Trisomy 21 (T21), or Down syndrome (DS), is one of the major causes of intellectual disability, this has been analyzed to differ in every individual by the intelligence quotient (IQ) test irrespective of other factors. It is a genetic disorder characterized by an extra copy of chromosome 21. PubMed database was used for searching relevant papers, and the following keys were used in the mesh (("Down syndrome " [Mesh]) AND ("Features and diagnosis" [Mesh]) OR ("Down syndrome Features and diagnosis " [Mesh])). Inclusion criteria were all the articles that consisted of one of the following topics: Down syndrome Features and diagnosis. Concerning exclusion criteria, all articles which did not have one of the inclusion criteria as their topic was not selected. To date, nothing has been developed that effectively improves cognition in children with DS, but effective early stimulation therapy, behavioral intervention, a positive home environment, education, and vocational training are all useful in improving their overall functioning and productivity.