RETN and obesity due to melanocortin 4 receptor deficiency: In individuals with obesity, adipose tissue—especially visceral fat—acts as an active endocrine organ that secretes various adipokines (e.g., leptin, resistin, adiponectin), pro-inflammatory cytokines (e.g., TNF-α, IL-6), and chemokines (e.g., MCP-1) (60).