Why patients with THBD c.1611C>A (p.Cys537X) nonsense mutation have high levels of soluble thrombomodulin?

The mechanism responsible for TM shedding is complex and is not completely understood: higher sensitivity of the TM1-536 to the proteolysis by metalloproteases and a defect of synthesis due to the decreased size of the transmembrane domain might explain the high levels of soluble TM in plasma of the carriers.