Hunter Syndrome (or Mucopolysaccharidosis/MPS II) is a very rare condition affecting approximately 1 in 166,000 male births. It is an X-linked recessive disorder; thus it occurs almost exclusively in boys. Mothers are either carriers of the defective gene or the genetic mutation can be spontaneous in the embryo.
Hunter Syndrome results from a missing enzyme called iduronate-2 sulfatase which is essential in breaking down certain molecules (known as mucopolysaccharides or gylcosaminoglycans/GAGs) called dermatan and heparan sulphate. The incomplete broken down GAGs remain stored in cells in the body causing progressive damage.
Signs and Symptoms
Signs and symptoms of Hunter Syndrome may include:
- Delayed development, such as late walking or talking
- Behavioral abnormalities similar to attention deficit hyperactivity disorder, autism, obsessive compulsive disorder, and sensory processing disorder
- Loss of previously mastered skills (cognitive regression)
- Lack of a sense of danger
- Aggressive behavior
- Changing facial features, including thickening of the lips, tongue and nostrils
- A broad nose and flared nostrils
- Claw-like hands
- A protruding tongue
- Abnormal bone size or shape and other skeletal irregularities
- Enlarged internal organs, such as the liver and spleen, resulting in a distended abdomen
- Respiratory difficulties including sleep apnea, a condition in which breathing intermittently stops during sleep
- Cardiovascular disorders, such as progressive thickening of heart valves, high blood pressure (hypertension) and obstruction of blood vessels
- Vision damage or loss from degeneration of cells that capture light and buildup of cellular debris in the brain causing pressure on the optic nerve and eye
- Progressive loss of hearing
- Stunted growth
- Joint stiffness
- Explosive diarrhea
- Carpal tunnel syndrome
- Pebbly, ivory-colored skin lesions
The majority of patients with Hunter Syndrome are affected both physically and mentally, although its effects are different in every child. Generally, cognitive development slows between ages 2 and 5 and then regresses after that, with loss of previous abilities. Even for those without cognitive regression, the physical effects of the disease are severe and life-limiting and they may also experience certain cognitive impairments, such as in attention span.
Unrelated children with Hunter Syndrome often look alike and have a distinctive coarseness in their facial features, including a prominent forehead, a nose with a flattened bridge, and enlarged lips and tongue. They may also have a large head, short neck, broad chest, thick hands, and an enlarged abdomen.
The only FDA-approved treatment for symptoms of Hunter Syndrome is idursulfase (Elaprase), made by Shire plc. Elaprase is not expected to cross the blood brain barrier in significant enough amounts to prevent the cognitive regression that is a part of the severe form of Hunter Syndrome. It involves a recommended weekly infusion of approximately 3-4 hours.
There are several treatments in development that seek to prevent or stabilize the cognitive regression. Some involve a weekly or monthly infusion and some, like gene therapy, contemplate a one-time treatment to address the root cause of the condition – the genetic mutation itself.
Meet Boys with Hunter Syndrome by visiting the Meet Our Dreamers page.