LRRK2 and Parkinson disease: Although it is unclear whether this upregulation was a direct effect of the LRRK2 transgene or an indirect effect of LRRK2-transgene-induced Parkinson’s-related phenotypes, we propose a dual-hit hypothesis: the LRRK2 transgene has both indirect and direct effects, as a recent study revealed a critical role of LRRK2 in mitochondrial homeostasis [27].