What Causes Down Syndrome?

Reviewed on 10/1/2020

What Is Down Syndrome?

Down Syndrome
People with Down syndrome are born with three, instead of two, copies of chromosome 21.

Down syndrome (trisomy 21) is a genetic disorder that is the most common form of intellectual disability in the world. Down syndrome occurs in about one out of every 1000 babies born alive worldwide. In addition to learning problems, Down syndrome can cause medical problems that affect the heart, blood, digestive system, and other organs.

What Are Symptoms of Down Syndrome?

Most people with Down syndrome have intellectual disability, a low IQ, and problems with language or memory. Problems can range from mild to severe.

Most babies with Down syndrome have some physical characteristics that indicate the presence of the disorder: 

  • Flattened face
  • Extra skin at the back of the neck
  • Upward-slanting eyes
  • Lack of muscle tone (hypotonia)
  • Abnormally flexible joints
  • Unusual-looking ears
  • A crease across the palm (transverse palmar crease)
  • A wide gap between the first and second toes (sandal gap deformity)

Babies with Down syndrome usually have developmental delays and take longer to learn how to sit, walk, and talk. 

Children with Down syndrome may also develop certain physical characteristics as they grow:

  • Flattened head in back (brachycephaly)
  • Skin folds on the eyelids
  • Flattened nose bridge
  • Folded, unusual, or small ears
  • Gaping mouth
  • Protruding tongue
  • Abnormal teeth
  • Short neck
  • Short, broad hands

Children with Down syndrome may also have behavioral problems such as difficulty sitting still or aggression. 

Medical problems caused by Down syndrome can affect the:

  • Heart
  • Blood
  • Immune system
  • Digestive system
  • Hormones
  • Breathing
  • Bone joints
  • Vision and hearing
  • Skin

What Causes Down Syndrome?

Chromosomes are structures found in the nucleus of cells that house thousands of genes. Cells normally contain 23 pairs of chromosomes, one from the mother and one from the father, and each pair is assigned a number between 1 and 23.

People with Down syndrome are born with three, instead of two, copies of chromosome 21. 

A risk factor for having a baby with Down syndrome is a mother over age 35. It is not known why this occurs. The father's age may also be a factor, but this is not clear.

How Is Down Syndrome Diagnosed?

Down syndrome is usually diagnosed during pregnancy with a screening test. 

If Down syndrome is not diagnosed during pregnancy, a blood test that examines the child's chromosomes (karyotype) performed after the baby is born can help diagnose Down syndrome, along with the infant's appearance.

What Is the Treatment for Down Syndrome?

There is no specific treatment for Down syndrome, but there are treatments for the complications that arise due to the condition. 

Treatments may include: 

What Are Complications of Down Syndrome?

Down syndrome can cause a number of medical complications: 

What Is the Life Expectancy for Down Syndrome?

Life expectancy for people with Down syndrome is shorter than for people without the condition. The average lifespan is 49 years, with the median age of death being almost 57 years.

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Reviewed on 10/1/2020