Parkinson's disease (PD) is an etiologically heterogeneous disorder 
characterized by parkinsonism (bradykinesia, resting tremor, rigidity, and 
postural instability) with good response to L-dopa. PD is the second most 
prevalent neurodegenerative disorder after Alzheimer disease. Although the 
majority of PD cases are sporadic, 5-10% of PD is monogenic form of PD as 
familial PD (FPD). Multifactorial genetic-environmental interaction has been 
thought in PD pathogenesis, although these interactions are still poorly 
understood. In 2004, LRRK2 was identified as the causative gene for PARK8 
originally mapped in the large Japanese Sagamihara family with late-onset 
autosomal dominant PD (ADPD). Patients with LRRK2 mutations account for 
approximately 2-13% of ADPD and 0.5-3% of sporadic PD. Genetically, LRRK2 
mutations have been distributed worldwide with some ethnic differences by single 
founder effect such as G2019S, R1441G, and G2385R variants. LRRK2 G2385R was 
reported to be a risk factor for sporadic PD in Asia. Clinically, most patients 
with LRRK2 mutations develop typical idiopathic PD, however, variable clinical 
features and pathologies such as diffuse Lewy body disease, multiple system 
atrophy, progressive supranuclear palsy, and amyotrophic lateral sclerosis have 
been reported. Although Lewy bodies have been considered as a pathological 
hallmark for sporadic PD classically, some FPD and sporadic PD patients with 
heterozygous LRRK2 mutations or homozygous parkin mutations have no Lewy bodies. 
On the other hand, LRRK2 was reported as a component of Lewy bodies. Based on 
the variability, multifunction of LRRK2 such as phosphorylation of other 
proteins, especially, alpha-synuclein and tau, have been suggested. As 
interaction of Parkin and LRRK2 was reported, interaction and intersection among 
the autosomal-recessive or autosomal-dominant PD proteins could be involved in 
some common pathways, and LRRK2 may play an important role as a key FPD gene 
product. Identification of PARK8 and LRRK2 has given meaningful insights in not 
only PD but also numerous neurodegenerative disorders such as synucleinopathies 
and tauopathies with or without Lewy bodies.