Down Syndrome

What Is Down Syndrome? Symptoms, Causes, Diagnosis, and Treatment

Moira Lawler
By Medically Reviewed by 
Reviewed:
Medically Reviewed
Down syndrome is the most common chromosome-related genetic condition in the United States.

A child born with this condition has extra genetic material caused by abnormal cell division. This results in an extra full or partial copy of chromosome 21.

That extra genetic material affects physical and cognitive development.

Three Types of Down Syndrome

There are three types of Down syndrome, each caused by specific circumstances related to the extra genetic material from chromosome 21.

  1. Trisomy 21 This is the most common type of Down syndrome, and it accounts for about 95 percent of all cases. It happens when a person has three copies of chromosome 21, instead of the usual two copies, in every cell. This is caused by abnormal cell division in a sperm or egg cell before or at conception, resulting in an embryo with an extra copy of chromosome 21 that gets replicated in every cell of the developing body.
  2. Translocation Down Syndrome Responsible for about 4 percent of Down syndrome cases, this is when a child is born with the usual 46 chromosomes but may have additional genetic material from chromosome 21 that attaches to another chromosome within the cell.

  3. Mosaicism Also called mosaic Down syndrome, this accounts for about 1 to 2 percent of cases. Babies born with mosaicism have some cells with the normal number of 46 chromosomes and others with 47, including an extra copy of chromosome 21, resulting in fewer and less severe symptoms.

Learn More About the Different Types of Down Syndrome

Signs and Symptoms of Down Syndrome

The physical and cognitive symptoms caused by Down syndrome aren’t the same for everyone. That said, there are certain symptoms commonly associated with Down syndrome, including:

  • Short, stocky body size
  • A short neck
  • Poor muscle tone with unusual flexibility
  • Flattened facial features, including the bridge of the nose
  • Small or unusually shaped ears
  • Almond-shaped eyes with an upward slant
  • Small hands and feet
  • Short fingers and a deep, single crease across the palm of each hand

Learning and developmental delays connected with Down syndrome can include:

  • Speech and language development delays
  • Attention and concentration issues
  • Difficulty sleeping
  • Delays in cognitive development
  • Mild to moderate cognitive impairments
  • Delayed toilet training

Causes and Risk Factors of Down Syndrome

The science behind why some babies are born with an extra copy of chromosome 21 is still unclear. “It’s almost always something that happens at the time of conception,” says Kishore Vellody, MD, the medical director at the Down Syndrome Center of Western Pennsylvania, located at UPMC Children’s Hospital of Pittsburgh. “It’s nothing that mom or dad did — we still don’t fully understand why it happens.”

The extra copy of chromosome 21 can come from the mother or the father. The only real risk factor for Down syndrome is a mother’s age at conception. As a woman gets older, her chance of having a baby born with Down syndrome increases.

A 20-year-old woman’s odds for having a baby with Down syndrome are 1 in 2,000. By age 35, the risk rises to 1 in 350. At 40, the risk is 1 in 100, and by age 45, it’s 1 in 30. Still, most babies with Down syndrome are born to women younger than 35, simply because there are more births in this younger group. “We theorize that for the mom, the longer the eggs have been sitting and waiting, the higher the chances of having an extra chromosome come along with the baby,” Dr. Vellody says.

Down syndrome affects people of all races and economic classes. And though it’s a genetic condition, it’s generally not passed down by family members. Sometimes there is a hereditary component with translocation, however, which is one of the more uncommon types of Down syndrome. About one-third of these cases can be traced back to family history. If you have a baby with a translocation, the chances it will reoccur in later children are 3 percent if the father is the carrier and 10 to 15 percent if the carrier is the mother, but precise chances depend on the chromosome numbers involved in the translocation. A genetic counselor can help you assess risk if you plan to have more children.

Learn More About What Causes Down Syndrome

How Is Down Syndrome Diagnosed?

Screening Tests

A woman can be screened during pregnancy to find out if her baby is likely to have Down syndrome. The screenings involve blood tests and an ultrasound. But a screening test is not a diagnosis.

During the first trimester, the two-part screening for Down syndrome includes a blood test for abnormal levels of pregnancy-associated plasma protein-A (PAPP-A) and the hormone human chorionic gonadotropin (HCG). Your doctor will also order an ultrasound, called the nuchal translucency test, that looks for higher-than-normal amounts of fluid behind a baby’s neck, as that can be a sign of Down syndrome.

Some women opt for blood screening tests during both the first and second trimesters of their pregnancy. The first-trimester test is the same as described above. The second-trimester test, called a quad screen, measures alpha fetoprotein, estriol, HCG, and inhibin A.

A newer test called cell-free DNA testing or noninvasive prenatal screening (NIPS) can also be performed starting in the 10th week of pregnancy. It uses a sample of a pregnant woman’s blood to check her baby’s DNA for Down syndrome risk. Both positive and negative results have nearly 100 percent accuracy.

Because false positives are a very small possibility, your doctor or genetic counselor will use the results and your age to determine your baby’s risk for Down syndrome. Further checks can verify or rule out a diagnosis.

Diagnostic Tests

Diagnostic tests are more accurate, but they carry some risk for mother and baby. Performed after the 10th week of pregnancy, the two available diagnostic tests are chorionic villus sampling, which tests chromosomes from a tiny sample of the placenta, and amniocentesis, which tests amniotic fluid for chromosome numbers. They are nearly 100 percent accurate in telling if the baby has Down syndrome, but come with a small risk of miscarriage — less than 1 percent, depending on the type of test and the mother’s age.

Post-Birth Diagnosis

Down syndrome can also be diagnosed at birth and may be relatively easy for medical professionals to spot. “Most of the time you can identify Down syndrome in the newborn nursery,” Vellody says. “The features that the baby would have are usually pretty evident to the doctor.” Babies with Down syndrome typically have a deep crease across their palm, eyes that slant upward, and a somewhat flattened face. Some babies without the syndrome have Down-like features at birth. If a baby is born with these features, the doctor will test the baby’s blood to determine if he or she has an extra full or partial copy of chromosome 21. Results are usually available within 48 hours, while a more thorough analysis can take between 5 and 10 days.

Learn More About How Doctors Diagnose Down Syndrome

Prognosis of Down Syndrome

The prognosis for people with Down syndrome has improved dramatically over the past 60 years. Life expectancy has increased from just 10 years in 1960 to 60 years or longer today. With support, education, and medical care for the various physical, cognitive, and social challenges related to Down syndrome, people with the disorder are living healthy, active lives — going to school, working, enjoying friends and loved ones, and engaging in a wide variety of recreational activities.

Treatment and Medication Options for Down Syndrome

Because Down syndrome is a chromosomal condition and not a disease, there are no medicines available to treat it, and there is no way to cure or reverse the disorder. The focus is on finding the therapies and services that aid in the physical and intellectual development of children with Down syndrome.

Early intervention programs are available for infants with Down syndrome until they reach their third birthday. These programs (and the availability of them) vary depending on where you live, but they generally provide children and families with professional help from physical therapists, occupational therapists, speech therapists, special educators, and social workers. Participating in these programs has been shown to improve the outcomes for children.

Government support options tend to go away as a child gets older and ages out of school, though there are many organizations that help people with Down syndrome find employment and housing, such as The Arc, HireDS, and Project SEARCH. As people with Down syndrome become adults, the focus of support services shifts from developmental therapies to treating the health issues associated with Down syndrome and helping people with the syndrome live full lives.

Learn More About Therapies and Services for People With Down Syndrome

Complications of Down Syndrome

Being born with an extra copy of chromosome 21 can contribute to a higher risk for a variety of health issues that need to be monitored throughout one’s life. The most common and most serious concern involves the heart. About half of people with Down syndrome are born with a heart defect, though the severity can vary drastically.

More than half of all children with Down syndrome also have vision problems and hearing loss. Immune-system problems are common, boosting risk for infections, including pneumonia. Starting early in life, people with Down syndrome are also more likely to have hypothyroidism (low thyroid function), gum disease and dental problems, digestion problems, and sleep difficulties, including obstructive sleep apnea. They also face a higher risk for anemia, leukemia, and epilepsy.

Learn More About Complications Linked to Down Syndrome

Research and Statistics: How Many People Have Down Syndrome?

Down syndrome affects about 1 in 700 babies in the United States, resulting in about 6,000 newborns a year with the condition. In 2010, there were 206,366 babies, children, teens, and adults with Down syndrome living in the United States.

Research Related to Down Syndrome

Recent research about Down syndrome is focused on everything from genetics to how children with the syndrome learn. Notable, ongoing studies are looking at:

Health Across the Life Span A large National Institutes of Health (NIH) project called INCLUDE (Investigation of Co-occurring Conditions Across the Lifespan to Understand Down Syndrome) aims to better understand health and life-quality issues for the growing number of people with Down syndrome living into their sixties and beyond.

Tracking Brain Development Researchers from Children’s Hospital of Philadelphia (CHOP) and the Infant Brain Imaging Study (IBIS) Network are preparing to examine brain development, via brain imaging, in children of various ages with Down syndrome. This could help researchers find new therapies.

Related Conditions of Down Syndrome

In addition to the Down syndrome–related complications outlined above, other health concerns may emerge as people with Down syndrome move into adulthood and old age. Menopause may arrive earlier for women, often in the late forties. Vision impairment becomes more severe, and eye problems like cataracts are more common. Hearing loss, an issue from birth for many with Down syndrome, may accelerate in young adulthood. Obesity, arthritis, osteoporosis, obstructive sleep apnea, and thyroid problems are also more likely in adults with Down syndrome.

There is also an increased risk of developing Alzheimer’s disease. The extra copy of chromosome 21 can cause problems within the brain cells, and about half of people with Down syndrome will show signs of dementia, usually once they enter their fifties or sixties.

Michelle Sie Whitten, the chief executive officer, president, and cofounder of Global Down Syndrome Foundation in Denver, says it’s important to note that none of these comorbidities is unique to people with Down syndrome. “All of these things happen within the general population,” she says. It’s also entirely possible that some people with Down syndrome won’t experience any of these problems, but it’s important to be aware of the potential complications so doctors can monitor closely to catch problems early, when they’re most treatable.

Resources We Love

Favorite Organizations for Essential Information About Down Syndrome

National Association for Down Syndrome

The oldest U.S. organization for people with Down syndrome and their families, NADS got its start in 1961 when a group of Chicago parents defied medical advice and raised their kids with Down syndrome at home. Today, NADS offers support for parents, self-advocacy programs for people with Down syndrome, and retreats, conferences, and seminars. One inspiring feature is a video featuring self-advocates called I Love My Life.

National Down Syndrome Society

The NDSS describes itself as “the leading human rights organization for all individuals with Down syndrome.” The group’s resource-packed website includes tips on everything from understanding what a Down syndrome diagnosis means to how to find employment opportunities for people with Down syndrome. One notable offering: The NDSS DS-Ambassador Program, which is seeking to have a Down syndrome ambassador in every congressional district in the United States with the goal of building relationships with elected government officials and championing measures that help the Down syndrome community.

Down Syndrome Resource Foundation

This Canadian website offers news, research updates, well-written and beautifully photographed articles about people of all ages with Down syndrome, and more. The foundation’s mission is to empower people with Down syndrome to reach their full potential. One highlight is the online magazine, 3.21: Canada’s Down Syndrome Magazine, published jointly by the foundation and the Canadian Down Syndrome Society.

MedlinePlus

This U.S. government website from the National Library of Medicine provides a wealth of consumer-friendly information about the effects of genetics on human health. There is easy-to-grasp information about more than 1,300 genetic conditions, including Down syndrome, plus basics like a useful primer called Help Me Understand Genetics, making this a go-to guide to this important, ever-changing field.

Global Down Syndrome Foundation

Established in 2009, the nonprofit Global Down Syndrome Foundation is dedicated to significantly improving the lives of people with Down syndrome through research, medical care, education, and advocacy. The website takes a deep dive into issues that matter, including adult healthcare for people with Down syndrome and medical disparities experienced by people with the condition. Practical resources include an interactive locator map for finding a Down syndrome medical care clinic near you.

Favorite Personal Blogs About Living With Down Syndrome

Baby Lemonade Blog

This compelling blog is about a family’s journey with their beloved daughter Kara, aka “Baby Lemonade,” who has Down syndrome. It also includes guest posts and resources. “My intent on sharing our journey is to provide some insight on what it REALLY looks like to raise my daughter with Down syndrome,” the blog’s author writes. “From this I want to see acceptance and awareness. I want to show society that a person has WORTH regardless of how many chromosomes they have.” One memorable post: My 4-Year-Old With Down Syndrome, celebrating Kara’s birthday.

Noah’s Dad

Enthusiastic, down-to-earth, and direct, this blog by the father of a boy with Down syndrome is upbeat and insightful. It’s earned a large and supportive community of fans, too. One particularly useful post gives advice to friends and family of expectant parents of a child with Down syndrome. What to Say to Someone Who Has Received a Down Syndrome Diagnosis includes advice offered by 300 people who follow Noah’s Dad on Facebook.

Additional reporting by Sari Harrar.

Editorial Sources and Fact-Checking

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