Mucolipidosis type II

Mucolipidosis type II (ML II), also known as I-cell disease (inclusion cell disease), is a severe autosomal recessive lysosomal storage disorder caused by mutations in the GNPTAB gene, which encodes the alpha/beta subunits of GlcNAc-1-phosphotransferase. This enzyme is essential for tagging lysosomal enzymes with mannose-6-phosphate, a signal required for their proper transport to lysosomes. When this process fails, lysosomal enzymes are secreted outside the cell instead of being directed to lysosomes, leading to the accumulation of undigested substrates within cells. The characteristic cytoplasmic inclusions seen in fibroblasts under microscopy give the disease its alternative name, I-cell disease. Mucolipidosis type II affects multiple organ systems. Key clinical features include severe skeletal abnormalities (dysostosis multiplex), coarse facial features, restricted joint mobility, short stature, and progressive psychomotor delay. Affected infants often present at birth or within the first months of life with gingival hyperplasia, thickened skin, hernias, and hepatomegaly. Cardiac involvement, including valvular disease and cardiomyopathy, is common. Recurrent respiratory infections and progressive respiratory compromise are frequent complications. Corneal clouding may also be present. The disease follows a severe and progressive course, with most affected children not surviving beyond early childhood, typically due to cardiorespiratory failure. There is currently no cure or disease-specific treatment for mucolipidosis type II. Management is supportive and multidisciplinary, focusing on symptom relief, physical therapy, nutritional support, and management of respiratory and cardiac complications. Unlike some other lysosomal storage disorders, enzyme replacement therapy has not proven effective for ML II because the underlying defect prevents proper enzyme targeting. Hematopoietic stem cell transplantation has been attempted in some cases with limited and variable outcomes. Genetic counseling is recommended for affected families, and prenatal diagnosis is available through enzymatic or molecular testing.

Data sourced from FDA regulatory filings and ClinicalTrials.gov. Updated periodically.

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