This is a lysosomal storage disorder that affects several parts of the body that occur when the lysosomes of the cell cannot effectively break down various types of complex sugars. As the result, it can accumulate in cells throughout the body causing the symptoms associated with this condition. This disease can affect individuals differently ranging from severe to less severe with varied symptoms and long-term outcome. The severe form of this disease is often known as Hurler syndrome and the milder form is called Scheie syndrome. Among the infants with this condition, the early detection and initiating the treatment can prevent or in some cases delay the severe health outcomes. The severe form of MPS is estimated to affect around 1 in 100,000 newborn infants.
Causes
This develops as the result of the mutations in the gene identified as IDUA which produces an enzyme that is necessary for the breakdown of sugar molecules known as glycosaminoglycans (GAGs). A genetic mutation in this gene affects the normal production of reduced function of the IDUA enzyme. The deficit of the functional enzymes causes the accumulation of GAGs within the cells particularly inside the structure known as lysosomes in the cell that is responsible for the digestion and recycling different types of molecules. As the result of the accumulation of GAGs, various organs and tissues of the body also become enlarged. This condition is inherited in an autosomal recessive pattern meaning both the copies of the gene in each cell are defective.
Symptoms
Infants born with this disease often appear to be normal at birth but may present umbilical hernias. The condition usually becomes evident between 6 and 24 months of age presenting coarse facial features, enlarged spleen or liver, a large tongue, skeletal abnormalities, joint stiffness, poor growth, clouding of the cornea and a prominent forehead. In the severe form of this condition, the symptoms can include developmental delays, upper respiratory infections, recurrent urine, persistent nasal discharge and noisy breathing. Additional symptoms can include misaligned teeth, curved back, severe joint stiffness, clouding of the cornea of the eye and a large tongue. The mental development can reach its peak around 2 years of age exhibiting progressive mental retardation. The milder form of this condition may become evident after the age of 5 but is generally diagnosed between 10 to 20 years of age. Individuals with the mild form have normal intelligence and stature but present symptoms such as clouding of the cornea, stiffness of the joints and the flow of blood from the aorta back into the left ventricle of the heart.
Diagnosis
The prenatal diagnosis of this condition is done through amniocentesis and sampling of the tissue layer of the embryo. After the birth, the diagnosis is possible by checking the infant’s blood and urine that indicates the disease. The diagnosis can be confirmed by detecting the missing or reduced activity of the enzyme responsible for the condition. The genetic testing can also help confirm the diagnosis.
Treatment
The treatment can include an enzyme replacement therapy for those with the moderate to severe form of this disease. Additional supportive treatments include physical therapy to preserve mobility, reduce pain and joint stiffness.
References
http://www.babysfirsttest.org/newborn-screening/conditions/mucopolysaccharidosis-type-i
https://rarediseases.org/rare-diseases/mucopolysaccharidosis-type-i/
https://ghr.nlm.nih.gov/condition/mucopolysaccharidosis-type-i#statistics
