THRB and obesity due to melanocortin 4 receptor deficiency: Thereafter, a second generation of TRβ-selective molecules with 40-fold higher affinity compared to TRα has been characterized, GC-24, whose administration for 45 days (8.5 ng/g body weight per day) protected from diet-induced obesity and metabolic alterations via increased resting metabolic response in BAT and upregulation of thermogenic markers (i.e. PGC1α, UCP1) [103].