Historical Overview
For several centuries, there have been references to people with Down syndrome in art, literature, and science. The English physician John Langdon Down was the first to provide an accurate description of the condition in 1866, and as a result he is credited with its discovery. Although others before him had identified some of its characteristics, Down was the one who described it as a distinct and independent condition in its own right.
In 1959, French physician Jérôme Lejeune identified Down syndrome as a chromosomal condition, observing that there were 47 chromosomes in each cell rather than the typical 46. It was subsequently established that the presence of a full or partial extra copy of chromosome 21 is what gives rise to the characteristics associated with Down syndrome.
In 2000, an international team of scientists succeeded in identifying and cataloguing each of the approximately 329 genes on chromosome 21. This achievement opened the door to significant advances in Down syndrome research.
Causes
The cause of the chromosomal error that leads to Down syndrome is still unknown. However, research has shown that the incidence increases with the mother's age at the time of birth. Due to higher birth rates among younger women, 80% of children with Down syndrome are born to women under the age of 35. To date, there is no conclusive scientific evidence indicating that Down syndrome results from environmental factors or from the activities of either parent before or during pregnancy.
The extra full or partial copy of chromosome 21 that causes Down syndrome can originate from either the mother or the father. Research has found that approximately 5% of cases are attributable to the father.
Source: The information in this article has been reproduced under an exclusive agreement with the National Down Syndrome Society. Available at: ndss.org
