Down Syndrome

Medically Reviewed by Amita Shroff, MD on September 19, 2022
5 min read

Down syndrome is a genetic condition that causes mild to serious physical and developmental problems.

People with Down syndrome are born with an extra chromosome. Chromosomes are bundles of genes, and your body relies on having just the right number of them. With Down syndrome, this extra chromosome leads to a range of issues that affect you both mentally and physically.

Down syndrome is a lifelong condition. Although it can’t be cured, doctors know more about it now than ever. If your child has it, getting the right care early on can make a big difference in helping them live a full and meaningful life.

Down syndrome can have many effects, and it’s different for each person. Some will grow up to live almost entirely on their own, while others will need more help taking care of themselves.

Mental abilities vary, but most people with Down syndrome have mild to moderate issues with thinking, reasoning, and understanding. They’ll learn and pick up new skills their whole lives, but they may take longer to reach important goals like walking, talking, and developing social skills.

People with Down syndrome tend to have certain physical features in common. These may include:

  • Eyes that slant up at the outer corner
  • Small ears
  • Flat noses
  • Protruding tongue
  • Tiny white spots in the colored part of the eyes
  • Short neck
  • Small hands and feet
  • Short stature
  • Loose joints
  • Weak muscle tone

Many people with Down syndrome don’t have any other health issues, but some do. Common conditions include heart problems and trouble hearing and seeing.

For most people, each cell in your body has 23 pairs of chromosomes. One chromosome in each pair comes from your mother and the other comes from your father.

But with Down syndrome, something goes wrong and you get an extra copy of chromosome 21. That means you have three copies instead of two, which leads to the symptoms of Down syndrome. Doctors aren’t sure why this happens. There’s no link to anything in the environment or anything the parents did or didn’t do.

While doctors don’t know what causes it, they do know that women 35 and older have a higher chance of having a baby with Down syndrome. If you’ve already had a child with Down syndrome, you’re more likely to have another one who has it as well.

It’s not common, but it is possible to pass Down syndrome from parent to child. Sometimes, a parent has what experts call “translocated” genes. That means some of their genes aren’t in their normal place, perhaps on a different chromosome from where they’d usually be found.

The parent doesn’t have Down syndrome because they have the right number of genes, but their child may have what’s called “translocation Down syndrome.” Not everyone with translocation Down syndrome gets it from their parents -- it may also happen by chance.

There are three types of Down syndrome:

  • Trisomy 21. This is by far the most common type, where every cell in the body has three copies of chromosome 21 instead of two.
  • Translocation Down syndrome. In this type, each cell has part of an extra chromosome 21, or an entirely extra one. But it’s attached to another chromosome instead of being on its own.
  • Mosaic Down syndrome. This is the rarest type, where only some cells have an extra chromosome 21.

You can’t tell what type of Down syndrome someone has just by how they look. The effects of all three types are very similar, but someone with mosaic Down syndrome may not have as many symptoms because fewer cells have the extra chromosome.

A doctor may suspect Down syndrome in a newborn based on the baby’s appearance. That can be confirmed by a blood test called a karyotype test that lines up the chromosomes and will show if there’s an extra chromosome 21.

Routine tests done during pregnancy can check if it’s likely your baby has Down syndrome. If those results are positive, or if you’re at high risk, you may choose to have additional, more invasive tests to be certain.

In the first trimester, you may have:

  • Blood tests. Your doctor will measure the levels of a protein called PAPP-A and a hormone called hCG in your blood. Anything out of the normal range could mean a problem with the baby. If you're at high risk for Down syndrome, they may also look for DNA from the baby in your blood, which they can examine for chromosome abnormalities.
  • Ultrasound. Your doctor will look at a picture of your baby and measure the folds of tissue at the back of their neck. Babies with Down syndrome tend to have extra fluid there.

In the second trimester, you may have:

  • Blood tests. Either a triple or quad-screen test measures other substances in your blood, including the protein AFP and the hormone estriol. Those levels, combined with the results from the first trimester tests, give your doctor a good estimate of the chances your baby has Down syndrome.
  • Ultrasound. When your baby is more developed, an enhanced ultrasound can show some of the physical features of Down syndrome.

Other kinds of tests can diagnose Down syndrome before your baby is born by checking a sample of their DNA for an extra chromosome 21:

  • Chorionic villus sampling (CVS). This can be done during the first trimester, using cells taken from the placenta.
  • Amniocentesis. Fluid is taken from the amniotic sac surrounding the baby, usually during the second trimester.
  • Percutaneous umbilical blood sampling (PUBS). This is also done in the second trimester using blood removed from the umbilical cord.

There’s no specific treatment for Down syndrome. But there is a wide range of physical and developmental therapies designed to help people with Down syndrome reach their full potential. The earlier you start them, the better. Each child will have different needs. Yours may benefit from:

  • Physical, occupational, and speech therapy
  • Specialized education services
  • Social and recreation activities
  • Programs that offer job training and teach self-care skills

You’ll also work closely with your child’s doctor to watch for and manage any health problems associated with the condition.

Babies with Down syndrome may be born with other physical problems, and they’re at higher risk for certain health issues later in life.

Possible complications of Down syndrome include:

Show Sources


National Institutes of Health: “The Genetic Basics: What Are Genes and What Do They Do?,” “Learning about Down Syndrome.”

KidsHealth: “Down Syndrome.”

Mayo Clinic: “Down Syndrome.”

National Health Service (U.K.): “Down’s Syndrome.”

CDC: “Facts about Down Syndrome.”

March of Dimes: “Down Syndrome.”

MassGeneral Hospital for Children: “Translocation Down Syndrome.”

U.S. National Library of Medicine: “Down syndrome.”

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