LRRK2 and Parkinson disease: The LRRK2 G2019S mutation is the most common genetic abnormality associated with Lewy body parkinsonism.94 However, a recent study from a consortium that includes our institute found that only two-thirds of patients with LRRK2 G2019S-associated parkinsonism have classic Lewy body PD at autopsy.95 Up to 30% showed focal brainstem degeneration, affecting particularly the substantia nigra and the locus coeruleus; interestingly, this alternative LRRK2 G2019S pathology appears to have a tau-based molecular etiology.