- Neuronal migration disorders of the cerebral cortex form a heterogeneous group of abnormalities, characterised by mental retardation, epilepsy and hypotonia.

- They are prevalent in 1 of the population and in 20-40 of the untreatable forms of epilepsy.

- Disorders at the start of the migration result in nodular heterotopias. Bilateral periventricular nodular heterotopias are X-linked disorders, in which cortical neurons are unable to leave their position at the ventricular surface due to the absence of filamin 1.

- The large group of lissencephalies can be divided into a number of syndromes, each of which is characterised by a gene mutation (LIS1, DCX, RELN). These mutations result in agyria and pachygyria, which are characteristic for this group.

- A number of these abnormalities, especially the smaller nodular heterotopias and focal cortical dysplasia, may be treated by neurosurgical excision.