C3 and obesity due to melanocortin 4 receptor deficiency: In fact, there is strong evidence suggesting that obesity triggers a chronic low-grade inflammation which is linked to insulin resistance (Żelechowska et al., 2018), while complement C3 appears to be involved in adipose tissue inflammation associated with weight gain and the development of diabetes and non-alcoholic liver disease (Engström et al., 2005a; Engström et al., 2005b; Hertle et al., 2014; Xu et al., 2016).