FSTL1 and obesity due to melanocortin 4 receptor deficiency: Although the function of FSTL1 is not completely understood, it has been shown that FSTL1 plays a key role in tumor bone metastasis [8, 9], chronic pain hypersensitivity [10], inflammation and insulin resistance in obesity [11], the regulation of erythropoiesis [12], physical development [13–16], and somatic sensation by binding to Na+,K+-ATPase [17].