Sanfilippo Syndrome is an inherited disease of metabolism that makes the body unable to properly break down long chains of sugar molecules called glycosaminoglycans (GAGs) or mucopolysaccharides. The syndrome belongs to a group of diseases called mucopolysaccharidoses (MPS). Specifically, it is known as MPS III.
Sanfilippo Syndrome occurs when the enzymes needed to break down the heparan sulfate sugar chain (glycosaminoglycans in case of MPS III) are missing or are defective. As the substrates cannot be properly disposed of, they are stored inside the lysosomes of every cell in the body. MPS is a Lysosomal Storage Disease (LSD). As the GAGs build up over time, they damage the cells which in turn leads to progressive central nervous system degeneration.
To date there are four types of Sanfilippo syndrome depending on which enzyme is affected:
Sanfilippo Type A is the most common. Patients with this type are missing or have an altered form of an enzyme called heparan N-sulfatase.
Sanfilippo Type B occurs when a person is missing or doesn’t produce enough alpha-N-acetylglucosaminidase.
Sanfilippo Type C occurs when a person is missing or doesn’t produce enough acetyl-CoAlpha-glucosaminide acetyltransferase.
Sanfilippo Type D occurs when a person is missing or doesn’t produce enough N-acetylglucosamine 6-sulfatase.
Type A is the most common and considered the most severe in that the symptoms manifest more quickly. Type B is less common and the symptoms may take longer to show up. Type C is rare and milder in the timing of symptoms. That being said, all types of Sanfilippo are variable in the aggressiveness of the timing of symptoms.
The mucopolysaccharidoses (including Sanfilippo syndrome) are inherited as an autosomal recessive traits. That means both parents must pass on the defective gene in order for their child to get this disease. Parents have a 25% chance of passing both genes to their children.
MPS III is possibly the most common form of MPS. It is seen in about 1 in 70,000 births, including:
Type A – 1 in 114,000 live births
Type B – 1 in 211,000 live births
Type C – 1 in 1,407,000 live births
Type D – 1 in 1,056,000 live births
What happens to a child with Sanfilippo Syndrome?
Sanfilippo is an insidious disease and often goes undetected for years. Most children are born with no visible signs that anything is wrong. It’s not until the preschool years (or later with some type C) that children start to show delays or deformities; even then, the disease is often misdiagnosed for years. Highly specialized and focused testing needs to be done to diagnose Sanfilippo.
Sanfilippo is progressive and can be broken down into stages:
In the first stage: The affected child will display delayed speech as well as mild facial abnormalities and behavioral issues. Some children will exhibit a large head, prominent forehead, bushy eyebrows, coarse hair, thick skin, short neck and full round bellies. Their facial features are described as “coarse.” Affected children are prone to sinus and ear infections, diarrhea, tight Achilles tendons and other muscular problems. They may have cavities or chipped teeth from weak enamel and headaches from accumulated fluid pressure. The problems associated are vast and varied.
In the second stage: The affected child will become extremely active, restless, suffer sleeplessness and exhibit difficult behavior. Many children are compelled to chew on things, grab at people or items, screech out loud or exhibit random fears. Again, these symptoms vary from child to child. Over time, speech and communication skills decline along with other milestones. Cognitive and motor skills diminish.
Third stage: The disease will take its ultimate toll. The child will lose the ability to walk, talk and eat on his own while his body shuts down. Death may occur in the early teens, although some have lived into their early 20s. (Some cases of mild forms have lived into their early thirties).
Currently there is no cure for Sanfilippo Syndrome. In most cases, treatment is limited to reducing or controlling the symptoms of this disorder by making sure that neurologists, ophthalmologists, and genetic counselors are consulted routinely. Medications to control the behavioral problems associated with this disorder have not proven effective. Anti-convulsant medication may control seizures, devices can be inserted in the mouth to assist swallowing, and wheelchairs are often required as the disorder progresses to its final and immobile stage.
Other potential treatments include enzyme replacement therapies that cross the Blood-Brain Barrier, therefore allowing the neurological symptoms to be treated. Stem cell transplants are presently under investigation. It is recognized within the medical community that a diagnosis made early in the course of this disorder will render treatment more effective than following a later diagnosis.