TN 69 (12-23)

DI 23022.495 MPS III




MPS III; Mucopolysaccaridoses III; Oligophrenic Polydystrophy; Polydystrophic Oligophrenia; Sanfilippo A; Sanfilippo Syndrome; Sanfilippo Type III


MPS III is a lysomal storage disease, which is caused by the absence or malfunctioning of certain enzymes needed to break down molecules called glycosaminoglycans (mucopolysaccharidoes) – long chains of sugar carbohydrates in each of our cells that help build bone, cartilage, tendons, corneas, skin, connective tissue and joints. Individuals with MPS III either do not produce enough of one of the enzymes or they produce enzymes that do not work properly. Over time, these sugar chains collect in the cells, blood and connective tissues resulting in permanent, progressive cellular damage that affects the individual’s appearance, physical abilities, organ and system functioning, and, in most cases mental development.

Sanfilippo A, the most severe of the MPS III disorders, is caused by the missing or altered enzyme heparan N-sulfatase. Individuals with this disease have the shortest survival rate among those with the MPS III disorders.

The disorder is seen in about 1 in 70,000 births.


Diagnostic testing:

  • Clinical examination;

  • Urine tests;

  • Enzyme assays;

  • Blood culture;

  • Echocardiogram;

  • Slit lamp eye exam;

  • Skin fibroblast culture; and

  • X-rays of the bones.

Prenatal diagnosis using amniocentesis and chorionic villus sampling (CVS) can verify if a fetus either carries a copy of the defective gene or is affected with the disorder.

Physical findings: A decline in learning ability typically occurs between ages 2 and 6. The child may have normal growth during the first few years, but final height is below average. Delayed development is followed by deteriorating mental status.

Other physical findings for individuals with MPS III may include:

  • Neurological damage;

  • Intellectual disability or developmental delay;

  • Behavioral problems;

  • Hearing loss;

  • Corneal degeneration;

  • Coarse or rough facial features;

  • Dysplasia (abnormal growth of tissue or organs);

  • Thickened skin;

  • Enlarged liver or spleen (hepatosplenomegaly);

  • Hernias;

  • Excessive body hair growth;

  • Claw-like hands;

  • Joint stiffness;

  • Carpal tunnel syndrome;

  • Respiratory infections;

  • Sleep apnea; and

  • Heart disease.

ICD-9: 277.5

ICD-10: C76.22


The syndrome causes significant neurological symptoms, including severe intellectual disability. IQs may be below 50. Most individuals with MPS III live into their teenage years. Some individuals live longer, while others with severe forms die at an earlier age.


Currently there is no known treatment. Medical care is directed at treating systemic conditions and improving the person's quality of life. Physical therapy and daily exercise may delay joint problems and improve the ability to move.


Suggested MER for Evaluation:

  • Clinical examination that describes diagnostic features of the impairment;

  • Laboratory tests showing results of genetic testing;

  • Enzyme study tests;

  • Urine tests; and

  • MRI or CT scan.

Suggested Listings for Evaluation:








110.08 B

Evaluate most severe forms with early childhood onset under 110.08 B; for less severe, late onset forms, evaluate under the affected body systems.

* Adjudicators may, at their discretion, use the Medical Evidence of Record or the listings suggested to evaluate the claim. However, the decision to allow or deny the claim rests with the adjudicator.

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DI 23022.495 - MPS III - 12/27/2023
Batch run: 12/27/2023