The causative gene product of pyogenic arthritis, pyoderma gangrenosum, and acne (PAPA) syndrome is proline-serine-threonine phosphatase-interacting protein 1 (PSTPIP1) (also called CD2-binding protein 1 (CD2BP1)) [124, 125]. The gene discussed is PSTPIP1; the disease is pyoderma gangrenosum.