Down Syndrome: Facts and Statistics: What You Need to Know

Risks, Life Expectancy, and More

Down syndrome is a congenital (present at birth) condition that occurs when a baby is born with three copies of chromosome 21 instead of two copies. It causes many specific physical characteristics and health complications.

The medical issues that are part of Down syndrome can cause disability and are sometimes life-threatening, but survival and quality of life are improving due to advances in medical interventions.

This article explains the facts about Down syndrome, including how many people have it, risk factors, and screening. 

Parent holds child who has Down syndrome

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Down Syndrome Overview

People who are born with Down syndrome, also called trisomy 21, have certain noticeable traits and health problems. 

The effects of Down syndrome include:

  • Short height, sometimes with subtle anatomical differences in the hands and feet 
  • A characteristic appearance of the eyes and face 
  • Skeletal malformations 
  • Impaired hearing 
  • Heart defects 
  • Lung defects
  • Weak immune system
  • Gastrointestinal malformations 
  • Overweight or obesity
  • Learning delays or impaired motor skills in some people
  • Early dementia

All children who are born with Down syndrome develop one or more of these effects. However, many people who have Down syndrome usually do not develop all of the characteristics. 

How Common Is Down Syndrome? 

Down syndrome affects about one out of every 700 babies born in the United States, which is approximately 6,000 live births per year. More than 200,000 people in the United States are currently living with this condition. The incidence of Down syndrome has remained stable within the population.

No therapy can prevent the effects of the extra chromosome if a child has it. But the overall health of people with Down syndrome is improving due to early detection and treatment of serious health issues, like heart disease.

The self-care abilities of people with Down syndrome have improved over the years due to interventions like physical therapy and occupational therapy that can help people improve mobility and maintain independence.

Down Syndrome by Ethnicity

The physical effects of Down syndrome are the same, regardless of ethnicity. Some aspects of managing Down syndrome are related to access to care and lifestyle factors that may differ by ethnic group. This may affect outcomes.

For example, children who begin occupational therapy at a young age or who receive learning interventions at school can achieve more independence than those who do not get these interventions. 

One small research study found that children with Down syndrome are more likely to be overweight or have obesity if their parents are not counseled about the harmful health effects of obesity. In this small study, Hispanic/Latino boys with Down syndrome were more likely to have obesity.

Down Syndrome by Age and Gender 

The genetic differences that cause Down syndrome are present while a baby is still developing. The incidence is approximately the same for babies of any sex. The developmental effects of Down syndrome begin in utero (before an affected baby is born).

Down syndrome cannot develop later in life—a person not having an extra copy of chromosome 21 in utero cannot develop an extra copy later on. Additionally, Down syndrome is a lifelong condition that is not curable, and it does not go away on its own. 

Because of the health effects and the risk of earlier-than-average age of death, Down syndrome is more common among children than adults, and the prevalence decreases with age.

Causes of Down Syndrome and Risk Factors

Normally, a baby inherits two copies of each chromosome—one from each parent. Down syndrome occurs when a developing baby inherits three copies of chromosome 21 instead of two copies.

The extra chromosome can come from either parent. This occurs due to a biological error called nondisjunction that affects the egg or the sperm that fertilized the egg.

While anyone of any age or background can have a child with Down syndrome, there are some risk factors. Risk factors include:

  • Advanced age of the parent contributing the egg and carrying the pregnancy is a known risk factor.
  • Having a sibling with Down syndrome is a risk factor.
  • Advanced age of the parent contributing the sperm is a mild risk factor.

What Are the Mortality Rates for Down Syndrome? 

There is a substantial variation in survival with Down syndrome, and severe heart and lung malformations are associated with lower survival.

Some babies born with severe organ defects might not survive beyond age 1, while children who have treatable defects or who do not have significant organ defects can survive for much longer.

The most common causes of death for people with Down syndrome are heart disease, lung disease, infections, dementia, and cancer.

Average Lifespan

The average lifespan of a person with Down syndrome in the United States is approximately 55 years, which is compared to an overall average U.S. lifespan of 79.

Screening and Early Detection 

The physical features of Down syndrome can be noticeable at birth, but sometimes parents, healthcare providers, and others might not notice that a child has Down syndrome until they are a few months old or older. Additionally, parents and others may be more likely to notice that a child looks like they have Down syndrome if there are risk factors.

Screening for Down syndrome includes testing during the pregnancy.

Prenatal Ultrasound

This noninvasive imaging test examines the baby’s physical features and may visualize certain organ abnormalities that are associated with Down syndrome.

However, not all babies with Down syndrome have developmental organ abnormalities. This test might not detect abnormalities even if they are present, and some abnormalities that are detected could be caused by another developmental condition that is not Down syndrome.

Quad Test

The quad test is a blood test that can be done after 15 weeks of pregnancy. It measures certain hormone levels that have been correlated with Down syndrome and other congenital conditions. This test does not provide a definitive diagnosis of Down syndrome.

Amniocentesis

Amniocentesis takes a sample of the amniotic fluid (the fluid surrounding the fetus) for chromosomal analysis. It is the most definitive diagnostic test for Down syndrome. It can be done after the 15th week of pregnancy. This procedure has a very low risk of complications.

Recommendations

Screening is recommended for pregnant people who are 35 years of age or older. It is also recommended for pregnant people younger than age 35 who have had a child with Down syndrome.

Pregnant people are not obligated to have screening for Down syndrome. Those who are at low risk can often request the screening tests.

Summary 

Down syndrome is a lifelong condition that occurs due to an extra copy of chromosome 21. This happens because of a genetic error that affects either the egg cell or the sperm cell that fertilized the egg to produce the child.

Down syndrome can cause many different physical problems, including abnormal musculoskeletal development, heart deformities, digestive problems, learning impairment, and more. It is a lifelong condition that can cause disabilities. Often, medical and practical interventions can alleviate some of the effects and improve quality of life. 

Frequently Asked Questions

  • Is Down syndrome hereditary?

    Most people who have Down syndrome do not have a family history of the condition. Down syndrome occurs due to a parental chromosomal abnormality, but it affects the child and not the parents. If a person with Down syndrome has a child, the child will have a 1 in 2 chance of inheriting Down syndrome.

  • How early can Down syndrome be diagnosed?


    Down syndrome can be diagnosed during early pregnancy with an amniocentesis chromosome test. Amniocentesis is a procedure in which a sample of fluid is taken from a pregnant person. The sample would be examined in a laboratory, and the results would show whether a baby had genetic abnormalities, such as three copies of chromosome 21. 

  • Does everyone with Down syndrome have the same physical and learning limitations?

    Certain physical features and health problems occur as a result of having an extra copy of chromosome 21, but the effects can be slightly different for each person.

    For example, some people with Down syndrome can have serious heart malformations, while others may have mild heart involvement. The type of malformations each person has may differ.

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