Down Syndrome is a genetic condition caused by extra genes from the 21st chromosome. The extra genes cause certain characteristics that we know as Down Syndrome. Individuals with Down Syndrome also have all other genes given to them by their parents. There also is a degree of mental retardation. Some of the physical features present are folds over theirs eyes and flattened bridge of nose. Their may be only the symptom of slow learning or a mental disability. There are not really any medical symptoms that can be found to prove that a child or person has down syndrome. There is the physical appearance and the lack of knowledge or learning disability that is present and noticeable. So unless mental retardation is a symptom of Down Syndrome, their aren't any.
When the child is born, there can be tests done to know for sure that the child has down syndrome. This will only tell them if the child has mental retardation though. The physical appearance when the baby is first born, would lead to anyone knowing that the child has down syndrome. Although it may take a few years for some to grow into having the Down Syndrome appearance. People with Down Syndrome do not have normal life expectancies. Generally, their life expectancy is reduced by 10-20 years. The have been some, though very few, that have had Down Syndrome and yet still managed to live to their 80's. Most common if this happens, then the person probably had a very mild case of Down Syndrome. Or, they just got really lucky and managed to live that long.
There are not that many people that are affected with Down Syndrome. The incidence of Down Syndrome has been recently reported as about 1 in 1,000 So it is a very slim chance that a child would have Down Syndrome and yet there are so many children/adults that do have it. But there is no association with Down Syndrome and any given culture, ethnic group, or geographic region. Although there have been proposed medical treatments for Down Syndrome, none of them have been proven effective.