Mucopolysaccharidosis II (MPS II, Hunter syndrome, MIM:309900) is an X-linked, recessive genetic disorder which therefore primarily affects males. MPS II was first described in 1917, by Major Charles Hunter (Hunter 1917) and is caused by a deficiency (or absence) of iduronate-2-sulfatase (IDS, MIM:300823), which would normally hydrolyse the 2-sulfate groups of the L-iduronate 2-sulfate units of dermatan sulfate, heparan sulfate and heparin. Without IDS, these GAGs accumulate in the body and are excessively excreted in urine. Although the disease was known since the early 1970s, being the first MPS to be defined clinically in humans, it wasn't until the 1990s that IDS was cloned. It is now known to be localized to Xq28 (Wilson et al. 1991) and contain 9 exons (Flomen et al. 1993) spanning approximately 24 kb (Wilson et al. 1993).
Build up can occur in the liver and spleen as well as in the walls and valves of the heart (reduced hepatic and cardiac function, liver/spleen hepatosplenomegaly), airways (leading to obstructive airway disease), all major joints and bones (joint stiffness and skeletal deformities) and in brain (severe mental retardation). The rate of progression and degree of severity of the disorder can be different for each person with MPS II. Severe forms of the disorder can result in death in childhood whereas those with a "milder" form can expect to live to their 20's or 30's. Some patients even survive into their fifth and sixth decades of life (Wraith et al. 2008, Beck 2011).