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Living with Mucopolysaccharidosis, MPS-III-A

A rare, progressive genetic condition that mainly affects the brain, with worsening thinking and memory, behavior changes, and seizures.

Understanding Mucopolysaccharidosis, MPS-III-A

Mucopolysaccharidosis MPS-III-A is a rare, progressive genetic disease that mainly affects the brain and spinal cord.

People cannot break down a large sugar molecule called heparan sulfate, so it builds up and damages brain cells. Signs usually begin in early childhood and include worsening thinking and memory, aggressive behavior, hyperactivity, seizures, hearing loss, vision loss, and sleeping only a few hours at a time.

Signs & symptoms

Symptoms vary from person to person. GARD lists these among the most common:

  • Delays in reaching developmental milestones
  • Sleep disturbance
  • Seizures
  • Hearing impairment
  • Diarrhea
  • Hernias

Not everyone has every symptom. GARD's list comes from the Human Phenotype Ontology.

Diagnosis

  1. Talk with your doctor

    Share the symptoms you've noticed, when they started and your family health history. Notes and photos can help.

  2. See a specialist

    Specialists who may be involved include bone and joint specialists, brain and nervous system specialists, eye disease specialists and genetic specialists.

  3. Consider genetic testing

    Changes in SGSH are linked to this condition. Genetic testing and counseling can help confirm a diagnosis and explain what it means for your family.

  4. Connect with expert centers

    World Craniofacial Foundation and Epilepsy Foundation may keep lists of experts for this condition.

Care & treatment

Care team
Bone and joint specialists (orthopedists or orthopedic surgeons); Brain and nervous system specialists (neurologists); Eye disease specialists (ophthalmologists); Genetic specialists (geneticists)
Expert care
Expert lists: World Craniofacial Foundation, Epilepsy Foundation
Treatment
GARD doesn't list specific treatments for this condition. Your care team will tailor care to your symptoms.
Research
Clinical trials and observational studies may be options. See the research section below.

General information, not medical advice. Your care team makes the decisions.

Everyday life

Living with a rare condition is easier with support.

  • Connect with Cure Sanfilippo Foundation and other patient organizations
  • Keep notes on symptoms, changes and questions for appointments
  • Ask about patient registries that help research
  • Look into financial aid and travel resources for care visits
Bring these questions to your next doctor visit
Can genetic testing for the SGSH gene confirm this diagnosis?
What can help with sleep, behavior, and seizures?
Are there clinical trials or treatments we should ask about?

Quick facts

InheritanceAutosomal Recessive
GenesSGSH

This condition is caused by changes in the SGSH gene. It is autosomal recessive, which means a child inherits a changed copy of the gene from each parent.

GeneticNeurologicalInherited MetabolicLysosomal Storage

Also known as: heparan sulfamidase deficiency; heparan-n-sulfatase deficiency; mps iii a; mps iii-a - mucopolysaccharidosis iii-a; mps3a; mpsiiia

Patient organizations

Source: NIH GARD · Mucopolysaccharidosis, MPS-III-AGARD ID 7071 · GARD page updated September 2026 · Plain-language summary by Know Rare; editorial review pending. General information, not medical advice.

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