NRG4 and diabetes mellitus: Several studies have identified elevated serum Nrg4 levels in patients with diabetes (Kang et al., 2016; Chen et al., 2017b; Kurek Eken et al., 2018; Kocak et al., 2019), while other studies have associated decreased serum Nrg4 levels with an increased risk of diabetes (Zhang et al., 2017; Kralisch et al., 2018; Zhang et al., 2021; Attique et al., 2022; Li et al., 2022).