Rare diseases · Sign or symptom
Lissencephaly
Fewer or absent grooves in brain
HP:0001339
What it means
A spectrum of malformations of cortical development caused by insufficient neuronal migration that subsumes the terms agyria, pachygyria and subcortical band heterotopia. See also neuropathological definitions for 2-, 3-, and 4-layered lissencephaly.
Lissencephaly (LIS, which subsumes the terms agyria and pachygyria), together with subcortical-band heterotopia (SBH) comprises a spectrum of malformations of cortical development caused by insufficient neuronal migration. The key features of LIS are an abnormally thick cortex with reduced or absent formation of the cerebral convolutions, while SBH consists of abnormal bands of neurons beneath a normal cortex, although the cerebral gyri may be separated by unusually shallow sulci.
Rare diseases that can present with this25
Very common80–99%
6Common30–79%
7Sometimes5–29%
9- Desmosterolosis
- Hypertelorism-hypospadias-polysyndactyly syndrome
- Iniencephaly
- Kagami-Ogata syndrome due to paternal uniparental disomy of chromosome 14
- Laminin subunit alpha 2-related congenital muscular dystrophy
- Microcephalic cortical malformations-short stature due to RTTN deficiency
- Phosphoserine aminotransferase deficiency, infantile/juvenile form
- Ring chromosome 17 syndrome
and 1 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
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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.