The higher level of Aβ observed in the brain of AD and PD patients, in the ischemic brain and the brain that was subjected to traumatic injury is postulated to be responsible for the alterations of neurotransmission processes including glutamatergic and cholinergic transmission connected with changes of PPAR-α signaling and its role in mitochondrial function. The gene discussed is PPARA; the disease is Parkinson disease.