Hunter syndrome (MPS II, mucopolysaccharidosis II): A genetic metabolic disorder that arises from deficiency of the enzyme iduronate sulfatase, resulting in tissue deposits of molecules called mucopolysaccharides. Hunter syndrome is inherited as an X-linked recessive trait. The characteristic features of Hunter syndrome include dwarfism, bone deformities, a thickened, coarse face, hepatosplenomegaly (enlargement of the liver and spleen) from mucopolysaccharide deposits, cardiovascular disorders from mucopolysaccharide deposits, and deafness. There are two forms of Hunter syndrome: a severe form that causes progressive mental retardation, physical disability, and death before age 20 in most cases; and a mild form in which patients survive to adulthood, are able to reproduce, and have intellect that is impaired minimally, if at all. The gene for the enzyme iduronate sulfatase (deficient in Hunter's syndrome) is on the X chromosome. Also known as mucopolysaccharidosis II and MPS II.