Mucopolysaccharidosis type II (MPS II), also known as Hunter Syndrome, is an X-linked recessive lysosomal storage disease that severely affects many different parts of the body. The estimated incidence of MPS type II is approximately 1 in 110,000 to 1 in 170,000 males. The deficiency of the lysosomal enzyme iduronate sulfatase is the cause of this condition, while its manifestations result from massive accumulation of glycosaminoglycans in the cell.
Patients with MPS II appear healthy at birth, with initial symptoms appearing between 18 months and 4 years of age. They develop full lips, large rounded cheeks, a broad nose, and macroglossia. The vocal cords also enlarge, which results in a deep, hoarse voice. Narrowing of the airway causes frequent upper respiratory infections and sleep apnea. There are two types of MPS II; type A (severe) and type B (mild). Patients with type A MPS II also manifest a decline in intellectual function and a more rapid disease progression, and they begin to lose basic functional skills between the ages of 6 and 8. The life expectancy of these patients is 10 to 20 years. Patients with type B MPS II also have a shortened lifespan, but they have normal intelligence.
Mutations in the IDS gene, located on Xq28 chromosome, are the cause of MPS II. It encodes a lysosomal enzyme called iduronate sulfatase (I2S), which is essential in glycosaminoglycans (GAGs) degradation of heparan sulfate and dermatan sulfate. Mutation in this gene leads to the accumulation of dermatan and heparan sulfate within the cells, resulting in the eventual damage or destruction to almost every system of the body.