AssessmentsMucopolysaccharide storage disease type 2 (Hunter syndrome) (NORD)
Mucopolysaccharide storage disease type 2 (Hunter syndrome) (NORD)
USMLE® Step 1 style questions USMLE
A 3-year-old boy is brought to the clinic by his mother because of aggressive behaviour and a loss of previously acquired motor skills. Physical examination shows distinctive coarse facial features including a prominent forehead, a nose with a flattened bridge, an enlarged tongue, and an absence of corneal clouding. The mother tearfully admits to consuming alcohol during pregnancy. Laboratory studies show an absent level of iduronate-2-sulfatase in his leukocytes. Which of the following is the most likely diagnosis?
Content Reviewers:Rishi Desai, MD, MPH
Hunter syndrome is a rare genetic metabolic disorder that occurs when lysosomal enzymes are absent.
Hunter syndrome is also known as mucopolysaccharidosis type 2.
Mucopolysaccharides or glycosaminoglycans are types of complex sugars, which are produced by the cells and exported to the extracellular space.
Examples include heparan sulfate and dermatan sulfate.
Both heparan sulfate and dermatan sulfate can be found on almost all cell surfaces as well as in the basement membrane, which separates epithelial cells from the connective tissue that lies beneath.
When mucopolysaccharides like heparin sulfate and dermatan sulfate need to get degraded, they are taken over to a lysosome, which contains enzymes needed to break down the mucopolysaccharides.
Each mucopolysaccharide requires multiple enzymes to fully degrade, and some mucopolysaccharides share certain enzymes in common.
For example, both heparan sulfate and dermatan sulfate need the iduronate sulfatase and alpha-L-iduronidase enzymes to get broken down.
Hunter syndrome is caused by a deficiency in iduronate sulfatase, and the result is that heparan sulfate and dermatan sulfate can’t be degraded, so they build up in various tissues.
Hunter Syndrome is an X-linked recessive disorder so it’s more common in males.