Down Syndrome In one in every one thousand births, an extra chromosome results in the birth of a baby with Down's Syndrome; a genetic disorder resulting in mental retardation. In 1866, physician John Langdon Down, in Surrey England, identified a set of children with common features of mental retardation. Down was first to identify a similar link of symptoms in many patients. Thus, the new disorder was named "Down's Syndrome". Though it wasn't until 1959, that Jerome Lejeune and Patricia Jacobs, speculated that Down's syndrome was caused by chromosomal abnormalities. They traced the disorder to the exact effected chromosome. Lejeune and Jacobs constructed phenotype and geno