I have POTS but most of my symptoms seem to have started after I had clotting problems. I had a DVT in Feb 2007, 2 PEs in Feb 2007, and another DVT in March 2007. My hematologist has tested me for a bunch of clotting abnormalities but everything has come up negative. There are 2 that she has not tested me for because I would have to be off Coumadin to test. However, her opinion is that I have a yet-to-be-discovered clotting abnormality. Of course, many of the clotting problems they know about today were unknown 10 years ago. In order to answer your questions, I have a couple questions for you. Do you know what the name of the clotting abnormality your siblings have is? What drug is your sister taking to prevent clotting currently? What has she taken in the past?