Contributor: Gordon K. Klintworth
Mucopolysaccharidosis type II (Hunter syndrome, iduronate 2-sulfatase deficiency, sulfoiduronate sulfatase deficiency, SIDS deficiency, OMIM #309900) is one type of  mucopolysaccharidosis that was first described by the Canadian physician Charles H. Hunter (1873-1955). It is an X-linked recessive syndrome caused by a mutation in the IDS gene, which encodes for iduronate-2-sulfatase. As in mucopolysaccharidosis type I-H and mucopolysaccharidosis type I-S excessive amounts of  heparan sulfate and dermatan sulfate are excreted in the urine, but the proportion of heparan sulfate that is excreted is slightly higher in mucopolysaccharidosis type II. Mucopolysaccharidosis type II resembles mucopolysaccharidosis type I-H clinically, but it is less severe and some cases survive to adulthood. Mental retardation is not always present. The cornea is usually clear, but it sometimes develops a slight haze in older patients or an abnormality is only evident on slit-lamp biomicroscopy. The manifestations of  mucopolysaccharidosis type II include dwarfism, dysostosis multiplex, hepatosplenomegaly and a grotesque facies. Mucopolysaccharidosis type II has been subdivided in two phenotypes: mucopolysaccharidosis type IIA and mucopolysaccharidosis type IIB. Cells within the cornea, iris, ciliary body, sclera have intracytoplasmic vacuoles that contain clear, fibrillogranular or membranous lamellar bodies. A pigmentary retinopathy with loss of photoreceptors and pigment epithelial migration into the retina occurs. The sclera may be thickened, but this is not a constant feature of mucopolysaccharidosis type II. The frequency of the disorder varies in different countries. In Israel it affects 1 in 34,000. In the United Kingdom it affects about 1 in 132,000 male births and it British Columbia 1 in 110,950 live male births are afffected.