When we imagine a brain, whether human or not, the image that comes to mind is generally composed of an organ whose outer layer is full of folds, between which you can see some indentations that allow us to appreciate the presence of two halves or brain hemispheres.
This separation is something that most human beings have, forming during our fetal development. But not all: there are boys and girls whose brain is not divided or whose hemispheres are fused: we are talking about children suffering from holoprosencephaly
Holoprosencephaly is called a type of malformation throughout fetal development in which there is no division between the different structures of the forebrain: there is a fusion between the cerebral hemispheres, as well as between some subcortical structures and the cerebral ventricles. This fusion or rather non-separation can occur at a complete or partial level (the hemispheres being fused completely or only in some parts).
Generally, the division of the brain into different lobes and hemispheres It occurs around the fourth week of gestation. In holoprosencephaly, this division does not occur or it cannot be completed, which has severe repercussions both before and after birth. This condition usually comes together with the presence of cranial and facial malformations, with alterations such as hypertelorism or close-set eyes, cyclopia or only one eye, nose alterations, cleft lip, cleft palate or hydrocephalus. Likewise, problems with feeding and thermal maintenance, cardiac and respiratory disorders, and seizures are common. It is also associated with different degrees of intellectual disability, in cases mild enough to allow life.
In general, holoprosencephaly has a very poor prognosis, especially in the alobar type: boys and girls They usually die either before birth or before reaching six months of age In the other types, survival is possible up to one or two years of life. Depending on whether there are other complications and the severity of the disorder. In milder cases, survival is possible, although they will generally suffer from cognitive deficits to a greater or lesser extent.
Some of its main main variants
Holoprosencephaly is a medical condition that can present in different ways, depending on the possible degree of separation of the cerebral hemispheres. Three first variants mainly stand out, the most common, although it must be taken into account that there are others. These types of holoprosencephaly are the following
1. Lobar holoprosencephaly
Lobar holoprosencephaly is the mildest form of this type of alteration. In this case it can be observed the presence of almost perfectly separated lobes although this separation has not been carried out in the frontal lobes and they do not usually have a septum pellucidum.
2. Semilobar holoprosencephaly
In this variant of holoprosencephaly there is a division between the hemispheres in part of the brain, but the frontal and parietal lobes are fused. The interhemispheric fissure is only observed in the temporal and occipital
It is common for hypotelorism to occur, that is, the baby’s eyes are much less separated than would be usual, they are small, or they do not exist at all. A cleft lip or palate may also be observed, as well as absence or malformations at the nasal level.
This is the most severe form of holoprosencephaly, in which the hemispheres do not separate to any degree, being completely fused. It is common that there is a single ventricle and/or a single thalamus.
Many of these children are also born with only one eye, in which case the existence of cyclopia is considered. In fact, the emergence of the mythical figure of the Cyclops was probably based on the observation of some cases of this type of holoprosencephaly. The nose usually has malformations, and may have a proboscis-shaped formation or even no nostril (something that can cause suffocation of the child) or only one of them.
4. Interhemispheric holoprosencephaly
This variant, less common than the previous three, occurs when the division of the brain does not occur in the middle part: the posterior parts of the frontal and parietal lobes. There is no corpus callosum (with the possible exception of the genu and splenium), although generally at the level of subcortical structures there is no overlap or fusion Also called syntelencephaly.
5. Aprosencephaly
Although technically it would no longer be holoprosencephaly, sometimes aprosencephaly is also considered a variant of this disorder, in which the forebrain does not form directly.
Causes of this problem
Holoprosencephaly is an alteration that occurs during fetal development, with a wide variety of possible factors that can lead to its emergence. The existence of a large number of cases has been observed in which There are genetic alterations in numerous genes (one in four has alterations in the ZIC2, SIC3, SHH or TGIF genes), as well as different syndromes and chromosomal disorders (Patau syndrome or Edwards syndrome among them).
A link has also been observed with environmental factors, such as uncontrolled diabetes in the mother or the abuse of alcohol and other drugs, as well as the consumption of some medications.
Treatment
This condition, generally genetic, has no curative treatment. The treatments to be applied will generally be palliative in nature aimed at maintaining their vital signs, correcting difficulties and improving their well-being and quality.
In mild cases that achieve survival, the use of occupational therapy and cognitive stimulation is recommended. The need to apply a multidisciplinary treatment involving professionals from different disciplines, including medicine and occupational therapy, clinical psychology, physiotherapy and logotherapy, must be assessed. And this without neglecting the treatment of parents and the environment (which will require psychoeducation and counseling, as well as possibly psychological intervention).
