About Glycoprotein Diseases
Glycoprotein and Related Storage Diseases are very rare, progressive, largely untreatable metabolic enzymatic defects inherited by children from both parents. The worldwide incidence for these diseases as a group has not yet been determined accurately, though they can certainly be classified as ultra-rare. The course of these disorders affects multiple systems of the body and clinical symptoms may vary patient-to-patient, and even among siblings. For most children the implications are eventual loss of mental and physical functions, and a premature death.
As the name implies, glycoproteins are complex compounds composed of a protein and a carbohydrate. There are many different types of glycoproteins and they are found in abundance in all kinds of cells, including those of the brain. Glycoproteins play many roles in cells; some of these are well known, but others have yet to be discovered. Known roles include acting as an agent for communication between cells and assisting in maintaining the cell’s structure. The carbohydrate portion of glycoproteins is usually made of combinations of sugar molecules such as glucose, galactose, mannose and fucose, which are collectively known as oligosaccharides.
Normal functioning of the cell is characterized by the continual degradation of glycoproteins by enzymes within the lysosomes, which are membrane-bound compartments in the cell and essentially the cell’s recycling center. Specific enzymes are needed along each “step” of the recycling process in order that the continual, complete breakdown of these chains of glycoproteins is carried out. Any malfunction along the way results in the premature termination of the process with a resulting accumulation of the undegraded material within the lysosome.
There are nine different types of Glycoprotein Storage Diseases. Seven of the diseases are caused by a defect in glycoprotein degradation:
- Schindler Disease
- Sialidosis, also known as Mucolipidosis I
Two other Glycoprotein Storage Diseases are characterised by trafficking errors that limit normal trageting of digestive enzymes, which are themselves glycoproteins, to the lysosomes and prevent the lysosome from functioning normally:
- Mucolipidosis alpha/beta, encompassing I-Cell Disease (Mucolipidosis II), Mucolipidosis II/III and Pseudo-Hurler Polydystrophy (Mucolipidosis III)
- Mucolipidosis III Gamma is a variant of Mucolipidosis III alpha/beta
These diseases are a subset of a larger group of disorders known as Lysosomal Storage Diseases, which consist of over 50 autosomal recessive inherited metabolic diseases. Our organization supports and promotes cooperative partnerships with other Lysosomal Disease non-profit organizations in order to maximize attainment of our common goals.
Storage in Lysosomal Diseases
Visit our “Storage in Lysosomal Diseases” page for an instructional comic penned for ISMRD by noted cartoonist Denis Rodier!