Inclusion-cell (I-cell) disease
, also referred to as mucolipidosis II (ML II), is so named because waste
products, thought to include carbohydrates
, 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
, otitis 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 an deficiency of GlcNAc phosphotransferase, which phosphorylates mannose residues to mannose-6-phosphate on N-linked glycoproteins in the Golgi apparatus within the cell. Without mannose-6-phosphate to target them to the lysosomes, the enzymes are transported from the Golgi to the extracellular space, resulting in large cellular inclusions in patients with the disease (hence the name of the disorder). Hydrolases secreted into the blood stream cause little problem as they are deactivated in the neutral pH of the blood.
It can be associated with GNPTA.
- - article derived from detail sheet available here