Hunter's syndrome, or mucopolysaccharidosis type II, is a rare genetic metabolic disease. Hunter's syndrome is distinguished from other types of mucopolysaccharidosis by a different mode of inheritance that puts the majority of men affected by the disease. What are the symptoms of Hunter syndrome? What is the treatment of patients with mucopolysaccharidosis type II?
Hunter syndrome , i.e.mucopolysaccharidosis type II , tolysosomal storage disease , i.e. disease genetically determined, in which - due to a defect or lack of activity of one of the enzymes - various substances are accumulated in lysosomes (cell organelles containing enzymes that break down many substances). The essence of Hunter's syndrome is the lack or defect of idursonate ultrafatase - the enzyme responsible for the synthesis of mucopolysaccharides, also known as glycosaminoglycans or GAGs. As a consequence, mucopolysaccharides accumulate in organs and lead to their failure.
Hunter's syndrome belongs to the so-called Rare diseases: the incidence is 1 in 150,000 births, mostly boys. According to the data of the MPS Association, in PolandHunter's diseaseaccounts for about 20 percent. all cases of mucopolysaccharidosis.
Hunter syndrome - causes
The disease is caused by a mutation in the gene that controls the production of idursonate. Due to a genetic error, an enzyme that breaks down mucopolysaccharides may not be produced, or an enzyme may be produced that is not capable of breaking down mucopolysaccharides, or does not do it as it should.
Hunter syndrome - inheritance
Unlike other forms of mucopolysaccharidoses, which are inherited autosomal recessively, the inheritance of Hunter syndrome is recessive in nature associated with the X chromosome (the disease gene is located on the X chromosome). This means that the child can receive the defective gene only from the mother. A woman has two X chromosomes: one from her father and one from her mother. On the other hand, a man has one X chromosome, which he inherits from his mother, and one Y chromosome, which he receives from his father. If a woman has one X chromosome with a defective gene towards Hunter's syndrome, and the othernormal, is a he althy carrier of the disease, as the correct gene protects it from the onset of its symptoms. For this reason, Hunter syndrome occurs almost exclusively in boys. If the mother passes on the abnormal gene to her son, he will develop symptoms of the disease because he does not have a second X chromosome to prevent him from activating the disease. If he passes on a he althy gene, the symptoms of the disease will not appear.
Hunter's syndrome - symptoms
There are two forms of the disease: type A, referred to as the classic form, and type B - with a milder course. Type A is dominated by the typical symptoms of mucopolysaccharidosis, such as:
- facial features thickening
- low rise
- changes in joints, with a significant reduction in their mobility
- enlargement of the liver and spleen (hepatosplenomegaly)
- umbilical and inguinal hernias (appear in infancy)
Type A is characterized by significant mental retardation, spinal deformity and severe kyphosis.
In type B, birth defects are less severe: bone changes are milder, and mental retardation is mild or absent.
Symptoms that distinguish Hunter's disease from other types of MPS are skin lesions of small raised lumps located on the arms, shoulder blades and back. In addition, there are no changes typical for mucopolysaccharidosis in the organ of vision in the form of corneal opacity, while damage to the hearing organ is often diagnosed, which is associated with hearing loss or deafness. In the course of Hunter's disease, there is also a discharge of mucous serous secretions from the nose, unrelated to respiratory tract infection. Other symptoms of Hunter's syndrome also include damage to the heart muscle and recurrent respiratory infections.
Hunter syndrome symptoms appear around 2-3. year of the child's life.
Hunter syndrome - diagnosis
In order to diagnose the disease, it is necessary to perform a test that consists in the quantification of mucopolysaccharides in the urine (in the case of mucopolysaccharidosis they are secreted in excess) and determine their type.
Hunter's syndrome - treatment
Only symptomatic treatment of Hunter's syndrome is possible, which consists in rehabilitation and treatment of organ complications. Therapy may also include the administration of an enzyme replacement therapy using a sulfatase iduronate. They are used to inhibit the progression of the disease.
Hunter syndrome - prognosis
The period of survival in the form of the classic Hunter syndrome is approx. 20 years. Survival of people who struggle with type B of Hunter's syndrome,is longer (up to the 3rd or even 4th decade of life).