| Early Infantile Developmental Epileptic Encephalopathy |
0–3 months of age |
Tonic and/or myoclonic seizures |
Developmental impairment is prior to or shortly after onset of seizures |
40% |
| Infantile Epileptic Spasm Syndrome |
1–24 months of age |
Flexor, extensor or mixed epileptic spasms, which often occur in clusters |
Developmental slowing after spasms onset, but may be absent early in course |
14% |
| Atypical Rett Syndrome |
N/A |
N/A |
A period of regression followed by recovery or stabilization with 2/4 of main criteria (loss of acquired purposeful hand skills, loss of acquired spoken language, Gait abnormalities, stereotypic hand movements) with 5/11 of supportive criteria |
2.6% |
| Lennox-Gastaut Syndrome |
Seizure onset prior to 18 years. (Often progress from IESS or severe infantile epilepsy syndrome) |
Tonic seizures with at least 1 other seizure type (atypical absence, atonic, myoclonic, focal impaired awareness, generalized tonic-clonic, epileptic spasms) |
Often have developmental slowing, plateauing or regression with moderate to severe ID in >90% of patients |
<1% |
| Dravet Syndrome |
6–15 months of age |
Focal seizures with impaired awareness, Absence seizures, Myoclonic seizures, Atonic seizure |
Often normal development followed by developmental plateauing |
<1% |
