A breakthrough for research on SPX in the context of lipids and carbohydrates occurred in the work of Walewski et al., who showed in 2014 that the amount of circulating SPX in the blood serum decreases under obesity and that the gene encoding this protein is one of the most strongly down-regulated genes in adipose tissue under this pathological condition in humans and mice [6]. This evidence concerns the gene SPX and obesity due to melanocortin 4 receptor deficiency.