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|Classification and external resources|
When originally named, the mucolipidoses derived their name from the similarity in presentation to both mucopolysaccharidoses and sphingolipidoses. A biochemical understanding of these conditions has changed how they are classified. Although four conditions (I, II, III, and IV) have been labeled as mucolipidoses, type I (sialidosis) is now classified as a glycoproteinosis, and type IV (Mucolipidosis type IV) is now classified as a gangliosidosis.
ML II and III
The other two types are closely related.
Mucolipidosis types II and III (ML II and ML III) result from a deficiency of the enzyme N-acetylglucosamine-1-phosphotransferase, which phosphorylates target carbohydrate residues on N-linked glycoproteins. Without this phosphorylation, the glycoproteins are not destined for lysosomes, and they escape outside the cell.
The mucolipidoses are inherited in an autosomal recessive manner, that is, they occur only when a child inherits two copies of the defective gene, one from each parent. When both parents carry a defective gene, each of their children faces a one in four chance of developing one of the MLs. At the same time, each child also faces a one in two chance of inheriting only one copy of the defective gene. People who have only one defective gene are known as carriers. These individuals do not develop the disease but they can pass the defective gene on to their own children. Because the defective genes involved in certain forms of ML are known, tests can identify people who are carriers in some instances.