Down syndrome is a chromosomal abnormality. It is the most frequent form of mental retardation and is characterised by well-defined, distinctive phenotypic features and natural history. An error in cell development results in forty-seven chromosomes rather than the usual forty-six. There are three major types of Down syndrome. About ninety-five percent of individuals with Down syndrome have Trisomy 21. There is also Translocation and Mosaicism. Down syndrome can also be referred to as Mongolism, the condition is named for John Langdon Down. ....