A. What if an individual with Down syndrome was bitten by a vampire?
B. What if someone with Ds was turned into a werewolf?
C. What if Hitler had a sibling with Ds?
D. What if someone with Ds got an ability like from Heroes?
E. What if someone with Ds was Aes Sedai?
F. What if someone with Ds was a major character in your favorite fictional work (book/tv show/movie)?
A. Anyone that has a child with Ds knows that their veins collapse and that it is practically impossible to get blood out of them. I think that individuals with Ds are likely to be mostly immune to vampire bites the way that they are mostly immune to all types of cancer (other than AML).
B. I think that if an individual with Ds were turned into a werewolf that it would depend on the individual as to the specific differences, but that in general they would likely experience a lot more domestic/dog-like traits than the general population. I imagine you would find a lot of them trying to cuddle instead of attack during the full moon.
C. If Hitler had had a sibling with Ds, he would have been much more likely to have learned compassion, empathy, love and respect for himself and others and would not have been able to have been a part of the atrocities that occurred. However, Germany was primed for what happened and I think likely a different leader would have arisen to cause a similar or the same thing to happen.
D. Again, I think the abilities of the person would depend on the individual. I imagine that my bear cub would have some sort of artistic ability since she likes to scribble so much. If not the prophecy painting ability, something like the ability to paint with her fingers or to create holographic 3-D paintings in the air.
E. Aes Sedai are so long lived that individuals with Ds would have plenty of time to learn the skills they need for whichever Ajah they chose. I imagine that you would find the most people with Ds in the Grey Ajah as sisters of the Grey Ajah are mediators, seeking harmony and consensus. As for my bear cub, I think she would choose the Blue Ajah because the Blue Sisters involve themselves with causes and justice and she is P's and my daughter.
F. For this one I'm going to choose my mom's favorite work since I have such a hard time choosing and put someone with Ds in Janet Evanovich's (JE) Stephanie Plum series. If JE wrote the person as a one time character, I imagine that that person was the key to Stephanie solving the mystery and saving Stephanie from almost death, due to the villains completely underestimating what someone with Ds is capable of. If JE wrote her in as a recurring character, the person would be as zany and fun as Grandma Mazur or Lula and could work at the donut shop or funeral parlor, maybe originally showing up in the series as a skip.