| Main clinical features
|
frequent early death
generalized, absence, or seizures, microcephaly (defined as having an occipitofrontal circumference [OFC] at or below −2.5 SD for age and sex)
severe developmental delay, progressing to profound intellectual disability, cerebral palsy with absent ambulation and lack of speech, and/or a progressive neurodegenerative course
no additional extra-CNS (central nervous system) malformations
at MRI, diffuse bilateral polymicrogyria (PMG), or diffuse pachygyria, and reduced central white matter volume |