Primary Lymphoedema Flashcards
Describe lymphatics
Functions
Fluid homeostasis
Immune function - lymph nodes
Fatty acid transport
Instead of fatty acids going to the liver via the portal vein, it is taken up by the lymphatics into the blood via the thoracic duct
Feeds the lipids back into circulation via the subclavian vein
The lymphatic interacts with the vascular capillary web
Interstitial fluid surrounds the cell, and is then taken up into the lymphatic vessels
Lymphatics in disease - cancer, CVS, obesity, infection and immunity
Describe lymphoedema
Chronic oedema that persists for more than 3 months
A compromised lymphatic system leads to localised fluid retention and swelling
Secondary (extrinsic) lymphoedema is far more common
E.g. lymph node removal from axilla during breast cancer treatment, filariasis
Primary lymphoedema (intrinsic/genetic) - Chronic oedema caused by a developmental abnormality of the lymphatic system
Describe primary lymphoedema and its management
Chronic oedema caused by a developmental abnormality of the lymphatic system
Often progressive
Phenotypes vary - age of onset, site, inheritance patterns, associated features, genetic causes
Susceptible to infections
Describe lymphangiogensis
VEGFR3 - vascular endothelial growth factor receptor 3
• Enables the specification of endothelial cells form the cardinal vein
• Some of the cells in the early cardinal vein start to get a different identify by upregulation of PROX1
• Then they start to express VEGFR3 which then is attracted by VEGFC molecule in the interstitium
• Forms a new network that becomes the lymphatic network
VEGFR3 and its ligand VEGF-C are important for lymphatic development during embryogenesis
• VEGFR3 can also be activated by VEGF-D
VEGFR3 is linked with Milroy disease
VEGFR3 mutations only explains:
• 70% of all congenital primary lymphoedema
• 15% of all primary lymphoedema
Conclusion: 1° lymphoedema is a heterogeneous condition
Describe generalised lymphatic dysplasia - Hennekam syndrome
Symptoms
Antenatal hydrops with ascites and pleural effusions
Oedematous at birth - can be seen in ultrasound scan - hydrops fetalis
Intestinal lymphangiectasia - intestinal problems, diarrhoea
Peripheral lymphoedema; arms, legs, face
Mild developmental delay
Describe use of linkage analysis in identifying lymphoedema
AR model
Analysis yielded “linkage” to only one chromosome
A LOD score > 3 translates to a p-value of approximately 0.05
This was NOT achieved, but there were only 2 peaks
This wasn’t statistically significant, but still promising
Haplotyping revealed
Haplotype of all affected are shared but different to unaffected
100 candidate genes and 2 years later with lots of Sanger sequencing
Mutations in CCBE1 was identified
Describe use of candidate filtering in identifying lymphoedema
Candidate genes include those such as PROX1 and VEGFC
A family was investigated
Frameshift variant found
The protein in this patients found to have an additional nine aa
This led to a TT followed by truncation
Mutation introduced into cells showed some production of protein
BUT it was not secreted - cleavage prevented secretion
Functional validation
In zebrafish, injection of WT human WEGFC you get excessive sprouting of lymphatics
Injection of mutant VEGFC = no sprouting of lymphatics
How and when is inheritance models applied in AD inheritance
AD subgroup identified with a small head circumference
Not ideal for linkage analysis due to no family history but exome sequencing allowed to compare them as they were not related
Comparing their WES we found coding errors in the KIF11 gene
Mix of nonsense, truncating and missense variants
How and when is inheritance models applied in AR inheritance
WES of a non-consanguineous family; compound heterozygosity
Important to identify if its trans (on separate chromosomes)
Requires identification of parental DNA
WES of a consagnuious family; homozygosity in proband
Expect proband to be homozygous
And unaffected being heterozygous
These two studies created a candidate gene list with one gene in common - PIEZO1
Describe mutation consequence in PIEZO1
This mutation disrupts protein function - affected have no protein
Carriers have some protein
WES of families with AR lymphatic hydrops fetalis identified PIEZO1
Symptoms
Non-immune hydrops fetalis
Chylothoraces
Pericardial effusions
Resolves after birth
Childhood onset lymphoedema
Peripheral and facial oedema
Recurrent facial and limb cellulitis
Describe VEGFR3 Activation by VEGFC and suggested role of CCBE1
VEGFC gets activated and secreted, binding to tyrosine kinase domain on VEGFR3 to cause signalling
CCBE1 is important for the cleavage and activation of VEGFC and also a protease called ADAMSTS3
Lymphoedema was seen in a family found with biallelic mutations in ADAMSTS3
What genes are involved in primary lymphoedema
VEGFC
CCBE1
PIEZO1
