Why do people with Down Syndrome have that same “look” to them?

Question

Why do people with Down Syndrome have that same “look” to them?

In: 3056

Answer 1

Down’s syndrome is caused by trisomy 21 –which means patients have three copies of chromosomes 21 instead of two. In essence their bodies are overdosing by 50% on every protein encoded on chromosome 21. All sorts of proteins have specific roles in early development so the results of messing with the same ones by the same amount are going to be fairly consistent across patients.

Grim fun fact, the only other chromosomes that you can survive a miscount on are X and Y. The other numbered chromosomes are all critical enough that it’s nearly impossible to survive past infancy with the wrong count.