Aspartylglucosaminuria, often referred to as AGU, is a rare genetic, autosomal recessive disease belonging to a group of lysosomal storage disorders. Lysosomes are cellular compartments that contain enzymes responsible for the final (cellular) breakdown of fats, proteins and sugars. This process is necessary for appropriate mental and physical development.
The basis for the disease presentation is the lack of a cellular enzyme that breaks down long sugars attached to proteins (glucoproteins). These proteins are most abundant in the body tissues and in major organs, such as the liver, spleen, thyroid and brain. When the enzyme is not working or not working properly, the sugars are not broken down in cells, leading to their excess accumulation in the body tissues and increased excretion in urine. The process is gradual, damaging the tissues and organs, progressively destroying cells and leading to eventual death. As the disorder progresses, patients typically become severely mentally and physically handicapped before dying in the third or fourth decade of their lives.
AGU is caused by mutations on the Aspartylglucosamidase (AGA) gene. Most of the reported medical information on AGU is derived from the observation of Finnish patients, which represent one genetic mutation. More than 30 different mutations of the AGA gene have been reported in patients of non-Finnish ancestry with more being discovered every year. Patients with different mutations might have different or milder/more profound signs.