Our results indicating that HAS1 gene expression could be up-regulated by pro-inflammatory cytokine IL-1β, and that obese patients show both elevated levels of HAS1 mRNA in adipose tissue and plasmatic LMW HA supports the notion that increased hyaluronan synthesis is close-related with the inflammatory state in obesity. The gene discussed is HAS1; the disease is obesity due to melanocortin 4 receptor deficiency.