The long form of the leptin receptor (Ob-Rb) is present in human platelets and can be related to platelet activation by a specific pathway downstream of leptin-induced Janus kinase 2 (JAK2) activation including PI3-K and phospholipases Cγ2 and A2, which influence cAMP hydrolysis, GPIIb/IIIa expression, and thromboxane synthesis [241]: these findings induced to consider circulating plaletets as a major target of leptin action, suggesting a possible direct link between obesity and thrombotic complication [241, 242]. The gene discussed is JAK2; the disease is obesity due to melanocortin 4 receptor deficiency.