Owing to the fact that serum creatinine is influenced by muscle mass whereas cystatin C has a direct relationship with fat mass [41], additional researches using alternative novel endogenous filtration markers such as beta-trace protein or β2-microglobulin might be needed for better accuracy of GFR estimating equations among people with obesity. This evidence concerns the gene PTGDS and obesity due to melanocortin 4 receptor deficiency.