Mucopolysaccharidosis Type II (Hunter Disease)

Hunter Disease, also known as Mucopolysaccharidosis Type II, is inherited in an X-chromosome-coupled recessive manner. It belongs to lysosomal storage diseases. 

Causes and Pathophysiology

Due to a deficiency in the activity of the enzyme iduronate sulphatase (one of the enzymes in lysosomes), there is an accumulation in cells and tissues of undegraded substrates: mucopolysaccharides, also known as glycosaminoglycans or GAGs. This results in organ changes and organ failure. Symptoms appear in childhood. 

Forms of Hunter Syndrome

Two forms of the disease are known and described: one with involvement of the nervous system and mental retardation (more common and severe) and one without changes in the nervous system but with somatic changes still present (less common and milder).

Symptoms and Diagnosis

Mucopolysaccharidosis Type II mainly affects boys. Women remain asymptomatic carriers of the defective gene, although isolated cases of MPS 2 are also known to occur in them. 

The clinical somatic manifestations of Hunter’s Disease are similar across the MPS spectrum, but MPS 2 does not have the corneal opacity of MPS1. The essence of Hunter Syndrome is the absence or defect of iduronate sulfatase, an enzyme that is responsible for the synthesis of mucopolysaccharides, also known as glycosaminoglycans or GAGs. 

Consequently, mucopolysaccharides accumulate in the organs and lead to organ failure. 

Treatment and Prognosis of Hunter Disease

The treatment available for this type of mucopolysaccharidosis is based on the administration of the missing exogenous enzyme via the intravenous route in order to alleviate the somatic symptoms present.

Hunter Disease is one of the most common mucopolysaccharidoses whose incidence in Europe is 1: 140-150,000 live births. The life expectancy of the patient depends on the form of the disease.