Patau’s syndrome

patau's syndrome

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Pregnancy is usually good news, accompanied by excitement, joy and courage. However, it is not only positive emotions. In addition to fear, it carries some risks for the fetus, such as the development of Patau’s syndrome, a very serious anomaly. We may be familiar with other syndromes, such as Dawn syndrome or Edwards’ syndrome, but it is also necessary to know the first one, which is the protagonist of this post.

Nowadays there are detection and prevention solutions available in case of pregnancy. It is very important to know that tests can be requested for the diagnosis of these syndromes in a future baby, since some of these syndromes cause the newborn not to exceed one year of life. Today we will look specifically at Patau’s syndrome and what the screening tests are like.

infographics patau's syndrome

It all starts with trisomies

Patau syndrome is a genetic disease caused by the presence of a total trisomy (a whole chromosome) or partial trisomy of chromosome 13. Before continuing, let us explain what a trisomy is: it is a chromosomal alteration that causes that, out of the 23 pairs that form the human genotype, there is an extra chromosome. Therefore, instead of 46 chromosomes, there would be 47.

The human genome is made up of 23 chromosomes that are inherited from the mother and 23 that are inherited from the father. When the chromosomes of the father and the mother are the same, they are paired. In each cell of our body we can find these 23 pairs of resulting chromosomes. Of the 23 pairs, the only ‘different’ chromosomes are the sex chromosomes, which form XX or XY pairs. This means that the fetus can inherit 2 X chromosomes (belonging to the mother) or one X and one Y (belonging to the father). This example would be the union that occurs in most cases. However, sometimes changes occur that affect a person’s chromosomal endowment.

Patau syndrome occurs when there is a third chromosome 13. The origin of this anomaly may be due to a defective separation of chromosomes in the formation of the eggs and sperm of the parents. Although it is very unlikely, it may also have its origin in a Robertsonian translocation, in which 2 chromosomes fuse into one.

A very serious anomaly

The sad reality is that, because it is such a serious anomaly, 95% of those diagnosed die before birth. Those born have a very low life expectancy; 50% die within the first month of life and 70% within 6 months. Average survival, therefore, is usually around 12 months. These babies usually die of cardiorespiratory problems.

Patau syndrome is not hereditary, but an advanced maternal age may be a risk factor. Medical care is necessary from the birth of the baby and should be followed up. However, the rate of miscarriages in fetuses with this anomaly must be taken into account; they represent about 1% of all recognized miscarriages.

Gynecologists and medical professionals are responsible for informing pregnant women of possible unknown fetal syndromes. Therefore, it is essential to consult a physician or request an analysis from an expert laboratory that offers these laboratory tests, such as AmbarLab.

Characteristics of Patau syndrome

This syndrome causes both intellectual disabilities and physical abnormalities. It also includes severe psychomotor retardation and an IQ that decreases with age. There are other alterations that arise due to this syndrome:

  • Alterations of the nervous system. Some characteristics are mental retardation, holoprosencephaly (defect in the division of the embryonic frontal lobe) and muscular hypotonia.
  • Physical abnormalities. Patients with Patau’s disease may have decreased interorbital distance, including ‘fusion’ of both eyes into one, coloboma (hole or slit in the iris) and cleft lip (opening in the upper lip). Those affected with this chromosomal alteration may develop 2 or more noses and have disorders in the formation of the tongue. Polydactyly (presence of extra fingers) is another complication.
  • Other alterations. There are other alterations, such as enlarged kidneys and hydronephrosis (accumulation of urine in the kidneys). They may also develop certain cardiovascular anomalies, such as valvular dysplasia.

Types of Patau syndrome

This anomaly can manifest itself in several forms. The most common is caused by partial or total trisomies in all of the patient’s cells (explained above). However, there is another less common form of this chromosomal disorder: mosaic. A person can have different genetic compositions in different parts of the body. These cases are known as ‘mosaics’ or ‘chimeras’ (depending on the origin). Therefore, patients with mosaic Patau syndrome have 2 or more genetically distinct cell populations in their body. They have cells with 46 chromosomes and cells with 47 chromosomes.

How to detect Patau syndrome

As we discussed at the beginning of the post, there are certain tests or analyses that can detect or prevent the birth of a baby with Patau syndrome. We will explain them below:

  • Amniocentesis. A small amount of amniotic fluid (the fluid that surrounds the fetus during pregnancy, inside the amniotic sac) is extracted. It undergoes various tests, including genetic testing to rule out the presence of certain diseases, including Patau’s syndrome.
  • Screening in the first trimester. This is a study that combines hormone analysis and ultrasound, taking into account the maternal age. It is performed between 9/13 weeks of pregnancy. Although it is only a predictive test, it can give some clue as to whether the baby is growing healthy.
  • Fetal ultrasound. It is performed at different times during pregnancy. It can be used to suspect Down’s, Edwards’ and Patau’s syndromes. However, a fetal ultrasound is not an official conclusion and requires a diagnostic test to confirm the result.
  • Chorionic biopsy. This is similar to amniocentesis. In this case a sample of the chorionic villi is extracted from the placenta, with which some genetic tests will be performed, such as karyotyping or array-CGH (detects microdeletions and microduplications in the fetal genome). It is performed from the 11th week and has a risk of miscarriage of 1-2%.
  • Non-invasive prenatal test, NIPT. This is the safest test for the fetus (amniocentesis and chorionic villus sampling pose certain risks for the development of the pregnancy) and can be performed from the 10th-11th week of pregnancy. It should be pointed out that a diagnosis cannot always be made with non-invasive prenatal testing alone. This type of test, which is performed on the basis of a blood sample from the mother, can help to detect most cases, leaving some which will then have to be confirmed with an invasive test.

Recap

Patau syndrome is a very severe polymalformative congenital anomaly. It affects approximately one in every 12,000 live births. It is a dangerous genetic variation: those affected rarely live beyond 12 months of age. It usually affects babies whose parents are older (31-37 years), although there are also cases in which the parents are younger.

Patau syndrome is caused by the existence of three copies of chromosome 13 in the karyotype. Hence, this genetic anomaly is also known as pair 13 trisomy. The physical anomalies of this syndrome allow its clinical suspicion at the time of birth of the baby. Some of them are cleft lip, cranial malformations, cardiac and renal malformations, growth retardation, hypotelorism, absence of palate in some cases, tongue disorders and appearance of more than 2 noses. Abnormalities may also appear in the abdomen, such as omphalocele and vesicular exstrophy. Cardiac malformations are also quite common, along with renal malformations and severe psychomotor retardation.

That is why it is so important to know the analyses and tests that can be performed during pregnancy to diagnose this syndrome and act as both the doctors and the pregnant woman deem appropriate. Some of the tests are fetal ultrasound (it is not an official diagnosis), amniocentesis, first trimester screening (it is only predictive), chorionic villus sampling (it has a risk of miscarriage) and non-invasive prenatal testing, NIPT.

Detection

Since this is a very serious disease, it is necessary to perform the appropriate analytical procedures, so that the pregnant woman is as comfortable as possible and does not run any risk. You should always be advised by your doctor or gynecologist. AmbarLab has a catalog of tests that is updated with each new scientific news and our team is responsible for advising on any of them. We also have the development of customized R&D projects and consulting services and acceleration of laboratory operations. Do not hesitate to contact us to make an appointment or to solve any doubt about our laboratory or about the tests we offer.

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