Facts about SYNGAP1 & Epilepsy

  • >85% of SYNGAP1 Patients have some type or combination of epilepsy
  • 5 – 500 DIAGNOSED with Epileptic Encephalopathy have SYNGAP1
  • SYNGAP1-ID/DEE should be considered in an individual with developmental delay or ID with or without generalized epilepsy and/or ASD.

General Facts

  • More than 80% of individuals with SYNGAP1 mutations have generalized epilepsy, with focal seizures occurring only in a minority of cases
  • The age of seizure onset ranges from 3 months to 7 years (most often at 2-3 years) 
  • Developmental delays typically precede seizure onset
  • Developmental plateau or regression accompanies seizure onset in many patients, consistent with a diagnosis of DEE.
  • Seizures are quite frequent, ranging from 10-100 per day, but brief, each lasting a few seconds

Types of Seizures

    • Absence seizures are the most common type of seizure
    • Focal seizures occur only in a minority of cases
    • Patients can manifest multiple seizure types; include eyelid myoclonia with absences, typical absences, atypical absences, and myoclonic absences
    • As many as 35% patients – eyelid myoclonia (EM) evolving to myoclonic seizures followed by drop attacks, or EM evolving directly to atonic seizures
    • Other seizure types such as myoclonic, atonic, myoclonic-atonic, and tonic-clonic are also observed 

Reflex Seizures

Evoked by a specific afferent stimulus:

  • startle
  • flash of light
  • reading
  • eating
  • photo-sensitivity

Chewing-induced reflex seizures:

  • biting
  • triggered by chewing
  • oral sensory stimuli such as touching the mouth or face
  • The most commonly observed reflex seizures are eyelid myoclonia
  • Seizures precipitated by photic stimulation during EEG or sunlight, and eye closure sensitivity (ECS) – eye closure-induced epileptiform discharges, appearing within 2-4 seconds of eye closure and lasting for 1-4 seconds
  • Fixation off sensitivity (FOS) has also been observed

Other General Resources

What is a seizure?

A seizure is a sudden surge of electrical activity in the brain.

A seizure usually affects how a person appears or acts for a short time.

Many different things can occur during a seizure. Whatever the brain and body can do normally can also occur during a seizure 

Types of Epilepsy Syndromes

An epilepsy syndrome is defined by a group of features usually occurring together.

The features in a syndrome may include types of seizures commonly seen, age when seizures commonly begin, part of the brain involved, usual course, genetic information, and much more.

Collectively this description provides information on what medicine and other treatments may be helpful.

Types of Seizures

Seizures are generally described in two major groups of seizures: generalized seizures and focal seizures.

The difference between the types of seizures is in how and where they begin in the brain.


Epilepsy Foundation – http://www.epilepsy.com/

Rare Epilepsy Network – https://ren.rti.org/

Agarwal M, Johnston MV, Stafstrom CE, Syngap1 Mutations:
Clinical, Genetic, And Pathophysiological Features, International Journal of Developmental
Neuroscience (2019), doi: Published Site

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