What is Down Syndrome?

People with Down syndrome are born with an extra chromosome, which changes the way their brain and body develop.

Down syndrome is a genetic disorder. Most babies are born with 23 pairs of chromosomes within each cell for a total of 46. A chromosome is a structure that contains genes, which are made up of your DNA. Genes determine how you form and develop growing in the womb and after birth. The majority of babies with Down syndrome are born with an extra copy of chromosome 21, with three copies of the chromosome instead of the usual two.

As a result people born with Down syndrome face some physical and mental challenges throughout life. They typically have distinctive body and facial features that set them apart. They are more likely to develop slowly, and are more at risk for some medical conditions.

Are there different types of Down syndrome?

Yes, there are three types of Down syndrome. They are:

  • Trisomy 21: The term “trisomy” means having an extra copy of a chromosome. The most common type of Down syndrome, trisomy 21, occurs when a developing baby has three copies of chromosome 21 in every cell instead of the typical two copies. This type makes up 95% of the cases.
  • Translocation: In this type of Down syndrome, there is an extra full or partial amount of chromosome 21 attached to another chromosome. Translocation accounts for 4% of the cases.
  • Mosaicism: In the rarest type (only 1%) of Down syndrome, some cells contain the usual 46 chromosomes, and some contain 47. The extra chromosome in these cases is chromosome 21.

How common is Down syndrome?

Down syndrome is the most common chromosome-related condition in the U.S. Roughly 6,000 babies are born with the condition in the U.S. every year (about 1 in every 700 babies). More than 400,000 people are living with the condition in the U.S. today.

What are the risk factors for having Down syndrome?

Researchers are unsure why Down syndrome occurs in certain people. Anyone of any race or societal level can be affected.

What is known is that the risk of giving birth to a child with Down syndrome increases as women grow older. Women aged 35 and older are more likely to have their pregnancy affected by the syndrome. But because younger women have higher fertility rates, most babies with Down syndrome are born to women under 35.

What causes Down syndrome?

Each human cell typically contains 23 pairs of chromosomes. Down syndrome occurs because of changes in the way cells in chromosome 21 divide. Every person with Down syndrome has an extra amount of this chromosome in some or all of their cells.

In the most common type of Down syndrome, trisomy 21, the condition occurs randomly and isn’t inherited. However, when translocation or mosaicism is the cause of Down syndrome, hereditary (passed down among family members) should be looked at as a cause.

What are the signs and symptoms of Down syndrome?

Down syndrome causes physical, cognitive (thinking) and behavioral symptoms.

Physical signs of Down syndrome can include:

  • Short, stocky physical size, with a short neck.
  • Poor muscle tone.
  • Flattened facial features, especially the bridge of the nose.
  • Small ears.
  • Almond-shaped eyes that slant upward.
  • Small hands and feet.
  • Single deep crease across the center of the palm of the hand.

Common learning and behavioral symptoms of Down syndrome include:

  • Delays in speech and language development.
  • Attention problems.
  • Sleep difficulties.
  • Stubbornness and tantrums.
  • Delays in cognition.
  • Delayed toilet training.

Not all people with Down syndrome have all these symptoms. Symptoms and their severity are different from person to person.

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