For more information please download our Guide to AGU.
What is AGU?
Aspartylglycosaminuria (AGU) was first described by Dr Pollitt et al in 1968 and is a rare lysosomal storage disorder of the oligosaccharide family, closely related to the mucopolysaccharidoses.
What causes this disease?
Oligosaccharides are long chains of sugar molecules used in the building of bones, cartilage, skin, tendons and many other tissues in the body. “Oligo” means a small number, “saccharide” is a general term for a sugar molecule. In the course of normal life there is a continuous process of building new oligosaccharides and breaking down old ones. This process requires a series of special biochemical tools called enzymes.
AGU is an enzyme deficiency disorder resulting in defective aspartylglycosaminidase enzyme activity which is essential for the chemical decomposition of oligosaccharides. Without the aspartylglycosaminidase enzyme used materials cannot be completely broken down and remain stored in the body causing progressive damage to cells. Babies may show little sign of the disease but symptoms start to appear as more and more cells become damaged by the accumulation of oligosaccharides.
Does AGU affect individuals differently?
Despite the rarity of diagnosed cases of AGU, follow-ups and studies carried out have shown consistency in the clinical picture. There do appear to be some differences in the severity of the disease between patients who carry the most common Finnish mutations of AGU and individuals from other countries who often have other, less well-known mutations. In these individuals the outcome can be much more severe, leading to a shorter life span than described in literature.
How common is AGU?
The MPS Society which co-ordinates the Registry for Mucopolysaccharide and Related Diseases has been contacted regarding 3 cases in the UK. Approximately 250 cases are reported worldwide. Around 200 patients are living in or originate from Finland. It was initially thought that the disorder was exclusively particular to the Finnish population but a few sufferers from different origins have since been diagnosed with AGU.
How is the disease inherited?
We all have genes inherited from our parents which control, for example, our height and the colour of our eyes. Some genes we inherit are “recessive” which means that although we carry the gene it does not have any effect on our development. AGU is caused by a recessive gene. If an adult carrying the abnormal gene has a partner who is also a carrier, there will be 25% (1:4) chance with every pregnancy that the foetus will inherit the defective gene from each parent and will be affected by the disease. There is a 2 in 3 chance that unaffected brothers and sisters of those affected by AGU will be carriers. However, as the disease is so rare the chance of meeting another carrier is slight.
There is a more detailed explanation of this complex subject in the booklet on inheritance available from the MPS Society.