Heather A. Lau, MD, Director, Lysosomal Storage Disease Program at NYU Langone in New York City discusses Mucopolysaccharidosis type III (MPS III), also known as Sanfilippo syndrome. This progressive disorder primarily affects the brain and spinal cord (central nervous system). Other body systems can also be involved. MPS III is the most common form of mucopolysaccharidosis; the estimated incidence of all four types combined is 1 in 70,000 newborns. MPS IIIA and MPS IIIB are much more common than MPS IIIC and MPS IIID.
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.
The physical features of MPS III are less pronounced than those of other types of mucopolysaccharidosis. Individuals with MPS III typically have mildly “coarse” facial features, a large head (macrocephaly), a slightly enlarged liver (mild hepatomegaly), and a soft out-pouching around the belly-button (umbilical hernia) or lower abdomen (inguinal hernia). Some people with MPS III have short stature, joint stiffness, or mild dysostosis multiplex, which refers to multiple skeletal abnormalities seen on x-ray. Affected individuals often experience chronic diarrhea and recurrent upper respiratory and ear infections. People with MPS III may also have hearing loss and vision problems.
MPS III is divided into types IIIA, IIIB, IIIC, and IIID, which are distinguished by their genetic cause. The different types of MPS III have similar signs and symptoms, although the features of MPS IIIA typically appear earlier in life and progress more rapidly. People with MPS III usually live into adolescence or early adulthood.