereditary stomatocytosis.

11. Outcome and prognosis

Prognosis is variable. Severe prenatal disease can cause miscarriage, stillbirth, or neonatal death; one reported fetus died at 34 weeks. Survivors may have complete early resolution of hydrops yet later develop chronic generalized lymphedema, recurrent cellulitis, respiratory compromise, chylothorax, pericardial effusion, ascites, or intestinal protein loss. No reliable five- or ten-year survival estimate, life-expectancy figure, validated prognostic score, or molecular prognostic biomarker exists. (fotiou2015novelmutationsin pages 1-2, fotiou2015novelmutationsin pages 2-3, cheng2025piezo1variantimplications pages 3-4)

Residual channel function, extent of thoracic/intestinal involvement, persistence of prenatal effusions, and ability to control chyle loss are plausible prognostic factors, but they have not been validated in a sufficiently large prospective cohort.

12. Treatment

There is no approved disease-modifying or PIEZO1-genotype-specific therapy. Management should be coordinated through a multidisciplinary vascular-anomalies/primary-lymphedema team.

  • Lymphedema care: compression garments or bandaging, skin care, exercise, manual lymphatic drainage where appropriate, weight optimization, rapid treatment of cellulitis, and physical/occupational therapy.
  • Effusions and chylothorax: respiratory support, drainage when clinically required, nutritional management with low long-chain-fat/high-medium-chain-triglyceride feeding or parenteral nutrition, and individualized lymphatic interventional procedures.
  • Surgery/intervention: pleurodesis, thoracic-duct or abnormal-channel embolization, lymphovenous procedures, or debulking may be considered according to anatomy and severity; no LM6-specific response rate is established.
  • Sirolimus/rapamycin: used for complicated lymphatic anomalies generally, but no controlled evidence establishes efficacy specifically for biallelic PIEZO1 LM6.
  • Alpelisib: appropriate only for proven PIK3CA-driven disease; it is not mechanistically indicated solely by a PIEZO1 diagnosis.

Current non-genotype-specific studies include NCT06673290 (sirolimus, recruiting, n=150), NCT03243019 (rapamycin, recruiting, n=28), NCT06239480 (topical rapamycin, phase 3, active-not-recruiting, n=51), NCT05948943 (alpelisib for PIK3CA-mutant malformations, recruiting, n=232), and completed NCT00975819 (sirolimus in complicated vascular anomalies, n=61). None should be represented as an LM6-specific trial. (OpenTargets Search: lymphatic malformation 6)

Experimental PIEZO1 agonism

Yoda1 accelerated valve formation, promoted lymphatic sprouting, reduced postsurgical lymphedema in mice, and rescued several mechanically insensitive human mutant channels in vitro. The 2023 study stated that “The potential to pharmacologically overcome the loss of force sensing was demonstrated.” This is promising precision-therapy evidence but remains preclinical; systemic PIEZO1 activation could affect erythrocytes and other vascular tissues and requires rigorous safety evaluation. DOI: https://doi.org/10.1101/2023.08.01.23292554. (choi2022piezo1regulatedmechanotransductioncontrols pages 1-3, ludlow2023smallmoleculefunctionalrescue pages 14-16, ludlow2023smallmoleculefunctionalrescue pages 5-8)

Suggested NCIT annotations include Genetic Counseling, Supportive Care, Lymphedema Therapy, Compression Therapy, Sirolimus, Alpelisib, Pleurodesis, and Clinical Trial; exact NCIT identifiers should be release-validated.

13. Prevention

No primary lifestyle or environmental prevention exists. The principal preventive strategy is genetic counseling with cascade testing of relatives, partner testing where appropriate, and discussion of prenatal diagnosis or preimplantation genetic testing when familial pathogenic variants are known. Prenatal molecular testing should be accompanied by serial ultrasound because severity is variable even within families.

Secondary prevention comprises early recognition of fetal effusions, anticipatory delivery planning at a tertiary center, and surveillance for recurrent pleural/pericardial effusion, intestinal lymph loss, and progressive edema. Tertiary prevention includes compression, meticulous skin care, prompt treatment of cellulitis, nutritional management of chyle loss, vaccination according to routine schedules, and rehabilitation. No vaccine or prophylactic medication prevents LM6 itself.

14. Other species and natural disease

No well-established naturally occurring PIEZO1-LM6 counterpart in companion animals, livestock, or wildlife was retrieved, and there is no zoonotic or transmissible component. PIEZO1 and lymphatic-valve mechanobiology are evolutionarily conserved. Zebrafish possess lymphatic valves and are useful for comparative developmental studies, but a validated natural zebrafish LM6 disease was not identified.

15. Model organisms

The strongest models are genetically engineered mice and cultured lymphatic endothelial cells.

  • Tie2Cre;Piezo1 conditional knockout mice: endothelial loss causes pleural effusion, marked lymphatic-valve reduction, and postnatal death.
  • Lyve1Cre;Piezo1 knockout mice: lymphatic/endothelial targeting confirms a valve requirement.
  • Prox1-CreERT2 and Cdh5(PAC)-CreERT2 models: temporally controlled deletion demonstrates requirements in neonatal valve formation and adult valve maintenance.
  • Lymphatic-specific embryonic/adult deletion models: reproduce sprouting defects, reduced branching, delayed valve formation, and adult vessel regression.
  • Cultured human or mouse lymphatic endothelial cells: support shear-stress, calcium imaging, patch-clamp, trafficking, RNA-expression, and ANGPT2/TIE/FOXO1 pathway studies.
  • Heterologous expression systems: determine whether individual human missense variants alter surface localization, mechanically activated current, calcium influx, or Yoda1 responsiveness. (du2024themechanosensorychannel pages 1-2, choi2019piezo1incorporatesmechanical pages 2-4, choi2022piezo1regulatedmechanotransductioncontrols pages 10-12, iyer2020lymphaticvalvesand pages 15-17, ludlow2023smallmoleculefunctionalrescue pages 8-10)

These models reproduce central mechanistic features but not the complete variability of human prenatal hydrops, multiorgan lymphangiectasia, or long-term treatment response. Consequently, Yoda1 rescue in cells or mice cannot yet be extrapolated to clinical efficacy.

Evidence limitations and curation recommendations

LM6 remains exceptionally rare, and most clinical evidence consists of small pedigrees and case reports. Phenotype frequencies, penetrance, prevalence, survival, quality of life, and treatment-response rates therefore remain uncertain. The 2023 functional-rescue report was retrieved as a medRxiv preprint and should be labeled accordingly. Ontology identifiers suggested above should be checked against current HPO, GO, CL, UBERON, NCIT, and HGNC releases before production ingestion. Most importantly, treatment evidence for broad lymphatic malformations should not be attributed automatically to PIEZO1-related LM6.

References

  1. (OpenTargets Search: lymphatic malformation 6): Open Targets Query (lymphatic malformation 6, 1 results). Buniello, A. et al. (2025). Open Targets Platform: facilitating therapeutic hypotheses building in drug discovery. Nucleic Acids Research.

  2. (iyer2020lymphaticvalvesand pages 15-17): Drishya Iyer, Melanie Jannaway, Ying Yang, and Joshua P. Scallan. Lymphatic valves and lymph flow in cancer-related lymphedema. Cancers, 12:2297, Aug 2020. URL: https://doi.org/10.3390/cancers12082297, doi:10.3390/cancers12082297. This article has 50 citations.

  3. (fotiou2015novelmutationsin pages 1-2): Elisavet Fotiou, Silvia Martin-Almedina, Michael A. Simpson, Shin Lin, Kristiana Gordon, Glen Brice, Giles Atton, Iona Jeffery, David C. Rees, Cyril Mignot, Julie Vogt, Tessa Homfray, Michael P. Snyder, Stanley G. Rockson, Steve Jeffery, Peter S. Mortimer, Sahar Mansour, and Pia Ostergaard. Novel mutations in piezo1 cause an autosomal recessive generalized lymphatic dysplasia with non-immune hydrops fetalis. Nature Communications, Sep 2015. URL: https://doi.org/10.1038/ncomms9085, doi:10.1038/ncomms9085. This article has 380 citations and is from a highest quality peer-reviewed journal.

  4. (du2024themechanosensorychannel pages 1-2): Jing Du, Pan Liu, Yalu Zhou, Sol Misener, Isha Sharma, Phoebe Leeaw, Benjamin R. Thomson, Jing Jin, and Susan E. Quaggin. The mechanosensory channel piezo1 functions upstream of angiopoietin/tie/foxo1 signaling in lymphatic development. The Journal of Clinical Investigation, May 2024. URL: https://doi.org/10.1172/jci176577, doi:10.1172/jci176577. This article has 33 citations.

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  7. (fotiou2015novelmutationsin pages 2-3): Elisavet Fotiou, Silvia Martin-Almedina, Michael A. Simpson, Shin Lin, Kristiana Gordon, Glen Brice, Giles Atton, Iona Jeffery, David C. Rees, Cyril Mignot, Julie Vogt, Tessa Homfray, Michael P. Snyder, Stanley G. Rockson, Steve Jeffery, Peter S. Mortimer, Sahar Mansour, and Pia Ostergaard. Novel mutations in piezo1 cause an autosomal recessive generalized lymphatic dysplasia with non-immune hydrops fetalis. Nature Communications, Sep 2015. URL: https://doi.org/10.1038/ncomms9085, doi:10.1038/ncomms9085. This article has 380 citations and is from a highest quality peer-reviewed journal.

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  9. (ludlow2023smallmoleculefunctionalrescue pages 5-8): Melanie J Ludlow, Oleksandr V Povstyan, Deborah M Linley, Silvia Martin-Almedina, Charlotte Revill, Kevin Cuthbertson, Katie A Smith, Emily Fay, Elisavet Fotiou, Andrew Bush, Claire Hogg, Tobias Linden, Natalie B Tan, Susan M White, Esther Dempsey, Sahar Mansour, Gregory Parsonage, Antreas C Kalli, Richard Foster, Pia Ostergaard, and David J Beech. Small-molecule functional rescue of piezo1 channel variants associated with generalised lymphatic dysplasia. MedRxiv, Aug 2023. URL: https://doi.org/10.1101/2023.08.01.23292554, doi:10.1101/2023.08.01.23292554. This article has 5 citations.

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  11. (choi2019piezo1incorporatesmechanical pages 2-4): Dongwon Choi, Eunkyung Park, Eunson Jung, Boksik Cha, Somin Lee, James Yu, Paul M. Kim, Sunju Lee, Yeo Jin Hong, Chester J. Koh, Chang-Won Cho, Yifan Wu, Noo Li Jeon, Alex K. Wong, Laura Shin, S. Ram Kumar, Ivan Bermejo-Moreno, R. Sathish Srinivasan, Il-Taeg Cho, and Young-Kwon Hong. Piezo1 incorporates mechanical force signals into the genetic program that governs lymphatic valve development and maintenance. JCI insight, May 2019. URL: https://doi.org/10.1172/jci.insight.125068, doi:10.1172/jci.insight.125068. This article has 180 citations and is from a domain leading peer-reviewed journal.

  12. (choi2019piezo1incorporatesmechanical pages 1-2): Dongwon Choi, Eunkyung Park, Eunson Jung, Boksik Cha, Somin Lee, James Yu, Paul M. Kim, Sunju Lee, Yeo Jin Hong, Chester J. Koh, Chang-Won Cho, Yifan Wu, Noo Li Jeon, Alex K. Wong, Laura Shin, S. Ram Kumar, Ivan Bermejo-Moreno, R. Sathish Srinivasan, Il-Taeg Cho, and Young-Kwon Hong. Piezo1 incorporates mechanical force signals into the genetic program that governs lymphatic valve development and maintenance. JCI insight, May 2019. URL: https://doi.org/10.1172/jci.insight.125068, doi:10.1172/jci.insight.125068. This article has 180 citations and is from a domain leading peer-reviewed journal.

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Artifacts

Reference Validation

Checked with linkml-reference-validator 0.2.1.

Outcome Count
References checked 10
Resolved 10
Unresolved (possible confabulation) 0
Unverifiable 0
References weighed for topical relevance 10
On topic 8
Off topic 0

All extracted references resolved successfully.