ACE2 and obesity due to melanocortin 4 receptor deficiency: In particular for obesity, the most remarkable risk factor in COVID-19, particularly among those below 50 y/o, multiple mechanisms have been proposed to justify the severity of COVID-19, including multiple sites of disruption in the RAAS system, ACE2 expression and activity, associated to an imbalance towards the hypertensive and pro-inflammatory angiotensin II- AT1 axis observed in obese subjects.