The Facts

Special Miracles believes in providing clear and correct information about Down syndrome to anyone who is wanting to know more about it. There are so many stigmas surrounding Down syndrome in addition to misconceptions and offensive use of language. We have compiled a list of frequently asked questions with current facts and statistics about Down syndrome.

What causes Down syndrome?

There is no known cause for Down syndrome. Down syndrome is a naturally occurring chromosomal arrangement that has always been a part of the human condition. The most common form of Down syndrome is known as trisomy 21, a condition where individuals have 47 chromosomes in each cell instead of 46. Trisomy 21 is caused by an error in cell division called nondisjunction, which leaves a sperm or egg cell with an extra copy of chromosome 21 before or at conception.

What are the types Down syndrome? Is there a "spectrum"?

There are three types of Down syndrome – Trisomy 21 (the most common type of Down syndrome), Translocation, and Mosaicism.

Trisomy 21

Trisomy 21 means there’s an extra copy of chromosome 21 in every cell. This is the most common form of Down syndrome.


Mosaicism occurs when a child is born with an extra chromosome in some but not all of their cells. People with mosaic Down syndrome tend to have fewer symptoms than those with trisomy 21.


In this type of Down syndrome, children have only an extra part of chromosome 21. There are 46 total chromosomes. However, one of them has an extra piece of chromosome 21 attached.


Is Down syndrome genetic? How is Down syndrome inherited?

Of the three types of Down Syndrome, only translocation can be a genetic (inherited) chromosomal arrangement.

What is the likelihood of having a baby with Down syndrome? 

Certain parents have a greater risk of giving birth to a child with Down syndrome. According to the Centers for Disease and Prevention, mothers aged 35 and older are more likely to have a baby with Down syndrome than younger mothers. The risk increases the older the mother is.

Research shows that paternal age also has an effect. One 2003 study found that fathers over 40 had twice the risk of having a child with Down syndrome.

Other parents who are at greater risk of having a child with Down syndrome include:

  • people with a family history of Down syndrome
  • people who carry the genetic translocation

It’s important to remember that no one of these factors mean that you’ll definitely have a baby with Down syndrome. However, statistically and over a large population, they can put you at higher risk.


Is there anything that can be done to increase or reduce the likelihood of having a baby with Down syndrome?

There is nothing that can be done to cause or prevent becoming pregnant with a baby with Down syndrome. 

What is the population of people with Down syndrome?

1. The Centers for Disease Control (CDC) in 2011 estimated the frequency of Down syndrome in the US is 1 in 691 live births (up from 1 in 1087 in 1990)

2. The estimate that 90% of pregnant women in the U.S. who get a diagnosis of Down syndrome through amniocentesis choose to terminate IS INACCURATE.

  • This statistic is based on studies done that merged findings from the U.S., UK and Europe in the mid- to late 1990s. The numbers do not represent the attitudes of the US population then or today.
  • A more targeted 2012 review of just United States data and termination rates following a prenatal diagnosis for Down syndrome estimates termination rates from 1995 – 2011 were about 67%.

3. Surprisingly, The population of people in the US with Down syndrome is currently unknown. What we do know is:

  • 38% of Americans know someone with Down syndrome.
  • Because of the increase of live births of people with Down syndrome and the recent dramatic increase in their lifespan, over the next 20 years a significant increase in the population of people with Down syndrome in the U.S. is expected.
  • The population of people with Down syndrome in the U.S. has been estimated to be over 400,000. However, this number is derived from faulty assumptions – the total population from the 2000 US census, 281.4 million people, divided by the most current frequency of live births, 691 equaling 407,236. Unfortunately, this technique takes no account of the gradual increase in frequency or the increase in lifespan of people with Down syndrome. Thus, we don’t actually know how many people with Down syndrome currently live in the U.S.4. Some estimates put the worldwide population of people with Down syndrome at more than 6 million. More research is needed to ascertain whether this number is accurate.

Is Down syndrome a disease? Is Down syndrome curable?

Down syndrome is not a disease, disorder, defect or medical condition and therefore does not require treatment, prevention or a cure. It is inappropriate and offensive to refer to people with Down syndrome as “afflicted with” or “suffering from” it.

Is Down syndrome a disability? Are there disabilities associated with Down syndrome?

The extra genetic component from Down syndrome results in a developmental delay, but it is impossible to suggest the level to which this will occur. Some individuals with Down syndrome may have moderate disabilities while some will have mild disabilities. 

How is Down syndrome detected?

Down syndrome may be detected through prenatal testing or after birth through a blood test.

First trimester

An ultrasound evaluation and blood tests can look for Down syndrome in your fetus. These tests have a higher false-positive rate than tests done at later pregnancy stages. If results aren’t normal, your doctor may follow up with an amniocentesis after your 15th week of pregnancy.

Second trimester

An ultrasound and quadruple marker screen (QMS) test can help identify Down syndrome and other defects in the brain and spinal cord. This test is done between 15 and 20 weeks of pregnancy.

If any of these tests aren’t normal, you’ll be considered at high risk for birth defects.

Additional prenatal tests

Your doctor may order additional tests to detect Down syndrome in your baby. These may include:

  • Amniocentesis. Your doctor takes a sample of amniotic fluid to examine the number of chromosomes your baby has. The test is usually done after 15 weeks.
  • Chorionic villus sampling (CVS). Your doctor will take cells from your placenta to analyze fetal chromosomes. This test is done between the 9th and 14th week of pregnancy. It can increase your risk of a miscarriage.
  • Percutaneous umbilical blood sampling (PUBS, or cordocentesis). Your doctor will take blood from the umbilical cord and examine it for chromosomal defects. It’s done after the 18th week of pregnancy. It has a higher risk of miscarriage, so it’s performed only if all other tests are uncertain.

Many women choose not to undergo these tests because of the risk of miscarriage

Tests at birth

At birth, your doctor will:

  • perform a physical examination of your baby
  • order a blood test called a karyotype to confirm Down syndrome

Why do people with Down syndrome look similar?

Some people with Down syndrome may share similar physical features. However, people with Down syndrome predominantly look like other members of their families.

Who does Down syndrome affect?

Down syndrome occurs universally across all racial and gender lines.

How was Down syndrome discovered?

John Langdon Down, a British physician, was the first person to fully describe the syndrome in 1866. It is one of the most common chromosomal abnormalities. The genetic cause of Down syndrome; an extra copy of chromosome 21; was identified by researchers in 1959.

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