DOWN'S SYNDROME

The word intelligence comes from the words intel-between and legare-to see interconnections, which together mean to see interconnections between things and phenomena. There is no single definition of this complex psychic function. Comprehensively, it can be said that it is the global ability of an individual to act purposefully, to think and act rationally and to deal successfully with his environment.
We divide intelligence disorders into two large groups according to whether it is a congenital or early acquired intelligence defect or a loss of intelligence that was properly developed. We are therefore talking about mental retardation-oligophrenia (a state of stopped or undeveloped mental development) or dementia (loss of previously acquired intellectual functions).
In genes, although stable physico-chemical structures, under the influence of natural and more often induced (artificial) agents-mutagens in human pathology, there is a change at the molecular level in the sequence of DNA nucleotides (bases) with altered and missing information for the synthesis of specific proteins. If the error that occurs in a part of DNA is not corrected by multienzyme (repair) systems, it is transmitted. Genetic diseases and diseases in which the genetic component is significant are classified as:
1. monogenetic diseases
2. chromosomal diseases or disorders
3. multifactorial diseases
4. mitochondrial diseases

Chromosomal diseases are caused by abnormalities in chromosomal number or structure, or both. Chromosomal aberrations are mutations that can be seen with a light microscope (visualization). Over 600 chromosomal abnormalities are known. Of the total number of children, 0.5-0.7% have chromosomal abnormalities. As a rule, autosomal aberrations give a significantly more serious clinical picture and prognosis than sex chromosome aberrations, which are indicated by microanomalies, growth retardation, mild mental retardation, and sexual development abnormalities. The most common type of this disease is trisomy 21, better known as Down's syndrome.

Down syndrome

Down's syndrome is a form of chromosomal pathology that occurs as a result of trisomy of chromosome 21 (picture 1). The characteristics are a specific facial appearance and mental retardation as a mandatory indicator of this syndrome. It was described for the first time by Lagdon Down in 1866. on his own child, and only in 1957 was it established that the cause of this syndrome was trisomy.


In 95-97% of cases, Down's syndrome is not a hereditary disease and occurs in all races and in all economic groups. The occurrence of Down's syndrome is not related to any lifestyle habits of the parents. It has been proven that the age of the mother (over 35 years of age) increases the possibility of Down's syndrome in the child. Down's syndrome is a consequence of the presence of one more chromosome in the child's cells. The frequency of this syndrome in the human population is 1:700 live births. This frequency is affected by the age of the mother, so that in women over 40 years of age, this frequency increases to 1:45 live births.
The karyotype of a person with Down syndrome is:

• 47 XX(21+) or

• 47 XY(21+) (total number of chromosomes, sex constitution + chromosome that is in excess).

The cause of trisomy 21 can also be a balanced translocation of chromosome 21 in one of the parents (it is believed that this is the cause in only about 5% of cases). Such a parent, in addition to normal gametes, can also produce gametes in which chromosome 21 is in excess. Combining such abnormal gametes (having two chromosomes 21) with normal ones (having one chromosome 21) will result in a zygote carrying an unbalanced translocation 21. A person with unbalanced translocation 21 will have a karyotype with 47 chromosomes because chromosome 21 is in excess (trisomic) and phenotypically Down syndrome.
With the use of prenatal diagnostics, the frequency of Down's syndrome in newborns has been significantly reduced.
For all these reasons, people with this syndrome live twice as long on average as compared to healthy people. People also have recognizable features such as (picture 2) :

• obliquely (mongoloid) set and widely spaced eyes;
• small nose, broad root;
• reduced head circumference and flat nape;
• the mouth is small, so a normally large tongue protrudes from it, and the tongue itself is often enlarged and furrowed;
• the auricles are almost always poorly formed, small and low;
• the teeth are irregular in shape and number and erupt late;
• hands are wide and with short fingers;
• on the palms, there may be a furrow of four fingers (monkey furrow) with altered dermatoglyphs (lines on the hands) and others.


The most distinctive features of this syndrome are:
• mental retardation (IQ= 40-50, although there is data that IQ can be from 25-80);
• anomalies of the heart followed to varying degrees by anomalies of other organs,
• reduced resistance to infections,
• increased risk of leukemia,
• premature aging, and for all these reasons, they live twice as long on average compared to healthy people.

However, like all people, they vary greatly in appearance, personality and abilities. With babies, it is difficult to determine the extent to which they will be affected as children or when they grow up. Some people with Down syndrome are able to get a job and lead a relatively independent life, but most of these people need help and support in the long run. In general, the maximum possible mental development reaches the level of an 8-year-old child. A number of health problems are associated with Down syndrome (most commonly heart problems and hearing and vision impairments), although some of these people have good health. In most cases, people with Down syndrome live up to the age of 50, but some of them live over 70. year. Alzheimer's disease (a form of senile dementia) occurs earlier in these people compared to the rest of the population.


Probability and cause of Down syndrome


People usually do not expect a baby to have Down's syndrome. It does not often run in families. The previously held opinion that only older women can have a child with Down syndrome is not correct. Any woman can have a child with Down syndrome, but the risk increases with age, the older a woman is the more likely she is to have a child with this condition. For example, the probability of having a baby with Down syndrome is 1 in 1,500 (0.07%) in a woman at age 20; 1 in 900 (0.1%) in women aged 30; while in women aged 40 it is 1 in 100 (1%).

Inside all body cells are tiny structures called chromosomes. They carry genes that determine the way we develop. Most people have 23 pairs of chromosomes in each cell. When our body creates special cells for fertilization, pairs of chromosomes divide and rearrange. Sometimes these pairs of chromosomes do not divide correctly, which then causes the baby's cells to have an extra copy of chromosome number 21. This leads to the appearance of Down syndrome and is the reason why this syndrome is also called Trisomy 21. The extra chromosome cannot be removed from the cells, so that there is no cure for this condition. Mispartitioning of chromosomes happens by chance and is not caused by the actions of the parents.



Down syndrome screening during pregnancy

Most women want to know if their baby has Down syndrome. Information about the tests and how they are performed can be helpful in making this decision.

There are tests that provide definite information and are called diagnostic tests. However, performing these tests increases the risk of spontaneous abortions. For this reason, they are not recommended for all women. Instead, the tests are performed in two stages. Initially, all women are offered tests in which there is no risk of spontaneous abortion. This type of test is called a screening test. They do not give a definitive answer, but tell us whether there is an increased risk for Down syndrome. After that, women at increased risk can be offered a diagnostic test. If the screening test result is between one in two and one in 250, a diagnostic test should be performed. (A one in 250 risk is at the same time a 0.4% risk)

It is important to understand that screening tests cannot determine with certainty whether or not a baby has Down syndrome, but are only used to avoid the risk of performing unnecessary diagnostic tests. The woman herself decides whether or not to do both phases of the test. If she decides to take a screening test, and later is offered a diagnostic test, she decides for herself whether she will agree to the test or not.

All the tests that will be described later give results in the form of one in ...., for example: one in 100 or one in 1500, the same result can be expressed in percentages. These values tell us how likely the baby is to have Down syndrome. So a result of one in 100 means that one in 100 babies has a chance of having Down syndrome. A result of one in 1,500 indicates that there is a probability that one in 1,500 children will be born with this condition. It should be emphasized that the higher the second number, the lower the possibility of this trisomy. In the following, we will explain how, based on the results of the screening test, the further course of the examination is decided.

Women in whom further examinations are unnecessary

If the screening test shows that the risk of Down syndrome is lower than one in 250, we will not insist on diagnostic tests. The majority of screening test results (about 95%) fall into this category and represent low risk results. Please note that low risk means exactly that, it does not mean that the risk of a child having Down's syndrome does not exist at all, but that it is unlikely and that the probability is obtained less than the result of one in 250 which is the limit for further testing.
Here, there is still a small possibility that some children with Down syndrome were not detected by the screening method. This happens if the expected model is not recognized by blood tests or scanning methods, due to a small natural difference. All together, a quarter of babies with Down syndrome are not detected by screening tests.


Women in whom further investigations are required

If the result of the screening test shows that the risk of the baby having Down's syndrome is higher than one in 250 (for example, one in 100), the possibility of performing diagnostic tests should be offered. These screening test results are sometimes labeled as high-risk results. A total of one in 20 women (5%) has these results.

Results of diagnostic tests

The baby does not have Down syndrome - is the most common result. For some women, this information is quite enough and they do not ask further questions, while others want to talk to someone about the results with someone. They want to know the reason why the results of the screening test and the diagnostic test do not match.
As already stated, by using the screening test, we decide whether the woman should be offered a diagnostic test. What we conclude from the screening tests is that there is a certain type of model in the blood test or ultrasound examination. This model is such that it can sometimes be found in babies with Down syndrome, but the problem is that it can also be found in normal pregnancies. The results of the mentioned tests vary slightly depending on the most different physiological conditions. A screening test detects a pattern, but not the reason that led to it. Only a diagnostic test can show whether the cause of the obtained results is the existence of Down's syndrome in the baby. When a woman takes a diagnostic test and the result shows that the baby does not have Down syndrome, the previously obtained results of the screening test are considered false positives.
The baby does not have Down syndrome, but another problem has been noticed - the main purpose of amniocentesis or chorionic villus sampling is to find out whether the child has Down syndrome or not. However, when examining the baby's chromosomes, other variations can very rarely be seen. Some of them can be very serious while others have very little or no effect on the baby. If the tests show this problem, the woman must consult a genetics consultant.
The baby has Down syndrome - a small number of tests indicate this outcome, in which case there are three possibilities that depend entirely on the parents.
Some people choose to continue the pregnancy, preparing for the additional challenges they will have to face raising a child with Down syndrome. Others opt for adoption because they consider themselves insufficiently capable of raising a child with this problem on their own. Some people decide that they do not want to continue the pregnancy and decide to terminate it.
Anyone faced with such a problem must try to make the right decision for himself based on all the information he has received. A woman will have the opportunity to discuss her options with a doctor, and support and additional information is also available outside of health services. She will have time to make a decision about the option that suits her best, regardless of it and the support of her doctor.