Notably, lipocalin 2 (LCN2), a fat factor that was previously considered to be associated with obesity (Soukas et al., 2000; Lin et al., 2001; Yan et al., 2007) was recently found to exhibit an expression level in osteoblasts that is at least 10 times higher than that in white fat. The gene discussed is LCN2; the disease is obesity due to melanocortin 4 receptor deficiency.