AUTHOR: Cassie Christianson

An Introduction to Down Syndrome

Down syndrome is a genetic variation that affects one out of 800 to 1,000 babies born in the United States. More than 350,000 people live with Down syndrome in the United States. Although all children are unique in their patterns of development, children born with Down syndrome learn differently. They have more variations in their intellectual, language, and movement development.

Symptoms of Down Syndrome

The symptoms of Down syndrome can vary a great deal. However, these are some of most common symptoms of Down syndrome:

  • Decreased muscle tone and loose joints
  • Upward slant of the eyes
  • Flattened face
  • Depressed nasal bridge with smaller nose
  • Mental retardation
  • Small mouth
  • Abnormally-shaped ears

Some children with Down syndrome also have visual, hearing, heart, and gastrointestinal problems. Many of these can now be corrected through medical interventions. With appropriate medical care, early intervention, education, and support throughout their lives, many adults with Down syndrome enjoy meaningful work and recreational opportunities. They may even live independently within the community.

The Genetics of Down Syndrome

The first comprehensive description of children with Down syndrome was published in 1866 by John Langdon Down, MD. His description still guides doctors who often make the clinical diagnosis shortly after birth. Because there is considerable variation in physical characteristics among children with Down syndrome, doctors confirm the diagnosis with genetic or chromosomal testing.

The genetic basis of Down syndrome was identified in 1959 by Jerome Lejeune and colleagues who found that Down syndrome was due to triplication of the 21st chromosome.

We are born with 46 chromosomes. Half are contributed by the mother and half contributed by the father, to equal 23 pairs. In Down syndrome, though, there are 47 chromosomes with an extra, or third, copy of chromosome 21, instead of two. This is why the scientific term for Down syndrome is “Trisomy 21.”

Today, through a blood test, physicians look at the karyotype to look for genetic abnormalities. A karotype is created by staining the chromosomes with dye and photographing them through a microscope.

AS Science for Public Understanding

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