Down Syndrome

Down syndrome, also called Down's syndrome or trisomy 21, is a congenital disorder caused by the presence of all or part of an extra 21st chromosome. This gives people with Down syndrome 47 chromosomes, rather than 46. It acquired the name after the British doctor John Langdon Haydon Down (1828–1896) who first described it in 1866. The outward physical signs of the disorder, usually identified at birth, are a range of major and minor differences in body structure, including an impairment of cognitive ability and also physical growth.

The incidence of Down syndrome is estimated at 1 for every 800 to 1,000 births, and it was first recognized by John L.H. Down as a different form of mental retardation in 1866, and four years later he published his report “Observations” on an Ethnic Classification of Idiots which was published in the Clinical Lecture Reports from London Hospital. Down, born in Torpoint, Cornwall, was from a well-connected fam-ily—his great-great grandfather on his father's side was the Roman Catholic Bishop of Derry, and the daughters of his sister married into the Darwin and Keynes families. Apprenticed to his father, a village apothecary, Down later went to work as a surgeon in London, and then to the Royal London Hospital and the Royal College of Surgeons, and became a Fellow of the Royal College of Physicians. He then worked at the Earlswood Asylum for Idiots in Surrey, and conducted much of his work at the Normansfield Asylum, in Teddington, Middlesex. His work used many terms such as mongolism which have long since stopped being used. There were various programs in the United States and also Nazi Germany involving identifying people suffering from Down syndrome, and then embarking on forcible sterilization, even though the cause remained unknown at the time, but was believed to be genetic.

In 1961, some 19 prominent geneticists wrote an open letter to The Lancet in which they argued that the “mongoloid” description should be dispensed with, and the journal supported the new term Down's Syndrome. Four years later, the delegate to the World Health Organization from Mongolia also objected to the term, forcing it to be dropped as an official term.

The vast majority of the people who suffer from Down syndrome have a third chromosome which is associated with the chromosome 21 pair. This is why the disorder is often known as trisomy 21. There are also some 4 percent of sufferers who have an abnormal condition known as translocation. This is because in their bodies, the extra chromosome in the 21 pair has broken off and attached itself to another chromosome. In spite of much research into the cause of Down syndrome, the reason for the chromosomal abnormalities is still unknown although it has been shown that there is a higher incidence of Down syndrome in the offspring of women who [Page 556]give birth over the age of 35. Although statistically the number of Down syndrome births in children remains one in 800–1,000, the level of incidence in women who give birth over the age of 40 are one in 40. This has led to a range of tests which can be used to diagnose Down syndrome prenatally by checking for the presence of the abnormal chromosome in samples of the fetal cells which can be collected from the amniotic fluid.

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