Chromosome 21 trisomy and the causes of Down's syndrome

Down's syndrome is basically a genetic disease that is caused by the presence of an extra chromosome. The chromosome that is defaulted in this syndrome is chromosome number twenty-one. It has been seen that Down's syndrome is one of the most common chromosome disease that is seen in humans. The major striking features of this disorder are physical and mental growth delay. It should be noted that the children appear small for their age and their actions and abilities are also slower than the children their age. It has been noted that Down's syndrome goes on to affect about one in every 800 hundred babies that are born in the United States.

Even though the signs and symptoms are quite variable in all of the children, there are some particular signs that are characteristic of Down's syndrome. Children with Down's syndrome usually have an abnormally small chin, a flat nasal bridge, and slanting eye fissures on the inner corner of their eyes. Most of the children also have a larger than normal sized tongue which usually tends to stick out because of the small size of the oral cavity. Furthermore, it is seen that they have a short nick and white spots on the iris that are also called Brushfield spots. Most of the children with Down's are obese and are of a small stature. They have a common Mongolian look on their face as well. These children also have a simian crease present on their hand along with short fingers.

Causes

As mentioned earlier, Down's syndrome is basically a result of an extra copy of the genetic material on the 21st chromosome. It is noted that can either be the replication of the entire chromosome or it can be the replication of only some material on the chromosome. In order to understand the major mechanism behind the cause of Down's syndrome, it is only necessary for us to note down the basics of human genome replications.

Every cell in the human body consists of genes that either arrives from the mother of the father. All the chromosomes are basically condensed in the nucleus in every cell. Quantitatively speaking, the nuclear material consists of 46 chromosomes where twenty three of the chromosomes come for the mother and twenty three of the chromosomes come from the father.

Trisomy 21 is the most common cause of Down syndrome. Normally, the chromatin material divides and is able to condense 23 chromosomes in every gamete. On fertilization, when the gametes fuse, the end result is an embryo consisting of 46 chromosomes. In Down's syndrome, there is a problem in the cell division which is known as nondisjunction. Due to this reason, one of the sperm or egg that goes for fertilization has an extra copy of the chromosome 21. An interesting thing to note is that 88% of the times, this nondisjunction arise from the mother's egg cell rather than the father's sperm.

There are two other causes present of Down's syndrome known as Mosaic Down Syndrome and Translocation Down Syndrome. The Mosaic Down Syndrome is a very rare form where children only have some cells with the extra copy that was mentioned earlier. As it would be expected, the disease would take a worse form if all the cells in the body are affected. Even though this is a milder film, Mosaic Down's Syndrome is also caused by abnormal cell division and subsequent fertilization. The translocation Down's syndrome is when Chromosome number 21 becomes translocated to another chromosome. This event is likely to occur either before or at conception. Even though these children have the normal two chromosomes 21, there is additional material present on chromosome number 21.

There are a lot of debates regarding what the actual cause of Down's Syndrome is. It was noted that there are many risk factors for Down's syndrome. One of the most common risk factor is increased maternal age. It was noted that as a woman's age increases, the eggs are likely to get defected. Older eggs do have an increased chance of errors during chromosomal division. It is seen that when a woman reaches 35, the risk of her conceiving a child with Down Syndrome is one in four hundred (Egen et.al, 2011) . Similarly, ten years later, the risk increases to one in thirty five. Furthermore, it was noted that when a woman has one baby with this disorder, there are increased chances of having another child with this disease. A lot of people also think that the parents have certain traits that make them more likely to a genetic translocation. Therefore, it is noted that that they pass the translocation for Down syndrome to their children.

Signs and Symptoms

As mentioned earlier, there are many distinct facial and physical features that accompany Down's syndrome. Therefore, some of the earliest signs appear when the baby is born. The baby would have a flat face that has a depressed nasal bright. The ears of the baby can be folded over at the top. Furthermore, the head, nose, feet and hands would be smaller than the normal baby's. The features of having a large protruding tongue and white spots on the iris have already been discussed above. Other apparent features include short hands with a one single crease in the palm. Another notable feature is that there is increased space between the first and the second toe.

It is noted that children with Down's Syndrome appear very floppy at birth because they have decreased muscle tone which is known as hypotonia. Along with hypotonia, these children also have poor muscle tone and loose joints. Most of the time, the facial features of the baby alert the parents that there is something wrong with their child. As the child grows, he or she attains his developmental milestones very late. These children tend to have a blank expression and don't develop the social milestones that a normal baby would have developed.

Furthermore, parents notice retardation as the child grows older. Children who are affected with Down's Syndrome tend to have a speech delay. They do require assistance such as a speech therapy y in order to express themselves in a proper way. Furthermore, they tend to be behind in their gross motor and fine motor skills. The normal age of a child to start walking is about fifteen months .However, children with Down Syndrome will begin to walk at the age of four on average.

Detection and Diagnosis

There are two ways in which health care providers go onto detect and diagnose Down's Syndrome. They can either check for the disease before the child is born or after the child is born. AT first, all women who are pregnant are recommended to get a screening test. During pregnancy, the mother can be screened for Down's Syndrome through ultrasound or testing maternal serum for certain markers. It has been stated that Trisomy 21 can be detected in the second or third trimester of pregnancy. Some findings on the ultrasound my include hypo plastic or absent nasal bone and echogenic bowel, and a thickened nuchal folds. Along with ultra sound, maternal serum is also checked for levels of Alpha feto protein, Hormone Beta HCG and a protein known as u3. It has been stated that decreased levels of AFP indicate towards Down Syndrome.

When there are many indications towards the presence of Down's Syndrome in the baby, then the doctors usually opt for a diagnostic test. There is a slight risk for a miscarriage during the diagnostic test and that is a major reason why woman aren't tested diagnostically in the first place. It is recommended that all women above thirty five who get pregnant should be checked diagnostically to rule out Down's syndrome. In Diagnostic tests, a sample of the genetic material of the fetus is extracted and then checked for the presence of an extra chromosome. The three a method through which diagnostic testing is performed are Amniocentesis, Chronic Villus sampling (CVS) and Percutaneous umbilical blood sampling (PUBS). In amniocentesis, a sample of the amniotic fluid is taking for sampling. As for CVS, a piece of the placenta is taken in order to be tested for the extra chromosome. In PUBS, a sample of the fetal blood is taken through the umbilical cord. This is the most reliable and accurate method that will go on to confirm the results of the aforementioned tests as well.

The presence of an extra chromosome is figured out by the method of karyotyping. If the parents do find out that the child is affected by Down's Syndrome, they might choose to terminate the pregnancy or keep the pregnancy. The decision is entirely up to the patients. Diagnosis and detection after birth is normally made on the physical features of the baby. After birth, baby tissues can be easily karyotyped in order to check for a trisomy.

It should be noted that there is not a single set treatment for Down's Syndrome. It is a disorder that the child is born with and it cannot be cured completely. What doctors can do is assist the individual with her or physical, intellectual, medical and social needs. Therefore, it is noted that children with down syndrome are given physical therapy which assists them in learning how to walk and to develop their motor skills. As mentioned earlier, these children are also provided with speech and language therapy. Because these children are developmentally slow, they need to put in extra effort to get their message across. It is very important for these children to have good communication skills because their needs are far more than that of a normal child.

As the child gets older, he is also provides with occupational therapies to carry out everyday tasks such as eating, writing and using a computer. As the child grows, he is also assist throughout school, university and in choosing career that is the best for him. As it would be expected, children with Down's syndrome might get annoyed and frustrated by the condition they are in. Due to this reason, emotional and behavioral therapy is also very important for these children.

Down's Syndrome itself might not have been so bad were it not with the associated clinical affects that come along with it. Firstly, these children have a very weak immune system due to which they are very prone to infections. It is also noted that about fifty percent of the babies with Down's syndrome are affected with some sort of a congenital heart disease. Even though most of the heart defects are not that serious, some do require immediate surgical intervention.

A large majority of children with Down's Syndrome have vision problems such as decreased visual acuity or cataracts. Due to this reason, they are directed to have frequent vision exams and a visual aid like glasses. Other conditions that might require further treatment are blood disorders like leukemia, hypotnoia, decreased thyroid hormone, celiac disease, gum disease, epilepsy and sleep disorders.

Current Research

Jiang et.al (2013) is working on the idea of manipulating the chromosomes that are involved in the presence of Down's syndrome. It has been noted that scientists are able to get far ahead while dealing with single gene disorders. Even though manipulation of an entire chromosome might be difficult, it is not impossible. Currently, they are making use of an RNA gene that is known as XIST. XIST basically goes on to silence one of the two X chromosomes that is found in female mammals. It is known that XIST basically functions to paint over the chromosome so that chromosome does not make the proteins or other things it has to make. Scientists are therefore working to find a way in which XIST would be able to silence the extra 21 chromosome that is present in patients with Down's syndrome.

This goes on to show that it is possible to able to cure this horrible disease. As it is stated earlier, the children with Down's Syndrome have a lot of associated conditions. Being mentally and socially slow is bad enough, but these children also need a lot of medical attention. Seeing how common this condition is, a cure and a definitive treatment for this condition would revolutionize the medical world.