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#1
Old 09-10-2013, 03:41 PM
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Are there some people with Down syndrome who are mentally normal?

I'd be interested to know if there are any known cases of a person with Down syndrome who has normal mental functioning? I read that people with Down syndrome usually have a range of IQ scores between 30 and 70, with an average of about 50. I came across this video on Youtube, in which a Down syndrome woman is being interviewed: http://youtube.com/watch?v=IaLcaOWX1y4. She seems very smart and doesn't appear to me to be in any way mentally impaired. She talks and comes across just like a normal person.

Have you ever known anyone with Down syndrome who is of normal (or near-normal) intelligence? Do you think the extra chromosome ALWAYS results in some level of cognitive impairment, or are there a few exceptions?
#2
Old 09-10-2013, 04:14 PM
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What about the actor from Life Goes On?
#3
Old 09-10-2013, 06:31 PM
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There's a variant called mosaic Down syndrome where the extra chromosome is only in a fraction of the cells. It could be anywhere from 12.5% to 87.5% because the cells begin to differentiate at the 8-cell stage. This is also believed to be a factor when a chromosome test is wrong - that the (ab)normal cells were evenly divided between the baby and the placenta.

People with MDS usually have less severe mental disability than people with "straight" DS, and are less likely to have other issues like heart and bowel defects. I'm not aware that anyone's been "normal", though.
#4
Old 09-10-2013, 08:49 PM
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Anecdotally I have had one patient with full Trisomy 21 who was actually somewhat bright academically.

In any case the GQ answer is yes.
Quote:
... average IQ of between 50 and 60 for Down's syndrome individuals although IQ scores of 120 have been found in some individuals with the syndrome.
So always? No.
#5
Old 09-10-2013, 11:21 PM
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Since Trisomy 21 is so nearly universally accompanied by some degree of mental retardation, and since mental impairment is the commonest component of the various features which combine to form the syndrome, I'd be inclined to think of an individual with normal mentation and trisomy 21 as a "Trisomy 21 variant" (and probably mosaic, at that) and not a "Down Syndrome." If you are missing a key component, it's harder to say you have the syndrome in question. But I guess that's a bit of a nitpick, and one completely unsupported by much of anything.

I think I'm bothered by the implication that a mental handicap should be something to be ashamed of, and therefore we're going to emphasize the "normal" spectrum of presentation for a given set of deficiencies. What happens is that the vast majority just end up looking even more deficient against the outliers. I'm not sure garnering publicity for a high-functioning Down child does much besides setting an unrealistic expectation for the average Down kid.
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Old 09-10-2013, 11:25 PM
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Originally Posted by want2befree View Post
What about the actor from Life Goes On?
Seriously??
#7
Old 09-11-2013, 12:28 AM
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Originally Posted by Ambivalid View Post
Seriously??
Chris Burke. No idea what his IQ is, but he's a talented actor, writer and a kickass advocate for people with Down Syndrome.
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Old 09-11-2013, 01:54 AM
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Originally Posted by WhyNot View Post
Chris Burke. No idea what his IQ is, but he's a talented actor, writer and a kickass advocate for people with Down Syndrome.
I'm familiar with him.
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Old 09-11-2013, 04:21 AM
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Originally Posted by Chief Pedant View Post
I'm not sure garnering publicity for a high-functioning Down child does much besides setting an unrealistic expectation for the average Down kid.
... and do you have something against Down grownups, or are you just falling into that trap of talking about anybody who has Down's as being a "kid"?
#10
Old 09-11-2013, 05:16 AM
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think I'm bothered by the implication that a mental handicap should be something to be ashamed of
Not ashamed of......they can't help it....but it's not exactly the best thing in the world to have KWIM? I see adults with mental disabilities and it's BEYOND sad how limited they are. And they ARE limited.....
#11
Old 09-11-2013, 05:23 AM
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Um no.... but I do see parents of mild MR kids pretending that their kid has a severe learning disability or is higher functioning then they actually are.....And the thing is... anyone with a mental disability IS pretty much a kid functionally.....Why is that considered offensive? They think like and function like a kid.......
#12
Old 09-11-2013, 06:06 AM
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Originally Posted by Nava View Post
... and do you have something against Down grownups, or are you just falling into that trap of talking about anybody who has Down's as being a "kid"?
He's a pediatrician.
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Old 09-11-2013, 09:20 AM
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Originally Posted by Ambivalid View Post
I'm familiar with him.
So why the response? Certainly, we don't have access to his IQ tests, but his chosen work in life indicates a pretty high IQ for his medical cohort, very possibly in the "mentally normal" range or even higher than average. Seems a valid example of what the OP was asking for. Speculative, but cromulent.
#14
Old 09-11-2013, 10:29 PM
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Originally Posted by Chief Pedant View Post
Since Trisomy 21 is so nearly universally accompanied by some degree of mental retardation, and since mental impairment is the commonest component of the various features which combine to form the syndrome, I'd be inclined to think of an individual with normal mentation and trisomy 21 as a "Trisomy 21 variant" (and probably mosaic, at that) and not a "Down Syndrome." ...
The "no true Down Syndrome" argument!

I don't know about emphasizing or not and don't see any implication of shame. Those with Trisomy 21 who are of normal IQ are rare. Yes outliers. IQ of 50ish is a realistic expectation but quite a bit higher and lower are both seen. Parents of Downs kids should not and do not expect kids with normal IQ and they generally do end up loving the kid they got as kids with Downs have lots of strengths and lots to love.
#15
Old 09-12-2013, 04:44 AM
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Originally Posted by AboutAsWeirdAsYouCanGet View Post
They think like and function like a kid.......
No they don't. They think and function like a person with a developmental disability of some kind (or not, as the case may be). So that's why it's offensive: it's rubbish, it reduces a person to something they are not.
#16
Old 09-12-2013, 05:12 AM
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How is that offensive? Seriously.........how is that offensive to say that a person with a mild MENTAL disabilty thinks and acts like a kid?
They do.........How come their functioning levels are described as being on "second grade" or 2 year old levels then?
I interact with mentally disabled adults.......Many of them do think and act like a child....that's the essense of their disability......Or is it just PC yammering along the lines of the type of parent who insists that their mildly MR kid is actually severely learning disabled?
#17
Old 09-12-2013, 06:25 AM
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Originally Posted by AboutAsWeirdAsYouCanGet View Post
Um no.... but I do see parents of mild MR kids pretending that their kid has a severe learning disability or is higher functioning then they actually are.....And the thing is... anyone with a mental disability IS pretty much a kid functionally.....Why is that considered offensive? They think like and function like a kid.......
An adult with Down's is not a kid, no matter how mentally impaired. They are an adult. Adults have different needs than kids, no matter how impaired. An adult with a disability needs to be treated as an adult and not a child. Infantilizing adults with disabilities doesn't help them.

There is also a considerable range in mental disabilities. It's not an either/or situation. One can be of less than average intelligence but still fully capable of holding a job and paying the bills. Yes, some mentally impaired adults do require a non-disabled guardian of some sort but that's by no means universal.

That aside, there has been at least one woman with Down's Syndrome who is also a National Merit Scholar, but her name eludes me, it was several years ago. Just as there are people of normal chromosomes who have exceptional intelligence I don't see it surprising that there are people with trisomy 21 with exceptional intelligence. Perhaps these are people who would have been some sort of extreme genius without the chromosomal disorder but due to it are now only slightly above average. Unquestionably, any high-functioning person with Down's has benefited by intensive support and educational effort.

It should be noted that even people with Down's Syndrome who test out as having a normal range IQ still have some pretty significant problems. It seems that Down's doesn't affect just raw intelligence but also to some degree social interactions. Hearing and vision problems are not uncommon, among other physical issues. Additionally, even those Down's Syndrome people who graduate high school or even attend college would still be considered learning disabled if they didn't have trisomy 21 but still functioned at their current level. They have to work much harder than the average student to achieve average performance.
#18
Old 09-12-2013, 07:11 AM
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Originally Posted by AboutAsWeirdAsYouCanGet View Post
How is that offensive? Seriously.........how is that offensive to say that a person with a mild MENTAL disabilty thinks and acts like a kid?
They do.........How come their functioning levels are described as being on "second grade" or 2 year old levels then?
I interact with mentally disabled adults.......Many of them do think and act like a child....that's the essense of their disability......Or is it just PC yammering along the lines of the type of parent who insists that their mildly MR kid is actually severely learning disabled?
Again, it's offensive because they DO NOT THINK AND ACT LIKE A CHILD. They think and act like a person of what ever age they are with a what ever kind of developmental disability they have.

The fact that you think they seem like a kid only speaks to your insight, not to their ability.

Sometimes, for some specific things, they might be described as being on the level of a certain age group. So you might say "reading ability of a 6 year old". It's fallen into disuse because it is inaccurate, mostly.

Consider the things that developmentally go with age, to name just a few:
- motor skills (dexterity, walking, different things)
- reading/writing ability
- maths
- speech
- vocabulary
- social skills
- sexual development
- experience (of all kinds of things)

The list goes on and on. The chance that someone with a developmental disability is like a 4 year old on all counts is almost nil. Four year olds don't have serious, respectful, sexual relationsips, but someone who writes like a four year old could. Four year olds can't take apart a car and put it back together, but someone who writes like a four year old might. If someone supposedly writes like a 6 year old, when you look at it properly you will find it is nothing like a 6 year old. Because they have been writing that way for years, they have more experience than a 6 year old, they have a different vocabulary etc.

If you want to be respectful of the people you supposedly interact with, stop thinking of them as children. They aren't.
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Old 09-12-2013, 01:17 PM
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Thanks for all the responses.

Having done a bit of googling, I’ve discovered a few things. I've found that yes, it is possible for a person with Downs to be of normal intelligence, but it is very rare. Only about 1% of them have an IQ within or above the borderline intellectual function range of 70-80. Most are either in the mild or moderate range of learning disability, with a small minority in the severe or profound range. According to globaldownsyndrome.org, 40% are in the mild range or higher.

Obviously, an IQ score is of limited use in determining a person's intelligence, because intelligence is such a complex thing and there are lots of different kinds of intelligence. People with Down syndrome are known as having comparatively good social and emotional intelligence, and this would not be picked up by an IQ test. Being emotionally and socially intelligent is, in my opinion, much more important than being a mathematical/scientific genius who has no understanding of social situations and is unable to feel any empathy for others. Yet, the latter person would probably score much higher on a standard IQ test than a Downs person.

I think that people with Down syndrome are capable of a lot more than we are led to believe, and it is important to treat them in a way that focuses on their abilities, not on their disabilities.
#20
Old 09-12-2013, 01:32 PM
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Originally Posted by inuittagluuqqak View Post
I think that people with Down syndrome are capable of a lot more than we are led to believe, and it is important to treat them in a way that focuses on their abilities, not on their disabilities.
I think that people with Down syndrome are capable of a lot more than we are led to believe, and it is important to treat them in a way that focuses on their abilities, not on their disabilities.

#21
Old 09-12-2013, 03:09 PM
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I had a friend who used to volunteer at the Special Olympics, and she said that one problem she faced was horny male athletes--grown men who had not been properly socialized to handle sexuality, I'm guessing because parents/teachers erroneously considered them big kids.
#22
Old 09-12-2013, 03:44 PM
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Originally Posted by TSBG View Post
I had a friend who used to volunteer at the Special Olympics, and she said that one problem she faced was horny male athletes--grown men who had not been properly socialized to handle sexuality, I'm guessing because parents/teachers erroneously considered them big kids.
Perhaps not just that. There is also a lot of misunderstanding, sometimes difficulty reading certain social cues etc. They have a developmental disability, it can extend to many areas. Also, people with Down syndrome can be very affectionate, which can be taken just a little too far.

But yes, I think sex ed is quite difficult for people with developmental disabilities, and in my experience there is room for improvement. Funny anecdote time:

I worked in a hotel, on a learning-and-working project for young people with developmental disabilities. I was checking in a couple, when S. bursts into the reception and interrupts me to say: "I need to ask an important question!" - "OK S., just let me help these people, and then I'll have time to answer your question." S. looks relieved, and says: "Oh good, because I really need to know how to finger a girl!"

(Also: see the above anecdote for why a developmental disability does not make a person a child. I've never had an emergency how-to-finger-a-girl question from a child. Thankfully.)
#23
Old 09-12-2013, 08:24 PM
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Originally Posted by WhyNot View Post
Chris Burke. No idea what his IQ is, but he's a talented actor, writer and a kickass advocate for people with Down Syndrome.
Sort of a separate question, but how is his health? Many folks with Down Syndrome die quite young. Does anyone know if Chris Burke has a bad heart or lung problems? I do see he has reached 48 and I thought many, many Down Syndrome folks don't make it into their 50's.
#24
Old 09-12-2013, 10:16 PM
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Originally Posted by WhyNot View Post
So why the response? Certainly, we don't have access to his IQ tests, but his chosen work in life indicates a pretty high IQ for his medical cohort, very possibly in the "mentally normal" range or even higher than average. Seems a valid example of what the OP was asking for. Speculative, but cromulent.
"...or even higher than average..."?? I say 'fantastical', not just speculative.
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Old 09-12-2013, 10:23 PM
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"...or even higher than average..."?? I say 'fantastical', not just speculative.
Average is pretty stupid. Have you read YouTube comments?
#26
Old 09-13-2013, 05:42 AM
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People with Down syndrome are known as having comparatively good social and emotional intelligence, and this would not be picked up by an IQ test. Being emotionally and socially intelligent is, in my opinion, much more important than being a mathematical/scientific genius who has no understanding of social situations and is unable to feel any empathy for others
I wouldn't quite say that......Down's folks have realitively good social/emotional development for someone with mental disabilities.....but it's not as good as someone without mental disability......they can be friendly and know how to interact etc but even a lot of the high functioning ones can and will do stuff like hug random strangers.....
#27
Old 09-13-2013, 11:34 AM
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My friend's daughter has Down Syndrome and seems perfectly "normal" to me. She's very tiny so when I first met her I asked how old she was, thinking she'd say "9", but she said "16." She's 17 now but looks like a 10 year old. Honestly, if you didn't look at her eyes you wouldn't even know she was Down's. She recently achieved her Black Belt in Karate.

One time the teachers in our area went on strike and stopped extra-curriculars. I knew my friend's kid was in Track & Field so I asked if the strike had affected her. My friend said "No, she's in the Special Olympics so she's not affected." I thought "That's funny, why would she be in the Special........oh right."
#28
Old 09-14-2013, 03:58 AM
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Average is pretty stupid. Have you read YouTube comments?
Hmmmm...good point...(looks off into the distance, meditating...)
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Old 09-14-2013, 09:56 AM
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Why is Down's Syndrome the only, uh, doubled chromosome disease you ever hear of? We've got 22 other chromosomes, why don't people sometimes end up with extra copies of one of those?
#30
Old 09-14-2013, 10:20 AM
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Originally Posted by StarvingButStrong View Post
Why is Down's Syndrome the only, uh, doubled chromosome disease you ever hear of? We've got 22 other chromosomes, why don't people sometimes end up with extra copies of one of those?
Marketing.

I'm dead serious. There are plenty of other chromosomal abnormalities, including doubling of other chromosomes. But they don't generally produce beautiful babies with chubby cheeks and winning smiles. Often, they don't produce babies who can live very long at all.
#31
Old 09-14-2013, 11:19 AM
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Why is Down's Syndrome the only, uh, doubled chromosome disease you ever hear of? We've got 22 other chromosomes, why don't people sometimes end up with extra copies of one of those?
Triploidy of other chroosomes does occur all the time but they don't make it to birth or even out of the first trimester very often. At least 15% of all conceptions result in spontaneous abortions and most of them have chromosomal abnormalities. Of triploidies that make it to term the only one with near the frequency of Downs is Klinefelter Syndrome (XXY) and it is not all that often immediately obvious at birth. Trisomy 18 and 13 sometimes make it to birth but they typically don't survive very long.
#32
Old 09-14-2013, 11:41 AM
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Why is Down's Syndrome the only, uh, doubled chromosome disease you ever hear of? We've got 22 other chromosomes, why don't people sometimes end up with extra copies of one of those?
Rick Santorum's daughter Bella has Edwards syndrome, which is trisomy 18, and there's also Patau syndrome, which is trisomy 13. Unless those are mosaics, life expectancy is very brief if they even survive birth, usually days or weeks.

There are some partial trisomy and translocation syndromes that cause varying levels of disability. One that comes to mind is IDIC-15, a partial duplication of the 15th chromosome. It causes autism-like symptoms and other developmental delays; my old hairdresser's grandson had this, which is how I know about it.

There's even a syndrome called mosaic tetraploidy, where some of the cells have double sets of all the chromosomes.

The sex chromosomes can be duplicated too. Women with Triple X syndrome have 3 X chromosomes, and AFAIK this usually doesn't affect their health except that they are a bit taller than average and are usually infertile. Men with Klinefelter syndrome (XXY) are also tall, infertile, and often have reduced body hair and gynecomastia. The XYY syndrome in men used to be believed to be associated with criminal behavior, and this has since been disproven. Those men do have a tendency towards severe acne and infertility, and are also taller than average.

p.s. There's also Turner syndrome, which is a woman with a single X chromosome. Many do not survive to birth, but the ones who do generally have a normal life expectancy, although they have a peculiar appearance, are shorter than average, often do not go through spontaneous puberty, and frequently have learning and social disabilities.

Last edited by nearwildheaven; 09-14-2013 at 11:44 AM.
#33
Old 09-14-2013, 12:26 PM
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Originally Posted by Chief Pedant View Post
Since Trisomy 21 is so nearly universally accompanied by some degree of mental retardation, and since mental impairment is the commonest component of the various features which combine to form the syndrome, I'd be inclined to think of an individual with normal mentation and trisomy 21 as a "Trisomy 21 variant" (and probably mosaic, at that) and not a "Down Syndrome." If you are missing a key component, it's harder to say you have the syndrome in question. But I guess that's a bit of a nitpick, and one completely unsupported by much of anything.

I think I'm bothered by the implication that a mental handicap should be something to be ashamed of, and therefore we're going to emphasize the "normal" spectrum of presentation for a given set of deficiencies. What happens is that the vast majority just end up looking even more deficient against the outliers. I'm not sure garnering publicity for a high-functioning Down child does much besides setting an unrealistic expectation for the average Down kid.
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Originally Posted by DSeid View Post
The "no true Down Syndrome" argument!

I don't know about emphasizing or not and don't see any implication of shame. Those with Trisomy 21 who are of normal IQ are rare. Yes outliers. IQ of 50ish is a realistic expectation but quite a bit higher and lower are both seen. Parents of Downs kids should not and do not expect kids with normal IQ and they generally do end up loving the kid they got as kids with Downs have lots of strengths and lots to love.
Just be be pedantic about Chief Pedants post, or simply add my +1 to his first paragraph, that he is perfectly correct in clearing up some definitions before language is promiscuosly abused--(mis)used--in the discussion now underway of his second paragraph.

Down Syndrome is a correct term for just what it is: a syndrome. The word is defined as a spectrum of symptoms. In this case, simply put, is that the syndrome we call Down comprises deficit of cognitive function. It is a sine qua non.

The rare cases of where a person with Trisomy 21 has normal cognition does not have Down Syndrome.

IOW, Whathesaid.
#34
Old 09-14-2013, 01:05 PM
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Huh, so there are a bunch of other trisomy problems -- ignorance fought.

I guess all the 'other' duplications are worse, as in, more likely to kill the fetus/child, and so there aren't enough people with them to form a 'known to the general public' group.
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Old 09-14-2013, 03:26 PM
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Actually I will disagree with you Leo. Quite strongly. Down Syndrome is not defined by cognitive impairment any more than it is defined by any other feature in isolation. It is not sine qua non and if you, or CP want to claim it is then I would ask you to provide a citation that supports such a claim. It is very commonly associated with such, is a typical feature of such, as are slanting eyes, a broad short skull, broad hands and short fingers. But it is not the defining feature.

If you showed any of my fellow pediatricians or a geneticist an individual with Trisomy 21 with slanting eyes, widely spaced nipples, bilateral simian creases, short fingers, low set ears, and low body tone and told them that the individual also had a normal range IQ I will guarantee you with absolute certainty that we would ALL say that that individual has Down Syndrome. No question whatsoever. Okay, they might first say "Really?" but once shown the test results they would without question say that the individual was a person with Down Syndrome and with normal range IQ.

Look at it this way: we often label a baby at birth on exam with no knowledge of future cognitive function and with the suspicion confirmed, in our minds, by the chromosome result. We are not waiting for a kid to demonstrate cognitive delay before they get the label and we would not remove the label if cognitive delay never occurs.
#36
Old 09-14-2013, 04:03 PM
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Originally Posted by StarvingButStrong View Post
Huh, so there are a bunch of other trisomy problems -- ignorance fought.

I guess all the 'other' duplications are worse, as in, more likely to kill the fetus/child, and so there aren't enough people with them to form a 'known to the general public' group.
The chromosomes pairs are numbered 1-22 by size (with 1 being the largest. The 23rd pair are the sex chromosomes). 21nd pair chromosomes are second to smallest, and are much smaller than the largest ones. It is thought that the impact of duplicating much larger amounts of DNA, as in some of the other trisomy defects, contributes to the more profound negative impact on zygotic/embryonic/fetal survivability.

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#37
Old 09-15-2013, 03:41 AM
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Originally Posted by DSeid View Post
Actually I will disagree with you Leo. Quite strongly. Down Syndrome is not defined by cognitive impairment any more than it is defined by any other feature in isolation. It is not sine qua non and if you, or CP want to claim it is then I would ask you to provide a citation that supports such a claim. It is very commonly associated with such, is a typical feature of such, as are slanting eyes, a broad short skull, broad hands and short fingers. But it is not the defining feature.

If you showed any of my fellow pediatricians or a geneticist an individual with Trisomy 21 with slanting eyes, widely spaced nipples, bilateral simian creases, short fingers, low set ears, and low body tone and told them that the individual also had a normal range IQ I will guarantee you with absolute certainty that we would ALL say that that individual has Down Syndrome. No question whatsoever. Okay, they might first say "Really?" but once shown the test results they would without question say that the individual was a person with Down Syndrome and with normal range IQ.

Look at it this way: we often label a baby at birth on exam with no knowledge of future cognitive function and with the suspicion confirmed, in our minds, by the chromosome result. We are not waiting for a kid to demonstrate cognitive delay before they get the label and we would not remove the label if cognitive delay never occurs.
Yes, you're right. In fact, I think by being pedantic I was actually paradoxically speaking for a more loose use of "syndrome," as long as it's understood. As you say, "Down Syndrome [but] ..."

Crucially, I spoke out of my league about sine qua non.

I have more familiarity with lay and to an extent technical discussion of mood disorders, which of course have shading-spectra galore of sets of symptoms.

Last edited by Leo Bloom; 09-15-2013 at 03:43 AM.
#38
Old 09-15-2013, 07:09 AM
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One thing Iíve wondered about: Are there any genetic benefits arising from Trisomy 21? Are there some genes on chromosome 21 for which it is more beneficial to have three copies of that gene than two copies? The substances produced by the genes on chromosome 21 are produced at a 1.5 times higher quantity in a person with Downs than a person without Downs, so maybe for some of these substances, having a higher quantity is better. For instance, Iíve heard that many common types of cancer are much less common in people with Trisomy 21 than in the general population. This is probably because they have three rather than two copies of certain tumor-suppressor genes found on chromosome 21.
#39
Old 09-15-2013, 01:13 PM
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Originally Posted by inuittagluuqqak View Post
One thing Iíve wondered about: Are there any genetic benefits arising from Trisomy 21? Are there some genes on chromosome 21 for which it is more beneficial to have three copies of that gene than two copies? The substances produced by the genes on chromosome 21 are produced at a 1.5 times higher quantity in a person with Downs than a person without Downs, so maybe for some of these substances, having a higher quantity is better. For instance, Iíve heard that many common types of cancer are much less common in people with Trisomy 21 than in the general population. This is probably because they have three rather than two copies of certain tumor-suppressor genes found on chromosome 21.
Isn't it also possible that people with this condition don't live long enough to develop cancer?
#40
Old 09-15-2013, 01:39 PM
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Except that I think (s)he must have misheard. Individuals with Down Syndrome are prone to more cancer, not less. In particular acute leukemia but also others.
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In this cohort study of individuals with DS, there was an elevated risk of incident leukemia and liver, testicular, and penile cancers compared with the general population. In addition, overall mortality risks were almost 8-fold higher for individuals with DS, reflecting increased mortality attributed to leukemia and a variety of nonneoplastic conditions. ... The 26-fold increases in the risk of incident acute lymphocytic leukemia and acute nonlymphocytic leukemia in this cohort are consistent with the elevated relative risks and confidence limits noted in previous cohort studies in Norway6 and the United States.19- 20 Risk was highest among those aged 1 to 4 years, but it remained elevated compared with background rates until age 20 years.
#41
Old 09-15-2013, 02:38 PM
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Originally Posted by inuittagluuqqak View Post
One thing Iíve wondered about: Are there any genetic benefits arising from Trisomy 21? Are there some genes on chromosome 21 for which it is more beneficial to have three copies of that gene than two copies? The substances produced by the genes on chromosome 21 are produced at a 1.5 times higher quantity in a person with Downs than a person without Downs, so maybe for some of these substances, having a higher quantity is better. For instance, Iíve heard that many common types of cancer are much less common in people with Trisomy 21 than in the general population. This is probably because they have three rather than two copies of certain tumor-suppressor genes found on chromosome 21.
I'm guessing that they don't usually live long enough to get most types of cancer associated with old age, and when they do, it's not treated as aggressively as if they were "normal". They are more likely to get certain types of leukemia, and if they live into their 40s or beyond, they often develop an Alzheimer's-like syndrome.
#42
Old 09-15-2013, 02:45 PM
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The following is stated on the wikipedia article on Down syndrome:

Quote:
Although the general incidence of cancer amongst individuals with Down syndrome is the same as in the general population,[33] there are greatly reduced incidences of many common malignancies except leukemia and testicular cancer.[34] People with Down syndrome also have a much lower risk of hardening of the arteries and diabetic retinopathy.[35]

Hematologic malignancies such as leukemia are more common in children with DS.[36] In particular, acute lymphoblastic leukemia is at least 10 times more common in DS and the megakaryoblastic form of acute myelogenous leukemia is at least 50 times more common in DS. Transient leukemia is a form of leukemia that is rare in individuals without DS but affects up to 20 percent of newborns with DS.[37] This form of leukemia is typically benign and resolves on its own over several months, though it can lead to other serious illnesses.[38] In contrast to hematologic malignancies, solid tumor malignancies are less common in DS, possibly due to increased numbers of tumor suppressor genes contained in the extra genetic material.[39]
So, if wikipedia is correct, people with Down syndrome are at a greatly increased risk for some types of cancer and a greatly reduced risk for others, with the overall incidence of cancer being about the same as in the general population. Also worth noting is their greatly reduced risk of hardening of the arteries and diabetic retinopathy.
#43
Old 09-15-2013, 03:44 PM
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Join Date: Mar 2002
Location: Richmond, VA
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Quote:
Originally Posted by inuittagluuqqak View Post
One thing Iíve wondered about: Are there any genetic benefits arising from Trisomy 21? Are there some genes on chromosome 21 for which it is more beneficial to have three copies of that gene than two copies? The substances produced by the genes on chromosome 21 are produced at a 1.5 times higher quantity in a person with Downs than a person without Downs, so maybe for some of these substances, having a higher quantity is better. For instance, Iíve heard that many common types of cancer are much less common in people with Trisomy 21 than in the general population. This is probably because they have three rather than two copies of certain tumor-suppressor genes found on chromosome 21.
There was once a girl in my yoga class who had Down's Syndrome. I noticed that while we were seated in cross-legged pose, her thighs were practically flush with the floor. Indicating that she was insanely flexible.

Hyperelasticity of joints and connective tissues is a symptom of Down's. It has more disadvantages than advantages, but I'm sure in some circumstances (such as auditioning as a contortionist), it could come in handy.

The truth is that most mutations are either going to have neutral or deleterious effects, because genes and traits don't work in isolation. A mutation that causes your brain to grow twice as large as normal is pretty worthless unless there's another set of mutations that allow for adjustments in bone, blood vessel, and connective tissue growth. The chances that one gene's mutation will be accompanied by all the "right" mutations somewhere else is pretty dang-on slim.
#44
Old 09-15-2013, 04:09 PM
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Join Date: Sep 2001
Location: Chicago, IL
Posts: 19,653
Hmmm. Looking up their citation we find a study that looked at what was put on death certificates. Looking for other studies besides the one I alreeady linked to I find this one which comes down in the middle:
Quote:
The risk ratio for all cancers combined, including leukaemia, was 2.7 (1.8 to 3.9). The risk ratio for cancers excluding leukaemia was 1.2 (0.6 to 2.2). Our results showed a significant increase in testicular cancer in people with Downís syndrome ... The level of risk of leukaemia found by us is very similar to the 20-fold increase quoted in standard texts.1,2 It is noteworthy that the data in an administrative NHS statistics database can indeed be used to quantify such a risk reliably. Other studies of linked datasets have also identified the high risk of leukaemia.14Ė16 These findings support the validity of the study methods in assessing levels of risk for the other diseases studied.

It is sometimes considered that the risk of leukaemia is particularly high for acute myeloid leukaemia, but we found similarly high risks for both myeloid and lymphoid forms. Our data add some evidence to the suggestion that there is an increase in the risk of testicular cancer. The elevated risk of leukaemia can be considered in the broader context of how much the overall risk of cancer is increased: in our data, the overall risk is 2.9 times that of the general population in the age range and follow up periods studied.
No protective effect on any cancer found in that study, overall an incresed risk, but pretty much exclusively becasue of the increase in leukemia.

Looking for more I found this, which provides more detail about life expectancy (now into 50s and some into 60s) and the following comment about the studies that do seem to show lower rates of some solid tumors.
Quote:
Possible explanations for the decreased risk of some cancers among adults with DS are that accurate population morbidity studies are rare. It has also been proposed that individuals with DS may be less exposed to environmental contributors to cancer risk (Satgť et al., 1998). Decreased alcohol and tobacco use, early menopause and other lifestyle and environmental factors may contribute to lower cancer risk. However, obesity and the lack of physical activity common in adults with DS would contribute to an increased risk of cancers. The shorter life expectancy of individuals with DS has also been suggested to contribute to lower risk for cancer (Satgť et al., 1998). However, as the life expectancy of individuals with DS has increased dramatically over the last few decades, shorter life expectancy becomes a less probable explanation for the apparent lower risk of solid tumors. Several tumor-suppressor genes have been identified on chromosome 21, potentially contributing to the decreased risks for many solid tumors (Lee, T. Park, S. Park & J. Park, 2003). Copper-zinc superoxide dismutase, also located on chromosome 21, and its contribution to the metabolism of oxygen free radicals are further hypothesized to reduce the risk of carcinogens (de la Torre, Casado, Lopez-FernŠndez, Carrascosa, Ramirez & Saez, 1996).
So while overall cancer is higher there may indeed be lower rates of some cancers. Sorry for having stated otherwise.
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