FTO and obesity due to melanocortin 4 receptor deficiency: As compared to risk-free carriers, active beige adipocytes with FTO obesity-risk genotype had lower expression of these thermogenic genes and also that of the neurotrophic factor S100b, which was postulated to stimulate sympathetic axon growth and to play an important role in BAT innervation (Zeng et al., 2019) (Figures 3A–K).