Mucopolysaccharidosis type III (MPS III), also known as Sanfilippo syndrome, is a progressive disorder that primarily affects the brain and spinal cord (central nervous system). It is characterized by deterioration of neurological function (neurodegeneration), resulting in many of the features of the condition. Other body systems can also be involved, although the physical features are usually mild in the early stages.
People with MPS III generally do not display any features of the condition at birth, but they begin to show signs and symptoms of the disorder during early childhood. Affected children often initially have delayed speech and behavior problems. They may become restless, destructive, anxious, or aggressive, and some display features of autism spectrum disorder, which is a condition characterized by difficulty with social interactions and communication. Sleep disturbances are also very common in children with MPS III. This condition causes progressive intellectual disability and the loss of previously acquired skills (developmental regression). In later stages of the disorder, people with MPS III may develop seizures and movement disorders.