Hunter syndrome is a rare X linked inherited disorder of carbohydrate metabolism (mucopolysaccharides). Mucopolysaccharidosis is of type I, type II, type III, type IV, type VI and type VII and mucopolysaccharidosis type II is popularly known as Hunter syndrome. It can be further divided into two types based on the severity and progression of the disease; mucopolysaccharidosis II type A, which is the severe form and mucopolysaccharidosis II type B, which is the milder form known as attenuated form. They can also be termed as early progressive and slowly progressive for severe and attenuated forms, respectively. Since, Hunter syndrome is X linked disorder, it is found exclusively in males; however, in rare cases females be affected by it. Although, there is no permanent cure for Hunter syndrome, the goal of the treatment is to manage the signs and symptoms and improve the quality of life.
Is Hunter Syndrome Fatal?
The development of various complications in Hunter syndrome can be fatal. The highest amount of morbidity and mortality associated with complications in Hunter syndrome include the respiratory and cardiac complications. Respiratory complications can be highly fatal and are associated with maximum death due to obstruction of airways, difficulty in breathing and pneumonia. Mortality related to cardiac complications includes myocardial infarction and cardiac failure. Respiratory and cardiac complications lead to premature death. Patient’s life span is dramatically reduced and patients with type A MPS II die before second decade of their lives. In MPS II B, patients hardly live up to fifth or sixth decade of life and usually die earlier due to respiratory or cardiac complications, despite treatment. (1)
The symptoms of Hunter syndrome can change in severity and progression depending on type A or type B Hunter syndrome. The symptoms do not start at birth, but start at around the age of 2-4 years in type A and 2 years later for type B. The signs and symptoms include coarse facial features, enlarged head, flat nasal bridge, broad nose and flared nostrils, thick lips, enlarged tongue, hoarse voice, stunted growth, skeletal deformities, enlarged stomach due to hepatomegaly and splenomegaly, diarrhea or constipation, pebbled appearance of skin, Mongolian spots, joint stiffness, delayed development.
What Are The Hunter Syndrome Complications?
There are various complications of Hunter syndrome, such as respiratory, cardiac, nervous system, skeletal and connective tissue.
Respiratory Complications have high mortality and morbidity attached to them and they are the leading cause of death in Hunter syndrome. The deposition of mucopolysaccharides can lead to thickening of nasal passages and trachea causing difficulty in breathing. Patients with Hunter syndrome have chronic sinus infections, ear infections, upper respiratory tract infections and pneumonia. Airway obstruction can lead to sleep apnea.
Cardiac Complications are the second leading cause of death in patients with Hunter syndrome. It leads to thickening of heart tissue that can lead to narrowing of aorta and other cardiac vessels elevating blood pressure and secondarily causing pulmonary hypertension. It causes valvular dysfunction, myocardial infarction and heart failure.
Neurological Complications can significantly reduce cognition and mental development of the child. Hydocephalus can secondarily cause symptoms due to intracranial pressure, including seizures, headaches, vision and mental state of the patient. Compression of upper spinal cord leading to fatigue, and weakening of muscles lead to reduced physical activity. Nerve compression can lead to carpal tunnel syndrome. Cognitive problems can lead to hyperactivity, attention deficit, aggressive behavior, and speech and communication problems. Neurological complications develop only in severe form of Hunter syndrome that dramatically reduces the quality of life.
Skeletal And Connective Tissue Complications occur due to deposition of mucopolysaccharides in connective tissue causing abnormality in joints, bone and ligaments. This has various implications, including stunted growth, skeletal deformities, joint stiffness, joint pain and abnormal gait. Group of abnormalities in skeletal system occurs known as dysostosis multiplex, which can lead to abnormality in fingers, arms, legs, ribs, vertebrae, spine, and pelvis. Mucopolysaccharide deposition in soft tissue can lead to umbilical or inguinal hernia.