Down syndrome - Wikipedia
Down syndrome (DS or DNS), also known as trisomy 21, is a genetic disorder caused by the Since the introduction of screening, pregnancies with the diagnosis are often terminated. Regular National Association for Down Syndrome. Down syndrome (trisomy 21) is the most common chromosomal disorder. Down syndrome is associated with a host of symptoms and characteristics . Many are able to have jobs, live independently, and have relationships. Nondisjunction results in an embryo with three copies of chromosome 21 instead of researchers feel may have a significant association with Down syndrome). Amniocentesis is usually performed in the second trimester between 15 and
More babies with Down's syndrome are conceived than are born, because the chance of miscarriage is higher if the foetus has Down's syndrome. The reason why older women are more likely to have children with Down's syndrome is unknown.
There are two main current theories. One theory suggests that all women have some eggs with an extra chromosome, and that these eggs are more likely to be used last, towards the end of a woman's reproductive life. The other theory suggests that the rate of trisomic conceptions is the same at all maternal ages, but that affected pregnancies are more likely to continue less likely to end in miscarriage in older women.
The assumption is that the body recognises that this is a late pregnancy, perhaps the last or only one, and thus tries harder to make sure the pregnancy comes to term. What is the chance of having another baby with the condition? Parents with one baby with regular trisomy 21 are usually told that the chance of having another baby with Down's syndrome is 1 in Very few families are known who have more than one child with Down's syndrome, so the real chance is probably less than this.Top IMPORTANT Facts about Down Syndrome - Trisomy 21 - 2017 - TheCoolFactShow Ep60
There are differences of opinion as to how the much-quoted figure of 1 in should be interpreted for older mothers who already have one child with Down's syndrome. Others feel that, when the age-related chance is more than 1 inthis alone gives the more realistic estimate so for a woman of 43, the chance remains 1 in This usually arises when the small arms of chromosome 21 and another chromosome break, and the two remaining long arms join together at their exposed ends.
This process of chromosomes breaking and rejoining to other chromosomes is known as translocation because the chromosome material has transferred its location. People with Down's syndrome which has arisen in this way still have an extra copy of a large part of chromosome Their features of Down's syndrome are no different from those in a child with regular trisomy The chromosomes that can be involved are numbers 13, 14, 15, 21, How does translocation occur?
In two-thirds of people with Down's syndrome due to a translocation, the translocation was an isolated event during the formation of the individual egg or sperm involved in their conception. As with regular trisomy 21, there is no known reason why this occurs. It cannot be predicted and it is not a result of anything the parents or other family members have done. Because it is a new event, this is sometimes called a de novo translocation. The egg or sperm contains the usual number of chromosomes i.
Thus there is one free, whole chromosome 21 and most of a second chromosome 21 attached to another chromosome. The translocated chromosome acts like a single chromosome in cell division, and hence all the cells produced from this first cell will contain the extra chromosome 21 portion.
This baby will therefore have Down's syndrome. In the other one third of people with the translocation type of Down's syndrome, the translocation is inherited from one of the parents. This parent has two whole number 21 chromosomes in each cell but one of them is attached to another chromosome. As there is no loss or gain of any genetic material this is known as a balanced translocation and the parent is a carrier of the translocation. It is important to realise that because such parents have the usual amount of genetic material, they have no traces of the syndrome themselves and never will have.
They cannot be expected to know they are carriers, as the only way of knowing is to study their chromosomes. When people who carry a translocation produce an egg or sperm, it is possible for them to pass on both the translocated chromosome and the free chromosome 21 in the egg or sperm.
This will result in a fertilised egg with two free 21 chromosomes and a translocated chromosome. The baby will therefore have Down's syndrome. Is age a factor in translocation Down's syndrome?
What is the chance of having another child with the condition? Translocation carriers can have children who are carriers, children whose chromosomes show no rearrangement at all, or children with Down's syndrome. For translocations involving chromosomes 21 and any other chromosome, the chance of another child with Down's syndrome being born is about one in six if the mother is the carrier and about one in twenty if the father is the carrier.
A few people are carriers for a translocation between two chromosomes 21; in these people, who are quite ordinary themselves, the only possible outcome is a child with Down's syndrome. How can we know which type of Down's syndrome a baby has? There are no differences in the features or ability levels of people with regular trisomy 21 and translocation Down's syndrome.
The only way of knowing what type of Down's syndrome a person has, is by taking a blood sample and looking at the chromosomes. A very few children with translocation have partial trisomy 21 - where only a part of chromosome 21 is present in 3 copies. These children may have fewer characteristics of Down's syndrome.
Like the more usual type of translocation described above, this type may arise de novo, or a parent may carry it. As one third of people with translocation Down's syndrome have inherited the condition, their parents have a high chance of having another affected child and may wish to know whether this is so. To identify these parents, chromosome tests are done on all new babies with Down's syndrome. Blood samples can then be taken from parents of babies with translocations, to find out whether one of the parents carries the translocation.
Genetic counselling should always be available to families with a child with Down's syndrome. Translocation carriers and other members of the family? Even if parents do not intend to have more children, knowing that one of them is a carrier can be important for all their children or other relatives. Relatives of a person who carries a translocation have an increased chance of being translocation carriers. Mosaicism People with mosaic Down's syndrome have an extra chromosome 21 in only some of their cells.
They therefore have a mixture of trisomic cells and ordinary cells. Depending on the proportion of trisomic cells, and which parts of the body contain these cells, individuals may be less affected both in their physical features and in their ability level than those with regular trisomy or translocation. As for all types of Down's syndrome, it is not possible to say at birth how affected a person will be, only time will tell as the child develops.
How does mosaic Down's syndrome happen? Mosaicism arises after the egg and sperm have fused at conception. As the cells divide and multiply by ordinary cell division, a chromosome goes astray and a single cell with an extra chromosome 21 is formed. This cell continues to divide by ordinary cell division together with the non-trisomic cells and a mixture is produced. As with the other two types of Down's syndrome apart from when a parent is a carrier there is no known reason why mosaic Down's syndrome occurs.
It happens equally often in parents of all ages. What are the chances of having another child with mosaic Down's syndrome? Mosaic Down's syndrome is very rare, therefore there are no accurate figures on this.
It is believed that the chance is lower than it would be if the child had regular trisomy Some questions we have been asked Can a test-tube baby have the condition?
Down Syndrome: Trisomy 21
Yes - full chromosome tests are not carried out before the embryo is implanted. Is trisomy 21 the only kind of trisomy? Chromosomes 13 and 18 are larger than chromosome 21 and so the genetic imbalance is greater and the effects on the baby are generally more severe than in trisomy Trisomy for the X chromosome or an extra copy of the Y can occur, with relatively few effects for the child.
Trisomies of every other chromosome can occur, but usually those pregnancies end in miscarriage. Parents who have had a baby with one kind of trisomy are not thought to be more likely to have a baby with any other kind of trisomy. Is trisomy much more frequent in miscarriages? In about half of all miscarriages occuring in the first 3 months of pregnancy, the developing baby has an altered number of chromosomes.
Will gene therapy make a difference? As we understand more about how the genes on chromosome 21 interact to cause Down's syndrome, we can imagine a situation in which it might eventually become possible to switch off some of the genes or maybe even the whole extra chromosome responsible for Down's syndrome. A great deal more understanding of the basic mechanisms of Down's syndrome and a great deal more development in gene therapy is needed before we can contemplate such treatment, but it remains a long-term possibility.
Are there any differences in the genes or chromosomes of grandparents of children with Down's syndrome? Unless the grandparent is a carrier of a balanced translocation a very rare event there are no known differences in the genes or chromosomes of grandparents of children with Down's syndrome from those of anyone else's grandparents. There is nothing known that the grandparents might have done which would explain their grandchild being born with Down's syndrome.
Can adults with Down's syndrome have children; and if so, what is the chance of their children having the condition? A woman with Down's syndrome can have children. There have been only a few reports of men with Down's syndrome fathering children. If both partners have Down's syndrome there is a high chance of their children having the condition.
As these events are still rare it is difficult to obtain accurate figures. My grandmother's sister had Down's syndrome. She died 40 years ago when she was Does this mean that I could have an increased chance of having a baby with the condition? There is a small chance that she would have had the inherited form of translocation Down's syndrome, in which case you could be a carrier.
Chromosome testing was not introduced until so the family may not know what kind of Down's syndrome she had. If your grandmother had a lot of children and grandchildren and none of them was affected, it is very unlikely that she was a carrier. If you want to be completely sure that you are not a carrier, chromosome test would need to be carried out on your blood.
People with Down's syndrome are all very different from each other, in looks and personality and ability. Why is this, when they all have extra material from chromosome 21? People with Down's syndrome get the extra chromosome material along with the full set of chromosomes from their parents.
All the genes they inherit are ordinary ones, which explains why they resemble their families in the same way as ordinary children. The differences in genes that children with Down's syndrome inherit from their parents, together with differences in their environment, explain the differences between one child with Down's syndrome and another.
Can the tests ever be wrong? If an experienced health professional has seen features of Down's syndrome in your child, and the blood test result shows regular trisomy 21 or a translocation type, there should be no doubt. In mosaic Down's syndrome, because all the cells in the body do not show trisomy, it is possible for a blood sample not to include any trisomic cells, or to contain only trisomic cells, which may lead to difficulties in arriving at the correct diagnosis.
In this situation, while further tests may help, it is not actually possible to disprove mosaicism. Blood tests are done by humans. Mistakes can, of course, be made at one of the many stages that a blood sample passes through before a result is given to the patient. This, however, is very rare. Summary Down's syndrome is always caused by the presence of extra chromosome 21 material in a person's cells.
There are 3 types of Down's syndrome. Most people with the condition have regular trisomy Much smaller numbers have translocation, or mosaic Down's syndrome.
- Down Syndrome: Causes, Symptoms and Risks
- What causes Down syndrome in a child?
- What is Down syndrome?
The only way of finding out what type of Down's syndrome people have is to do a blood test and examine their chromosomes under a microscope. One of their parents will be a carrier of the translocation. They also tend to have many colds, as well as bronchitis and pneumonia. Your child should get regular medical care and stay up to date on vaccines. These vary widely from child to child. They can be mild, moderate, or severe. But most learning problems are mild to moderate. Many children are helped with early intervention and special education.
Some people claim that giving high-dose vitamins to children with Down syndrome will improve their learning and development problems. No studies have proved that this works. What are the possible complications of Down syndrome in a child? Complications of Down syndrome vary depending on the body organ affected and the severity of the problem. Problems includes certain birth defects, learning problems, and facial features.
A child with Down syndrome also may have heart defects and problems with vision and hearing. How severe the complications are varies from child to child. Treatment will also vary depending on the body organ affected and the severity of the problem. What can I do to help prevent Down syndrome in my child? There is no reason to believe a parent can do anything to cause or prevent Down syndrome in their child.
Age is one factor. Most babies with Down syndrome are born to women younger than Your healthcare provider may refer you to a genetic counselor. This expert can explain the results of chromosome tests in detail. He or she can talk about risks for future pregnancies and what tests are available to diagnose chromosome problems before a baby is born. Some medical organizations advise that all pregnant women of any age be offered screening for Down syndrome.
Down Syndrome (Trisomy 21)
Talk with your healthcare provider about this prenatal screening test. How can I help my child live with Down syndrome? Children with Down syndrome can usually do most things that any young child can do.
They can walk, talk, dress themselves, and be toilet trained. But they usually do these things at a later age than other children. The exact ages of these development milestones is different for each child.
Early intervention programs that begin when a child is a baby can help the child reach his or her potential. A child with Down syndrome can go to school. Special programs beginning in the preschool years help children with Down syndrome develop skills as fully as possible. They can also enter a regular classroom. Many children will learn to read and write. They can take part in childhood activities, both at school and in their community.
Your child may need physical, occupational, and speech therapy to help with his or her development. You can also learn what may be helpful in raising a child with Down syndrome.
Special work programs are designed for adults with Down syndrome. More and more adults with Down syndrome live semi-independently in community group homes. They take care of themselves, do household chores, develop friendships, do leisure activities, and work in their communities. Some people with Down syndrome marry. Most men with Down syndrome cannot father a child. In any pregnancy, a woman with Down syndrome has a 1 in 2 chance of conceiving a child with Down syndrome.