Several studies have confirmed that a large number of genes, such as the apolipoprotein E gene (APOE) in Alzheimer’s disease (AD), α-synuclein gene (SNCA) in Parkinson’s disease (PD), Cu/Zn-superoxide dismutase 1 gene (SOD1) in amyotrophic lateral sclerosis (ALS), and microtubule-associated protein tubulin-associated unit (Tau) gene (MAPT) in frontotemporal dementia (FTD), are pathogenic or risk to diseases. The gene discussed is SNCA; the disease is early-onset autosomal dominant Alzheimer disease.