Inclusion-cell (I-cell) disease, also referred to as mucolipidosis II (ML II), is so named because waste products, thought to include carbohydrates, lipids, and proteins, accumulate into masses known as inclusion bodies. When tissues are examined under a microscope, the detection of inclusion bodies often provides a diagnosis of the disease.
ML II is a particularly severe form of ML that resembles one of the mucopolysaccharidoses called Hurler syndrome. Some physical signs, such as abnormal skeletal development, coarse facial features, and restricted joint movement, may be present at birth. Children with ML II usually have enlargement of certain organs, such as the liver or spleen, and sometimes even the heart valves. Affected children often fail to grow and develop in the first months of life. Delays in the development of their motor skills are usually more pronounced than delays in their cognitive (mental processing) skills. Children with ML II eventually develop a clouding on the cornea of their eyes and, because of their lack of growth, develop short-trunk dwarfism (underdeveloped trunk). These young patients are often plagued by recurrent respiratory tract infections, including pneumonia, otis media (middle ear infections), and bronchitis. Children with ML II generally die before their seventh year of life, often as a result of congestive heart failure or recurrent respiratory tract infections.
I-cell disease is caused by a defect in mannose phosphorylation of lysosomal enzymes. Without mannose-6-phosphate to target them to the lysosomes, the enzymes are transported from the endoplasmic reticulum to the extracellular space.
^ Tiede S, Storch S, Lübke T, et al (2005). "Mucolipidosis II is caused by mutations in GNPTA encoding the alpha/beta GlcNAc-1-phosphotransferase". Nat. Med.11 (10): 1109-12. doi:10.1038/nm1305. PMID 16200072.
mucolipidoses at NINDS - article derived from detail sheet available here