A disorder caused by a deficiency of the enzyme N-acetylglucosamine-1-phosphotransferase which phosphorylates target carbohydrate residues on N-linked glycoproteins. These abnormal glycoproteins escape outside the cell.
Originally these were thought to encompass 4 conditions
1. Sialosis
2. I-cell disease
3. Pseudo-Hurler polydystrophy
However Sialosis (Type 1) is now classified as a glycoproteinosis and Mucolipidosis type IV as a gangliosidosis.