NRTN and Parkinson disease: The present study shows that Parkinson’s disease–associated LRRK2 mutation is associated with a significant loss of Nrtn expression in the mouse striatum, likely because of the loss of primary cilia in PV neurons that rely on cilia to produce NRTN in a hedgehog-responsive manner; Gdnf expression in cholinergic interneurons is also decreased in these animals (Khan et al, 2024).