LRRK2 and Parkinson disease: LRRK2 mutations were originally identified as the causative factor in dominantly inherited forms of PD linked to the PARK8 locus (Paisán-Ruíz et al., 2004; Zimprich et al., 2004) and, more recently, sequence variation at the LRRK2 locus has been associated with an increased risk of developing sporadic PD in genome-wide association studies (Satake et al., 2009; Simón-Sánchez et al., 2009).