Sometimes the alteration of the neuronal migration process causes agyria, a brain malformation that causes the cortex to have an abnormally smooth appearance, with the gyri and grooves characteristic of this region being absent. When these signs appear, the diagnosis of “lissencephaly” is used.
In this article we will describe What is lissencephaly, what are its causes and its most common symptoms? and how such alterations can be treated or at least managed.
Lissencephaly is a set of disorders characterized by a smoothing of brain regions in which there are generally folds and crevices. These malformations frequently cause alterations in the development of the nervous system and therefore cognitive and psychomotor functions.
During intrauterine development the cerebral cortex folds back on itself in many parts. This allows the volume of nervous tissue that fits inside the skull to be much greater than if the surface of the brain were completely smooth.
However, in cases of lissencephaly the furrows and folds of the brain do not form correctly, so that this organ shows a homogeneous appearance. The intensity of this smoothing can vary in each individual, depending on the causes of the alteration.
It is a very rare disorder that can have important consequences for physical and mental development. In the most severe cases, intellectual functioning is very severely affected, while in others the deficits may be minimal.
Life expectancy is around 10 years. The most frequent causes of death are asphyxiation due to choking, diseases of the respiratory system and epileptic seizures, which can be very serious.
The symptoms of lissencephaly depend on the severity of the malformations in the cerebral cortex, as well as the specific regions that are affected. The fundamental aspect is agyria, a technical term used to refer to the flat appearance of the cerebral cortex.
In many cases the head size of babies born with this disease is very small compared to that of other newborns. Although this is a very characteristic sign of lissencephaly, it is not present in all people affected by a disorder of this type. Sometimes hydrocephalus (accumulation of cerebrospinal fluid) occurs.
Alterations in the cerebral cortex cause delays and deficits in physical, psychomotor and cognitive development. It is also common for physical malformations to occur in the hands, as well as in their fingers and toes. On the other hand, muscle spasms and seizures are common.
Lissencephaly also tends to cause swallowing problems, which in turn makes it difficult to eat and drink. Consequently, in many cases physical development is even more altered by nutrient deficiency.
Causes of this alteration
Lissencephaly appears as a consequence of alterations in the formation of the cerebral cortex that occur during pregnancy. The causes of these errors can be very diverse; however, the most common are related to genetic factors.
When intrauterine development progresses normally, between the twelfth and fourteenth weeks after fertilization, the embryo’s nerve cells begin to move from the regions of the brain where they are generated to different ones. In lissencephaly this cell migration process does not take place properly.
Scientific research reveals that this problem is usually due to mutations in multiple genes: brain development is affected by not being able to express them correctly. The genes involved seem to be located on chromosomes X, 7 and 17, although they are probably not the only ones.
Virus infections and decreased blood flow that the fetus receives can also cause signs of lissencephaly by interfering with the development of the central nervous system.
An association has been identified between lissencephaly and two genetic diseases: Miller-Dieker and Walker-Warburg syndrome. It is very common for agyria to occur in the broader context of one of these disorders.
Treatment
Since it is an alteration in the morphology of the brain, lissencephaly cannot be corrected in itself. It is evident that it is not possible to go back in the development of the nervous system once it has occurred.
Because of this The treatment of lissencephaly is basically symptomatic and its objectives are to improve the quality of life and enhance the functioning of affected people.
Thus, for example, in cases where swallowing difficulties are very marked a gastric tube may need to be placed into the stomach of babies so they can feed properly.
Muscle spasms and epileptic seizures can be managed through the use of specific medications for these types of disorders. On the other hand, when there is hydrocephalus, surgical interventions are carried out to drain the accumulated cerebrospinal fluid.
