Holoprosencephaly: types, symptoms, and treatments

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, among which you can see some cracks that allow us to appreciate the presence of two halves or hemispheres cerebral.

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 with holoprosencephaly.

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Holoprosencephaly: what is it?

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 ventricles cerebral. This fusion or rather non-separation can occur at a complete or partial level (the hemispheres being completely fused or only in some parts).

Usually, 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, existing alterations such such as hypertelorism or eyes together, cyclopia or one eye, alterations of the nose, cleft lip, cleft palate or hydrocephalus Likewise, it is frequent that problems appear in feeding and in thermal maintenance, cardiac and respiratory disorders and seizures. 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 being born or before reaching six months of life. In the other types, survival up to one or two years of life is possible. Depending on whether there are other complications and the severity of the disorder. In milder cases, survival is possible, although in general they will suffer from cognitive deficits to a greater or lesser extent.

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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. Mainly three first variants stand out, the most common, although it must be taken into account that there are others. These types of holoprosencephaly are as follows.

1. Lobar holoprosencephaly

Lobar holoprosencephaly is the mildest form of this type of disorder. In this case you can see 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 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.

Hypotelorism is common, that is, the baby's eyes are much less separated than would be usual, that they are small or that they do not exist at all. Cleft lip or palate can also be observed, as well as absence or malformations at the nasal level.

3. Alobar holoprosencephaly

It is the most serious form of holoprosencephaly, in which the hemispheres do not separate to any degree, being completely fused. A single ventricle is common 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 case of this type of holoprosencephaly. The nose usually has malformations, being able to have a proboscis-shaped formation or even no nostril (something that can cause suffocation of the minor) 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 genu and splenium), although generally at the level of subcortical structures there is no overlap or fusion. Also called synthelencephaly.

5. Aprosencephaly

Although technically it would no longer be holoprosencephaly, aprosencephaly is also sometimes considered a variant of this disorder, in which the forebrain does not directly form.

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. A large number of cases have 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).

An association with environmental factors has also been observed, 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 of a genetic type, does not have a curative treatment. The treatments to be applied will generally be palliative., 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, both medicine and occupational therapy, clinical psychology, physiotherapy and logotherapy. And this without neglecting the treatment of the parents and environment (which will require psychoeducation and counseling, as well as possibly a psychological intervention).

Bibliographic references:

• Monteagudo, A. & Timor-Tritsch, I.E, (2012). Prenatal diagnosis of CNS anomalies other than neural tube defects and ventriculomegaly (online). Available in: http://cursoenarm.net/UPTODATE/contents/mobipreview.htm? 9/28/9665 / abstract / 4-12
• Cohen, M.M. & Sulik, K.K. (1992). Perspectives on holoprosencephaly: Part II. Central nervous system, craniofacial anatomy, syndrome commentary, diagnostic approach, and experimental studies. J. Craniofac. Genet. Dev. Biol., 12: 196.