What causes LGS?


  • LGS occurs secondary to many different causes including injury, brain malformations, infections, and genetic factors.

  • Most with LGS may have abnormal brain imaging, but some have normal brain imaging prior to developing LGS.

  • LGS can also develop from other epilepsy syndromes such as West, Ohtahara, Hypothalamic Hamartoma, etc.

  • Many genes are associated with LGS and each gene is a risk factor for developing LGS if seizures remain uncontrolled.

  • Emerging evidence suggests that genetic factors account for most unknown causes of LGS.


Who has LGS?

  • LGS constitutes between 3-4% of all children with epilepsy and 1-2% of all people with epilepsy.

  • LGS typically appears between age 2-5 years of age, but can be seen in younger and older children. LGS is established in the majority of children by age 6 years of age.

  • Approximately 13,400 children under the age of 18 in the United States are estimated to have LGS.

  • Approximately 34,300 adults 18 years and older in the United States are estimated to have LGS.

  • This means approximately 48,000 children and adults in the United States currently have LGS.

  • Click here for more information on the epidemiology of LGS. 

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What is LGS?

  • Lennox-Gastaut Syndrome (LGS) is a rare epilepsy syndrome.

  • Nobody is born with LGS. It may develop over time from childhood seizures that remain uncontrolled by treatments.

  • Children and Adults with LGS share similar features:

    • Seizures that start in childhood

    • More than one seizure type

    • Slow spike-and-wave on EEG

    • Developmental delay/cognitive impairment (70% have this at diagnosis of LGS)

  • Any seizure type can be seen in LGS. The most common seizure types are:

    • Tonic

    • Atonic Drop Seizures

    • Generalized Tonic-Clonic

    • Atypical Absence

    • Non-convulsive status epilepticus

    • Myoclonic

  • While developmental delay/cognitive impairment occurs in most with LGS, it is not always present at the start of LGS and is not required for the diagnosis to be made.

How does LGS change over time?

  • There is no cure for LGS. Seizures may go into remission, and may also recur.

  • 30-50% of children with infantile spasms will develop LGS.

  • 80-90% of children with LGS will continue to have seizures into adulthood.

  • Up to 70% with LGS will no longer show slow spike-and-wave (<3Hz) on EEG in adulthood.

  • Most with LGS show paroxysmal fast rhythms (10-20 Hz) on EEG, mainly during non-REM sleep, at some point in their life.

  • 70% with LGS will show cognitive impairment at diagnosis and more than 50% suffer behavioral issues including hyperactivity, sleep disturbances, rage attacks, aggression, and autistic features.

  • The mortality rate is 5%. Those with LGS are 24 times more likely to die prematurely.

  • Premature death in LGS is often due to Sudden Unexpected Death in Epilepsy (SUDEP), seizures, injury, or the underlying brain disorder.



More about LGS:


Adults with LGS:

  • As children with Lennox-Gastaut Syndrome grow older, types of seizures may change. Nearly all adults with LGS have tonic seizures (GPFA on EEG).

  • Older children with LGS often experience acute psychotic episodes, forms of psychosis with aggressiveness, behavioral problems, and irritability.

  • Cognitive issues in adults include slowed reaction time and information processing.

  • More information on adults with Lennox-Gastaut Syndrome including the process of transitioning can be found on our adults page

School-age Children:

  • School-age children are usually placed into a special education classroom or will receive home tutoring.

  • Parents and caregivers may need to consider future options for their child, including legal guardianship, respite care, group home facilities, and/or day programs.

  • For those individuals with LGS who do not have adequate neurological services in their state of residency, an out-of-state facility is suggested.

  • Level 4 facilities (facilities which provide intensive neurological services, elaborate evaluations and treatment options) are typically recommended if the local neurologist or epileptologist does not have experience in treating Lennox-Gastaut Syndrome.

  • For a listing of epilepsy centers in the United States, visit the National Association of Epilepsy Centers


  • The prognosis of Lennox-Gastaut Syndrome can greatly vary from person to person. Complete recovery, with freedom of seizures and normal development, is unusual for a child with LGS. Although there is no cure, there are various treatment options available which can be further explored on our treatments page.

Arzimanoglou A, et al. Epileptic Disord. 2011;13(Suppl 1):S3-S13.

Berg AT, et al. Epilepsia, 2018;59(11).

Bourgeois BF, et al. Epilepsia, 2014;55(Suppl 4).

Cross JH, et al. Front Neurol. 2017;8:505.

Goldsmith IL, et al. Epilepsia, 2000;41(4).

LGS Foundation Caregiver Concerns Survey 2018.

McTague A, et al. Lancet Neurol. 2016;15(3).