Anti-C9orf99 antibodies enable researchers to detect and measure the C9orf99 antigen in biological samples. This target is a reported synonym of the HSDL2 gene, which encodes hydroxysteroid dehydrogenase like 2. This protein is known to have apparently no steroid dehydrogenase activity. The human version of C9orf99 has a canonical amino acid length of 418 residues and a protein mass of 45.4 kilodaltons, although 2 isoforms have been identified. It is reported to be localized in the peroxisomes of cells and widely expressed in many tissue types. C9orf99 is a member of the Short-chain dehydrogenases/reductases (SDR) protein family.