TNF and obesity due to melanocortin 4 receptor deficiency: Previous studies showed the relationship between obesity and sphingolipid metabolism.11,12 In addition, obesity is associated with a chronic low-grade inflammation.25 Tumor necrosis factor-α, an inflammatory cytokine, is released from macrophages and adipocytes, and is involved in the increase in Cer level by activating sphingomyelinase.26 In the present study, the total Cer level in the obese group did not increase (Figure 1) and the levels of almost all Cer species did not correlate with obesity parameters (Table 4).