The twenty-first day of the third month was not chosen by chance, but to show that Down syndrome is associated with trisomy (three copies) of the 21st chromosome pair. Down syndrome was described in 1866 by John Langdon Hayden Down, a British physician and geneticist who defined “Mongolism”. One hundred years later, the extra chromosome was discovered, so in 1965 the chromosomal abnormality was officially defined as “Down Syndrome” in honor of its first discoverer. However, the doctor’s last name coincides with the English word – “below”, so for a long time in society there is a false misconception that people with Down Syndrome are mentally retarded.