Most babies are born with 46 chromosomes. These contain the DNA that determine how a baby develops. Babies with Down syndrome are born with an extra copy of chromosome 21. This extra chromosome changes how the baby’s brain and body develop, and causes the physical features and traits linked to Down syndrome. It is a lifelong condition.

Down syndrome is the most common genetic chromosomal condition diagnosed in the U.S. Although children with Down syndrome share many traits and challenges, the symptoms can vary from mild to severe. Some children with Down syndrome may be more prone to serious health problems, such as heart conditions and ear and eye problems.

There are three main types of Down syndrome:

  • Trisomy 21. About 95% of people with Down syndrome have Trisomy 21. Children with this type have three separate copies of chromosome 21 instead of the typical two copies.
  • Translocation Down syndrome. This less common type of Down syndrome occurs when an extra chromosome 21 is attached to another chromosome.
  • Mosaic Down syndrome. Children with this type of Down syndrome have some cells with three copies of chromosome 21 and other cells with two copies.

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What are the signs and symptoms of Down syndrome?

Babies and children with Down syndrome share many of the same physical traits, including:

  • A flattened face and small head
  • A short neck
  • Upward-slanting eyes
  • A tongue that sticks out
  • Small ears or unusually-shaped ears
  • Poor muscle tone
  • Shortened height
  • Small hands and feet
  • Small white spots on the iris (the colored part of the eye)
  • Loose joints
  • Delayed language
  • Mild to moderate cognitive impairment

What causes Down syndrome?

Down syndrome is caused by an extra chromosome, but experts are not certain why this occurs or what factors may play a role. One factor experts do know about is a mother’s age during pregnancy. Pregnant women who are age 35 and older are more likely to have a baby with Down syndrome than younger women.

How is Down syndrome treated?

There are not any specific treatments for Down syndrome. Children with Down syndrome may have physical, speech and occupational therapy to help them overcome challenges in these areas. Children with more serious medical problems, such as a heart condition, may need treatment for these conditions.

Doctors at Connecticut Children’s can determine the right plan if your child requires treatment for Down syndrome.