Neuronal migration disorder
Definition & Facts
Neuronal migration disorders are a heterogeneous group of disorders that result from abnormalities in neuronal migration which is a process by which neurons travel from the place at which they were created (neurogenesis) to the part of the brain that they ultimately settle in.
NMDs are a series of birth defects (that is, congenital disorders) that formulate as a baby’s brain is taking shape, which can begin as early as the second month of pregnancy though neuronal migration can continue until the infant is five months old. More than 25 different variations of NMD have been described and diagnosed.
Neuronal migration disorders are very rare and not much is known about their origin, their cause or how to go about treating or preventing them. There is, however, much research being done to study and explore the science behind how these disorders affect the brain and the body.
Syndromes and diseases that fall into the category of neuronal migration disorders include the following: schizencephaly, porencephaly, lissencephaly, argyria, polymicrogyria, pachygyria, microgyria, micropolygyria, neuronal heterotopias, agenesis of the corpus callosum, and agenesis of the cranial nerves.
Symptoms & Complaints
People with symptoms of neuronal migration disorders may also have difficulty eating due to dysphagia and occasionally experience swelling and pain in the arms, legs, and other extremities such as the fingers. In rarer cases, neuronal migration disorders may result in a smaller than normal head (microcephaly).
The symptoms that tend to arise from this disease tend to be static in nature and normally do not improve. Individuals that have severe neuronal malformations, such as individuals with lissencephaly, have a greater chance of dying at a young age. People with neuronal migration disorders are also more susceptible to infections such as pneumonia.
Neuronal migration occurs in the fetus as early as the second month of gestation. Neuronal migration is controlled by a web of interrelated chemicals that guide and give signals to neurons within the brain. When these signals fail to function or when they are not present in the body, neurons can end up in incorrect places within the brain and give unreadable or incorrect signals to the brain.
There are a variety of genetic factors and environmental factors that may play a role in causing neuronal migration disorders. Genetic mutations have been identified and may occur spontaneously as opposed to being inherited.
Factors affecting a pregnant woman's health that have not been conclusively proven may include viral infections, bacterial infections, smoking, and diabetes mellitus. Infections that are known to interfere with neural development but not necessarily neuronal migration disorders include rubella, toxoplasmosis, HIV, cytomegalovirus (CMV) infection, and group B streptococcal infection.
Diagnosis & Tests
A neurologist will play a significant role in determining whether or not a neuronal migration disorder is present in an individual. Neurologists will physically examine an individual's external facial and skull features.
A diagnosis is made utilizing the technologies of neuroimaging and it is common to perform a computed tomography (CT) scan or an magnetic resonance imaging (MRI) of the brain, which will quickly show the characteristic abnormality of cells and brain formation.
Typically, blood tests are also helpful in determining which diseases may or may not be present. Electroencephalography (EEG's) may also be performed. These examine the electrical activity of the brain and can detect the presence and location in the brain of seizures.
Treatment & Therapy
Treatment for neuronal migration disorders focuses on addressing symptoms. While there is no definitive cure, treatment usually includes the administration of anti-seizure medication. Such drugs include valproate, carbamazepine, and lamotrigine. Occupational therapy, physical therapy, and speech therapy are often encouraged to address disabilities. Special education may also be utilized.
Other types of treatment and therapy include surgery such as neurosurgical removal of abnormal brain tissue which can help to prevent seizures. In cases of extreme or condensed buildup of muscle tissue, muscle relaxants may be injected into the body as a form of treatment. Finally, as brain function is impaired, patients may be required to receive assistance from feeding tubes for basic functions such as eating and swallowing.
Since this disorder is most common among infants and babies, physicians encourage parents to seek some type of support group for emotional support and informational resources.
Prevention & Prophylaxis