Investigating Candidate Genes and Disease Mechanism for the Childhood Blinding Disease Familial Exudative Vitreoretinopathy
Date
2024-11-22
Authors
Journal Title
Journal ISSN
Volume Title
Publisher
Abstract
Familial exudative vitreoretinopathy (FEVR) is a childhood blinding disorder that causes
incomplete vascularization of the retina. Though the Norrin/FZD4 signalling pathway is
established as the disease mechanism of FEVR, the specific interaction of the pathway in
retinal angiogenesis is unclear. The aim of this thesis is to expand the FEVR genotype
and further characterize the Norrin/FZD4 signalling pathway in the context of retinal
vascular development. I determine the pathogenic variant frequency of the FEVR genes
FZD4, NDP, LRP5, TSPAN12, and KIF11 in a cohort of FEVR patients. I show that the
use of an expanded FEVR gene panel containing all 25 genes with a connection to FEVR
does not increase the diagnostic rate for patients without a molecular diagnosis. I
establish Norrin/FZD4 binding as the exclusive disease mechanism of Norrie disease. A
young girl presenting with a Norrie disease phenocopy was determined to have biallelic
FZD4 variants, rendering FZD4 functionally knocked out. The loss of FZD4 resulted in
the same phenotype as loss of NDP, underscoring the centrality of Norrin ligand binding
to Frizzled-4 receptor in FEVR pathogenesis. Norrin/FZD4 is implicated in retinal
angiogenesis, and with human retinal microvascular endothelial cell assays I determine
that Norrin contributes to morphogenesis but not cell migration. With Norrin/FZD4
signalling implicated in vessel stabilization and barriergenesis, I establish for the first
time the downstream target genes for Norrin/FZD4 signalling at different stages of
development. Norrin/FZD4 signalling is bimodal, with the early response targeted
towards deactivating Notch signalling. Late-stage Norrin activation targets are involved
in formation of junctional complexes to establish the blood retinal barrier. I show the
importance of re-evaluating historic sequencing and variant interpretation. The re-
analysis of a cohort collected over a two-decade period resulted in the identification of
novel variants in FEVR genes. Finally, I demonstrate that FEVR candidate genes should
be carefully evaluated with the up-to-date variant classification guidelines. DVL3 was
identified as a candidate gene in 2019, but after five years of improving technology and
expanding databases, the identified patient-derived DVL3 variants were debunked as
potentially FEVR-causal. All together, these findings have expanded upon the role of
Norrin/FZD4 signalling in retinal angiogenesis.
Description
Keywords
Genetics, FEVR