Also Known As
Trisomy 21
DS
This article was last reviewed on
This article waslast modified on
January 19, 2018.
What is Down syndrome?

Down syndrome (DS) is a group of signs, symptoms, birth defects, and complications that arise from an error in cell division that results in an extra 21st chromosome. This error may occur before, or shortly after, conception and has a widespread effect on the physical and mental development of the affected person. DS is one of the most common and well known chromosome disorders and the most common genetic cause of learning disabilities. It is a congenital condition caused by an extra copy or piece of chromosome 21 in all or most of the affected person's cells.

Chromosomes hold the body's genetic blueprint. Most cells in the body contain 22 pairs of chromosomes and a 23rd set of either XX (in females) or XY (in males) for a total of 46 chromosomes. The 46 chromosomes come together when the woman's egg, containing a single set of 23 chromosomes, is fertilized by a single sperm, containing a single set of 23 chromosomes. The fertilized egg will then divide repeatedly as it grows and develops into a fetus.

In most cases of Down syndrome, random chance leads to the insertion of an extra copy of chromosome 21 in either the egg or sperm. This extra copy becomes part of the fertilized egg and is replicated in all of the embryo's cells. This form of Down syndrome is called trisomy 21, and it accounts for about 95% of DS cases.

Less commonly, an error may occur after conception, in the developing embryo. As the fetus grows, some cells have 47 chromosomes, while others have 46. This form of Down syndrome is called mosaic trisomy 21.

In a rare form of Down syndrome called translocation trisomy 21, a piece of chromosome 21 adheres to another chromosome before or at conception. Even though the fetus has 46 chromosomes, it still has an extra portion of chromosome 21 in its cells.

All individuals with additional chromosome 21 genetic material, regardless of the cause, will develop some of the features of Down syndrome.

In the United States, about 6,000 babies each year are born with Down syndrome. The risk of having an affected baby increases significantly as a woman ages. According to the National Institute of Child Health & Human Development, the risk increases from about 1 in 1,300 for women who are 25 years old to about 1 in 55 for women who are 42 and 1 in 25 for those who are 49. However, since younger women have the greatest number of babies, the majority of those with Down syndrome are born to women under 35.

Accordion Title
About Down Syndrome (DS)
  • Signs and Symptoms

    There are many characteristic signs and symptoms associated with Down syndrome. Not every child will have every one, and the degree to which they are affected may vary greatly. Some physical signs and symptoms include:

    • A small head with small, low-set ears
    • Slanting eyes, a broad flat face, and a short nose
    • A small mouth and protruding tongue
    • Short, small but broad hands and feet and a single crease across the palm
    • Short fingers and an abnormal bone in the 5th (pinky) finger
    • Poor muscle tone (hypotonia)
    • Hyperflexible joints
    • Atlantoaxial instability (a malformation of the top of the spine)


    Problems with thinking and learning (cognitive impairment) and intellectual disability range from mild to moderate and may include:

    • A short attention span
    • Hyperactivity
    • Poor judgment
    • Disruptive or impulsive behavior
    • Delays in language and speech development
    • Anxiety
    • Sleep difficulties
  • Complications

    Complications of Down syndrome vary greatly. Some may be present at birth, some may arise during childhood, others during adulthood, and others may never be experienced. Health practitioners and family members must be aware of these potential complications as those with DS may or may not be able to clearly communicate their symptoms and/or may express them in unexpected ways.

    Complications can include:

    • Celiac disease
    • Dental disease
    • Diabetes
    • Food sensitivities and constipation
    • Gastrointestinal abnormalities and obstructions (5-10%)
    • Hearing loss (75%)
    • Heart defects and disease (close to 50%)
    • Increased incidence of respiratory and ear infections, colds, bronchitis, tonsillitis, and pneumonia
    • Increased risk of leukemia
    • Premature aging, loss of cognitive abilities, and Alzheimer disease-type symptoms in those under 40 years of age
    • Seizure disorders
    • Sleep apnea (50-75%)
    • Spinal cord compression
    • Thyroid disease (about 15%)
    • Visual problems, including cataracts (about 60%)
  • Tests

    The goals of testing are to screen for Down syndrome during pregnancy, diagnose it in a fetus or newborn, detect any malformations or complications that will require medical interventions shortly after birth, and monitor the person who has Down syndrome for complications throughout his or her life. Testing is usually a combination of laboratory and non-laboratory evaluations.

    Laboratory Tests
    Screening and diagnostic tests may be done during a woman's pregnancy, in either the first or the second trimester. Screening tests are not diagnostic; they indicate an increased likelihood of the fetus having Down syndrome. The American College of Obstetricians and Gynecologists (ACOG) has recommended that all pregnant women be offered DS screening tests.

    Prenatal screening tests

    • First trimester screen – nuchal translucency (non-laboratory test, see below), pregnancy-associated plasma protein A (PAPP-A), and free beta or total hCG (human chorionic gonadotropin), usually performed between 10 weeks, 4 days and 13 weeks, 6 days of pregnancy
    • Second trimester screen (triple/quad screen) – alpha feto-protein (AFP), chorionic gonadotropin (hCG), and unconjugated estriol (uE3); quad screen adds inhibin A test; performed at 15 to 20 weeks of pregnancy
    • Sequential and integrated maternal serum screening – combined first and second trimester screening test for open neural tube defects (ONTD), DS, and trisomy 18 (T18). Tests performed at the times noted in the two bullets above.
    • Cell-free fetal DNA analysis – analyzes fetal DNA circulating in the mother's blood; the test is usually recommended at 10 weeks for women who are considered at a higher risk for having a baby with Down syndrome.


    Prenatal diagnosis
    Prenatal diagnostic tests may be performed when screening tests are abnormal. They involve taking samples of the fluid or tissues surrounding the baby and evaluating them for an additional copy or portion of chromosome 21. A very small risk of infection and miscarriage is associated with these diagnostic tests. A sample may be obtained using one of the following techniques and chromosomal analysis (karyotype) is performed on the genetic material:

    • Chorionic villus sampling (CVS) – 9th to 11th week of pregnancy
    • Amniotic fluid analysis (amniocentesis) – 14th to 18th week of pregnancy
    • Percutaneous umbilical blood sampling (PUBS) – 18th to 22nd week of pregnancy
    • Chromosomal microarray testing – also uses samples collected via CVS or amniocentesis to examine the DNA of the unborn fetus for abnormalities


    Diagnosis after birth
    A diagnosis after birth is usually based initially on physical signs and characteristics. However, these signs and symptoms may also be seen in babies without Down syndrome. Diagnostic testing performed after birth involves taking a sample of blood from the baby and evaluating his or her chromosomes:

    • Chromosomal karyotype – cells are grown from a blood sample and chromosomes are evaluated for an extra copy of chromosome 21; the presence and type of Down syndrome can be determined from this test.


    Identifying complications
    Tests that detect the complications often seen in those with Down syndrome are used to help diagnose conditions that arise and to monitor the effectiveness of treatment. Some of the complications, such as congenital heart defects and gastrointestinal obstructions, may be present at birth. Others, such as hearing loss, vision disorders, leukemia, and thyroid disease, may develop at any time during the person's life. A variety of laboratory tests may be used to detect conditions in an individual with Down syndrome as they arise. Some examples of these tests include:

    • TSH and/or T4 – to detect thyroid disease, especially hypothyroidism. This condition may develop at any age for a person with Down syndrome, so screening is usually done as a newborn and then at regular intervals throughout the person's life.
    • Complete blood count (CBC) – to detect anemia or infections and sometimes leukemia
    • Glucose – to identify diabetes
    • Celiac disease antibody tests – these tests may be recommended for children with Down syndrome as young as 2 years old or younger if they have signs and symptoms of the condition.


    Non-Laboratory Tests

    Prenatal

    • Nuchal translucency – an ultrasound measurement of the space between the fetal spine and the skin at the back of the neck; not diagnostic, but in a fetus with Down syndrome, there may be an increased amount of space. This test requires a person with specialized training to perform and interpret. It may be performed as part of the first trimester pregnancy screen.
    • Second trimester high-resolution ultrasound – can help monitor fetal development and detect malformations, such as cardiac and gastrointestinal defects


    At or soon after birth

    • Echocardiogram and chest x-rays  – to help detect cardiac defects
    • Ultrasound and/or MRI (magnetic resonance imaging) – to evaluate any suspected congenital conditions, such as cardiac defects and gastrointestinal obstructions
    • Hearing evaluation
  • Treatment

    Currently there is no way to prevent or cure Down syndrome. Prenatal screening and diagnosis is performed to detect the condition in the fetus and to allow the pregnant woman and her family to make informed choices. Early diagnosis allows the family and health practitioner to work together to monitor the baby and to prepare for complications that may require attention shortly after birth. Medical treatments may include surgical interventions, such as repairing cardiac defects and removing gastrointestinal obstructions, and starting medications for conditions such as thyroid disease.

    In individuals with Down syndrome, careful monitoring, prompt attention to acute and chronic conditions that arise, and "early intervention" to maximize the potential of the individual are important. The symptoms, signs, complications, and abilities of people with Down syndrome will vary widely. It is not possible to determine early in a child's life what he or she will be able to learn, do, and accomplish. Those affected should be given encouragement and stimulation from an early age, given a healthy diet, and engage in regular physical activities to maintain muscle strength. Families should work closely with their health practitioners and other specialists to develop life, monitoring, and treatment plans that meet the unique needs of those affected.

    There are national, state, and local "early intervention" programs and resources that can help children with Down syndrome develop their physical, communication, and cognitive skills. Many children will be able to join regular classes in schools, participate in sports, and as adults hold jobs and live semi-independent lives. Most will be able to live relatively normal and healthy lives. The average lifespan of those with Down syndrome has increased in recent years with most living to their mid 50's and many into their 60's and 70's.

View Sources

NOTE: This article is based on research that utilizes the sources cited here as well as the collective experience of the Lab Tests Online Editorial Review Board. This article is periodically reviewed by the Editorial Board and may be updated as a result of the review. Any new sources cited will be added to the list and distinguished from the original sources used.

Sources Used in Current Review

Birth Defects. March of Dimes. Available online at http://www.marchofdimes.com/baby/down-syndrome.aspx through http://www.marchofdimes.com/index.aspx. Accessed July 28, 2014.

Down Syndrome Facts. National Down Syndrome Society. Available online at http://www.ndss.org/Down-Syndrome/Down-Syndrome-Facts/ through http://www.ndss.org. Accessed July 28, 2014.

Down Syndrome and Celiac Disease. National Foundation for Celiac Awareness. Available online at http://www.celiaccentral.org/Celiac-Disease/Related-Diseases/Down-Syndrome/48/ through http://www.celiaccentral.org. Accessed July 27, 2014.

Facts about Down Syndrome. Centers for Disease Control and Prevention. Available online at http://www.cdc.gov/ncbddd/birthdefects/DownSyndrome.html through http://www.cdc.gov. Accessed July 27, 2014.

How is Down Syndrome Diagnosed? Down Syndrome Association of Charlotte. Available online at http://www.dsa-gc.org/about_ds/diagnosis/ through http://www.dsa-gc.org. Accessed July 28, 2014.

Understanding a Diagnosis of Down Syndrome. National Down Syndrome Society. Available online at http://www.ndss.org/Resources/New-Expectant-Parents/Understanding-a-Diagnosis-of-Down-Syndrome/ through http://www.ndss.org. Accessed July 28, 2014.

What is Down Syndrome? Genetics Home Reference. Available online at http://ghr.nlm.nih.gov/condition/down-syndrome through http://ghr.nlm.nih.gov. Accessed July 28, 2014.

The Use of Chromosomal Microarray Analysis in Prenatal Diagnosis. The American Congress of Obstetricians and Gynecologists. Available online at https://www.acog.org/Resources-And-Publications/Committee-Opinions/Committee-on-Genetics/The-Use-of-Chromosomal-Microarray-Analysis-in-Prenatal-Diagnosis through https://www.acog.org. Accessed July 27, 2014.

Lott, I.T. Cognitive deficits and associated neurological complications in individuals with Down's syndrome. June 2010. Lancet Neurology, Vol. 9. Available online at http://www.ncbi.nlm.nih.gov/pubmed?term=20494326 through http://www.ncbi.nlm.nih.gov/pubmed. Accessed July 2014.

Parker SE, et al. National Birth Defects Prevention Network. Updated national birth prevalence estimates for selected birth defects in the United States, 2004-2006. Birth Defects Res A Clin Mol Teratol. 2010;88:1008-16. Available online at http://www.ncbi.nlm.nih.gov/pubmed/20878909 through http://www.ncbi.nlm.nih.gov/pubmed. Accessed July 27, 2014.

(Updated April 9, 2014) Eunice Kennedy Shriver National Institute of Child Health and Human Development. Down Syndrome: Condition Information. Available online at http://www.nichd.nih.gov/health/topics/down/conditioninfo/Pages/symptoms.aspx through http://www.nichd.nih.gov. Accessed September 2014.

Sources Used in Previous Reviews

Thomas, Clayton L., Editor (1997). Taber's Cyclopedic Medical Dictionary. F.A. Davis Company, Philadelphia, PA [18th Edition]. Pp 382-383.

(2005 March 29, Updated). Facts About Down Syndrome. National Institute of Child Health & Human Development [On-line information]. Available online at http://www.nichd.nih.gov/publications/pubs/downsyndrome/down.htm through http://www.nichd.nih.gov.

Van Cleve, S. and Cohen, W. (2006 January 27). Part I: Clinical Practice Guidelines With Down Syndrome From Birth to 12 Years. Medscape from J Pediatr Health Care. 2006;20(1):47-54 [On-line journal article]. Available online at http://www.medscape.com/viewarticle/521906?src=search through http://www.medscape.com.

(© 2005). Down Syndrome Facts. National Association for Down Syndrome [On-line information]. Available online at http://www.nads.org/pages/facts.htm through http://www.nads.org.

Sondheimer, N., Updated (2005 April 20). Down syndrome. MedlinePlus Medical Encyclopedia [On-line information]. Available online at http://www.nlm.nih.gov/medlineplus/ency/article/000997.htm.

(2005 September, Reviewed). Down syndrome. Genetics Home Reference [On-line information]. Available online at http://ghr.nlm.nih.gov/condition%3Ddownsyndrome through http://ghr.nlm.nih.gov.

Cleary-Goldman, J. and Malone, F. (2005 September 26). Advances in Prenatal Diagnosis. Medscape from Appl Radiol. 2005;34(9):8-18. [On-line journal article]. Available online at http://www.medscape.com/viewarticle/513126?src=search through http://www.medscape.com.

(2006 January 6). Improved National Prevalence Estimates for 18 Selected Major Birth Defects --- United States, 1999—2001. MMWR 54(51&52); 1301-1305 [On-line information]. Available online at http://www.cdc.gov/mmwr/preview/mmwrhtml/mm5451a2.htm through http://www.cdc.gov.

Barclay, L. and Nghlem, H. (2005 November 9). Eleven Weeks May Be the Best Time to Screen for Down's Syndrome. Medscape Medical News [On-line CME]. Available online at http://www.medscape.com/viewarticle/516329?src=search through http://www.medscape.com.

(2003 February 1, Reviewed). Down Syndrome. Merck Manual Home Edition [On-line information]. Available online through http://www.merck.com.

Smith, D. (2001 September 15). Health Care Management of Adults with Down Syndrome. American Family Physician [On-line journal]. Available online at http://www.aafp.org/afp/20010915/1031.html through http://www.aafp.org.

(2004 December, Reviewed). Down Syndrome. March of Dimes Fact Sheet [On-line information]. Available online at http://www.marchofdimes.com/professionals/681_1214.asp through http://www.marchofdimes.com.

(2004 January). Down Syndrome. National Dissemination Center for Children with Disabilities [On-line information]. Available online at http://www.nichcy.org/pubs/factshe/fs4txt.htm through http://www.nichcy.org.

Pagana, Kathleen D. & Pagana, Timothy J. (© 2007). Mosby’s Diagnostic and Laboratory Test Reference 8th Edition: Mosby, Inc., Saint Louis, MO.

(2006 August 18, Updated). Facts About Down Syndrome. National Institute of Child Health & Human Development [On-line information]. Available online at http://www.nichd.nih.gov/publications/pubs/downsyndrome.cfm through http://www.nichd.nih.gov. Accessed on 2/25/07.

(2007 January 2). New Recommendations for Down Syndrome Call for Screening of All Pregnant Women [On-line information]. Available online at http://www.acog.org/from_home/publications/press_releases/nr01-02-07-1.cfm through http://www.acog.org. Accessed on 2/25/07.

(2007 February 16, Updated). Down Syndrome. National Institute of Child Health & Human Development [On-line information]. Available online at http://www.nichd.nih.gov/health/topics/Down_Syndrome.cfm/ through http://www.nichd.nih.gov. Accessed on 2/25/07.

(03/2002). Chromosomal Abnormalities. March of Dimes [On-line information]. Available online at http://www.marchofdimes.com/professionals/681_1209.asp through http://www.marchofdimes.com. Accessed on 2/25/07.

Van Cleve, S. and Cohen, W. (2006 January 27). Part I: Clinical Practice Guidelines with Down Syndrome from Birth to 12 Years. Medscape from J Pediatr Health Care 2006;20(1):47-54 [On-line Journal]. Available online at http://www.medscape.com/viewarticle/521906 through http://www.medscape.com. Accessed on 2/17/07.

Van Cleve, S., Cannon, S., and Cohen, W. (2006 May 30). Part II: Clinical Practice Guidelines for Adolescents and Adults with Down Syndrome 12-21 Years. Medscape from J Pediatr Health Care 2006;20(3):198-205 [On-line Journal]. Available online at http://www.medscape.com/viewarticle/532190 through http://www.medscape.com. Accessed on 2/17/07.

(2003 February, Revision). Down Syndrome. Merck Manual of Medical Information – Second Home Edition [On-line Journal]. Available online at http://www.merck.com/mmhe/print/sec23/ch266/ch266b.html through http://www.merck.com. Accessed on 2/17/07.

(2004 June). Maternal Blood Screening for Down Syndrome and Neural Tube Defects. March of Dimes [On-line information]. Available online at http://www.marchofdimes.com/professionals/681_1166.asp through http://www.marchofdimes.com. Accessed on 2/25/07.

ACOG Practice Bulletin. Obstetrics & Gynecology 109: 217-227 (2007).

(Updated 2010 May 25). Down Syndrome. National Institute of Child Health & Human Development [On-line information]. Available online at http://www.nichd.nih.gov/health/topics/Down_Syndrome.cfm through http://www.nichd.nih.gov. Accessed January 2011.

Chen, H. (Updated 2010 March 22). Down Syndrome. eMedicine [On-line information]. Available online at http://emedicine.medscape.com/article/943216-overview through http://emedicine.medscape.com. Accessed January 2011.

(Reviewed 2010 December 20). Learning About Down Syndrome. National Human Genome Research Institute [On-line information]. Available online at http://www.genome.gov/19517824 through http://www.genome.gov. Accessed January 2011.

(2010 February 2). Down Syndrome. Centers for Disease Control and Prevention, Birth Defects [On-line information]. Available online at http://www.cdc.gov/ncbddd/birthdefects/DownSyndrome.htm through http://www.cdc.gov. Accessed January 2011.

Mayo Clinic Staff (2009 April 7). Down Syndrome. MayoClinic.com [On-line information]. Available online at http://www.mayoclinic.com/health/down-syndrome/DS00182 through http://www.mayoclinic.com. Accessed January 2011.

(2009 July). Down Syndrome. March of Dimes [On-line information]. Available online at http://www.marchofdimes.com/baby/birthdefects_downsyndrome.html through http://www.marchofdimes.com. Accessed January 2011.

(Reviewed 2008 June). Down Syndrome, Genetics Home Reference [On-line information]. Available online at http://ghr.nlm.nih.gov/condition/down-syndrome through http://ghr.nlm.nih.gov. Accessed January 2011.