Professor Jerome Lejeune and his colleagues discovered that Down syndrome, first classified by J. L. H. Down in 1866, is caused by trisomy 21 - that is, having three instead of 2 copies of chromosome 21. The extra copies of the genes on chromosome 21 affect the development of the brain and body.
Lejeune, J., Gautier, M., Turpin, R. Etude des chromosomes somatiques de neuf enfants mongoliens. C R Acad Sci, 248: 1721-1722. 1959. [PubMed]
Ford, C.E., Miller O.J., Polani P.E., de Almeida, J.C., Briggs, J.H. A sex-chromosome anomaly in a case of gonadal dysgenesis (Turner's syndrome). Lancet, 1: 711-713. 1959. [PubMed]
Jacobs, P.A., Strong, J.A.. A case of human intersexuality having a possible XXY sex-determining mechanism. Nature, 183: 302-3.1959. [PubMed]
Last Reviewd: April 23, 2013