LRRK2 mutation is the most prevalent cause of familial PD and happens in ~1% of sporadic PD.252 LRRK2 is expressed at low level in resting neuronal cells, including neurons, microglia, and astrocytes, but its expression is upregulated in neuronal cells and many immune cells (i.e., monocytes, macrophage, T cells, B cells) after stimulation by pro-inflammatory mediators, such as TNFα, IFNβ, IL-6, IFN-γ and LPS.253 LRRK2 has been found to promote neuron death and enhance immune response.254 So far, eight LRRK2 genetic variants have been identified in PD patients. Here, LRRK2 is linked to Parkinson disease.