SNCA and Parkinson disease: Approximately 5–10% of PD cases are familial and rare dominant familial PD has been linked to the point mutations A53T, E46K, and A30P in α-synuclein (SNCA) on chromosome 4 (Kruger et al., 2001, Polymeropoulos et al., 1997, Zarranz et al., 2004).