NNMT and osteoporosis: Yu et al. (Yu et al., 2021) and Wang et al. (Wang et al., 2021) found that XIST and HOTAIR are long non-coding RNAs (lncRNAs) with significantly elevated expression in the serum of patients with osteoporosis, and that XIST and HOTAIR acted as ceRNAs (competing endogenous RNAs) to upregulate NNMT expression by adsorbing miR-29b-respectively.