Variants in NUS1 are associated with a congenital disorder of glycosylation, developmental and epileptic encephalopathies, and are possible contributors to Parkinson disease pathogenesis. How the diverse functions of the NUS1-encoded Nogo B receptor (NgBR) relate to these different phenotypes is largely unknown. We present three patients with de novo heterozygous variants in NUS1 that cause a complex movement disorder, define pathogenic mechanisms in cells and zebrafish, and identify possible therapy.
Comprehensive functional studies were performed using patient fibroblasts, and a zebrafish model mimicking NUS1 haploinsufficiency.
We show that de novo NUS1 variants reduce NgBR and Niemann–Pick type C2 (NPC2) protein amount, impair dolichol biosynthesis, and cause lysosomal cholesterol accumulation. Reducing nus1 expression 50% in zebrafish embryos causes abnormal swim behaviors, cholesterol accumulation in the nervous system, and impaired turnover of lysosomal membrane proteins. Reduction of cholesterol buildup with 2-hydroxypropyl-ß-cyclodextrin significantly alleviates lysosomal proteolysis and motility defects.
Our results demonstrate that these NUS1 variants cause multiple lysosomal phenotypes in cells. We show that the movement deficits associated with nus1 reduction in zebrafish arise in part from defective efflux of cholesterol from lysosomes, suggesting that treatments targeting cholesterol accumulation could be therapeutic.
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Data and code availability
All variants described in this study have been deposited in ClinVar; accession numbers are VCV000981036, VCV000981034, VCV000981035 (Submission ID: SUB8124960; Organization ID: 1019).
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We acknowledge the patients and their families for their willingness to participate in this study. This work was supported by the Greenwood Genetic Center and grants from the National Institutes of Health (5R01-GM086524-11 to R.S. and H.F-S; AI108819 to M.B.C). We acknowledge the support of the Hazel and Bill Allin Aquaculture Facility housed at the Greenwood Genetic Center and thank the facility staff for their excellent animal care.
Informed consents were signed by the parents of the proband and other patients prior to participation in the research. All procedures were employed after being reviewed and approved by the Institutional Review Board, and compliant with practices, at the Greenwood Genetic Center (GGC). Handling and euthanasia of fish complied with policies of the GGC, as approved by the GGC’s Institutional Animal Care and Use Committee (permit #A2019-01-003-A1).
The authors declare no competing interests.
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Yu, SH., Wang, T., Wiggins, K. et al. Lysosomal cholesterol accumulation contributes to the movement phenotypes associated with NUS1 haploinsufficiency. Genet Med 23, 1305–1314 (2021). https://doi.org/10.1038/s41436-021-01137-6