Down Syndrome
Down syndrome is a genetic abnormality that occurs due to an extra copy of chromosome 21. It causes lifelong developmental delays that can rang...

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What Is Down Syndrome?

Down syndrome (sometimes spelled “Down’s syndrome”) is a genetic abnormality. It is the most common single cause of birth defects in the United States (NIH, 2012).

This syndrome occurs because of an extra copy of chromosome 21. Your chromosomes contain your genetic material, and any problems with your chromosomes can cause serious physical and mental health problems.

Down syndrome causes lifelong developmental delays that can range from moderate to severe. It cannot be cured, but there are options. Down syndrome can be managed with educational interventions, specialized parenting techniques, and community engagement. These all can encourage a person with Down syndrome to develop life skills and social bonds, so that they can live a long (many Down syndrome patients live past the age of 50) and fulfilling life.

What Causes Down Syndrome?

Down syndrome is e genetic disorder. TO understand how it happens, you need to understand some basic genetics. In all cases of reproduction, both parents pass their genes on to their children. These genes are carried on chromosomes. When the baby’s cells develop, each cell is supposed to receive 23 pairs of chromosomes. Half of the chromosomes are from the mother and half from the father.

In children with Down syndrome, one of the chromosomes does not separate properly. The baby ends up with three copies of chromosome 21 instead of two. This extra chromosome causes problems as the brain and physical features develop.

Types of Down Syndrome

There are three types of Down syndrome:

Trisomy 21

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


Mosaicism means there is an extra chromosome in some but not all of a child’s cells. Individuals with mosaic Down syndrome tend to have fewer symptoms.


In this condition, 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.

Will My Child Be at Risk for Down Syndrome?

Certain parents have a greater risk of giving birth to a child with Down syndrome:

  • women age 35 and older
  • males 50 and older
  • people with a family history of Down’s syndrome
  • people who carry the genetic translocation

What Are the Symptoms of Down Syndrome?

During pregnancy, there are no signs that a child will have Down syndrome. At birth, babies with Down syndrome usually have certain characteristic signs, including:

  • flat facial features
  • small head and ears
  • short neck
  • bulging tongue
  • eyes that slant upward
  • oddly shaped ears
  • poor muscle tone

A Down syndrome infant can be born a normal size. However development is twice as slow as for an unaffected child. There is usually some degree of mental retardation, but it is often mild to moderate.

Mental and social development delays may mean that the child will have:

  • impulsive behavior
  • poor judgment
  • short attention span
  • slow learning capabilities

Medical complications often accompany Down syndrome. These are caused by the extra chromosome. These may include:

  • congenital heart defects
  • hearing loss
  • poor vision
  • cataracts (clouded eyes)
  • hip problems, such as dislocations
  • leukemia
  • chronic constipation
  • sleep apnea (interrupted breathing during sleep)
  • dementia (thought and memory problems)
  • hypothyroidism (low thyroid function)
  • obesity
  • late tooth growth, causing problems with chewing

Today, despite the medical and developmental delays, a child born with Down syndrome can live past the age of 50 (Mayo Clinic).

Screening for Down Syndrome During Pregnancy

Screening is offered as a routine part of prenatal care in the United States. However, it is not required.

First Trimester

An ultrasound evaluation and blood tests can look for Down syndrome in your fetus. These tests are done between the 10th and 14th week of pregnancy.

An ultrasound looks at the back of the baby’s neck, called the nuchal translucency. If there are problems with the baby’s development, more fluid collects in this area.

Blood tests looks at the level of pregnancy-associated plasma protein-A (PAPP-A) and human chorionic gonadotropin (HCG). High levels of these proteins suggest a developmental problem.

These tests have a higher false-positive rate than tests done at later pregnancy stages. If results are not normal, your doctor may follow up with an amniocentesis. In this test, an amniotic fluid sample is used to confirm the results.

Second Trimester

An ultrasound and quadruple marker screen (QMS) test can help identify Down syndrome and other neural tube defects. This test is done between 15 and 20 weeks. These tests measures four pregnancy-related factors:

  • human chorionic gonadotropin (HCG)
  • unconjugated estriol
  • alpha-fetoprotein (AFP)
  • inhibin-A

If any of these tests are not normal, you will be considered at high risk for birth defects.

Additional Prenatal Tests

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

  • amniocentesis: Your doctor takes a sample of amniotic fluid to examine the number of chromosomes the baby has. The test is usually done at 15 weeks. It carries a one in 200 miscarriage risk.
  • chorionic villus sampling (CVS): Your doctor will take cells from your placenta to analyze fetal chromosomes. This test is done during the ninth and 14th week of pregnancy. It carries a miscarriage risk of one in 100.
  • percutaneous umbilical blood sampling (PUBS): Your doctor will take blood from the umbilical cord and examine it for chromosomal defects. It is done after the 18th week of pregnancy. It carries an even higher rate of miscarriage, so it is performed only if all other tests are uncertain.

Some women choose not to undergo these tests, because of the risk of miscarriage. They would rather risk having a child with Down syndrome than losing the pregnancy.

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

Treating Down Syndrome

There is no cure for Down syndrome. However, parents can provide early intervention and opportunities to help their child with Down syndrome succeed. Early intervention programs promote a child’s learning. They offer the best chance for success.

In these programs, special education teachers and therapists will help your child learn:

  • sensory skills
  • social skills
  • self-help
  • motor skills
  • language and cognitive abilities

Children with Down syndrome often meet age-related milestones. However, this may take up to two times longer than for other children.

A team of physicians and specialists can help provide medical care and manage the medical complications. Because obesity can be particularly dangerous to the health of children with Down syndrome, it is important to encourage physical activity and avoid high-calorie foods. However, before beginning exercise or sports, the child’s hip, neck, and spine should be examined.

It is important to teach children with Down syndrome about being independent and staying safe. Parents should establish a support network in the family and community. Learn as much as possible about your child’s condition. This can help you understand what it means as your child grows and develops.

Many people with Down syndrome lead successful lives in their community. They often go to school, hold jobs, and become independent.

Preventing Down Syndrome

There is no way to prevent Down syndrome. You may want to speak with a genetic counselor:

  • before having a child, to see if you are at risk
  • if you already have a child with Down syndrome and are considering getting pregnant again
Written by: Cindie Slightham
Edited by:
Medically Reviewed by: George Krucik, MD
Published: Jul 2, 2012
Published By: Healthline Networks, Inc.
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