Please note that the content of this book primarily consists of articles available from Wikipedia or other free sources online. Down syndrome is a chromosomal condition and a type of mental retardation caused by an abnormal number of chromosomes. According to statistics, Down syndrome affects 1 in 1,000 to 1 in 1,100 newborns worldwide, causing intellectual and physical disabilities. While in the early 1900's people affected by the disease had an average life expectancy of ten years, today 80% of patients reach the age of 50. Learn more about the causes and symptoms of the genetic abnormality as well as management of Down syndrome in this book.