The COG5 gene encodes a protein that forms a part of the Conserved Oligomeric Golgi (COG) complex. This complex, located in the Golgi apparatus, is essential for normal Golgi morphology and function, namely protein modifications such as glycosylation. The complex is specifically involved in the intra-Golgi and ER to Golgi vesicle-mediated transport of proteins, particularly the enzymes responsible for glycosylation. It carries out this function by controlling the tethering of vesicles to the Golgi membrane.
Mutations in the gene can thus have strong pathological consequences. The gene is associated with Congenital Disorder of Glycosylation, Type IIi (CDG2I), a disorder characterized by developmental delay, intellectual disability, brain atrophy, truncal ataxia and hypotonia.