Hunter Syndrome - A Rare Genetic Disorder

Introduction:
Hunter syndrome is a rare genetic disorder that occurs due to a deficiency of an enzyme. It is a Lysosomal storage disease and the deficient enzyme is iduronate-2-sulfatase. As a result the long chain of sugar molecules ( mucopolysaccarides) are not broken down by the body and start to accumulate. The accumulated substrates are heparan sulphate and dermatan sulphate. This syndrome has X linked inheritance and so the boys are mostly affected. It is also known as Mucopolysaccharidosis II.

Clinical Features:
The symptoms of Hunter syndrome are usually not apparent at birth. The signs and symptoms usually start to appear around the age of 18 months. The condition varies from patient to patient with some having only minor problems while others showing very sever problems. The signs and symptoms include:

• Growth delay resulting in a short stature
• Delayed development with late walking.
• Change in facial features like thickening of the lips, tongue and nostrils.
• Aggressive behavior.
• Mental function getting worse over time with intellectual disability.
• Claw like hands
• Abnormal bone size and skeletal irregularities.
• Enlarged internal organs like liver and spleen leading to a distended abdomen
• Abdominal hernias.
• Recurrent ear infections, runny nose and cold.
• Deafness getting worse over time.
• Joint stiffness.
• Cardiovascular disorders like progressive thickening of heart valves leading to impaired heart function, high blood pressure and obstruction of blood vessels.
• Respiratory difficulties.
• Carpal tunnel syndrome.

Diagnosis:
The condition may be suspected by the gradual appearance of the signs and symptoms in young children age 2 to 4 years. Laboratory workup includes enzyme study, genetic testing for a mutation in the enzyme idouronate-2-sulfatase and urine can be checked for substrates heparan sulphate and dermatan sulphate.

Treatment:
There is no permanent cure for Hunter syndrome, but certain options may help delay the disease progression as well as manage and prevent the complications.

• Bone marrow transplantation from a healthy matched donor may help treat some symptoms in milder forms of Hunter syndrome.
• Genetically engineered enzyme can be given to replace the deficient enzyme idouronate-2-sulfatase ,that is given once a week intravenously, this therapy may delay or prevent the symptoms but is still under studies.

Prognosis:
Life expectancy of patients with Hunter syndrome is usually 10-20 years. The complications associated with the condition is mostly the cause of death.