Hyaluronidase-1 (HYAL1) is a secreted lysosomal hyaluronidase that belongs to the glycosyl hydrolase 56 family. HYAL1 contains one EGF-like domain and is highly expressed in the liver, kidney, and heart, but it is weakly expressed in the lung, placenta, and skeletal muscle. HYAL1 is thought to be involved in cell proliferation, migration, and differentiation. It may play a role in promoting tumor progression and blocking the TGFB1-enhanced cell growth. Mutations in HYAL1 are associated with mucopolysaccharidosis type IX, or hyaluronidase deficiency.