Sanfilippo syndrome, or mucopolysaccharidosis type III (MPS III), is a genetic disorder that leads to a form of childhood dementia. The Cure Sanfilippo Foundation describes Sanfilippo syndrome as “Alzheimer’s, but in children.”
Mutations in genes that code for enzymes necessary to break down heparan sulfate, a complex sugar molecule, cause Sanfilippo syndrome. Because of these mutations, the body cannot make a functional enzyme, and heparan sulfate builds to toxic levels inside cells, causing damage systemwide and especially to brain tissue.
Mutations in four different genes cause the four different types of Sanfilippo syndrome. All four types are inherited in an autosomal recessive manner. This means that a person must inherit two faulty copies of the same gene (one from each biological parent) to have the disease.
Symptoms of Sanfilippo syndrome usually become evident between the ages of 2 and 6. Common early symptoms include behavioral problems (most notably hyperactivity), difficulty sleeping, and developmental delays, particularly delayed language acquisition. Many children with Sanfilippo also exhibit autistic traits, and families often go for years with a wrongful diagnosis of autism or attention deficit hyperactivity disorder.
Recurrent ear or sinus infections can be common in young children with the disease, as can be frequent diarrhea. Hearing and vision problems and seizures can also occur.
Sanfilippo syndrome is a progressive disorder, whose symptoms tend to continually worsen in severity. As patients age, they undergo developmental regression, losing age-appropriate skills that they previously acquired. Most eventually lose their ability to talk, walk, and feed themselves.
The gold standard for a definitive diagnosis of Sanfilippo syndrome are blood tests (or tests in cell samples) to measure the activity of relevant enzymes in the cell pathway that breaks down heparan sulfate. This test looks for a missing enzyme.
Urine tests to measure levels of heparan sulfate and related compounds can aid in arriving at a diagnosis.
Genetic testing can identify disease-causing mutations, which is also important.
Currently, no cure exists for Sanfilippo syndrome. Treatment generally aims to ease symptoms and improve patients’ quality of life.
Various treatments are being developed, and generally aim to restore the activity of the missing enzyme. They include enzyme replacement therapy, which involves administering the missing enzyme, and gene therapy, which aims to deliver a healthy version of the mutated gene to a patient’s cells.