A type of mucolipidosis that is similar to I-cell disease in a way that both are caused by a deficiency in N-acetylglucoseamine-1-phosphotransferase resulting in the accumulation of mucopolysaccharides and mucolipids in tissues, but has milder symptoms than the I-cell disease
Mucolipidosis is a lysosomal storage disease caused by a deficiency of the enzyme N-acetylglucosamine-1-phosphotransferase. The enzyme is involved in the phosphorylation of carbohydrate residues on N-linked glycoproteins. Without the appropriate level of functional N-acetylglucosamine-1-phosphotransferase, mucopolysaccharides and mucolipids tend to accumulate inside the cell. There are different types of mucolipidosis and one of them is pseudo-Hurler polydystrophy (also referred to as mucolipidosis type III).
Pseudo-Hurler polydystrophy is inherited in autosomal recessive manner. This means that the individual with this disease bears two copies of the defective GNPTG gene or GNPTAB gene. A single copy of the defective gene means that the individual may not show symptoms but becomes a carrier of the disease. GNPTG gene normally codes for the gamma subunit whereas GNPTAB gene codes for the alpha and beta subunits of the enzyme, N-acetylglucosamine-1-phosphotransferase (also called GlcNAc-1-phosphotransferase). In this regard, GNPTG gene defects cause mucolipidosis III gamma whereas GNPTAB gene defects cause mucolipidosis III alpha/beta. The enzyme, N-acetylglucosamine-1-phosphotransferase, catalyzes the addition of mannose-6-phosphate to certain lysosomal enzymes, tagging the latter as molecules to be transported to the lysosome. Individuals with pseudo-Hurler polydystrophy (as well as mucolipidosis type II) do not have lysosomal enzymes in the lysosomes but are subsequently secreted outside the cell. Thus, the symptoms associated with Pseudo-Hurler polydystrophy is caused by the lack of functional levels of lysosomal enzymes or by the effects these enzymes have outside the cell.1
- mucolipidosis III
1 U.S. Department of Health & Human Services. (2018). Mucolipidosis III alpha/beta. Retrieved from ://ghr.nlm.nih.gov/condition/mucolipidosis-iii-alpha-beta#genes.