LRRK2 and Parkinson disease: By first identifying differentially expressed genes between four groups of mice (overexpressing wild-type LRRK2, overexpressing G2019S LRRK2, LRRK2-knockout and wild-type mice) and combining them with previously proposed PD marker genes from the literature, a panel of 113 candidate marker genes was assembled and their expression measured for 34 symptomatic PD patients (both wild-type LRRK2 and G2019S LRRK2) and 32 asymptomatic controls using a digital gene expression platform.