La sindrome di Berlusconi
Down syndrome is a genetic condition in which a person has 47 chromosomes instead of the usual 46. 
Causes, incidence, and risk factors
In most cases, Down syndrome occurs when there is an extra copy of chromosome 21. This form of Down syndrome is called Trisomy 21. The extra chromosome causes problems with the way the body and brain develop. Down syndrome is the most common single cause of human birth defects.
Symptoms 
Down syndrome symptoms vary from person to person and can range from mild to severe. However, children with Down syndrome have a widely recognized appearance. The head may be smaller than normal and abnormally shaped. For example, the head may be round with a flat area on the back. The inner corner of the eyes may be rounded instead of pointed. Despite all these challenges a child with Down Syndrome can grow up just like any other child and overcome the challenges along the way.