Why do those with down's syndrome (trisomy 21)...?

Question

have such a wide range of ability? Some are able to function very highly and others are not capable of simple tasks. I don't understand why there is such variability when they all suffer from the same condition.

Answer 1

I think it's kind of like how other people have wide ranges of ability. My close friends and I all have the same number of chromosomes, and our scores on the ACT in high school varied from 17-33. I'm terrible at basketball, but a guy from my high school is NBA-bound. There's no telling why some function highly and others have more difficulty, just like the rest of us.

Answer 2

Mosaicism ....not all cells have 3x chromosome 21 in their bodies and brains...some % are normal

Also - some speculation the extra dosage effects of the third chromosome only effects a few genes and that the new RNAI technology might be able to simply shut down the extra chromosome in a few key gene locations ( Ref: Prof. Peter Humphries Smurfitt Institute of Genetics)

Answer 3

But not all higher functioning person with down syndrome are mosaics.

It is said that Down syndrome robs you of 30 IQ points. If so, it would mirror the variation of IQ in persons with a normal complement of chromosomes. Personally, I think this may be oversimplification.