P4HA1 and systemic sclerosis: Amongst the SSc-specific proteins were the protease inhibitor TIMP1 and several involved in collagen modification, including three proline hydroxylases (LEPRE1/P3H1, LEPREL2/P3H3 and P4HA1) and two lysine hydroxylases (PLOD1 and PLOD3), while control-specific proteins included several other protease inhibitors (CSTB, SERPINB10/B2, and SERPINB6)15.