BRD2 and obesity due to melanocortin 4 receptor deficiency: Based on own previous studies with dietary intervention and a normal weight control group [16, 17] and a study by Li et al. [18], our general assumption is that NAT availability as a marker of the central noradrenergic tone significantly decreases with reduction in BMI from severe (BMI > 35 kg/m2) to moderate obesity (BMI 30–35 kg/m2) but increases with reduction from moderate obesity to normal body weight (BMI 18.5–25 kg/m2) describing a U-shaped curve, specifically in the hypothalamus, the insula, and the prefrontal brain area.