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Mucopolysaccharidosis type III
Reviewed by Medicinsk Expert•Last updated: 2026-10-22•Condition

Mucopolysaccharidosis type III

Mucopolysaccharidosis type III, or Sanfilippo syndrome, is a progressive disorder primarily affecting the central nervous system, leading to neurological deterioration and behavioral challenges.

Overview

Mucopolysaccharidosis type III (MPS III), also known as Sanfilippo syndrome, is a disorder that primarily affects the brain and spinal cord. While physical features are often mild in early stages, the condition is characterized by progressive neurodegeneration.

Symptoms

  • Developmental delay or delayed speech
  • Behavioral problems (restlessness, hyperactivity, anxiety, impulsivity, or aggression)
  • Features of autism spectrum disorder
  • Sleep disturbances
  • Progressive intellectual disability and developmental regression
  • Late-stage seizures, loss of mobility, and movement disorders
  • Physical features: coarse facial features, prominent forehead, large head (macrocephaly), and thick hair/eyebrows
  • Mild skeletal abnormalities, joint stiffness, or short stature
  • Mildly enlarged liver (hepatomegaly) or spleen (splenomegaly)
  • Umbilical or inguinal hernias
  • Cardiac abnormalities, chronic diarrhea, and recurrent infections

Causes

MPS III is caused by variants in the GNS, HGSNAT, NAGLU, and SGSH genes. These genes provide instructions for enzymes required to break down heparan sulfate, a type of glycosaminoglycan (GAG). When these enzymes are deficient, partially broken-down heparan sulfate accumulates within the lysosomes, interfering with cellular function and primarily impacting the central nervous system.

Inheritance

This condition is inherited in an autosomal recessive pattern. Both copies of the gene in each cell must have variants for the condition to occur. Parents of an affected individual are typically carriers who do not exhibit symptoms.

Types

MPS III is divided into four types based on the specific gene involved:

  • MPS IIIA:SGSH gene variants
  • MPS IIIB:NAGLU gene variants
  • MPS IIIC:HGSNAT gene variants
  • MPS IIID:GNS gene variants

Frequently Asked Questions

Establish a strict bedtime routine, use low‑dose melatonin (0.5–3 mg) 30 minutes before sleep, and limit screen exposure after 6 pm. For severe agitation, a pediatric neurologist may prescribe low‑dose clonidine or trazodone. Environmental modifications—white‑noise machines, weighted blankets, and a cool bedroom—often improve continuity.
When gait becomes unstable, a pediatric gait trainer or powered wheelchair with tilt‑in‑space seating helps preserve independence. Home modifications include installing grab bars in the bathroom, a stair lift or ramp, non‑slip flooring, and a bedside commode. Occupational therapists can assess for adaptive utensils and communication devices as speech declines.
Enzyme replacement therapy (ERT) is not yet approved for the CNS manifestations of MPS III, but several intrathecal ERT and gene‑therapy trials (e.g., AAV‑mediated SGSH delivery for type A) are recruiting. Your metabolic specialist can refer you to ongoing studies listed on clinicaltrials.gov, and compassionate‑use programs may be an option for select patients.
Key clues include a normal developmental trajectory in the first year followed by a sudden plateau or regression around ages 2–4, progressive loss of previously acquired speech, and emerging sleep disturbances or hyperactivity that worsen over time. Laboratory testing for elevated urinary glycosaminoglycans and confirmatory enzyme assays are definitive.
Source: MedlinePlus, National Library of Medicine

MedlinePlus brings together authoritative health information from the National Library of Medicine (NLM), the National Institutes of Health (NIH), and other government agencies and health-related organizations.

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