Down syndrome (Trisomy 21)


When babies are conceived, they normally inherit 46 chromosomes – 23 from each parent. Babies with the genetic disorder known as Down syndrome, however, inherit an extra chromosome, for a total of 47.

This extra genetic material typically causes delays in a child’s physical and intellectual development that can range from mild to severe. Down syndrome is also called Trisomy 21, because the baby inherits an additional copy of chromosome 21.

Characteristics of Down Syndrome

Down syndrome affects about 1 in every 800 babies. Children with down syndrome tend to have features and characteristics including:

  • A flat facial profile with eyes that slant upward and small ears
  • Low muscle tone (hypotonia) which may improve over time
  • Delays in physical skills such as crawling, walking and self-care
  • Smaller size and a slower rate of growth than average
  • Mild to moderate intellectual impairment
  • Delays in language development

The developmental delays caused by Down syndrome can vary widely; some children function well and grow into fairly independent adults, while others require specialized medical attention throughout their lives. The average life expectancy for a person with Down syndrome is about 60.

Medical Problems Associated with Down Syndrome

Children with down syndrome also may have an increased risk of medical problems, including:

  • Vision problems such as strabismus (crossed eyes) and cataracts
  • Thyroid problems
  • Respiratory problems
  • Congenital heart defects
  • Pulmonary hypertension
  • Hearing problems

Fortunately, many of these conditions are treatable, and Mercy neonatologists, pediatric cardiologists and other pediatric specialists are experts in caring for babies with medical issues related to down syndrome.

Detecting & Diagnosing Down Syndrome

Down syndrome is usually caused by an error in cell division at the time of conception. It can’t be prevented, but the risk is significantly higher in pregnant women who are age 35 and older. 

Prenatal testing can detect the condition during pregnancy. If you want to do prenatal testing, you may have the opportunity to meet with a genetic counselor before testing to determine which testing is best for you. If testing during pregnancy determines or suggests that your baby may have Down syndrome, you can begin to plan and prepare to care for your child’s special needs.

Despite their differences, most children with down syndrome are very much like other children. With physical, speech and developmental therapies, many can attend the same schools and may attend specialized classes. Your Mercy team, including Mercy Kids pediatricians and pediatric specialists, is here to help you find medical care, education and community resources to support you and your family.

Connect to Mercy Experts

View More View More