Rare diseases · Sign or symptom
Atonic seizure
HP:0010819
What it means
Atonic seizure is a type of motor seizure characterized by a sudden loss or diminution of muscle tone without apparent preceding myoclonic or tonic event lasting about 1 to 2 seconds, involving head, trunk, jaw, or limb musculature.
This term describes the initial semiology of the seizure without specifying whether the onset is focal or generalized. Thus it can be used for coding atonic seizures when the onset is not known.
Rare diseases that can present with this27
Common30–79%
5Sometimes5–29%
22- 3-phosphoglycerate dehydrogenase deficiency, infantile/juvenile form
- Alacrimia-choreoathetosis-liver dysfunction syndrome
- Angelman syndrome
- Bilateral frontoparietal polymicrogyria
- Bilateral generalized polymicrogyria
- Coffin-Lowry syndrome
- Developmental and epileptic encephalopathy with spike-wave activation in sleep
- DPM1-CDG
and 14 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: Astatic seizure · Astatic seizures · Atonic seizures · Drop attacks · Drop seizures · Hypotonic seizure · Hypotonic seizures · Sudden loss of muscle tone
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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.