The PPMI study sample now enables demonstration that asyn-negative LRRK2 parkinsonism cases are much more likely to be normosmic.4 One possible explanation for these findings is the preferential susceptibility of olfactory bulb52 and anterior olfactory nucleus53,54 cells to asyn pathology, as evidenced by data from animal models. This evidence concerns the gene LRRK2 and Parkinson disease.