Down syndrome is a genetic, not inherited condition, characterized by the presence of 47 chromosomes in the cells of its carrier, instead of 46. The 21st pair carries an extra chromosome and that is why it is also called Trisomy 21. Down syndrome is today the most frequent cause of mental disability: in Italy about 1 in 1,000 children is born with this condition. Today there are an estimated 38,000 people in our country, 23,000 of whom are already adults. When the right conditions are created, most of these people can achieve a good level of personal autonomy and make an active contribution to society.