[thedoc (OP)]

Luke Pullar asked the Naked Scientists:
   A potentially politically incorrect question (and in no way is this meant to be derogatory), but why do Downs Syndrome people all have similar facial features? How does this look cross ethnic boundaries when there's no apparent relation between them?
What do you think?

[evan_au]

In Down's syndrome, an extra copy of chromosome 21 (or part of chromosome 21 added to another chromosome) means that these genes are over-expressed in all cells of the body, causing a wide variety of changes.

However, our first impressions often come from looking at someone's face. One of the changes is that the tongue is larger than the mouth, causing deformation of teeth, jaws and difficulty with speech.

I have heard it suggested that by performing surgery on newborn children with Downs syndrome, the oversize tongue can be reduced; this reduces a couple of the more obvious characteristics. It was claimed that with this surgery, children are not treated so "different" by adults and children, and tend do better in schooling.

So some of the disability may be due to the environment (people's reactions). But there are still a wide variety of health impacts that must be continually monitored.
 
See: https://en.wikipedia.org/wiki/Down_syndrome#Mechanism

There are some other cases of multiple chromosomes which occur at similar rates to Downs syndrome. Some of these have detectable characteristics (eg Klinefelter's syndrome and Turner's syndrome), while for the XXY syndrome, there are no obvious characteristics (apart from being a tall man), and most cases are undiagnosed.
https://en.wikipedia.org/wiki/XYY_syndrome