PNPLA2 and obesity due to melanocortin 4 receptor deficiency: BAT ‘whitening’ and decrease of its activity have been described in obesity, during adaptation to thermoneutral conditions, or due to leptin receptor deficiency, β-adrenergic signaling impairment or deficiency of adipose triglyceride lipase (ATGL; officially known as PNPLA2) (Kotzbeck et al., 2018).