Novel biallelic variants in NRROS associated with a lethal microgliopathy, brain calcifications, and neurodegeneration

Negative regulator of reactive oxygen species (NRROS) is a leucine-rich repeat protein expressed by microglia and perivascular macrophages. To date, 9 individuals have been reported with biallelic NRROS variants. Here, we report one individual with a severe neurodegenerative phenotype in which exome sequencing identified 2 novel variants in NRROS , a missense variant (c.185T>C, p.Leu62Pro) and a premature stop codon (c.310C>T, p.Gln104Ter). Pathological examination revealed both extensive grey and white matter involvement, dystrophic calcifications, and infiltration of foamy macrophages. This is the first reported case of NRROS variants with a mitochondrial ultrastructure abnormality noted on electron microscopy analysis of post-mortem tissue.