Hunter syndrome falls in a group of lysosomal storage diseases known as mucopolysaccharidoses of which it is also known as mucopolysaccharidosis type II (MPS II). It is a rare X linked recessive disorder that is found exclusively in males, although sporadic female cases are also found. Hunter syndrome occurs in 1 in 100,000 to 1 in 170,000 males. It is a progressive disorder that affects most of the organs and systems in the body, including central nervous system, eyes, ears, respiratory system, skin, liver, spleen, heart, gastrointestinal system, skeletal system, and joints.
What Is The Life Expectancy Of A Person With Hunter Syndrome?
There are very few studies that have covered the survival and cause of death of patients with Hunter syndrome. The life expectancy of patients with Hunter syndrome has improved in recent times due to early diagnosis, specialist care, proper medical treatment and improvements in multidisciplinary approach. Studies have shown that patients with neurological involvement and cognitive disability have a shorter life span. The patients with milder form show longer survival rate. Patients with severe form do not live post second decade of life and their life expectancy are in the age group 10-20 years. However, patients with milder form of the disease can live a normal life and live up to the fifth and sixth decade of life. The life expectancy in these patients is in the age group 20-60 years. The primary cause of death in both the severe and milder form is due to respiratory problems followed by cardiac disease. In respiratory problems, pneumonia is the leading cause of death, while in cardiac problems is myocardial infarction. (1)
Clinical Presentation Of Hunter Syndrome
Hunter syndrome is further classified into two types, namely MPS II type A and MPS II type B. MPS II type A is the severe form of Hunter syndrome whereas MPS II type B is the milder form of the syndrome. The differentiating factor between the two forms is that in type A neurological involvement is present whereas in type B there is no neurological involvement. Otherwise, most of the other symptoms are similar except the progression in clinical features of type B is slower than type A. Higher degree of morbidity and mortality is associated with MPS II type A.
The classical clinical presentation of Hunter syndrome starts at the age of 2-4 years for severe form whereas for milder form it is delayed by 2 years since progression of the disease course is slower in the milder form. Hunter syndrome typically presents with neurological involvement in severe forms. Physical appearance has typical coarse facial features with large head and broad forehead, short neck, short stature, broad nose, flattened bridge, thick lips, enlarged tongue, thick hair and brows, excessive hair growth in the body, protruded stomach, hepatomegaly, splenomegaly, hernias (inguinal or umbilical), dysostosis complex, kyphosis, recurrent ear infections, hearing loss (conductive, sensorineural or both), papilledema, reduced vision (especially night vision), hydrocephalus, glaucoma, seizures, respiratory problems, recurrent respiratory tract infections, sore throat, rhinorrhea, sinus infections, cough, cold, throat infections, snoring, sleep apnea, and dysphagia.
Other clinical features include carpal tunnel syndrome, spinal stenosis, heart valve abnormalities, myocardial infarction, ventricular hypertrophy, cardiac failure, joint deformities, joint stiffness, stiff gait, spacing between teeth, malformed teeth with thin enamel, enlargement of gums, skin changes including pebbled skin appearance, Mongolian spots.
Treatment Of Hunter Syndrome
Hunter syndrome is treated after the definitive diagnosis with the help of urine test and blood test. Urine test will show elevated levels of mucopolysaccharides indicating mucopolysacchridoses. Blood test is the definitive test for Hunter syndrome, which will show deficient or very low levels of iduronate sulfatase enzyme and elevated levels of heparan sulfate and dermatan sulfate.
The treatment of Hunter syndrome is IV enzyme replacement therapy, which is quite effective for managing physical symptoms; however, the cognitive symptoms still persist and worsen with time. Physical therapy, speech therapy and other habilitation programs assist in improving the quality of life of patients with Hunter syndrome.