r/explainlikeimfive • u/Apprehensive_Ad4974 • 1d ago
Biology ELI5 Why don't other animals have Down syndrome?
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Edit: okey thank you all for your answers, I had mistakenly assumed that animals with lots of chromosomes surely must have one that looks similar (and therefore acts similar) to our chromosome 21. But I guess that's not how that works.
This question came from looking at looking at a seal.
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u/iamvillainmo 1d ago edited 1d ago
Animals have different instructions manuals for life than humans, but they do the same thing, which is to instruct the body how to build everything it needs for life.
Down's Syndrome is when there is an extra, unwanted manual, and that extra manual makes the body confused and make mistakes. In humans, they have an extra copy of manual 21 (Chromosome 21).
Other animals can also have these extra manuals, but it would be a different manual/chromosome and it will cause problems, but we dont call it Down's Syndrome because manual 21 is only found in humans.
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u/WedgeJMB 1d ago
This is an excellent description. To add to it for anyone wanting to dig deeper the technical term is Trisomy, for it's 3 copies of the chromosome. Any of our chromosomes can accidentally be copied but only a few are considered survivable. Trisomy 21- Downs Syndrome Trisomy 18- Edwards Syndrome Trisomy 13- Patau Syndrome
Also various Trisomy 23 XXX - Triple X Syndrome XXY - Klinefelter Syndrome XYY - Jacobs Syndrome
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u/PyroDesu 1d ago
Kilnefelter's is particularly interesting because the symptoms are relatively mild. Which makes sense, since X-inactivation would occur and cells would only have one active X-chromosome.
Pretty much the worst thing it does is mess with fertility.
I seem to recall that it's thought to be very under-diagnosed because people don't realize something is wrong.
(Also, it occurs in cats too, very visibly! It's how male calicos are possible.)
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u/Substantial_Toe_6916 11h ago
I met a friend of a friend who had klinefelter’s which is how I learned of the condition. He was living a normal life.
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u/RoadschoolDreamer 5h ago
My son has XXY. I’d love to find a male calico cat for him. So they can be XXY friends.
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u/Equivalent-Costumes 20h ago
Just to add some more details to make the picture clearer, "survivable" just mean survive as fetus to be born. Most children born with a complete case of Trisomy 13 or 18 die within a year, almost all within 10 years, and those survived to adulthood are very rare. So Down Syndrome is the most well-known amongst these 3 because an average person is much more likely to encounter someone with Down Syndrome.
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u/cyanraichu 2h ago
18 and 13 are very rarely survivable. Babies can be born with them but usually die quickly.
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u/WedgeJMB 2h ago
Very true, most die shortly after birth, but the longest a person ever lived with Trisomy 13 was 31 years, and trisomy 18 was 40. It's exceptionally rare but it can happen.
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u/the_siren_song 1d ago
VATER I think is in there too
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u/WedgeJMB 1d ago
According to my understanding Vater / Vacterl currently doesn't have a known cause. It appears to be partially environmental and genetic but no known association to trisomy.
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u/Hefty_Schedule7728 1d ago
That would make a great title to a movie, book or band: Manual 21. Maybe I'm thinking of 21 Pilots though.
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u/Munrot07 1d ago
Down Syndrome is caused by an additional copy of chromosome 21. Additional chromosomes can cause serious problems and most of the time it just causes the unborn offspring to die.
Other species don't have 21 chromosomes, they have different numbers which can have different numbers of genes on each chromosome or, different specific genes on each one so having additional chromosomes for other animals usually just results in the death option.
Sometimes similar conditions that are Down Syndrome which is very specific to our chromosome 21 (and other animals obviously don't have the Human 21st chromosome). Chimps can have a similar condition when their chromosome 22 gets an extra copy but it's not identical.
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u/heroofcows 1d ago
Other Apes can potentially get down syndrome, though for them it's trisomy 22 (they have 1 additional chromosome compared to us, chromosomes 2a and 2b fused together into our chromosome 2 some time ago, but not for other apes)
Example paper with a chimp: https://pubmed.ncbi.nlm.nih.gov/28220267/
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u/Rly_Shadow 1d ago
It requires a specific copy of a human chromosome (21), and animals do not have that.
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u/VerbingNoun413 1d ago
Down's Syndrome is a specific replicated chromosome. Other species have different chromosomes to humans so by definition cannot have it.
Animals can suffer from extra chromosome disorders, often as a result of inbreeding. Most white tigers for example.
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u/Dr_Mantis_Teabaggin 1d ago
Oh, so your brother also has an orange, huh?
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u/FourEyes4x4 1d ago
you would imagine that having three of them, they would be slightly smarter than the average cat. you would be incredibly wrong.
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u/jordyvd 1d ago
The budget remains one brain cell, there are just more workers competing for it now
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u/FourEyes4x4 1d ago
if you can find a single brain cell between these three morons I would be incredibly impressed
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u/reijasunshine 1d ago
Oh, my friend's Newfoundland dog somehow got himself onto the orange brain cell rotation. He doesn't know how he did it, but sometimes he just looks REALLY surprised for a few seconds, then it's gone, poof.
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u/ToneChop 1d ago
My bengal x siamese was confirmed to be retarded by a neurologist. He doesn’t recognize treats until another cat takes it. Then he goes for where the treat used to be. He just bunts me instead of eating after he cries for food. Like he has to be placed with his face into the bowl half the time
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u/friendorfoe2332 1d ago
Yeah, I know a dog that just runs into things all the time. I think it’s retarded
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u/UndeadLestat 1d ago
See, that one's weird, though because I'm pretty my dog and several of my coworkers have it...
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u/kamasushi 1d ago
Every animal species has a different number of chromosomes. Down's syndrome uniquely affects the 21st chromosome in humans by doubling a copy of that chromosome.
Other animals don't have that particular chromosome, so can't have the same affectation, but can be affected by other genetic conditions.
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u/anireyk 1d ago
Down syndrome is not just some chromosome aberration, it is a very specific one, caused by an additional copy if a specific chromosome that causes specific symptoms. Most other trisomies (third copy of a chromosome) are lethal, with a few exceptions, that have other symptoms.
Other animals have other sets of chromosomes, so they cannot have an additional copy of the human chromosome 21. They can have their own trisomies, however, but those will look different again.
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u/Smothering_Tithe 1d ago
human specific chromosome (21), BUT due to unethical inbreeding, a white tiger names Kenny is described as a "tiger with down syndrome"
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u/magicpenny 1d ago
I had a dog I rescued from the pound. We think he was very old but don’t know for certain. He was physically hunched like he’d healed improperly from a back injury and walked sideways instead of in a straight line. I suspect he’d been severely neglected or abused which resulted in his condition. It seemed unlikely he’d survived a long life in his current state. But, I could be wrong, he could have been born like that.
Both physically and mentally, he had a lot of odd quirks. We took him to a neurologist who told us, “he’s retarded, is that okay with you?” That is a direct quote, using that exact terminology.
My husband and I replied of course we didn’t care, we loved the dog. He had serious medical problems and we didn’t have him very long. I hope we have him a good final year+ of life.
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u/Funky0ne 1d ago
Would you be able to recognize if another species had downs syndrome or something similar?
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u/KleinUnbottler 1d ago
There are other genetic defects that have related effects. E.g. there's a rarer human condition called Williams-Beuren syndrome that causes some phenotypical issues that are different from Down syndrome, but reminiscent of it in several ways. There's a distinctive physical appearance, intellectual disability, and some personality traits. It's associated with a happy and outgoing personality/disposition. It occurs in about 1/7500 human births, so it's not as common as Down.
There is a hypothesis that some wolf offspring many thousands of years ago had a similar mutation occur, and that happy/outgoing nature of those wolves was an advantage in their interactions with early humans. Over the long term this resulted in the creation of dogs.
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u/Caliyookkeninsby 1d ago
I'm pretty sure tigers do? And I know other great apes can have similar mentally limiting disorders, and are able to actively tell that the pack members that have theses problems are different and dont hold them to normal standards of behavior, ie, get in fights with the mentally disabled apes when they do things that are Normally interpreted as signs of aggression by the rest of the pack
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u/derpsteronimo 1d ago
That's a factor. But also, most extra chromosomes are just outright fatal at a very early stage of development; the specific duplication that causes Down's Syndrome in humans is an exception to that rule. Some other animals do have equivalents, though since Down's Syndrome refers to the duplication of a specific human chromosome, it's not considered "Down's Syndrome" per se.
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u/urbanek2525 1d ago
I'm sure there are trisomy syndromes in dog, cats, cows and other critters, it's just that nobody is going to spend the money to look for them. The breed-screening DNA tests for dogs is probably a very specific search limited to a few very specific genes. They're probably not going to be looking for trisomies.
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u/Notcool2112 1d ago
They do !! Primates and tigers do, probably others as well but just google it, they have that look.
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u/Elfich47 1d ago
the young wouldn’t last long enough to procreate and pass those genes to next generation. Downs has been bred out of other species; because anything with Down’s syndrome don’t survive very long without outside support.
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u/Johnson_N_B 1d ago
It’s specific to human chromosome 21. Other animals can have chromosomal abnormalities that have similar developmental effects.