Develop. & epileptic encephalopathy

Understanding developmental and epileptic encephalopathy

Developmental and epileptic encephalopathy (DEE) is a group of rare and severe epilepsies that start in infancy or childhood and are associated with developmental challenges, drug-resistant seizures, and significant impact on daily life.1

What is DEE?

DEE is a medical term that describes the most severe group of rare epilepsies which often share certain challenges, including:

• Delay of physical and mental development1
• Early onset seizures1
• Resistance to anti-seizure medications (ASMs)1-3
• Significant impact on daily life for both individuals and caregivers1

D evelopmental:

• Challenges with learning, growth, or development that may begin early in life and continue over time1,2

E pileptic:

• Seizures that occur as part of the disease, typically multiple, co-occurring seizure types1,2

E ncephalopathy:

• The effects of any syndrome on the structure or function of the brain2-4

Facts about DEE

DEE syndromes are characterized by drug-resistant seizures and developmental or intellectual disabilities, requiring heavy dependence on caregivers.1

Some DEE syndromes are closely linked to a specific genetic, structural, or metabolic cause and others may have multiple possible causes—or no clear cause at all.1,5

DEE syndromes have been defined based on factors such as the type of seizures experienced, age at first seizure, and the part of the brain involved.6

There are many distinct syndromes that fall into the DEE group, including, but not limited to:1,6

• Angelman syndrome
• CDKL5 Deficiency Disorder (CDD)
• Dravet syndrome (DS)
• Infantile spasms or West syndrome
• KCNT1
• Lennox-Gastaut syndrome (LGS)
• Myoclonic Atonic Epilepsy (Doose syndrome)
• Ohtahara syndrome
• SCN8A
• STXBP1
• SYNGAP1
• Tuberous Sclerosis Complex (TSC)

Facts about DEE (Continued)

Diagnosing a specific DEE syndrome can be challenging, as different DEEs share very similar symptoms and even the same DEE can manifest differently from one person to another.3

Beyond the persistent and often poorly controlled seizures, people living with DEE can experience severe wide-ranging comorbid conditions that can significantly impact their quality of life.1

Caregivers who are often parents, siblings, and extended family members have reported high rates of emotional distress, anxiety, and depression, which are exacerbated by sleep disruption due to the need for constant vigilance and seizure unpredictability.7

Epidemiology and burden

DEEs affects an estimated one in every 590 children. 1,3 While it differs among people living with DEEs, the median age of onset is 15.4 months. 8

People often experience many different types of seizures, including:1,3

• Epileptic spasms (brief muscle jerks)
• Focal seizures (affecting specific body parts)
• Tonic-clonic (full-body convulsions)
• Absence seizures (momentary lapses of consciousness)

These can lead to difficulty in performing everyday tasks.

In addition to the severe and unpredictable seizures, people can experience complications with:1,5

• Communication
• Motor function
• Sensory function
• Behavioral and emotional disruptions

As a result, people living with DEE typically require life-long, full-time care – often from family members who serve as primary caregivers.1,7

DEEs are associated with significant mortality:

• For severe forms like early infantile epileptic encephalopathy (onset before three months), 58% of infants may die by their first birthday.9
• Sudden unexpected death in epilepsy (SUDEP) is the most common cause of death among those with genetic DEEs, accounting for approximately 48% of mortality.10

The long-term burden of managing various co-morbid conditions, in addition to life-long, often poorly controlled seizures can severely limit independence for people.1,7

1 in 590

children are affected by DEEs.1,3

15.4 months

is the median age of onset for DEEs.8

People who are concerned that their loved ones are experiencing symptoms of developmental and epileptic encephalopathy should see their doctor for help and advice.

Diagnosis and care

Diagnosing DEE is complex due to the wide-range of underlying causes – over half of DEE cases are genetic (with over 1,000 genes implicated), and others can arise from brain malformation, brain damage, or have an unknown cause.1,3,5 Adding to this complexity, about one-third of people do not fit into any specific, recognized DEE syndrome.1,8 Due to the difficult diagnosis, detection of DEE is often delayed or missed, particularly in older patients.

Diagnosis begins when an infant presents with seizures or infantile spasms, or when they present with developmental delays or regression.1 Initial clinical examinations and tests like electroencephalogram (EEG) and brain imaging are important to characterize the condition.3,10 While these preliminary assessments may not yield a definitive diagnosis, genetic testing can help to precisely identify or confirm a specific disorder, if there is a genetic underlying cause.1

Seizure control is the primary focus of treatment for people living with DEE.1,2 People living with DEE often experience multiple, co-occurring seizure types,1,3 some of which may be more responsive to a particular anti-seizure medication (ASM) than other seizure types.1 Current treatments for DEEs are limited to specific syndromes,1 leaving the broader DEE population without specifically approved treatment options.

Adding to this complexity, the majority of DEEs are resistant to currently available ASMs, which can lead to a trial-and-error approach to treatment management, and the frequent use of multiple ASMs in an attempt to adequately control seizures.1,5 However, combining multiple ASMs can increase the side effect burden and cause significant drug-drug interactions.1,2

References

1. Scheffer IE. Nat Rev Dis Primers. 2024;10:61.
2. Strzelczyk A, et al. CNS Drugs. 2022;36(10):1079 1111.
3. Scheffer IE, et al. Epilepsia. 2025; 66(4):1015-1023.
4. Surdi P, et al. Epilepsia. 2024;65(11):3279 3292.
5. Medyanik AD, et al. Biomolecules. 2025;15:133.
6. Mastrangelo M, et al. Seizure. 2026;134:190-197.
7. Gallop K, et al. Epilepsy Behav. 2021;124:108324.
8.  Poke G, et al. Neurol. 2023;100:e1363-e1375.
9.  Raedelli G, et al. Epilepsy Behav. 2018;85:32-36.
10. Donnan A, et al. Neurol. 2023;100:e1712-e1722.