β-ureidopropionase deficiency mimicking Leigh syndrome associated with methylmalonic aciduria

variants, and urinary analysis confirmed marked elevation of pyrimidine degradation metabolites, establishing the diagnosis of βUP deficiency.This case expands the clinical and neuroradiological spectrum of βUP deficiency and identifies elevated urinary MMA as a previously unreported finding in this disorder. Given the widespread availability of urinary organic acid analysis, MMA may represent a possibly useful and accessible biomarker to support diagnosis. βUP deficiency should be considered in the differential diagnosis of children with Leigh-like encephalopathy and unexplained MMA elevation.