I-Cell Disease

I-Cell disease (Mucolipidosis II), unlike most Lysosomal Storage Diseases which involve the lack of one particular enzyme, is due to the lack of a number of enzymes which, while present in the cell, are lacking a signal that is necessary to get them inside the lysosome. Thusly, an accumulation of molecules in the enzyme occurs similar to if there were no enzyme produced at all. I-Cell disease is closely related to Pseudo-Hurler Polydystrophy, both disorders bearing these “targeting” defects. The enzyme that is responsible for putting the targeting signal on the lysosomal enzymes that is not working in both I-Cell disease and Pseudo-Hurler Polydystrophy is N-acetylglucosamine-1-phototransferase. The unique feature of I-Cell disease is the presence of abnormalities in the cells that give rise to connective tissue, termed inclusion-cells, for which the disorder is named.
I-Cell disease is characterized by severe psychomotor retardation. Typically, failure to thrive and developmental delay are obvious by the age of 6 months. Other symptoms are coarse facial features, skeletal problems, vertebral body anomalies and claw-hand deformities. Individuals with I-Cell disease are prone to carpal tunnel syndrome and can experience pain and loss of feeling in their fingertips. Other musculoskeletal problems include hernias and joint contractures and restriction. Individuals with I-Cell disease may also have enlarged organs, chronic ear infections and corneal clouding. A specific dental problem associated with I-Cell disease is gingival hyperplasia (prominent gums) as well as late and poorly formed teeth. Unfortunately, due to the severity of progression of I-Cell disease, individuals with this disorder typically do not live past the first decade. Many pass away within the first three to four years of life.