LRRK2 and Parkinson disease: The precise mechanism by which variations around the LRRK2 gene region contribute to disease risk are not fully resolved, but given that the polymorphisms associated with sporadic PD are in the promoter region of LRRK2, a reasonable hypothesis is that these variants do not change protein structure or function but instead alter expression levels of the gene, although this remains to be formally demonstrated for LRRK2.