HBD and obesity due to melanocortin 4 receptor deficiency: A study by Wang et al. found 32 differentially expressed genes (DEGs) that were upregulated in the higher BMI twins including DEGs associated with obesity (e.g. NAMPT, TLR9, PTGS2, HBD, and PCSK1N), immunological (e.g., TLR9), and metabolic functions (e.g., PTGS2).