SERPINE1 and obesity due to melanocortin 4 receptor deficiency: Moreover, a recent observational study done in inhabitants of Tromsø, Norway (cases = 383, controls = 782) found that PAI-1 increased the risk of future VTE, and that PAI-1 mediated ~ 15% of the obesity-VTE relationship [66], a number comparable to our MR estimate (18.6%).