P2RX5 and obesity due to melanocortin 4 receptor deficiency: A novel and interesting feature of the inflammatory response present in obesity is that it seems to start and reside within the adipose tissue [29,30,31,32] and it has been previously demonstrated that adipocytes can produce a number of different inflammatory cytokines [19]; since its first classification as a mediator of cell-to-cell communications, ATP and its purinergic receptors have been shown to be involved in the complex series of events initiating inflammation [33,34].