On the other hand, key metabolic genes were found downregulated in BC tissue samples, including genes related to: (1) pyruvate metabolism: pyruvate dehydrogenases (PDHA1, PDHB, PDHX) and pyruvate dehydrogenase kinase 4 (PDK4); (2) TCA cycle: FH, IDH3A, IDH3B, MDH1, MDH2, ACO1, OGDH and SUCLG1; (3) polyamine metabolism: AMD1, SMS, ODC1, SAT2, AOC3; (4) AA metabolism: GLS, GOT2, MUT, ASS1, MAOA, MAOB; (5) redox status: peroxidases, catalase, superoxide dismutase, and glutaredoxin. The gene discussed is MDH2; the disease is breast cancer.