GDF5OS (Growth/differentiation factor 5 opposite strand transcript protein) is a 250 amino acid protein that is expressed in mitochondria. The gene encoding GDF5OS maps to human chromosome 20. Comprising approximately 2% of the human genome, chromosome 20 contains nearly 63 million bases that encode over 600 genes, some of which are associated with Creutzfeldt-Jakob disease, amyotrophic lateral sclerosis, spinal muscular atrophy, ring chromosome 20 epilepsy syndrome and Alagille syndrome. Additionally, human chromosome 20 contains a region with numerous genes which are thought important for seminal production and may be potential targets for male contraception.