In-House Targeted Gene Sequencing Reveals Rare Variants Linked to FEVR, Norrie Disease and Persistent Fetal Vascular Syndrome
Vincent Le1,2, Savyo Krikor1, Wendy A. Dailey1, Kimberly A. Drenser MD, PhD1,3, Kenneth P. Mitton PhD1,2
1. Eye Research Institute, Pediatric Retinal Research Lab, Oakland University, Rochester, MI
2. Oakland University William Beaumont School of Medicine, Rochester, MI
3. Associated Retinal Consultants, Royal Oak, MI
Introduction
Familial Exudative Vitreoretinopathy (FEVR), Norrie Disease (ND), and Persistent Fetal Vascular Syndrome (PFVS) belong to a family of retinopathies that are often present at birth and are associated with irregular development of the retinal microvasculature and subsequently decreased vision1. All three conditions have been linked to variants in the NDP gene located on the X chromosome, which encodes for Norrin — the ligand for the Frizzled-4 Wnt receptor2. FEVR has been linked to variants in at least 7 genes (NDP, FZD-4, LRP-5, TSPAN-12, ZNF408, CTNNB1, KIF11), and sequencing of affected patients suggests that it is a multigenic condition with incomplete penetrance 3,4. Custom, targeted, next generation sequencing panels can play a significant role in identifying novel variants in a way that is efficient and economical, which ultimately benefits the patient, researchers, and clinicians involved in their care.
Figure 1. Roles of NDP, FZD-4, LRP-5, TSPAN-12, ZNF408, CTNNB1, and KIF11 in the cell4. NDP, FZD-4, LRP-5, and TSPAN-12 make up the canonical Wnt-signaling complex, while ZNF408, CTNNB1, and KIF11 encode a zinc-finger transcription factor, ß-catenin, and kinesin motor protein, respectively. (From graphical abstract 4 , Le et al., 2023)
Methods
Results and Discussion
References and Support
Figure 3. Novel/rare likely pathogenic variants in NDP. The likely pathogenic variants identified in NDP are highlighted in the context of NDP’s functional domains. Variants are labelled with their corresponding patient ID found in Figure 2. The cysteine knot domain is a highly conserved region of NDP, and variants that affect this motif have been associated with more severe clinical presentations1.
1) Arg37Ter. An early stop codon renders the Norrin protein non-functional, and subsequently, this variant is likely the cause of the patient’s ND. 2) Met32TrpfsTer9. A novel frameshift variant results in a premature stop codon, also rendering the Norrin protein nonfunctional. This is likely the driving factor behind this patient’s PFVS. 3) Leu13_Met19del. This novel seven amino acid deletion occurs within the ”signal peptide” domain of NDP. This variant may affect the protein’s extracellular transport out of Müller cells, thus impacting its impact on the retinal vasculature during early development.
3)
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4,5)
Figure 4. Novel variant of unknown significance in ZNF408. The variant identified in ZNF408 is highlighted in the context of ZNF408’s functional domains. The variant is labelled with its corresponding patient IDs found in Figure 2.
4,5) Ser225Phe. This variant does not fall in any of the major domains of ZNF408.
Support
Work supported by grants from:
Pediatric Retinal Research Foundation (KPM), Carls Foundation (KPM)
Figure 2. Results of sequencing run. Out of 20 patients sequenced, 16 presented with variants resulting in missense, in-frame insertions, in-frame deletions, or premature stop codons. Diagnoses were provided by physicians at Associated Retinal Consultants, PC. Two patients with ND and PFVS (1,2) presented with rare variants resulting in early termination codons in NDP, and another patient with ND (3) presented with a novel in-frame deletion in NDP. A young female diagnosed with FEVR (5) was found to have a novel missense variant in ZNF408. Her father (4), who is not a patient but agreed to sequencing, shares the same variant.
Conclusion