Mutations in the LRRK2 locus are the most common cause of inherited PD, particularly the G2019S substitution mutation in LRRK2. Histological examinations of post-mortem brain tissues of PD patients with LRRK2 mutations, including those with G2019S mutations, show neuronal loss in the SN, and nearly half of the post-mortem brain tissues exhibit α-synucleinopathy (Ross et al., 2006). This evidence concerns the gene LRRK2 and Parkinson disease.