Down SyndromeTrisomy 21 is caused, as the name suggests, by the triplication of the 21st chromosome. The genes, which, to put it simply, contain the blueprints for our cellular structure, are grouped along rod-like structures called chromosomes. Normally, the nucleus of each cell contains 23 pairs of chromosomes, half of which are inherited from each parent. In Down syndrome (DS), however, the cells usually contain not 46, but 47 chromosomes. This excess genetic material, in the form of additional genes along the 21st chromosome, causes DS. The estimated incidence of Down syndrome is between 1 in 1,000 and 1 in 1,100 live births. Every year approximately 3,000-5,000 children are born with this chromosomal disorder. There are believed to be approximately 250,000 families affected by DS in the United States. (Berg, 614) A more detailed description of the pathophysiology of Down syndrome will be discussed in this article, as well as the finding, possible causes, physical characteristics, associated conditions, possible treatment, electroneurodiagnostic corollaries, and psychosocial issues. Trisomy 21 has been talked about for centuries in art, literature and science. One of the most interesting is the "Change" in Gaelic myth. It was believed that when a child was born with the dysmorphic features now associated with DS, i.e. epicanthal folds, simian folds, small ears, etc., an elf or evil spirit replaced the child that should have been theirs with the offspring of a mischievous . creature. However, it was not until 1866 that a doctor named John Langdon Down published an essay in England in which he described a group of children with common characteristics that were distinct from other mentally retarded children. Down was superintendent of an asylum for mentally retarded children in Surrey, England, when he first made the distinction between idiot children (who were later found to have hypothyroidism) and what he called "Mongoloids." Down based this unfortunate name on his idea that these children resembled people from Mongolia, who were then thought to have arrested development. This ethnic slur was criticized in the 1960s by Asian genetic researchers and the term was dropped from scientific use. Instead, the condition came to be called “Down syndrome.” In the 1970s, an American revision of the scientific terms changed it simply to "Down's syndrome", due to the insinuation of ownership caused by the possessive apostrophe, although in Europe it is still called "Down's".