Increased levels of α-synuclein or α-synuclein containing protein aggregates are not only a hallmark of PD but are characteristic for a whole group of neurodegenerative diseases including dementia with Lewy bodies (DLB), multiple system atrophy (MSA), Alzheimer’s disease, different forms of neurodegeneration with brain iron accumulation and others [3, 6–8]. The gene discussed is SNCA; the disease is early-onset autosomal dominant Alzheimer disease.