|Other names||Mucopolysaccharidosis III; MPS III|
|12-year-old girl with Sanfilippo Syndrome Type A|
|Symptoms||Deafness; intellectual disability; dementia; loss of mobility|
|Usual onset||Birth; symptoms usually become apparent between ages 2-6|
|Types||Sanfilippo Syndrome Types A, B, C, and D|
|Causes||Inherited enzyme deficiency|
|Prognosis||Lifespan is reduced; most patients survive until the teenage years, but some may reach their 30s|
|Frequency||1 in 70,000|
Sanfilippo syndrome, also known as mucopolysaccharidosis type III (MPS III), is a rare autosomal recessive lysosomal storage disease that primarily affects the brain and spinal cord. It is caused by a buildup of large sugar molecules called glycosaminoglycans (AKA GAGs, or mucopolysaccharides) in the body's lysosomes.
Affected children generally do not show any signs or symptoms at birth. In early childhood, they begin to develop developmental disability and loss of previously learned skills. In later stages of the disorder, they may develop seizures and movement disorders. Patients with Sanfilippo syndrome usually live into adolescence or early adulthood.
Signs and symptoms
The disease manifests in young children. Symptoms usually begin to appear between 2 and 6 years of age. Affected infants appear normal, although some mild facial dysmorphism may be noticeable. Of all of the MPS diseases, Sanfilippo syndrome produces the fewest physical abnormalities. After an initial symptom-free interval, patients usually present with a slowing of development and/or behavioral problems, followed by progressive intellectual decline resulting in severe dementia and progressive motor disease. Acquisition of speech is often slow and incomplete. The disease progresses to increasing behavioral disturbance including temper tantrums, hyperactivity, destructiveness, aggressive behavior, pica, difficulties with toilet training, and sleep disturbance. As affected children initially have normal muscle strength and mobility, the behavioral disturbances may be difficult to manage. The disordered sleep in particular presents a significant problem to care providers. In the final phase of the illness, children become increasingly immobile and unresponsive, often require wheelchairs, and develop swallowing difficulties and seizures. The life-span of an affected child does not usually extend beyond late teens to early twenties.
Individuals with MPS Type III tend to have mild skeletal abnormalities; osteonecrosis of the femoral head may be present in patients with the severe form. Optic nerve atrophy, deafness, otitis can be seen in moderate to severe individuals. Other characteristics include coarse facial features, thick lips, synophrys, and stiff joints. Chronic diarrhea, enlarged liver and spleen are also common.
It is difficult to clinically distinguish differences among the four types of Sanfilippo syndrome. However, type A is usually the most severe subtype, characterized by earliest onset, rapid clinical progression with severe symptoms, and short survival. The median age of death for children afflicted with type A is 15.4 years, ±4.1 years.
It is important that simple and treatable conditions such as ear infections and toothaches not be overlooked because of behavior problems that make examination difficult. Children with MPS type III often have an increased tolerance to pain. Bumps, bruises, or ear infections that would be painful for other children often go unnoticed in children with MPS type III. Some children with MPS type III may have a blood-clotting problem during and after surgery.
Mutations in four different genes can lead to Sanfilippo Syndrome. This disorder is inherited in an autosomal recessive pattern. People with two working copies of the gene are unaffected. People with one working copy are genetic carriers of Sanfilippo Syndrome. They have no symptoms but may pass down the defective gene to their children. People with two defective copies will suffer from Sanfilippo Syndrome.
|Sanfilippo Syndrome type||Gene||Enzyme||Chromosomal region||Number of known mutations causing this type|
|Type A||SGSH||heparan N-sulfatase||17q25.3||137|
|Type B||NAGLU||Alpha-N-acetylglucosaminidase||17q21.2||152|
|Type C||HGSNAT||acetyl-CoA:alpha-glucosaminide N-acetyltransferase||8p11.21||64|
|Type D||GNS||N-acetylglucosamine-6-sulfatase||12q14.3||23|
Glycosaminoglycans (GAGs) are chains of sugar molecules. They are found in the extracellular matrix and the cell membrane, or stored in the secretory granules. GAGs are stored in the cell lysosome, and are degraded by enzymes such as glycosidases, sulfatases, and acetyltransferases. Deficiency in these enzymes lead to the four subtypes of MPS III.
Sanfilippo Syndrome Types A, B, C, and D are considered to be clinically indistinguishable, although mutations in different genes are responsible for each disease. The following discussion is therefore applicable to all four conditions.
A urinalysis can show elevated levels of heparan sulfate in the urine. All four types of Sanfilippo syndrome show increased levels of GAGs in the urine; however, this is less true of Sanfilippo syndrome than other MPS disorders. Additionally, urinary GAG levels are higher in infants and toddlers than in older children. In order to avoid a false negative urine test due to dilution, it is important that a urine sample be taken first thing in the morning. The diagnosis may be confirmed by enzyme assay of skin fibroblasts and white blood cells, as well as gene sequencing. Prenatal diagnosis is possible by chorionic villus sampling or amniocentesis.
Treatment remains largely supportive. The behavioral disturbances of MPS-III respond poorly to medication. If an early diagnosis is made, bone marrow replacement may be beneficial. Although the missing enzyme can be manufactured and given intravenously, it cannot penetrate the blood–brain barrier and therefore cannot treat the neurological manifestations of the disease. Along with many other lysosomal storage diseases, MPS-III exists as a model of a monogenetic disease involving the central nervous system.
Several promising therapies are in development. Gene therapy in particular is under Phase I/II clinical trial in France since October 2011 under the leadership of Paris-based biotechnology company Lysogene. Other potential therapies include chemical modification of deficient enzymes to allow them to penetrate the blood–brain barrier, stabilisation of abnormal but active enzyme to prevent its degradation, and implantation of stem cells strongly expressing the missing enzyme. For any future treatment to be successful, it must be administered as early as possible. Currently MPS-III is mainly diagnosed clinically, by which stage it is probably too late for any treatment to be very effective. Neonatal screening programs would provide the earliest possible diagnosis.
The flavonoid genistein decreases the accumulation of GAGs. In vitro, animal studies and clinical experiments suggest that the symptoms of the disease may be alleviated by an adequate dose of genistein. Despite its reported beneficial properties, genistein also has toxic side effects.
According to a study of patients with Sanfilippo syndrome, the median life expectancy varies depending on the subtype. In Sanfilippo syndrome type A, the mean age at death (± standard deviation) was 15.22 ± 4.22 years. For Type B, it was 18.91 ± 7.33 years, and for Type C it was 23.43 ± 9.47 years. The mean life expectancy for Type A has increased since the 1970s.
Incidence of Sanfilippo syndrome varies geographically, with approximately 1 case per 280,000 live births in Northern Ireland, 1 per 66,000 in Australia, and 1 per 50,000 in the Netherlands.
The Australian study estimated the following incidences for each subtype of Sanfilippo syndrome:
|Sanfilippo syndrome type||Approximate incidence||Percentage of cases||Age of onset|
|A||1 in 100,000||60%||1.5-4|
|B||1 in 200,000||30%||1-4|
|C||1 in 1,500,000||4%||3-7|
|D||1 in 1,000,000||6%||2-6|
- Hurler syndrome (MPS I)
- Hunter syndrome (MPS II)
- Morquio syndrome (MPS IV)
- List of neurological conditions and disorders
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- Jonah's Just Begun - Foundation to Cure Sanfilippo, Inc.
- Phoenix Nest, Inc., a biotech company seeking treatments and cures for Sanfilippo Syndrome
- Phunk Phenomenon HipHop For Hope, a dance crew in Boston raising awareness for Sanfilippo Syndrome
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- Media related to Sanfilippo syndrome at Wikimedia Commons