Definition of Down syndrome in US English:

Down syndrome

(also Down's syndrome)


  • A congenital disorder arising from a chromosome defect, causing intellectual impairment and physical abnormalities including short stature and a broad facial profile. It arises from a defect involving chromosome 21, usually an extra copy (trisomy-21).

    • ‘Congenital heart disease is common in Down's syndrome, occurring in about 40% of individuals.’
    • ‘Cells from the baby found in the fluid are tested for chromosomal abnormalities such as Down's syndrome.’
    • ‘Several teeth may be absent in disorders such as Down's syndrome and ectodermal dysplasia.’
    • ‘It is probably unlawful to place lower priority on children with Down's syndrome and other disabilities who need heart transplants.’
    • ‘It is known that head injury is a risk factor, and also that Alzheimer's disease often affects people with Down's syndrome.’
    • ‘We have used a video of women describing their experiences when undergoing screening for Down's syndrome and open neural tube defects in pregnancy.’
    • ‘When women take the decision to end a pregnancy affected by Down's syndrome or spina bifida they are making a personal or individual choice.’
    • ‘Sex chromosome anomalies as a group are as common as Down's syndrome, but most affected individuals are never identified’
    • ‘In these analyses children with pre-existing conditions, such as Down's syndrome or cerebral palsy, were excluded.’
    • ‘Women over 35 are more likely to have a child with a chromosomal abnormality, such as Down's syndrome.’
    • ‘This is the same chromosome of which an extra copy is present in every body cell of people with Down's syndrome.’
    • ‘This latest research shows that there is an even higher risk of ‘chromosomal abnormalities’ such as Down's syndrome.’
    • ‘For that reason society offers testing for Down's syndrome, haemophilia, cystic fibrosis, and a range of other genetic conditions.’
    • ‘This is an accurate way of finding out whether the baby has a number of genetic or inherited disorders, such as Down's syndrome or cystic fibrosis.’
    • ‘In Down's syndrome, an extra copy of chromosome number 21 is included when the sperm and the egg come together to form the embryo.’
    • ‘Some women aged over 35 years opted directly for amniocentesis, and in others an abnormal scan result led to the diagnosis of Down's syndrome.’
    • ‘There are a number of similarities in the brains of individuals with Down's syndrome and Alzheimer disease.’
    • ‘For example, the presence of an extra twenty-third chromosome causes Down's syndrome.’
    • ‘Ultrasound scanning is combined with a number of blood tests spread over a few weeks to look for conditions such as spina bifida and Down's syndrome.’
    • ‘For example, people who have severe genetic disorders or handicaps like Down's syndrome or Siamese twins are kept alive.’


Of relatively recent coinage, Down syndrome is the accepted term in modern use, and former terms such as mongol, Mongoloid, and mongolism, which are likely to cause offense, should be avoided. See also Mongoloid


1960s: named after John L. H. Down (1828–96), the English physician who first described it.


Down syndrome

/ˈdaʊn ˌsɪndroʊm//ˈdoun ˌsindrōm/