Three of the genes quoted at the OMIM database were associated with mtDNA depletion (OMIM: Phenotypic Series—PS603041, mitochondrial DNA depletion syndrome) have been reported in isolated single cases to date (SCL25A21 [38], SCL25A10 [39] and MRM2 [46]), and for two of these, the reported degree of mtDNA depletion is mild (SCL25A10 and MRM2). The gene discussed is MRM2; the disease is mitochondrial DNA depletion syndrome.