Down syndrome

Down syndrome, or Down's syndrome, trisomy 21, is a chromosomal condition caused by the presence of all or part of an extra 21st chromosome. It is named after John Langdon Down, the British physician who described the syndrome in 1866. The condition was clinically described earlier in the 19th century by Jean Etienne Dominique Esquirol in 1838 and Edouard Seguin in 1844. Down syndrome was identified as a chromosome 21 trisomy by Dr. Jérôme Lejeune in 1959. Down syndrome in a fetus can be identified through chorionic villus sampling or amniocentesis during pregnancy, or in a baby at birth. Down syndrome is a chromosomal condition characterized by the presence of an extra copy of genetic material on the 21st chromosome, either in whole...