Rare diseases · Sign or symptom
4-layered lissencephaly
HP:0006818
What it means
A form of lissencephaly in which the cortex is thickened and has four more or less disorganized layers rather than six normal layers resulting from incomplete neuronal migration during brain development. At neuropathological examination, a 4-layered cortex consists of an upper molecular layer, a second thin cellular layer containing pyramidal neurons usually observed in layer V, a third pale poorly cellular layer and a fourth thick deep layer made up of neurons which had failed to migrate. Radiologocally would manifest as agyria or pachygyria with cortical thickness greater than 10 mm.
Rare diseases that can present with this2
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: Classic lissencephaly · Four-layered lissencephaly · Lissencephaly, type I · Type 1 lissencephaly · Type I lissencephaly
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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.