Research indicates that PD is the product of a complex interaction of genetic and environmental factors.[1] Around 15% of individuals with PD have a first-degree relative who has the disease,[2] and 5–10% of people with PD are known to have forms of the disease that occur because of a mutation in one of several specific genes.[64][65] Harboring one of these gene mutations may not lead to the disease; susceptibility factors put the individual at an increased risk, often in combination with other risk factors, which also affect age of onset, severity and progression.[64] At least 11 autosomal dominant and 9 autosomal recessive gene mutations have been implicated in the development of PD. The autosomal dominant genes include SNCA, PARK3, UCHL1, LRRK2, GIGYF2, HTRA2, EIF4G1, TMEM230, CHCHD2, RIC3, VPS35. Autosomal recessive genes include PRKN, PINK1, PARK7, ATP13A2, PLA2G6, FBXO7, DNAJC6, SYNJ1, and VPS13C.