OR4K2 and Alzheimer disease: For example, G protein-coupled receptor activity pathway, including important features (TAS2R20, CNR1, OR4K2, KISS1R, FFAR3, OR2B11, OR13D1, OR6Q1 and GPRC5C), is essential in neurodegenerative diseases such as AD and Parkinson’s disease (Wong et al., 2023; Schöneberg et al., 2004; Guimaraes et al., 2021).