Down Syndrome | Symptoms & Causes

What causes Down syndrome?

Down syndrome is a common genetic condition that occurs when a child has an extra copy of chromosome 21.

Chromosomes are structures inside every human cell that contain DNA. These tiny structures that children inherit from their parents play a key role in determining how a baby develops, for instance, whether they will be tall or short, have dark or light skin, curly or straight hair.

Normally, a mother's egg and a father's sperm each start out with 23 chromosomes. When the egg and sperm meet at conception, a child inherits 23 chromosomes from each parent, ending up with a total 46 chromosomes.

In Down syndrome, a change occurs during cellular division such that the egg or sperm has an extra chromosome 21. Researchers are still unsure of what causes the cells to divide in this manner (though the chance of this happening increases with increasing maternal age). If this egg or sperm is fertilized, the baby ends up with three copies of the twenty first chromosome or Trisomy 21. This extra genetic material causes the health and developmental issues of Down syndrome.

What are the symptoms of Down syndrome?

Down syndrome can affect children physically, cognitively and behaviorally. Every child with the condition is unique and may possess the following characteristics to different degrees, or not at all.

Physical characteristics

Children with Down syndrome have some of the following physical features:

  • eyes that slant upward, from inner corner to outer corner
  • small ears that may fold over slightly at the top
  • a smaller-than-average mouth, and larger appearing tongue
  • a smaller-than-average nose, with a flattened nasal bridge
  • short, stocky arms and legs
  • a wide space between the big toe and second toe
  • short necks and small hands with short fingers
  • one single crease that goes straight across the palm, and a second crease that curves down by the thumb, rather than three creases in the palm of the hand
  • shorter-than-average height
  • low muscle tone (hypotonia) throughout the body and excessively loose joints

Developmental, cognitive and behavioral symptoms

Most children with Down syndrome meet developmental milestones later than other children, including the ability to walk and talk. They often have mild to moderate intellectual disability and may have specific challenges with attention span, verbal memory and expressive communication.

Behavioral problems such as stubbornness, impulsivity and temper tantrums may be more common in children with Down syndrome. Many children talk out loud to themselves as a way of understanding and processing information.

On the other hand, many children with Down syndrome have strong social skills. Even as infants, many use non-verbal communication to connect with others. They are often strong visual learners, understanding information best when they can see it, either through pictures, objects or demonstration. Many children with Down syndrome learn to read words sooner than their parents or teachers expect.