XPNPEP1 and Behcet disease: Recently, adducins have been shown to form ladder-like structures in axons similar to those observed for actin and spectrin.51 Previously, genetic alterations in other components of the actin cytoskeleton have been suggested as risk factors for both BD and SCZ.52 Second, XPNPEP1 is an X-prolyl aminopeptidase that mediates the proteolytic cleavage of the N-terminal amino acid in peptides with proline.