Will a reduction in tau protein in brain neurons protect against Parkinson’s disease and Lewy body dementias? A new study suggests the answer is no. If this is borne out, that result differs from Alzheimer’s disease, where reducing endogenous tau levels in brain neurons is protective for multiple models of the disease — and thus suggests that the role of tau in the pathogenesis of Lewy body dementias is distinct from Alzheimer’s disease.