In 15 of 28 patients from this group (Fig. 1c), molecular variants in LS-associated genes, including genes responsible for deficiency of complex I (MTND1, MTND3, MTND5, NDUFV1), complex IV (COX10), complex V (MTATP6), combined OXPHOS defect (EARS2, PARS2, RARS2, RRM2B, SERAC1, SLC19A3), and pyruvate dehydrogenase complex deficiency (DLD, PDHA1) [23] were identified. This evidence concerns the gene RRM2B and Leigh syndrome.