The invention provides a transgenic non-human animal expressing von Willebrand Factor A1 protein containing at least one mutation selected from the group consisting of: 1263P>S, 1269N>D, 1274K>R, 1287M>R, 1302G>D, 1308H>R, 1313R>W, 1314I>V, 1326R>H, 1329L>I, 1330E>G, 1333A>D, 1344T>A, 1347I>V, 1350T>A, 1370G>S, 1379H>R, 1381T>A, 1385T>M 1391P>Q, 1394A>S, 1397L>F, 1421S>N, 1439L>V, 1442G>S, 1449R>Q, 1466A>P, 1469Q>L, 1472Q>H, 1473V>M, 1475H>Q, 1479S>G, and any combination thereof.