IGF1 and obesity due to melanocortin 4 receptor deficiency: On the other hand, low tissue oxygen tension associated with obesity is likely to upregulate hypoxia-inducible factor-1 (HIF-1) and, together with an exaggerated response to growth hormone and insulin-like growth factor 1 (IGF-1), may contribute to bulky hypertrophic and keloid scarring in susceptible individuals.