| Domain | Evidence summary for Myoclonic Epilepsy in Infancy (MEI) | Suggested ontology terms | Key citation |
|---|---|---|---|
| Classification / scope | Rare infant-onset epilepsy syndrome recognized by ILAE 2022; a self-limited infantile generalized epilepsy syndrome. **Do not conflate** with Dravet syndrome (formerly severe myoclonic epilepsy in infancy; developmental/epileptic encephalopathy, usually SCN1A-related) or with **familial infantile myoclonic epilepsy** (distinct familial/genetic entity). MONDO: **MONDO_0100566**. | MONDO: MONDO_0100566; NCIT: Epilepsy syndrome-related concept; HPO: HP:0002123 (Generalized myoclonic seizure) | (pqac-00000000, pqac-00000002) |
| Epidemiology | Rare: **<0.8%** of children with epilepsy in specialty settings; **1.1%** of all epilepsy with onset before 36 months in a population-based cohort. Male predominance about **2:1**. | PATO/clinical descriptor: male predominance | (pqac-00000002, pqac-00000005) |
| Onset | Usual onset **4 months to 3 years**, with peak **6–18 months**. Onset at **≤4 months** or **>3 years** is a warning/exclusionary feature for classic MEI. | HPO: HP:0011463 (Childhood onset), HP:0003593 (Infantile onset) | (pqac-00000002, pqac-00000003, pqac-00000004) |
| Core seizures | Mandatory phenotype: frequent **myoclonic seizures** involving **head and upper limbs/upper arms**, occurring **multiple times daily**, during **wakefulness and sleep**. At syndrome onset, other seizure types should be absent. | HPO: HP:0002123 (Generalized myoclonic seizure) | (pqac-00000002, pqac-00000004) |
| Triggers / reflex features | About **one-third** have reflex-provoked seizures triggered by **sudden noise, touch, or startle**; intermittent photic stimulation may also precipitate events in some reports. | HPO: HP:0025258 (Startle-induced seizure) or related reflex-seizure descriptor | (pqac-00000002, pqac-00000003, pqac-00000005) |
| EEG | Background typically **normal while awake**. Interictal EEG shows **generalized spike-wave or polyspike-wave** discharges, often around **~3 Hz**, more evident in **early sleep**. If sleep EEG lacks generalized spike-wave, **ictal EEG is strongly recommended** because some myoclonic events may lack a clear EEG correlate. | HPO: HP:0010848 (Abnormality of EEG); EDAM/EEG descriptor: generalized spike-wave discharge | (pqac-00000002, pqac-00000003) |
| MRI / imaging | **No causal lesion** expected; **nonlesional brain MRI** supports diagnosis. Structural lesion argues against classic MEI. | UBERON: brain; RadLex/SNOMED descriptor: normal brain MRI | (pqac-00000003) |
| Development / exam | **Development before seizure onset is typically normal** and neurological examination is normal. Long-term development is normal in **63–85%**; some later show **mild intellectual disability, learning disorder, or attention problems**; rarely moderate-severe ID occurs. | HPO: HP:0001263 (Global developmental delay) when present; HP:0001249 (Intellectual disability); HP:0007018 (Attention deficit) | (pqac-00000002, pqac-00000005) |
| Genetics | Family history of epilepsy or febrile seizures in about **10%**. **No causal genes are established for classic MEI** in the ILAE 2022 definition. Reported gene-associated “myoclonic epilepsy of infancy” cases should be interpreted cautiously as possible **phenocopies/etiology-specific epilepsies**, not proof of monogenic classic MEI. | No validated causal gene annotation for classic MEI; avoid asserting SCN1A/SLC2A1/YWHAG as established MEI causes | (pqac-00000002, pqac-00000003, pqac-00000004) |
| Course / prognosis | Favorable seizure course: myoclonic seizures remit in **nearly all cases** within **6 months to 5 years**; most children can discontinue antiseizure medication. About **10%** later develop another epilepsy, most commonly **juvenile myoclonic epilepsy**. | HPO: HP:0011458 (EEG with generalized spike-wave); clinical course descriptor: self-limited/remitting | (pqac-00000002, pqac-00000004, pqac-00000005) |
| Diagnosis / differential | Diagnosis is syndrome-based using age at onset, seizure semiology, normal development, normal exam, normal/nonlesional MRI, and generalized spike-/polyspike-wave on EEG. Exclusionary seizure types at onset include **absence, atonic, epileptic spasms, focal seizures, generalized tonic-clonic, or clonic seizures**. Key differentials: **benign myoclonus of infancy**, **hyperekplexia**, **hypnic jerks**, **Dravet syndrome**, and **epilepsy with myoclonic-atonic seizures**. | HPO: HP:0002376 (Febrile seizures) when present; SNOMED/NCIT differential diagnosis descriptors | (pqac-00000002, pqac-00000003) |
| Treatment / evidence gaps | No MEI-specific modern trials were identified. Standard practice in reviews has favored antiseizure medication with later withdrawal after remission; ILAE evidence notes that **most children discontinue treatment** after remission, but robust comparative data are lacking. **Evidence gaps:** no established biomarker, no confirmed molecular pathway, no precision therapy, no prevention strategy, no disease-specific clinical trials located for classic MEI. | NCIT: Anticonvulsant therapy; evidence-gap flag for biomarker/genetic/advanced-therapy fields | (pqac-00000005, pqac-00000004) |


*Table: This table compiles ontology-ready, knowledge-base-focused evidence for classic Myoclonic Epilepsy in Infancy, centered on the 2022 ILAE definition and supporting review data. It highlights key diagnostic and prognostic facts while explicitly separating MEI from Dravet syndrome and familial infantile myoclonic epilepsy.*