GRM5 and Huntington disease: Plenty of studies have found that mGluR5 participates in the development and progression of neurodegenerative diseases, including Alzheimer’s disease (AD) (Abd-Elrahman and Ferguson, 2021), Parkinson’s disease (PD) (Zhang et al., 2019), and Huntington’s disease (HD) (Ribeiro et al., 2014).