A broadgroup of disorders resulting from genetic, chromosomal or environmental causesthat disturb the process by which newly generated neural cells migrate to theirproper position in the brain, causing distinctive morphological patternsaccording to the causal agent, affected site and gestational age at which thedisturbance occurs. It is a disturbancein migration that typically starts in the second month of gestation from theplace of origin along the lining of the lateral ventricle to a correct positionin one of the lamina of the cerebral cortex, the cerebellum, brain stem andhippocampus. It is controlled by avariety of different cells including Cajal-Retzius neurons and radialglia cells. Resultant structural abnormalitiesinclude, for example, agenesis of the corpus callosum and cranial nerves, andlissencephaly. At birth, however, therecan be little evidence that an infant has a neuronal migration disorder, butthe signs become increasingly more obvious with age, with indications ofatypical developmental and growth patterns. For an experienced neurologist, early signs can include characteristicfacial and skull features. Other signsare poor muscle tone, seizures, feeding difficulties, and microcephalyassociated with mental retardation. Improvements in brain imaging has greatly improved the diagnosis ofthese disorders. Incidence and prevalenceof most of them are not exactly known, but are generally considered to be (extremely)rare occurrences.
See Brain (neuro)-imaging, Brain stem, Cajal-Rezius cells, Cell migration, Cerebellum (anatomy), Cerebellum (development), Cerebral cortex, Corpus callosum, Cranial nerves, Gestationalage, Hippocampus, Incidence, Lissencephaly, Mental retardation, Muscle tone (or power), Prevalence, Radial glia cells, Signs and symptoms, Ventricle