Mucopolysaccharidosis Type I (MPS I)
Description
Mucopolysaccharidosis Type I (MPS I), also known as Hurler syndrome, is a rare genetic disorder that affects the body‘s ability to break down complex sugars called glycosaminoglycans (GAGs). These sugars are essential for the development and function of various tissues, including cartilage, bone, skin, and blood vessels. When MPS I occurs, these GAGs accumulate in cells and organs, leading to a range of health problems.
Genes Involved
MPS I is caused by mutations in the α-L-iduronidase gene, located on chromosome 4. This gene provides instructions for making an enzyme called α-L-iduronidase. This enzyme is essential for breaking down GAGs. When the gene is mutated, the enzyme is either deficient or absent, leading to the accumulation of GAGs.
Recognizing the Signs and Symptoms
The signs and symptoms of MPS I can vary widely depending on the severity of the disorder. Common symptoms include:
- Delayed development: Children with MPS I may experience delays in physical and cognitive development, such as delayed walking or talking.
- Facial features: Characteristic facial features may include a coarse face, prominent forehead, flattened nasal bridge, and large tongue.
- Skeletal abnormalities: Bone abnormalities, such as short stature, joint stiffness, and skeletal deformities, are common.
- Cardiovascular problems: Heart valve problems, enlarged heart, and other cardiovascular issues may occur.
- Hearing loss: Hearing loss can develop due to the accumulation of GAGs in the inner ear.
- Vision problems: Clouding of the cornea, a condition known as corneal clouding, can affect vision.
- Respiratory problems: Recurrent respiratory infections and difficulty breathing may occur.
- Hepatosplenomegaly: Enlargement of the liver and spleen is common.
- Neurological problems: Seizures, intellectual disability, and behavioral problems can develop in some cases.
Causes
MPS I is caused by a genetic mutation in the α-L-iduronidase gene. This gene provides instructions for making an enzyme called α-L-iduronidase. This enzyme is essential for breaking down GAGs, a type of complex sugar found in connective tissues. When the gene is mutated, the enzyme is either deficient or absent, leading to the accumulation of GAGs in cells and organs.
Inheritance/recurrence risk
MPS I is an autosomal recessive disorder. This means that both parents must carry a copy of the mutated gene for their child to inherit the disorder. If both parents are carriers, there is a 25% chance that their child will inherit MPS I, a 50% chance that their child will be a carrier, and a 25% chance that their child will not inherit the gene at all.
If one parent has MPS I and the other parent is not a carrier, all their children will be carriers, and they will not develop the disorder. However, if both parents have MPS I, all of their children will also have the disorder.
