– Probable Xaa-Pro Aminopeptidase 3 (XPNPEP3) is a member of the peptidase M24B family. XPNPEP3 has two isoforms and both are widely expressed. XPNPEP3 is localized in the Mitochondrion. XPNPEP3 catalyzes the release of any N-terminal amino acid, including proline, that is linked to proline, even from a dipeptide or tripeptide. Defects in XPNPEP3 are the cause of nephronophthisis-like nephropathy type 1 which is a disorder with features of nephronophthisis, a cystic kidney disease leading to end-stage renal failure.