Bi-allelic LoF NRROS Variants Impairing Active TGF-β1 Delivery Cause a Severe Infantile-Onset Neurodegenerative Condition with Intracranial Calcification.

Negative regulator of reactive oxygen species is a leucine-rich repeat-containing protein that uniquely associates with latent transforming growth factor beta-1 (TGF- β1) and anchors it on the cell surface; this anchoring is required for activation of TGF-β1 in macrophages and microglia. We report six individuals from four families with bi-allelic variants in All affected individuals had neurodegenerative disease with refractory epilepsy, developmental regression, and reduced white matter volume with delayed myelination. The clinical course in affected individuals began with normal development or mild developmental delay, and the onset of seizures occurred within the first year of life, followed by developmental regression. Intracranial calcification was detected in three individuals. The phenotypic features in affected individuals are consistent with those observed in the Nrros knockout mouse, and they overlap with those seen in the human condition associated with TGF-β1 deficiency. The disease-causing variants involve two significant functional NRduanyu1670 domains. These variants result in aberrant NRduanyu1670 proteins with impaired ability to anchor latent TGF-β1 on the cell surface. Using confocal microscopy in HEK293T cells, we demonstrate that wild-type and mutant NRduanyu1670 proteins co-localize with latent TGF-β1 intracellularly. However, using flow cytometry, we show that our mutant NRduanyu1670 proteins fail to anchor latent TGF-β1 at the cell surface in comparison to wild-type NRduanyu1670. Moreover, wild-type NRduanyu1670 rescues the defect of our disease-associated mutants in presenting latent TGF-β1 to the cell surface. Taken together, our findings suggest that loss of NRduanyu1670 function causes a severe childhood-onset neurodegenerative condition with features suggestive of a disordered response to inflammation.

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