In previous reports, serum SIRT1 (s120S) was consistently decreased with aging,17 and there was an accelerated reduction of serum SIRT1 in neurologic disorders such as Alzheimer’s disease,16 as well as in frailty18 and obesity,19, 20 all of which suggest that serum SIRT1 may be a potential biomarker for various aging-associated diseases. Here, SIRT1 is linked to obesity due to melanocortin 4 receptor deficiency.