NRG4 and obesity due to melanocortin 4 receptor deficiency: Our systematic search yielded thirty-one (n = 31) studies reporting the circulating levels of Nrg4 in participants with obesity and MetS (n = 4), NAFLD (n = 4), GDM (n = 7), T2DM (n = 12), and CVD-related disorders (n = 4) (Tables 1–5).