The present invention relates to a ubiquinone-independent cytoplasmic DHODH (DHODH), and/or to a nucleic acid molecule comprising a nucleotide sequence encoding the ubiquinone-independent DHODH, and/or to a recombinant expression vector comprising the nucleic acid molecule comprising the nucleotide sequence encoding the ubiquinone-independent DHODH for use as medicament or rather for use in the treatment of mitochondrial diseases. Such mitochondrial diseases are associated with a defective functional link between the pyrimidine de novo biosynthesis and the mitochondrial OXPHOS and are accompanied with pyrimidine auxotrophy. According to the present invention, such pyrimidine auxotrophy is rescued by xenoexpression of a simple single-protein enzyme, i.e. of a DHODH from other eukaryotic species, which is ubiquinone-independent so that the pyrimidine de novo biosynthesis is not linked to the mitochondrial OXPHOS.
