No single cause of OS has been identified. In most cases, there is severe atrophy of both hemispheres of the brain. Cerebral malformations such as hemimegalencephaly, porencephaly, Aicardi syndrome, olivary-dentate dysplasia, agenesis of mamillary bodies, linear sebaceous nevus syndrome, cerebral dysgenesis, and focal cortical dysplasia have been noted as suspect causes.
Ohtahara syndrome
Pallister–Killian syndrome
Cohen syndrome
Cohen-Gibson syndrome
Berdon syndrome
Scheie syndrome
Gleich's syndrome
Christianson syndrome