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What does It Mean to Have an Extra Chromosome?

By Erin J. Hill
Updated Mar 03, 2024
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Someone who has an extra chromosome has 47 total chromosomes instead of the typical 46, or 23 from each parent. This results in a condition known as trisomy. Trisomy is associated with mental retardation and often death, depending on which chromosome has malfunctioned.

Trisomy which occurs on the 13th or 18th chromosomes results in severe mental retardation. Babies born with this condition generally die from medical complications within days, and sometimes sooner. The vast majority of chromosomal disorders happen in early pregnancy and cause the fetus to abort itself, resulting in a miscarriage. Therefore, most babies who have an extra chromosome die.

In one condition, however, children can live and even have productive lives if treatment and special education and attention is given. Babies born with trisomy 21, or an extra chromosome 21, have a condition known as Down Syndrome. Although children with Down Syndrome do suffer form some level of mental retardation, the majority of them are high-functioning.

Children with Down Syndrome generally have a distinctive physical appearance, with smaller heads than normal and eyes that are rounded at the ends instead of pointed. They may also have lack of muscle tone, small ears and mouths, and wide hands with short fingers. The mental capabilities of these children vary widely, but most can live productive lives if the proper interventions are taken early.

A mother is more likely to have a child with an extra chromosome as she gets older. This could be because her eggs are aging and are more likely to have chromosomal defects than those of a younger woman. There is no known prevention for Down Syndrome, although diagnostic testing can be performed during pregnancy to determine if an unborn child has the condition. These are not always accurate, as most babies with abnormal tests do not have Down Syndrome.

Aside from physical characteristics and mental differences in children born with an extra chromosome, serious health conditions can often occur. These can include vision problems, intestinal blockages, heart problems including an enlarged heart, constipation, sleep apnea, and hypothyroidism. Many of these things can be successfully treated, although severe heart conditions may require surgery to correct.

Diagnosis for Down Syndrome can generally be made based on blood test results which test for an extra chromosome 21. Suspicion of Down syndrome will generally occur right at birth though when the doctor notices the typical physical characteristics common with trisomy 21. The infant will be checked for additional health problems once a diagnosis has been made.

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Discussion Comments
By snickerish — On Aug 27, 2011

I work with children with various disorders and I have seen quite a few rare disorders but I have seen only one child with a Trisonomy disorder.

He is a very sweet boy, and his family does such a wonderful job of including him in all of their activities, and you can absolutely see how much he loves them.

One of the things I always champion for the families I work with is to find a support group of people who are dealing with the same things you are; and that is the one thing I found was difficult to aid this family with.

Because the Trisonomy type that this child was so rare, they could not find a single family in our metropolitan area to share their story with.

Luckily they have a strong parent support group within our school since rare disorders are common here and although their challenges can be a bit different from the other parents, I hope they can find support!

But I would suggest such a support group for anyone; parents often find support in just having help navigating the insurance and medical system!

By julies — On Aug 26, 2011

I know of several Down Syndrome children who have led highly functioning lives. Most of them are in special educations classes, but some of their classes are integrated with the main stream classes too.

Just like any kid, they always do best when they have teachers and adults around them who work with them and encourage them in their pursuits.

One of my friends has a daughter who had an absolutely wonderful teacher for a few years. She learned how to read and participated in Special Olympics events and always looked forward to school.

When that teacher left and they hired a new one, she never did quite as well in school after that and even regressed in some areas. It was sad to see this happen, as she had formed such a close bond with the other teacher, and really struggled after that.

By myharley — On Aug 26, 2011

One of my nephews has Down Syndrome or what some call extra chromosome syndrome. He is an only child and his parents have worked very diligently with him throughout his whole life.

Now that he is an adult, he is able to live in a group home and go to a job everyday. He is very social and likable, and has many people who love him and enjoy being around him.

There is a sense of joy that he brings to those around him. He is happy with the simple things in life and is content with what he has. One of his biggest pleasures is watching sporting events on TV.

He recognizes many of the players on his favorite teams, and always roots for them with enthusiasm.

By SarahSon — On Aug 25, 2011

My younger sister was born with Down Syndrome, and although there have been challenges, she is now in her mid 40's and has been quite healthy up to this point.

When she was a baby she had a very bad case of the croup. An emergency tracheotomy was done and she did not receive oxygen to her brain for a short time.

The doctor believes this set her back even further. She is not as high functioning as many other Down Syndrome kids I know because of this.

This does not mean she doesn't enjoy life and she understands most everything that is being spoken to her. It is just hard for her to communicate back in words what she would like to express.

You can tell this is very frustrating for her, but she has brought a lot of joy to all of our lives.

By SZapper — On Aug 25, 2011

@ceilingcat - I don't think that's strange at all. Everyone deals with miscarriage in a different way, after all.

I wanted to also point out that those amniocentesis tests are often wrong. I know of two different people who had the tests done and the results said their children would have a genetic disorder. In both instances, the children were born perfectly healthy.

If I'm ever pregnant, I'm going to say no to those tests. In addition to being incorrect, they can also harm the fetus.

By ceilingcat — On Aug 24, 2011

A friend of mine had a miscarriage not too long ago. It may sound weird, but she was comforted when she read that the reason a lot of miscarriages happen is because the baby would be born severely disabled and possibly die shortly after birth.

I think it makes sense-if she had carried her baby to term she would have been even more attached to it. I'm glad that she had a somewhat early miscarriage and didn't have to go through her whole pregnancy only to give birth to a child that wasn't going to make it.

By Bakersdozen — On Aug 23, 2011

@Windchime - Don't even think of apologizing for being 'sappy'. Your comment was very thoughtful and it touched my heart.

As the parent of a son born with an extra y chromosome I find every day brings a new challenge. Sometimes it's hard to get through, but mostly I'm grateful that he is alive and battling on.

I would love it if more people in the world could come to see that we each bring something unique to the table. Of course the reality is often quite different.

I've found attending a support group to be invaluable. Integration is always the goal, but sometimes I need to talk freely with those who understand how it is.

By Windchime — On Aug 22, 2011

One of the best years of my life was spent as a support assistant at a day center for kids with Down Syndrome.

What started as a way to earn money during a gap year became one of the biggest influences on my life - as I went on to change my college program, and this time next year I'll be teaching children with special needs!

I know that there will always be debates about quality of life and health when it comes to children born with an extra 21 chromosome, but my view on this is pretty simple.

Basically, I believe that we are all born to teach something to others, and these children have shown me how to take pleasure in everything I achieve.

On the rare occasions when someone tries to debate this with me I like to say that they have the one extra chromosome so many of us lack: joy. This genetic gift ensures they give love in an unconditional way, take pleasure from the simplest things, and look beyond the material must haves which dominate so many lives.

Sorry if this is all a bit sappy. I just feel so passionate about championing the case for those with genetic disorders.

By dfoster85 — On Aug 21, 2011

@robbie21 - I’m sorry for your cousin’s loss! My sister suffered a relatively late miscarriage (17 weeks) and I saw how traumatic it was for her and her husband. She has since welcomed healthy twins, “rainbow babies,” and I hope that your cousin has the same happy ending, though I’m sure she will never forget her “angel baby.”

Chromosomes like 13 and 21 are called somatic chromosomes to tell them apart from the sex chromosomes. As long as you have at least one X, having too many or two few sex chromosomes is not as big a problem as having a trisomy of the somatic chromosomes.

A lady I used to work with had a son with Klinefelter syndrome, which is when a male has two X chromosomes instead of just one. He's a little funny-looking and he will be infertile as an adult, but otherwise he's quite healthy.

By robbie21 — On Aug 21, 2011

My cousin found out through amniocentesis that she was carrying a boy with trisomy 13 (also called Patau syndrome, one of the few extra chromosome disorders that can result in a life birth). She and her husband really agonized about whether to try to carry to term or to abort. They weren't sure what would be the best thing for them, their daughter, and the baby. My cousin is also an older mom - she was thirty-nine at the time - and was thinking about how much time she had left to try again for a younger sibling for her daughter.

But about a week after she got the test results, she spontaneously miscarried. Mother Nature knew better, I guess.

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