Rare diseases · Sign or symptom
Focal-onset seizure
Seizure affecting one half of brain
HP:0007359
What it means
A focal-onset seizure is a type of seizure originating within networks limited to one hemisphere. They may be discretely localized or more widely distributed, and may originate in subcortical structures.
In 2017 the ILAE Commission for Classification and Terminology recommended classifying a seizure as having focal or generalized onset only when there is a high degree of confidence (>80%, arbitrarily chosen to parallel the usual allowable beta error) in the accuracy of this determination; see Dialeptic seizure.
Rare diseases that can present with this64
Very common80–99%
8Common30–79%
24- Alpers-Huttenlocher syndrome
- Bilateral perisylvian polymicrogyria
- Bilateral polymicrogyria
- CDKL5-deficiency disorder
- Developmental and epileptic encephalopathy with spike-wave activation in sleep
- Familial adult myoclonic epilepsy
- Focal facial dermal dysplasia type IV
- FOXG1 syndrome
- Isolated focal cortical dysplasia
- Lissencephaly type 1 due to doublecortin gene mutation
- Macrocephaly-intellectual disability-neurodevelopmental disorder-small thorax syndrome
- MELAS
- Meningioma
- Mowat-Wilson syndrome due to a ZEB2 point mutation
- Mowat-Wilson syndrome due to monosomy 2q22
- Myoclonic epilepsy of infancy
- Periventricular nodular heterotopia
- Pyridoxine-dependent-developmental and epileptic encephalopathy
- Rolandic epilepsy-speech dyspraxia syndrome
- Self-limited epilepsy with centrotemporal spikes
- Self-limited infantile epilepsy
- Sneddon syndrome
- Subependymal nodular heterotopia
- Tuberous sclerosis complex
Sometimes5–29%
26- 17q11microdeletion syndrome
- Bilateral generalized polymicrogyria
- Contractures-developmental delay-Pierre Robin syndrome
- Cortical dysgenesis with pontocerebellar hypoplasia due to TUBB3 mutation
- Cysticercosis
- DK1-CDG
- DNM1L-related encephalopathy due to mitochondrial and peroxisomal fission defect
- Early infantile developmental and epileptic encephalopathy
and 18 more in this range
The range is how often this sign appears among people diagnosed with each disease — it is not a probability of having any of them. Many of these signs also occur in common, non-rare conditions. A sign on this page is a conversation to have with a clinician, not a conclusion.
Part of the broader category
Also called: Focal onset seizure · Focal seizure · Focal seizures · Focal-onset seizures · Partial seizure · Partial seizures
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Start free with EleplanThis page uses the Human Phenotype Ontology (2026-06-23) — Human Phenotype Ontology Consortium, hpo.jax.org. Disease associations from Orphanet (INSERM), CC BY 4.0. Content is educational and is not medical advice.