Why is Down Syndrome the most common type of syndrome in the world?

Why is it the most common type of syndrome in the world? Why would it happen at all? Is every human on Earth susceptible to this syndrome? Why would there be an spectrum of Down Syndrome cases? Is there a way to prevent Down Syndrome? Is there a way to reverse Down Syndrome? Is Down Syndrome induced by some kind of embryonic effect? Is Down Syndrome caused by genetic reasons or protein-related reasons? Why are the morphological features of people with Down Syndrome similar? Can Down Syndrome appear combined with other syndromes? Are we able to detect Down Syndrome at the embryo stage? What are the technologies capable of detecting Down Syndrome early in pregnancy?you do not need to answer them one by one. The essay must be at least five paragraphs long, and each paragraph must contain at least five sentences (you can write more than five paragraphs and more than five sentences per paragraph if you wish to do so).