Background：17b-HSD13 （17b hydroxysteroid dehydrogenase type 13）, also designated Short-chain dehydrogenase/reductase 9 （SCDR9）, belongs to the 17b-HSD family of proteins, which regulate the availability of steroids within various tissues throughout the body. 17b-HSD13 is a 300 amino acid secreted protein that is highly expressed in liver and is also detected in ovary, bone marrow, kidney, brain, lung, skeletal muscle, bladder and testis. The gene encoding 17b-HSD13 maps to chromosome 4, which houses nearly 6％ of the human genome and has the largest gene deserts （regions of the genome with no protein encoding genes） of all of the human chromosomes.
