Prostaglandin-H2 D-isomerase, also known as PTGDS, is a glutathione-independent prostaglandin D synthase that catalyzes the conversion of prostaglandin H2 (PGH2) to postaglandin D2 (PGD2). It is likely to play important roles in both maturation and maintenance of the central nervous system and male reproductive system. PTGDS is the most abundant protein in the cerebral spinal fluid and recent evidence suggests that PTGDS acts as a beta-amyloid chaperone and may have a role in the deposition of Ab plaques in Alzheimer’s disease.