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Down Syndrome

(DS; Trisomy 21)

Definition

Down syndrome is a common genetic disorder. Down syndrome causes birth defects, medical problems, and some degree of intellectual disability.

Causes

Chromosomes contain the genetic makeup of your body. They occur in 23 pairs within the body. Down syndrome is a problem with chromosome pair 21. There is extra genetic material on the chromosome that may be caused by:
  • An extra chromosome—This type is called Trisomy 21. This results from an error in cell division in the egg or sperm.
  • Extra chromosomes in some cells—This type is called Mosaic Trisomy 21.
  • Part of the chromosome breaking off and reattaching to another chromosome—This type is called translocation trisomy. In about one third of individuals, the translocation is inherited from a parent.

Risk Factors

Factors that increase the chance for Down syndrome include:
  • Genetics: If either parent is a carrier of Translocation Down syndrome, there is an increased risk.
  • Age: The chance of having a child with Down syndrome increases after a woman reaches age 35.
  • Sex: More boys than girls are born with Down syndrome.
  • History of a previous child with Down syndrome.

Symptoms

Infants born with Down syndrome may have some or all of the following physical features:
  • Flat facial features, a somewhat depressed nasal bridge and a small nose
  • Upward slanted eyes, small skin folds on the inner corner of the eyes
  • Short neck with loose skin
  • Misshaped and/or low set ears
  • White spots on the colored part of the eye
  • Single skin crease in the palm of the hand
  • Excess flexibility in joints
  • Sight and hearing problems
  • Large and protruding tongue
  • Excessive space between the large and second toe
The degree of medical problems and intellectual disability is different for each person. Talents, abilities, and pace of development will be different, too. People with Down syndrome may be born with or develop:
  • Vision problems
  • Hearing loss
  • Heart defects
  • Acute leukemia
  • Frequent ear infections
  • Instability of the back bones at the top of the neck, can result in compression injury of the spinal cord
  • Gastrointestinal obstruction
  • Hirschsprung disease, celiac disease
  • Sleep problems such as blocked airways during sleep, daytime sleepiness, sleep anxiety, and sleep walking
  • Increased incidence of dementia in older adults
  • Urinary system defects
  • High blood pressure in the lungs
  • Seizures
  • An under-active thyroid
  • Slow growth
  • Late to sit, walk, and toilet train
  • Speech problems
  • Obesity
  • Emotional problems
Most of these health problems are treatable. The majority of people born with Down syndrome have a life expectancy of about 55 years.

Diagnosis

Doctors can usually identify a child born with Down syndrome at birth. When Down syndrome is suspected, a blood test will be done to confirm it.
Down syndrome may also be diagnosed before birth. There are screening tests and diagnostic tests to help identify chormosome abnormalities before birth.

Screening Tests

A screening test is done to estimate the risk of having a child with Down syndrome. Your doctor will use the results of a variety of blood tests and the mother's age to estimate the risk. Blood tests may include:
  • Triple screen—Alpha-fetoprotein Plus
  • Quadruple screen
  • Cell-Free Fetal DNA Testing
Screening may be done as early as 11 weeks. It may also include both ultrasound imaging and blood screening. There should be a follow-up in the second trimester for those who screen negative.
A small amount of women who have screening will be given false-positive readings. This means the test indicates Down syndrome even when it does not exist.

Diagnostic Tests

Diagnostic tests will tell if the fetus actually has Down syndrome. These tests include:
  • Chorionic villus sampling (CVS)—Usually done between 10 and 12 weeks
  • Amniocentesis—Usually done between 12 and 20 weeks of gestation
  • Percutaneous umbilical blood sampling (PUBS)—Usually done after 20 weeks
These tests are about 98%-99% accurate. Each test requires that a small piece of tissue be removed from the placenta or umbilical cord. This creates a small risk of miscarriage with these tests.
Amniocentesis
Fetus Chromosomes
Copyright © Nucleus Medical Media, Inc.

Treatment

There is no cure for Down syndrome.
Some newborns may need surgery to repair serious medical problems, like heart defects.
Treatment may be needed for severe problems or to help with developmental delays. Living at home and receiving special therapy helps children with Down syndrome achieve their full potential. Most people with the condition can actively participate in the community. This includes activities at schools, jobs, and various leisure activities. Some people with Down syndrome live with family, some live with friends, and some live independently.

Baby Care

Infants with Down syndrome may take longer to feed. A child with Down syndrome will also start talking, playing, and performing other activities later than normal.

Education

Learning opportunities may be increased with:
  • School programs designed to meet the child's special needs.
  • Mainstreaming children into regular public school classes with additional support as needed

Rehabilitation Services

Speech, physical, and occupational therapy may improve abilities. Therapy can help with speech, walking, and performing activities of daily living.

Social Services

Professional support helps a family cope with caring for a child with birth defects and intellectual disability. Mental health professionals offer help with managing emotional problems.

Prevention

There are no guidelines for preventing Down syndrome. If you have concerns about having a child with Down syndrome, consider getting genetic counseling before becoming pregnant.

RESOURCES

National Down Syndrome Congress http://www.ndsccenter.org

National Down Syndrome Society http://www.ndss.org

CANADIAN RESOURCES

Canadian Down Syndrome Society http://www.cdss.ca

Health Canada http://www.hc-sc.gc.ca

References

Behrman RE, Kliegman R, Jenson HB. Nelson Textbook of Pediatrics. 18th ed. Philadelphia, PA: Saunders; 2007.

Benn P, et al. Prenatal detection of Down syndrome using massively parallel sequencing (MPS): a rapid response statement from a committee on behalf of the Board of the International Society for Prenatal Diagnosis, 24 October 2011. Prenat Diagn. 2012;32:1-2.

Committee opinion No. 545: noninvasive prenatal testing for fetal aneuploidy. Obstet Gynecol. 2012;120(6):1532-4.

Down syndrome. EBSCO DynaMed website. Available at: https://dynamed.ebscohost.com/about/about-us. Updated November 2, 2012. Accessed May 21, 2013.

Down syndrome. National Down Syndrome Society website. Available at: http://www.ndss.org/Down-Syndrome. Accessed May 21, 2013.

Down Syndrome. National Institute of Child Health and Human Development website. Available at: http://www.nichd.nih.gov/health/topics/down/Pages/default.aspx. Updated April 3, 2013. Accessed May 21, 2013.

Ferri F, ed. Ferri’s Clinical Advisor 2010. Philadelphia, PA: Mosby Elsevier; 2009.

Malone FD, Canick JA, Ball RH, et al. First- and second-trimester evaluation of risk (FASTER) research consortium. First-trimester or second-trimester screening, or both, for Down's syndrome. N Engl J Med. 2005;353:2001-2011.

3/12/2010 DynaMed's Systematic Literature Surveillance https://dynamed.ebscohost.com/about/about-us: Carter M, McCaughey E, Annaz D, Hill CM. Sleep problems in a Down syndrome population. Arch Dis Child. 2009;94(4):308-310.

Revision Information

This content is reviewed regularly and is updated when new and relevant evidence is made available. This information is neither intended nor implied to be a substitute for professional medical advice. Always seek the advice of your physician or other qualified health provider prior to starting any new treatment or with questions regarding a medical condition.

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