The membrane-bound X-prolyl aminopeptidase 2, also known as XPNPEP2, belongs to the peptidase M24B family, and has been reported to associate with Aminopeptidase P (APP) activity. The C-2399A variant in XPNPEP2 is associated with reduced APP activity and a higher incidence of AE-ACEi. APP is a hydrolase specific for N-terminal imido bonds, which are common to several collagen degradation products, neuropeptides, vasoactive peptides, and cytokines. A membrane-bound and soluble form of this enzyme (XPNPEP2) have been identified as products of two separate genes. The translocation disrupts XPNPEP2, which encodes an XaaPro aminopeptidase that hydrolyzes N-terminal Xaa-Pro bonds. XPNPEP2 mRNA was detected in fibroblasts that carry the translocation, suggesting that this gene at least partially escapes X inactivation. XPNPEP2 is a candidate gene for premature ovarian failure (POF).