Any mitochondrial DNA depletion syndrome in which the cause of the disease is a mutation in the RRM2B gene. The disease is Monarch Disease Ontology identifier MONDO_0012792 (mitochondrial DNA depletion syndrome 8a). Also known as: RRM2B mitochondrial DNA depletion syndrome, mitochondrial DNA depletion syndrome caused by mutation in RRM2B, mitochondrial DNA depletion syndrome type 8a, mtDNA depletion syndrome, encephalomyopathic form with renal tubulopathy.