What are the genetic changes related to mucopolysaccharidosis type IV ?
Mutations in the GALNS and GLB1 genes cause MPS IV. These genes provide instructions for producing enzymes involved in the breakdown of large sugar molecules called glycosaminoglycans (GAGs). GAGs were originally called mucopolysaccharides, which is where this condition gets its name. When MPS IV is caused by mutations in the GALNS gene it is called MPS IV type A (MPS IVA), and when it is caused by mutations in the GLB1 gene it is called MPS IV type B (MPS IVB). In general, the two types of MPS IV cannot be distinguished by their signs and symptoms.  Mutations in the GALNS and GLB1 genes reduce or completely eliminate the activity of the enzymes produced from these genes. Without these enzymes, GAGs accumulate within cells, specifically inside the lysosomes. Lysosomes are compartments in the cell that break down and recycle different types of molecules. Conditions such as MPS IV that cause molecules to build up inside the lysosomes are called lysosomal storage disorders. In MPS IV, GAGs accumulate to toxic levels in many tissues and organs, particularly in the bones. The accumulation of GAGs causes the bone deformities in this disorder. Researchers believe that the buildup of GAGs may also cause the features of MPS IV by interfering with the functions of other proteins inside lysosomes and disrupting the movement of molecules inside the cell.