Down syndrome (DS) is a condition due to a chromosome abnormality. The chromosome abnormality leads to impairment of both the physical and intellectual development of the individual.
In 1959, the late French physician Jerome Lejeune and coworkers reported finding an extra chromosome in each of nine children with DS. The extra chromosome in all of the children seemed to be the same-an extra copy of chromosome number 21 . Since having three instead of the normal two chromosomes of a specific type is referred to as trisomy, these children had trisomy 21, now recognized as the cause of DS.
A DS baby has certain characteristic features that may individually be quite subtle but together permit the clinical diagnosis of DS to be made at birth.
These signs of DS include:
- Slight flattening of the face
- Minimal squaring off of the top of the ear
- Low bridge of the nose (lower than usual)
- A fold of skin over the inner corner of the eye
- A ring of tiny harmless white spots around the iris
- Short, incurved fifth finger
- A single transverse crease across the palm
- Increased space between the first and second toes
There are many, many more minor malformations in DS.
DS is associated with major malformations, too. For example, approximately half of DS children are born with a heart defect, most often a hole between the two sides of the heart. Hirschprung's disease (congenital aganglionic megacolon) which can cause intestinal obstruction occurs more frequently in DS.
DS also carries an increased risk of acute leukemia. This risk is small in absolute terms but is still a significant added risk. The intellectual handicaps in DS are of great importance.
These handicaps may not be immediately evident, but they become increasingly apparent during infancy and early childhood as developmental delay and later in childhood and adulthood as mental retardation.
Very few adults with Down syndrome can lead independent lives because of their mental retardation. It was once thought that nearly all adults with Down syndrome developed Alzheimer's disease (dementia) so that on top of their mental handicap most people with Down syndrome were slated for premature senility. However, it now appears that a much lower proportion, perhaps 20 to 25%, of Down's adults develop dementia. The majority of adults with Down syndrome may thus be spared this fate.
Confirmation of the trisomy 21 requires a chromosome test which also serves to rule in or out a translocation (a rearrangement) of chromosome 21 that may be heritable and give rise to more cases of DS in the family.
Evaluation of the DS baby and the family by a medical geneticist may be useful.
Down syndrome is named after the 19th century English physician J. Langdon Down who described the condition in 1866. As a matter of fact, Langdon Down was not the first person to describe the condition. It was clearly recognized 20 years earlier by the French physician E. Seguin who descibed the condition in a book he published in 1846 in Paris. Such historical inaccuracies in naming diseases are common. However, there are stronger grounds for not calling this condition after Langdon Down.
In great error, Langdon Down attributed the condition to a "reversion" to the "mongoloid race." He held that evolution had been reversed and there had been a sort of backslide from the superior Caucasian to the inferior Oriental race. Hence, the name Down syndrome smacks of racism.
The disorder was also once called mongolism, a term now considered perjorative, and to be avoided in English. (It is still used in some countries). Other names that have been used over the years include mongol, mongoloid, mongolian imbecile, mongoloid idiot, mongoloid deformity, Kalmuck idiocy, Tartar, unfinished child, Langdon-Down syndrome, Down's anomaly, and Down's deformity.
All of these names should, in our view, be jettisoned. The least controversial and most appropriate name for this syndrome may simply be what causes it: TRISOMY 21.
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Last Editorial Review: 4/26/2002