SIRT3 and obesity due to melanocortin 4 receptor deficiency: Interestingly, overweight subjects showed lower SIRT3 and SIRT6 mRNA levels than normal-weight subjects; no differences in SIRT1 or SIRT6 levels were observed between obese and overweight subjects; the obesity group exhibited the highest expression, while overweight subjects showed the lowest expression of SIRT2 (103).