Mucopolysaccharidosis, Type IIIA (Sanfilippo Syndrome A)

Gene : SGSH

What is mucopolysaccharidosis type IIIA?

Mucopolysaccharidosis type IIIA (MPS3A), also known as Sanfilippo syndrome type A, is an inherited lysosomal storage disorder that mainly affects the brain and spinal cord. It is due to a deficiency of the N-sulfonoglucosamine sulfohydrolase enzyme. Children with MPS3A appear normal at birth, but develop symptoms during early childhood. Early symptoms of MPS3A include delayed speech and behavior problems. Children with MPS3A will have worsening intellectual disability and will lose skills they had previously learned, such as crawling and walking. They will eventually develop seizures, movement problems, and hearing and vision loss. People with MPS3A may live into early adulthood. There is no cure for MPS3A; however medical surveillance and care may help to improve some symptoms and overall condition of life. MPS3A is caused by pathogenic variants in the SGSH gene.

How is mucopolysaccharidosis type IIIA inherited?

MPS3A is inherited in an autosomal recessive manner. This type of inheritance requires the presence of two copies of a pathogenic variant in the gene for a person to have the genetic disease. Both parents must be carriers of a pathogenic variant in the gene in order to be at risk to have an affected child. The child must inherit a pathogenic variant from each carrier parent in order to be affected. There is a 1 in 4 chance that a baby will inherit two mutated copies of the gene and be affected when both parents are carriers.

What does it mean to be a carrier?

There are generally no signs or symptoms associated with being a carrier for MPS3A. However, the risk to have a child affected with MPS3A increased. Testing of reproductive partners is recommended for carriers of MPS3A.

How common is mucopolysaccharidosis type IIIA?

MPS3A is a rare disorder that is estimated to occur in 1 in 70,000 newborns. There are four types of MPS3. Type A is the most common and most severe.

Family References and Resources
Clinician References
What is Analyzed?
  • Full gene sequencing
Affected Systems






GI Tract

Carrier Rates
Detection Rate
Carrier Frequency
General Population > 99% 1 in 151

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