Down Syndrome (Trisomy 21)

Claudia Perry, A3

What is this disorder?

This disorder is Down syndrome, or Trisomy 21, which is where there is an extra copy of chromosome 21 (Boyse 1). This disease is acquired when autosomal nondisjunction occurs and extra genetic material from chromosome 21 is then moved into the developing embryo (Wedro 1). This is not an extremely rare disorder- Trisomy 21 is the cause of Down syndrome in 95% of those with the disorder (Wedro 4).

Who can acquire the disorder- and how?

Since Down syndrome occurs when an extra copy of chromosome 21 is a nondisjunction (duplication) of chromosome 21, it is not necessarily inherited. The disease is just caused when chromosome 21 happens to be duplicated/go through nondisjunction.

Anyone can have the disorder, but is more common when the mother is 35 or older. They have a higher risk, although the mothers can have a child with Down syndrome and be younger. Also, more children born with Down syndrome live in countries where abortion is forbidden and (again) when the mother is older (Langtree 24, 47).

How is it inherited? Is it even inherited?

Since Down syndrome is a nondisjunction (duplication of chromosome 21, i is not necessarily inherited. The disease is just caused when chromosome 21 happens to be duplicated/goes through nondisjunction.

Are there prenatal test to look for Trisomy 21?

There are prenatal tests that can be done to determine whether a child has Down syndrome or not. The most common test is a chromosome analysis where blood is taken from the baby and observed by scientists/doctors. Amniocentesis (by taking fetal tissue samples) and chorionic villus sampling can also be done, but are not used as often as they could potentially harm the child. Ultrasound imaging can also be used to screen for the disease (Langtree 23,27).

What are the symptoms?

Children with Trisomy 21 grow and learn slower than children without the disorder, and also have a difficulty with reasoning and judgement. Normally, children with the disorder have short attention spans (Boyse 12).

Other physical symptoms are:

  • having decreased muscle tone when born
  • extra skin on the back of the neck
  • a flattened nose
  • joints that are not together between bones in the skull
  • only one crease in the palm of the hand instead of multiple
  • small ears and mouth
  • upward slanting eyes (almond-like)
  • short, wide hands that have short fingers, and
  • Brushfield sports
(Kaneshiro 6).
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What population is affected by Down syndrome? Could this have been prevented in anyone?

All people around the world can develop Down syndrome, as it is just a factor of nondisjunction. Although the disorder is found all over the world, at this time, Down syndrome cannot be cured or prevented (Wedro 7). There are no known ways to prevent the disorder, but many want to find the answer soon.

Can someone with the disorder have children in the future? Will they be affected?

Someone with Down syndrome is able to have children unless they are somehow infertile. The disorder does not stop those who want to have children, unless they are infertile or unable to procreate (Stumbo 11-12). There is a larger chance the child will be affected, but that does not mean there is a 100% chance the child will have the disorder. To increase the chances, take two people with Down syndrome for example. There is a 25% chance the child will not have the disorder, 50% chance they will, and a 25% chance that they would not be able to become pregnant (Stumbo 12).

See chart below

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What kind of medical assistance will the affected child need? Will further assistance be needed, as the child grows older?

Medical assistance may or may not be needed depending on how severe of a case of Down syndrome the child has. Normally though, the child has regular screenings, checkups and medications, and some even some kinds of surgery or therapy. Since those with Down syndrome are at a higher risk to develop other serious medical problems, like cancers, premature aging, and so on, screening are done often to ensure the child is in good condition (Schoenstadt 3-4).

As for the child having further assistance, this again depends on the severity of the disorder. Assistance may be needed if the disorder is serious enough to cause and kinds of extreme impairment, but others will not need as much help. It is normal for a person with Down syndrome to have someone with them often, but some may need more assistance than others.

What is the long-term outlook for the child?

Children with Down syndrome can live their own lives well after they become adults (Kaneshiro 24). Adults with the disorder have increased risk for different types of diseases, like dementia, but can still live a fulfilling life (Kaneshiro 25-27).
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Where does research currently stand?

Most researchers studying Down syndrome have been focusing on understand its symptoms and why they occur (McNamee 3). Another scientist, Jeanne Lawrence, is trying to directly address the third extra copy of chromosome 21 to better understand the disorder (McNamee 3). Other research projects include XIST chromosome therapy, new medicines trying to be developed to help improve cognitive functions, address the lower IQ, sleep apnea, and adaptive behavior (McNamee 5, 16, 21). Altogether, a lot of research is being done to discover the secrets of the obscure disease.

Are there any treatments or cures? Are there any coming soon?

No one knows how Down syndrome became a problem, and there are no cures for the disease as of now (Langtree 11). Although, scientists may have come across a potential cure. Scientists discovered a compound that, when used on mice, cured their learning disabilities when administered at birth, as well as the cerebellum growing to a normal size. The mixture has not been tested on humans or made to be sold, but could be a probably cure to the disease (Innes 1-2).