Neuronal migration disorders are the birth defects that develop because of the abnormal migration of neurons in the developing brain and the nervous system. As the fetus continues to grow in the womb, the neurons are required to migrate and settle to their proper neural circuits. The neuronal migration typically occurs in the second month of pregnancy which is controlled by a complex chemical signaling system. The neuronal migration disorders can occur when these signals are either absent or are incorrect resulting in the neurons not settling where they should. This can cause structural abnormality or missing part of the brain. The symptoms of the neuronal migration disorders can vary based on the abnormality but often presents poor muscle tone, seizures, developmental delays, a problem with the motor function, failure to grow and thrive normally, difficulties with feeding and a smaller than a normal head. There are more than 25 different syndromes identified resulting from the problem of neuronal migration with different patterns of inheritance. Some of the structural abnormalities associated with the neuronal migration disorders include schizencephly, polymicrogyria, macrogyria, pachygyria, lissencephaly, porencephaly and neuronal heterotopias.
Schizencephaly
This is a rare cortical malformation resulting in grey matter- line clefts that can either affect a single or both the sides of the brain. This is considered to be one of the rarest forms of brain malformation. There are various causes associated with the development of this abnormality which can include folic acid deficiency, certain environmental issues and genetics. The affected individuals commonly have developmental delays, delays in speech, language skills and seizures. The treatment is based on the severity of symptoms and is based on the specific medical needs of the individual.
Porencephaly
This is a rare disorder of the central nervous system where a cyst or cavity filled with cerebrospinal fluid develops in the brain. In addition to the abnormal development before the birth, it can also occur because of a damage from stroke or an infection after the birth of the infant. The symptoms include delayed growth, slight or incomplete paralysis, larger or smaller than a normal sized head and low muscle tone. These affected children can also present absent speech development, epilepsy and hydrocephalus which is the accumulation of fluid in the brain. The treatment consists of medications for the symptoms and the placement of a shunt in the brain to drain the excess fluid accumulation.
Lissencephaly
This is a brain malformation that can either occur as an isolated abnormality or in association with another underlying syndrome. Lissencephaly is characterized by the absence or the incomplete development of ridges of the outer region of the brain resulting in the unusually smooth appearance of the brain’s surface. The symptoms can include a small head, seizures, severe intellectual disability, feeding difficulties, impaired motor abilities and feeding difficulties. The treatment aims at providing symptomatic relief and supportive care.
References
http://wearerare.org/schizencephaly/
https://www.ninds.nih.gov/Disorders/All-Disorders/Porencephaly-Information-Page
https://rarediseases.org/rare-diseases/lissencephaly/
