• Down Syndrome

    (DS; Trisomy 21)

    Definition

    Down syndrome is a common genetic disorder. It occurs in 1 out of 700-800 live births. Down syndrome causes birth defects, medical problems, and some degree of intellectual disability.
    In fact, down syndrome is the most common genetic cause of mild to moderate intellectual disabilities.

    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—Called Mosaic Trisomy 21.
    • Part of the chromosome has broken off and reattached to another chromosome—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:
    • Muscle hypotonia, low muscle tone
    • 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
    • Misshaped ears
    • White spots on the colored part of the eye
    • Single skin crease in the palm of the hand
    • Excess flexibility in joints
    • Heart defects
    • Sight and hearing problems
    • Large and protruding tongue
    • Fifth finger has one flexion furrow instead of two
    • Excessive space between 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
    • Increased incidence of acute leukemia
    • Frequent ear infections and increased susceptibility to infection in general
    • Gastrointestinal obstruction (imperforate anus and similar problems)
    • Esophageal atresia or duodenal atresia
    • Sleep problems (eg, blocked airways during sleep, daytime sleepiness, sleep anxiety, sleep walking)
    • Increased incidence of dementia in older ages
    • Instability of the back bones at the top of the neck, can result in compression injury of the spinal cord
    • Urinary system defects
    • High blood pressure in the lungs
    • Seizures
    • An under-active thyroid (hypothyroidism)
    • Slow growth
    • Late to sit, walk, toilet train
    • Speech problems
    • Obesity
    • Emotional problems
    Most of these health problems are treatable. The majority of people born with Down syndrome today 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.
    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

    Some newborns may need surgery to repair serious medical problems, like heart defects.
    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)—In children who have accomplished academic milestones

    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: http://www.ebscohost.com/dynamed/. Updated September 14, 2012. Accessed September 20, 2012.

    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.

    National Down Syndrome Society. Associated conditions. National Down Syndrome Society website. Available at: http://www.ndss.org/Down-Syndrome/. Accessed September 20, 2012.

    National Institute of Child Health and Human Development. Down Syndrome. National Institute of Child Health and Human Development website. Available at: http://www.nichd.nih.gov/health/topics/Down%5FSyndrome.cfm. Accessed July 28, 2008.

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

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