These studies have shown that obesity and excess body fat mass are related to the activation of serine/threonine kinase and lead to inhibition of insulin receptor signaling through phosphorylation of insulin receptor substrate (IRS-1); this process is the main mechanism of insulin resistance and metabolic disorders (https://www.hsph.harvard.edu/gsh-lab/research/inflammation/). Here, IRS1 is linked to obesity due to melanocortin 4 receptor deficiency.