Down Syndrome is much more worse than Autism.

At least autism usually not a sickness. Your kid will become normal as the grow and mature.

Correct me if I am wrong.

Really? Source?

AFAIK, both down syndrome and autism will bring parents and kids disaster for life. I might say nightmares hunting you for life.

Your life as couples will be broken for life.
Your life as parents will be broken for life.
Your career and hobbies will be end road.
You will have sleepness nights for the rest of your life.
Both husband and wife couldn't travel abroad and leave your child alone at home even if your child reaches 18.
Both mum and dad will need to take care of your kid for the rest of your life even during your retirement life as your kid is unable to take care of himself/herself
Results in more and more arguments between child, parents, spouse, parents-in-law etc
Results in hate more than love between parents and your child.
The worst part is... your kid doesn't even know you are his dad/mum even if your kid matures. THINK ABOUT IT

Basically is like taking care of a very ill patient on bed for the rest of your life without having any time for rests.

You will eventually think that if can turn back time, I rather not having any child or even getting married in the first place.

Well, you can always go Singapore or Taiwan to abort it and nobody gonna know about it