Mucopolysaccharidosis Type VII

Mucopolysaccharidosis type VII (MPS VII) is caused by a change (also called a mutation or a variant) in the GUSB gene which causes the gene to not work correctly. GUSB carries the instructions for making β-glucuronidase, which is an enzyme required for breaking down large sugar molecules called glycosaminoglycans (GAGs). We normally have two working copies of GUSB in our cells and we inherit one copy from our biological mother and the other from our biological father. In order to develop symptoms of MPS VII, both copies of GUSB are not working properly. This is also called autosomal recessive inheritance, which means that both parents of someone with MPS VII are carriers of one working and one non-working copy of the GUSB gene. Since each parent has one working copy, they don't have symptoms of MPS VII themselves. However, when they have children, they each have a 1 in 2 or 50% chance of passing on the non-working copy to their child. When both parents are carriers, there is a 1 in 4 or 25% chance of both of them passing on the non-working copy and having a child with MPS VII. Even if a couple already has one child with MPS VII, it is important to know that they can have another affected child because the chances are 1 in 4 for each pregnancy.