erred to as "Mongoloids." Down based this unfortunate name on his notion that these children looked like people from Mongolia, who were thought then to have an arrested development. This ethnic insult came under fire in the 1960s from Asian genetic researchers, and the term was dropped from scientific use. Instead, the condition became called "Down's syndrome." In the 1970s, an American revision of scientific terms changed it simply to "Down syndrome," due to the insinuation of ownership caused by the possessive apostrophe, although it is still called "Down's" in Europe. The causes of DS were much speculated over during the first part of the twentieth century. The first to speculate that Down syndrome might be chromosomal in nature were Waardenberg and Bleyer during the 1930's. However it wasn't until 1959 that Jerome Lejeune and Patricia Jacobs, working independently, first determined the cause to be trisomy (triplication) of the 21st chromosome. To understand the pathophyisology of Trisomy 21 you must first understand the basic structure of chromosomes. Chromosomes are thread-like structures composed of DNA and other proteins. They are present in every cell of the body and carry the genetic information needed for that cell to develop. Genes, which are units of information, are "encoded" in the DNA. Human cells normally have 46 chromosomes, which can be arranged in 23 pairs. Of these 23, 22 are alike in males and females; these are called the "autosomes." The 23rd pair are the sex chromosomes ('X' and 'Y'). Each member of a pair of chromosomes carries the same information, in that the same genes are in the same spots on the chromosome. However, variations of that gene ("alleles") may be present. (Example: the genetic information for eye color is a "gene;" the variations for blue, green, etc. are the "alleles.") Human cells divide in two ways. The first is ordinary cell division ("mitosis"), by which the body grows. In this method, one ...
