As the two key enzymes of BCAA oxidation, BCAT and BCKDH (α-keto acid dehydrogenase), are widely expressed in the brain [37], the decrease in BCAA levels detected in the cerebrospinal fluid of HD patients [16] may indicate that BCAA oxidation is also activated in the brain to compensate for the local energy deficit. The gene discussed is PPM1K; the disease is Huntington disease.