GFAP and obesity due to melanocortin 4 receptor deficiency: The molecular weights of NfL (61.5 kDa35) and GFAP (50 kDa36) are similar to that of albumin (66.5 kDa), and thus, obesity could also lead to relatively higher loss of these proteins in urine, explaining the decreased circulating levels of NfL and GFAP in the obese.