A homozygous missense variant in NRROS gene is associated with intracranial calcifications, neurodegeneration, and severe infantile epilepsy syndrome.

Biallelic loss-of-function variants in NRROS (Negative regulator of reactive oxygen species, previously LRRC33) cause a progressive neurodegenerative disorder characterized by early-onset seizures with brain calcifications. To date, 16 affected individuals from 13 unrelated families have been reported for this condition. We describe two siblings from a consanguineous family with this disorder, carrying a homozygous NRROS missense variant (c.1222A>C, p.(Asn408His), NM_198565.3). The mutational spectrum of NRROS disorder is characterized primarily by loss-of-function variants, with only four missense variants identified in affected individuals to date p.(Leu10Pro), p.(Leu62Pro), p.(Leu86Pro), and p.(Asn408His). We characterized these missense variants using silico predictions, molecular modelling and in-vitro cellular localization studies. In silico tools predict that p.(Leu10Pro) alters signal peptide cleavage, while p.(Asn408His) impedes N-linked glycosylation. Molecular modelling suggests that p.(Leu62Pro) and p.(Leu86Pro) variants may destabilize NRROS structure, while p.(Asn408His) interferes with NRROS glycosylation. In-vitro studies overexpressing HA-tagged NRROS wild type and missense variants in HEK293 cells showed altered subcellular distribution patterns for the variant proteins. In summary, we report a homozygous missense variant in NRROS associated with severe infantile epilepsy syndrome with intracranial calcifications, and neurodegeneration.