What Are The Symptoms

Children with Sanfilippo Syndrome appear healthy at birth and typically do not show obvious signs of the disease.

However, even early on, many common childhood conditions are consistently seen in children with Sanfilippo that are related to the disease. These can be easily dismissed and families are often reassured that the child “will grow out of it.”

It is necessary to look at the whole picture of what is going on with your child. If more than one of the following signs or symptoms are noted, it is important to consider checking for Sanfilippo.


  • Transient Tachypnea Of Newborn*
    (fast breathing after birth)
  • Coarse Facial Features*
    (frontal bossing/prominent forehead, full lips and nose)
  • Prominent, thick eyebrows*
  • Persistent Hirsutism*
    (execessive body hair)
  • Macrocephaly*
    (large head size)
  • Speech & Developmental Delays+
  • Hearing Loss+
    (typically high-frequency, sensorineural hearing loss)
  • Recurrent Ear/Sinus Infections
  • Chronic Upper Respiratory Congestion
    (persistent nasal congestion/drainage)
  • Challenging Behaviors
    (hyperactivity, impulsivity, poor sense of safety, difficulty cooperating)
  • Features of Autism
    (speech regression, mouthing/oral fixation, loss of interest in social interactions, repetitive speech/behaviors)
  • Sleep Disturbances
    (difficulty going to sleep; frequent nighttime waking, often with disruptive behaviors; difficulty getting back to sleep)
  • Diarrhea/Chronic Loose Stools
  • Umbilical/Inguinal Hernia
  • Enlarged Liver/Spleen

*The most-specific indicators of Sanfilippo syndrome in infants, as reported in Escolar C, Bradshaw J, Byers V, et. al, 2020, Development of a Clinical Algorithm for the Early Diagnosis of Mucopolysaccharidosis III. Journal of Inborn Errors of Metabolism & Screening. 2020, Volume 8: e20200002.
+Early neurological features of Sanfilippo.

Signs of Sanfilippo can be present in the newborn period, but often go unnoticed without newborn screening. Most symptoms begin to be recognized between 1 and 6 years of age when the child begins showing signs of developmental delay. and undertake formal assessment.

Because of its rarity, the disease remains largely unfamiliar to most medical practitioners. It is not uncommon that parents search for years to find the cause of their child’s difficulties before a correct diagnosis is made.Sanfilippo can masquerade as ADHD (attention deficit hyperactivity disorder), autism, and intellectual disability.Because of this delay in finding the underlying diagnosis, many families have had other children born in the meantime … only to find out that their younger children are also affected with the disease.

As Sanfilippo progresses, children will typically develop extreme hyperactivity and behavioral problems. Sleep problems become so severe that they may not sleep for days or for only a few hours per night. They gradually lose all the abilities and skills they had acquired, such as speaking, walking, and the ability to eat by mouth.


  • Continued Coarsening of Facial Features
  • Development of features of Autism
  • Progressive Intellectual Disability
  • Brain Atrophy (
    shrinking of brain tissue from loss of nerve cells)
  • Seizures/Movement Disorders
  • Behavioral problems
  • Hyperactivity
  • Impulsivity
  • Loss of Ambulation
  • Loss of Oral Feeding
    (chewing and swallowing problems)
  • Enlarged Liver/Spleen
  • Hearing Loss
    (typically high-frequency, sensorineural hearing loss)
  • Early Death
Figure depicting progressive disability of Sanfilippo Syndrome in child compared to a neurotypical child

For Additional Information: