The serum level of several bone-derived mediators has been found modulated in patient affected by bone diseases, as osteoporosis, but also in the case of neurodegenerative diseases, such as AD [e.g., OCN, OPN, sclerostin (Yuan et al., 2019), Dkk-1 (Huang et al., 2018), and lipocalin 2 (Song and Kim, 2018)] and PD [e.g., bone morphogenic protein 2 (Goulding et al., 2020), OCN (Shan et al., 2019)]. The gene discussed is DKK1; the disease is Alzheimer disease.