Developmental and epileptic encephalopathies are severe epilepsies in which developmental impairment arises from the underlying disorder, epileptic activity, or both.
What the term means
The modern DEE concept recognises that development may be affected both by the cause of the condition and by frequent seizures or epileptiform activity.
That is different from assuming every developmental difficulty is caused solely by seizures.
The phenotype changes with age
Some DEEs begin with catastrophic seizures in infancy, while others emerge later with language, cognitive or behavioural regression.
The seizure burden may lessen with age even when motor, cognitive or behavioural disability persists.
Comorbidity is the rule, not the exception
Intellectual disability, autism, movement problems, sleep disturbance, gastrointestinal difficulties and psychiatric features are common across many DEEs.
The exact pattern depends on the syndrome and aetiology.
Genetics has transformed diagnosis
Many DEEs are now linked to pathogenic variants in ion channels, synaptic proteins, transcription factors and metabolic pathways.
A molecular diagnosis can affect prognosis, counselling, treatment and trial eligibility.
EEG and neuropsychology can show disease evolution
Longitudinal EEG and developmental assessment may reveal changing patterns over time.
Recent work argues that disease progression cannot be understood from seizure counts alone.
Related reading
Sources and further reading
- Developmental and epileptic encephalopathies, Nat Rev Dis Primers 2024
- DEE trajectories from childhood to adulthood, 2026
- EEG and neuropsychology in DEE progression, 2024
Evidence checked: September 2026.