Figure 2.

Stepped approach to explore the pathogenesis of sporadic PD. The basic tenet underlying this approach is that subgroups of familial and sporadic PD with similar clinical and pathological phenotypes are likely to share pathogenic mechanisms. (1) Define the spectrum of clinical phenotype, findings of pathological imaging, and genotype in familial monogenic PD. (2) Identify a cluster of sporadic PD, whose clinical phenotype and pathological imaging findings are similar to those of a subtype of familial PD. (3) Epidemiological and clinico-genetic studies are conducted in this relatively homogeneous subgroup of sporadic PD to identify genetic susceptibility factors and gene-environmental interactions.