Hunter’s Syndrome is one of a family of disorders called enzyme deficiencies. Enzymes are special types of proteins required to break down food molecules into fuel during metabolism, the process by which the body gets energy for normal growth and development. Enzyme deficiencies, or the absence of these enzymes, are inherited defects that result in a number of life-changing or life-threatening conditions.
Hunter’s syndrome is an inherited disease in which long chains of sugar molecules (mucopolysaccharides) build up in various body tissues because the enzyme necessary to break them down (iduronate sulfatase) is missing. Boys are most often affected.
Mucopolysaccharides, also known as glycosaminoglycans or GAG, cause significant damage as they accumulate. The early-onset, severe form of the disease is generally diagnosed at about age 2. A late-onset, milder form causes less severe symptoms to appear later in life. While the symptoms of Hunter’s syndrome are generally not apparent at birth, they usually start to become noticeable sometime during the first year of life. The first symptoms of Hunter’s syndrome may include abdominal hernias, ear infections, runny noses and colds. Since these symptoms are quite common among all infants, they are not likely to lead a doctor to make a diagnosis of Hunter’s syndrome right away. As GAG continues to buildup in the cells of the body, signs and symptoms of Hunter’s syndrome become more visible. The physical appearance of many children with Hunter’s syndrome include a distinctive coarseness in facial features, including a prominent forehead, a nose with a flattened bridge and an enlarged tongue. For this reason, unrelated children with Hunter’s syndrome often look alike. They may also have a large head as well as an enlarged abdomen. Many continue to have frequent infections of the ears and respiratory tract.
The continued storage of GAG in cells can lead to organs being affected in important ways. The thickening of the walls of the heart and heart valves can result in progressive decline in cardiac function. The walls of the airway may become thickened as well, leading to breathing problems while sleeping (obstructive airway disease). People with Hunter’s syndrome may also have limited lung capacity due to pulmonary involvement. As the liver and spleen grow larger with time, the belly may become distended, making hernias more noticeable. All major joints may be affected by Hunter’s syndrome, leading to joint stiffness and limited motion. Progressive involvement of the finger and thumb joints results in decreased ability to pick up small objects. The effects on other joints, such as hips and knees, can make it increasingly difficult to walk normally. If carpal tunnel syndrome develops, a further decrease in hand function can occur. The bones themselves may be affected, resulting in short stature. In addition, pebbly, ivory-colored skin lesions may be found on the upper arms, legs and upper back of some people with Hunter’s syndrome. Finally, the storage of GAG in the brain can lead to delayed development with subsequent mental retardation. The rate and degree of progression may be different for each person with Hunter syndrome.
There is a broad range of severity in the symptoms of Hunter syndrome. It is important to note that although the term “mild” is used by physicians in comparing people with Hunter’s syndrome, the effects of even mild disease are quite serious. Two of the most significant areas of variability concern the degree of mental retardation and expected lifespan. Some people who have Hunter’s syndrome are not mentally retarded and live into their 20s or 30s. There are occasional reports of people who have lived into their 50s or 60s.