The human cartilage link protein, also designated HAPLN1, is a member of the hyaluronan and proteoglycan link protein (HAPLN) family of proteins. This family contains 4 proteins with approximately 50% homology. The human cartilage link protein strengthens tissue architecture by using hyaluronic acid to stabilize the aggregates of proteoglycan monomers inside the extracellular cartilage matrix. It is widely expressed in most tissue types except brain tissue where, much like the other human cartilage link protein genes, it is weakly expressed. The HAPLN and the brain-specific CSPG genes, as well as other members of the link module superfamily, appear to have a common ancestral gene origin.