(DS; Trisomy 21)
Down syndrome (DS) is a common genetic disorder. It results in birth defects, medical problems, and some degree of intellectual disability]]> .
DS is the most frequent genetic cause of mild to moderate intellectual disability. It occurs in one out of 800 to 1,000 live births. DS occurs in all races and economic groups.
Chromosomes contain the genetic makeup of your body. They occur in 23 pairs within the body. Three types of chromosomal changes that lead to DS include:
- There is an extra chromosome (3 instead of 2) in the chromosome 21 pair. This type is called Trisomy 21. This results from an error in cell division in the egg or sperm.
- In Mosaic Trisomy 21, some cells have the extra chromosome and some do not.
- In translocation trisomy, part of the chromosome number 21 has broken off. The broken piece reattaches onto another chromosome. In about one third of individuals, the translocation is inherited from a parent.
In all cases, it is the extra chromosome 21 genetic material that causes problems.
Factors that increase the chance for DS include:
- Genetics: If either parent is a carrier of Translocation DS, there is an increased risk.
- Age: The chance of having a child with DS increases after a woman reaches age 35.
- Sex: More boys than girls are born with DS.
Infants born with DS may have some or all of the following physical characteristics:
- 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 varies. Talents, abilities, and pace of development differ. People with DS 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
- An under-active thyroid ( ]]>hypothyroidism]]> )
- Slow growth
- Late to sit, walk, toilet train
- Speech problems
- Emotional problems
Most of these health problems are treatable. The majority of people born with DS today have a life expectancy of approximately 55 years.
There are two types of procedures available to pregnant women:
- Screening tests estimate the risk of the fetus having DS
- Diagnostic tests tell whether or not the fetus actually has the condition
Screening tests include the triple screen and the alpha-fetoprotein Plus .
- These tests measure amounts of various things in the blood. Together with the woman's age, the doctor can estimate the risk of having a child with DS.
- New data suggests that screening should begin as early as 11 weeks. It also should include both ultrasound imaging]]> and blood screening. There should be a follow-up in the second trimester for those who screen negative.
- Five percent of women who undergo these tests will be given false-positive readings. This means the test indicates DS even when it does not exist.
- The tests include chorionic villus sampling (CVS), ]]>amniocentesis]]> , and percutaneous umbilical blood sampling (PUBS).
- Each one carries a small risk of ]]>miscarriage]]> as tissue is extracted from the placenta or the umbilical cord to examine the fetus' chromosomes.
- The procedures are about 98%-99% accurate in the detection of DS.
- Amniocentesis is usually performed between 12 and 20 weeks of gestation, CVS between 10 and 12 weeks, and PUBS after 20 weeks.
Doctors can usually identify a child born with DS at delivery. When DS is suspected, a blood test will be done for study and a definitive diagnosis.
There is no cure for DS. Some newborns may need surgery to repair serious medical problems, like heart defects. Living at home and receiving special therapy helps children with DS achieve their full potential. Most people with the condition can actively participate in the community—at schools, jobs, and various leisure activities. Some live with family, some with friends, and some independently.
Infants with DS may take longer to feed. A child with the condition will start talking, playing, and performing other activities later than normal.
School programs designed to meet the child's special needs may help to increase learning opportunities. Children who have accomplished academic milestones may be mainstreamed into regular public school classes, with additional support as required.
Speech, physical, and occupational therapy may improve the ability to speak, walk, and perform activities of daily living.
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.
National Down Syndrome Congress
National Down Syndrome Society
Canadian Down Syndrome Society
Behrman RE, Kliegman R, Jenson HB. Nelson Textbook of Pediatrics. 18th ed. Philadelphia, PA: Saunders; 2007.
DynaMed Editorial Team. Down syndrome. EBSCO DynaMed website. Available at: http://www.ebscohost.com/dynamed/what.php . Updated September 2, 2010. Accessed November 17, 2010.
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 . Accessed July 28, 2008.
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_Syndrome.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.
Last reviewed September 2010 by ]]>J. Thomas Megerian, MD, PhD, FAAP]]>
Please be aware that this information is provided to supplement the care provided by your physician. It is neither intended nor implied to be a substitute for professional medical advice. CALL YOUR HEALTHCARE PROVIDER IMMEDIATELY IF YOU THINK YOU MAY HAVE A MEDICAL EMERGENCY. Always seek the advice of your physician or other qualified health provider prior to starting any new treatment or with any questions you may have regarding a medical condition.
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