Well, first, I would not refer to the distinctive look of people with Down syndrome as “disfigured.” That will get you some hate right there. No one knows exactly, but there is a good theory. Down syndrome is, above all things, a growth disorder. read more
As for why "people with Down's syndrome look alike", they don't. They have a series of shared facial features, but they have as much variation within their facial features as neuro-normatives do. It's like how "all Asians look alike" to other ethnic groups, despite plenty of in-group variation. read more
Well it is wrong to say that people with Down syndrome look alike, but they do have a similar aesthetics. Down syndrome is what happens when the baby is born with 3 copies of chromosomes 21, instead of 2. Having 3 copies of the chromosomes 21 lead to the change in the body, including the unique facial shape and the developmental delay. read more