ADAMTS13 and obesity due to melanocortin 4 receptor deficiency: Obesity has also been linked to acquired thrombotic thrombocytopenic purpura induced by ADAMTS13 deficiency.[27,37] While we did not find a significant correlation between BMI and ADAMTS13 activity in our study, low ADAMTS13 activity was found to be a significant predictor of prolonged time to viral clearance, after adjusting for BMI.