Pregnancy Zone protein is a 1,482 amino acid secreted protein that belongs to the protease inhibitor I39 family and exists as multiple alternatively spliced isoforms. Expressed predominately in plasma and in late-pregnancy sera, Pregnancy Zone protein functions as a disulfide-linked homotetramer that is able to trap and inhibit proteinases, thus playing a role in the regulation of protein splitting and small peptide formation. The gene encoding Pregnancy Zone protein maps to human chromosome 12, which encodes over 1,100 genes and comprises approximately 4.5% of the human genome. Chromosome 12 is associated with a variety of diseases and afflictions, including hypochondrogenesis, achondrogenesis, Kniest dysplasia, Noonan syndrome and Trisomy 12p, which causes facial developmental defects and seizure disorders.