The majority of PD cases are sporadic, and only 5% to 10% are genetic, caused by either autosomal dominant (e.g., SNCA gene encoding α-synuclein) or recessive (e.g., PARK7 gene encoding DJ1 protein, PINK1 gene encoding phosphatase, and tensin homolog-induced kinase 1) mutations. Here, SNCA is linked to Parkinson disease.