NRG4 and obesity due to melanocortin 4 receptor deficiency: A cross-sectional study that included 1,212 patients with obesity found significantly lower serum Nrg4 levels in patients with metabolic syndrome (MetS) compared to normal controls, and circulating Nrg4 levels were negatively correlated with waist circumference and body mass index (BMI), although no significant differences in Nrg4 expression were found in overweight/obese patients (Cai et al., 2016).