Biochemical and structural characterization of LRRK2 and/or related Roco proteins can give important information about the dimerization mechanism, how the kinase domain regulates GTPase activity, how LRRK2 activity is regulated by binding of input or substrate to the LRR and WD40 domains, and how the PD mutations influence the complex regulatory mechanism. The gene discussed is LRRK2; the disease is Parkinson disease.