I-cell

I-cell disease, also known as Mucolipidosis II, is a rare lysosomal storage disease characterized by severe psychomotor impairment and skeletal abnormalities. It is caused by a deficiency in the enzyme N-acetylglucosamine-1-phosphotransferase, which leads to improper processing and distribution of lysosomal enzymes.

Symptoms and Signs

The symptoms of I-cell disease are typically present at birth and may include growth retardation, coarse facial features, gingival hypertrophy, and skeletal deformities. Other symptoms may include cardiomegaly, hepatomegaly, splenomegaly, and hernias.

Cause

I-cell disease is caused by mutations in the GNPTAB gene, which provides instructions for making the alpha and beta subunits of the enzyme N-acetylglucosamine-1-phosphotransferase. This enzyme is responsible for adding a molecule called mannose-6-phosphate to certain proteins, which directs these proteins to lysosomes. Without this tag, these proteins are secreted outside the cell instead of being transported to lysosomes, leading to the symptoms of I-cell disease.

Diagnosis

Diagnosis of I-cell disease is based on clinical findings, enzyme assays showing deficient activity of multiple lysosomal enzymes, and molecular genetic testing of the GNPTAB gene.

Treatment

There is currently no cure for I-cell disease, and treatment is supportive. Management may include physical therapy to improve mobility and speech therapy to address feeding difficulties.

Prognosis

The prognosis for individuals with I-cell disease is poor, with most individuals not surviving past early childhood due to respiratory infections or cardiac complications.

See also

• Lysosomal storage disease
• Mucolipidosis
• GNPTAB

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