Pathological protein aggregates, such as α-synuclein in Parkinson’s disease, β-amyloid and tau in Alzheimer’s disease, and misfolded superoxide dismutase 1 and transactive response DNA-binding protein 43 in amyotrophic lateral sclerosis, further aggravate mitochondrial stress, establishing self-perpetuating cycles of neurotoxicity. The gene discussed is SOD1; the disease is Parkinson disease.