Down syndrome (or Trisomy 21 or Trisomy G) describes a chromosomal abnormality, and refers to a set of features related to aberrations, mental development and psychosocial development.

People with Down Syndrome have a round face, split eyes, small tongue-shaped tongue, short fingers at their ends and low height.

They are usually characterized by hypotonia, as well as a high rate of cardiac abnormalities. The intensity of learning difficulties varies from person to person and presents a mental retardation. They usually do not exceed the age of 50 years.

The term "autism" originates etymologically from the Greek word "self" and suggests the isolation of a person to himself. Autism falls into the category of Diffuse Developmental Disorders. These disorders are characterized by severe deficits at the same time in many areas of development. There are deficits in social development, peculiar linguistic development and limited stereotypes of interest.

In particular, they are characterized by incomplete social skills, they have a particular difficulty in developing emotional relationships. Many times there is a lack of eye contact and speech (peculiar linguistic development). Stereotypical movements characterize people with autism as well as stereotypical behavior with persistence and maintenance of specific "ritual" habits. Finally, they may have suicidal or aggressive behavior as well as hyperactivity and distraction.

"Mental retardation or retardation" (NK) characterizes people with a significantly low mental level (<70 IQ) as well as significant adaptation problems in day-to-day activities. People with NK are distinguished in educative (55-69 IQ), that is, they can learn to write or read as a fourth-grade elementary school child and play relatively independently. They are distinguished in exercising (40-54 IQ), ie they develop nursery skills and need supervision in their everyday lives. Finally, they may fall into a category with serious difficulties in many areas and they need very much help from third parties.