COG4 is a component of the conserved oligomeric Golgi (COG) complex, an octameric protein complex essential for normal Golgi function and intra-Golgi trafficking of glycosylation enzymes 1. COG4 plays critical roles in SNARE-pin assembly and Golgi-to-ER retrograde transport through interaction with SCFD1 2. The protein's C-terminal domain stabilizes the complex via a salt bridge network centered at Arg729, which is essential for proper glycosylation of cell surface proteins despite not being required for COG complex incorporation 3. COG4 mutations cause two distinct disease entities. Biallelic mutations cause congenital disorder of glycosylation type 2J (CDG-2J), characterized by neurological, skeletal, and hepatic abnormalities 1. The recurrent heterozygous COG4 p.Gly516Arg substitution causes Saul-Wilson syndrome, a primordial dwarfism with spondyloepimetaphyseal dysplasia, microcephaly, facial dysmorphism, and skeletal abnormalities 4. This mutation disrupts vesicular trafficking equilibrium, causing decreased Golgi volume and selective impairment of proteoglycan secretion, particularly affecting chondrogenic proteins like MMP13 and IGFBP7 5. Growth hormone therapy does not improve stature in affected individuals 6. Ocular manifestations including cataracts, retinitis pigmentosa, and nystagmus have been reported 7.