Mucolipidosis Type II (I-cell disease)
Description
Mucolipidosis Type II, also known as I-cell disease, is a rare genetic disorder that affects the body‘s ability to break down certain complex molecules. This breakdown process happens within lysosomes, tiny organelles in cells that act as recycling centers. In I-cell disease, a defect in a specific enzyme prevents lysosomes from functioning properly, leading to the accumulation of undigested materials. This buildup causes various health problems, primarily affecting bone development, facial features, and cognitive function.
Genes Involved
Genes Involved:
- GNPTAB: The gene responsible for I-cell disease is called GNPTAB. It provides instructions for making an enzyme called GlcNAc-1-phosphotransferase. This enzyme is crucial for tagging specific molecules within the cell for breakdown in lysosomes.
Recognizing the Signs and Symptoms
Recognizing the Signs and Symptoms:
- Delayed development: Infants with I-cell disease may show delays in reaching developmental milestones, such as sitting, crawling, or walking.
- Skeletal abnormalities: They may have short stature, bone deformities, and joint problems.
- Facial features: Common facial features include a broad forehead, flattened nose, and a large, protruding tongue.
- Vision problems: I-cell disease can cause clouding of the cornea (corneal clouding), leading to vision impairment.
- Hearing loss: Some individuals with I-cell disease may experience hearing loss.
- Cardiovascular issues: Heart problems can also occur, including heart valve defects and heart rhythm abnormalities.
- Seizures: Seizures can be a serious complication of I-cell disease.
Causes
Causes:
I-cell disease is caused by a genetic mutation in the GNPTAB gene. This mutation prevents the production of the GlcNAc-1-phosphotransferase enzyme, leading to the inability of lysosomes to break down complex molecules properly.
Inheritance/recurrence risk
Inheritance or Recurrence Risk:
I-cell disease is inherited in an autosomal recessive pattern. 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, they have a 25% chance of having a child with I-cell disease, a 50% chance of having a carrier child, and a 25% chance of having a child who is not a carrier.
