Several mutations have been found in the leucine-rich repeat kinase 2 gene (LRRK2), encoding the protein dardarin, which are associated with autosomal dominant Parkinson disease. We have previously shown that mutant LRRK2/dardarin is toxic to neurons and neuron-like cell lines in culture and that some mutations are also associated with an inclusion-body phenotype. There is a homologous kinase, LRRK1, which has a similar domain structure but is not known to carry mutations causing Parkinson disease. In the current study, we introduced mutations at equivalent residues in both LRRK2 and LRRK1 to determine their effects in cells. We show that mutations in dardarin are more prone to form inclusion bodies in transfected cells and are more toxic than equivalent mutations in LRRK1. This work suggests that dardarin/LRRK2 is inherently more damaging than LRRK1.