Previously identified non-GFR-related factors such as inflammation, obesity [17], insulin resistance [35, 36], oxidative damage [37], growth hormone [38], thyroid hormone [39] and glucocorticoids [10] have all instead been linked to increased cystatin C production and thus an underestimation of GFR. Here, GH1 is linked to obesity due to melanocortin 4 receptor deficiency.