In line with the current study, increased levels of serum NRG4 in insulin resistance-associated diseases, such as type 2 diabetes (Kang et al., 2016; Chen et al., 2017a; Kurek Eken et al., 2018; Wang et al., 2019c; Kocak et al., 2019) and polycystic ovary syndrome (Kurek Eken et al., 2019; Cao and Hu, 2021) have been reported. Here, NRG4 is linked to polycystic ovary syndrome.