LRRK2 and Alzheimer disease: It has been shown that heterozygous mutations of the AD genes, including SNCA (PARK1and4), LRRK2 (PARK8), VPS35 (PARK17), and CHCHD2 (PARK21), result in various cellular impairments, involving dysfunction of mitochondria, ubiquitin-proteasome system, and autophagy in aging, leading to late-onset PD (Figure 1(b)).