HYAL1 and mucopolysaccharidosis type 9: Hyal1 knockout mice also suffer from osteoarthritis9, which is in line with the skeletal alterations seen in humans suffering from mucopolysaccharidosis IX, a HYAL1 deficiency of genetic origin9,10.Some patients with congenital HYAL1 deficiency exhibit juvenile idiopathic arthritis with proliferative synovitis, macrophage infiltration of the synovial membrane, synovial effusion and articular pain11,12.