I-cell Disease

I-cell Disease

Inclusion-cell (I-cell) disease, also referred to as mucolipidosis II (ML II), is part of the lysosomal storage disease family and results from a defective phosphotransferase (an enzyme of the Golgi apparatus). This enzyme transfers phosphate to mannose residues on specific proteins, and serves as a marker for them to be targeted to lysosomes within the cell. Without this marker, the proteins are instead excreted outside the cell -- the default pathway for proteins moving through the Golgi apparatus. Lysosomes cannot function without these proteins, which function as catabolic enzymes for the normal breakdown of substances throughout the body. As a result, a build up of these substances occurs within lysosomes because they cannot be degraded, resulting in the characteristic "I cells," or "inclusion cells." These cells can be identified under the microscope. In addition, the defective lysosomal enzymes normally found only within lysosomes are instead found in high concentrations in the blood.