LEP and obesity due to melanocortin 4 receptor deficiency: The authors concluded that an elevated BMI in patients with narcolepsy could be related to neuroendocrine abnormalities related to the condition rather than to HLA-DR2 antigen or narcolepsy medications [36], as the prepro-orexin gene is downregulated in mice with hereditary obesity due to multiple leptin system abnormalities, suggesting that orexins play a role in endocrine systems [37].