Reviewed June 2012
What is Down syndrome?
Down syndrome is a chromosomal condition that is associated with intellectual disability, a characteristic facial appearance, and weak muscle tone (hypotonia) in infancy. All affected individuals experience cognitive delays, but the intellectual disability is usually mild to moderate.
People with Down syndrome may have a variety of birth defects. About half of all affected children are born with a heart defect. Digestive abnormalities, such as a blockage of the intestine, are less common.
Individuals with Down syndrome have an increased risk of developing several medical conditions. These include gastroesophageal reflux, which is a backflow of acidic stomach contents into the esophagus, and celiac disease, which is an intolerance of a wheat protein called gluten. About 15 percent of people with Down syndrome have an underactive thyroid gland (hypothyroidism). The thyroid gland is a butterfly-shaped organ in the lower neck that produces hormones. Individuals with Down syndrome also have an increased risk of hearing and vision problems. Additionally, a small percentage of children with Down syndrome develop cancer of blood-forming cells (leukemia).
Delayed development and behavioral problems are often reported in children with Down syndrome. Affected individuals' speech and language develop later and more slowly than in children without Down syndrome, and affected individuals' speech may be more difficult to understand. Behavioral issues can include attention problems, obsessive/compulsive behavior, and stubbornness or tantrums. A small percentage of people with Down syndrome are also diagnosed with developmental conditions called autism spectrum disorders, which affect communication and social interaction.
People with Down syndrome often experience a gradual decline in thinking ability (cognition) as they age, usually starting around age 50. Down syndrome is also associated with an increased risk of developing Alzheimer disease, a brain disorder that results in a gradual loss of memory, judgment, and ability to function. Approximately half of adults with Down syndrome develop Alzheimer disease. Although Alzheimer disease is usually a disorder that occurs in older adults, people with Down syndrome usually develop this condition in their fifties or sixties.
How common is Down syndrome?
Down syndrome occurs in about 1 in 830 newborns. An estimated 250,000 people in the United States have this condition. Although women of any age can have a child with Down syndrome, the chance of having a child with this condition increases as a woman gets older.
What are the genetic changes related to Down syndrome?
Most cases of Down syndrome result from trisomy 21, which means each cell in the body has three copies of chromosome 21 instead of the usual two copies.
Less commonly, Down syndrome occurs when part of chromosome 21 becomes attached (translocated) to another chromosome during the formation of reproductive cells (eggs and sperm) in a parent or very early in fetal development. Affected people have two normal copies of chromosome 21 plus extra material from chromosome 21 attached to another chromosome, resulting in three copies of genetic material from chromosome 21. Affected individuals with this genetic change are said to have translocation Down syndrome.
A very small percentage of people with Down syndrome have an extra copy of chromosome 21 in only some of the body's cells. In these people, the condition is called mosaic Down syndrome.
Researchers believe that having extra copies of genes on chromosome 21 disrupts the course of normal development, causing the characteristic features of Down syndrome and the increased risk of health problems associated with this condition.
Changes involving this chromosome are associated with Down syndrome.
Can Down syndrome be inherited?
Most cases of Down syndrome are not inherited. When the condition is caused by trisomy 21, the chromosomal abnormality occurs as a random event during the formation of reproductive cells in a parent. The abnormality usually occurs in egg cells, but it occasionally occurs in sperm cells. An error in cell division called nondisjunction results in a reproductive cell with an abnormal number of chromosomes. For example, an egg or sperm cell may gain an extra copy of chromosome 21. If one of these atypical reproductive cells contributes to the genetic makeup of a child, the child will have an extra chromosome 21 in each of the body's cells.
People with translocation Down syndrome can inherit the condition from an unaffected parent. The parent carries a rearrangement of genetic material between chromosome 21 and another chromosome. This rearrangement is called a balanced translocation. No genetic material is gained or lost in a balanced translocation, so these chromosomal changes usually do not cause any health problems. However, as this translocation is passed to the next generation, it can become unbalanced. People who inherit an unbalanced translocation involving chromosome 21 may have extra genetic material from chromosome 21, which causes Down syndrome.
Like trisomy 21, mosaic Down syndrome is not inherited. It occurs as a random event during cell division early in fetal development. As a result, some of the body's cells have the usual two copies of chromosome 21, and other cells have three copies of this chromosome.
Where can I find information about diagnosis or management of Down syndrome?
These resources address the diagnosis or management of Down syndrome and may include treatment providers.
- GeneFacts: Down Syndrome: Diagnosis (http://genefacts.org/index.php?option=com_content&view=article&id=412&Itemid=570)
- GeneFacts: Down Syndrome: Management (http://genefacts.org/index.php?option=com_content&view=article&id=415&Itemid=571)
- Genetic Testing Registry: Complete trisomy 21 syndrome (http://www.ncbi.nlm.nih.gov/gtr/conditions/C0013080)
- National Down Syndrome Congress: Healthcare (http://www.ndsccenter.org/resources/healthcare/)
- National Down Syndrome Congress: Speech and Language (http://www.ndsccenter.org/resources/speech-and-language/)
- National Down Syndrome Society: Health Care (http://www.ndss.org/Resources/Health-Care/)
- National Down Syndrome Society: Therapies and Development (http://www.ndss.org/Resources/Therapies-Development/)
You might also find information on the diagnosis or management of Down syndrome in
Educational resources (http://ghr.nlm.nih.gov/condition/down-syndrome/show/Educational+resources) and Patient support (http://ghr.nlm.nih.gov/condition/down-syndrome/show/Patient+support).
General information about the diagnosis (http://ghr.nlm.nih.gov/handbook/consult/diagnosis) and management (http://ghr.nlm.nih.gov/handbook/consult/treatment) of genetic conditions is available in the Handbook.
Read more about genetic testing (http://ghr.nlm.nih.gov/handbook/testing), particularly the difference between clinical tests and research tests (http://ghr.nlm.nih.gov/handbook/testing/researchtesting).
To locate a healthcare provider, see How can I find a genetics professional in my area? (http://ghr.nlm.nih.gov/handbook/consult/findingprofessional) in the Handbook.
Where can I find additional information about Down syndrome?
You may find the following resources about Down syndrome helpful. These materials are written for the general public.
MedlinePlus - Health information
- Encyclopedia: Down Syndrome (http://www.nlm.nih.gov/medlineplus/ency/article/000997.htm)
- Health Topic: Congenital Heart Defects (http://www.nlm.nih.gov/medlineplus/congenitalheartdefects.html)
- Health Topic: Down Syndrome (http://www.nlm.nih.gov/medlineplus/downsyndrome.html)
- Genetic and Rare Diseases Information Center - Information about genetic conditions and rare diseases (http://rarediseases.info.nih.gov/gard/10247/down-syndrome/resources/1)
Additional NIH Resources - National Institutes of Health
- Eunice Kennedy Shriver National Institute of Child Health and Human Development (http://www.nichd.nih.gov/health/topics/down/Pages/default.aspx)
- National Human Genome Research Institute (http://www.genome.gov/19517824)
- National Institute of Diabetes and Digestive and Kidney Diseases: Hypothyroidism (http://www.endocrine.niddk.nih.gov/pubs/Hypothyroidism/)
Educational resources - Information pages
- Boston Children's Hospital (http://www.childrenshospital.org/conditions-and-treatments/conditions/d/down-syndrome)
- Centre for Genetics Education (http://www.genetics.edu.au/Publications-and-Resources/Genetics-Fact-Sheets/FactSheet28)
- Cleveland Clinic: Alzheimer's Disease and Down Syndrome (http://my.clevelandclinic.org/health/diseases_conditions/hic_Alzheimers_and_Dementia_Overview/hic_Alzheimers_Disease_and_Down_Syndrome)
- Disease InfoSearch: Down Syndrome (http://www.diseaseinfosearch.org/Down+Syndrome/2327)
- Down Syndrome: Health Issues (Len Leshin, M.D., F.A.A.P.) (http://www.ds-health.com/)
- Genetic Science Learning Center, University of Utah (http://learn.genetics.utah.edu/content/disorders/chromosomal/down/)
- Genetics Education Materials for School Success (GEMSS) (http://www.gemssforschools.org/conditions/down/default)
- Kennedy Krieger Institute (http://www.kennedykrieger.org/patient-care/diagnoses-disorders/down-syndrome)
- KidsHealth from the Nemours Foundation (http://kidshealth.org/kid/health_problems/birth_defect/down_syndrome.html)
- Madisons Foundation (http://www.madisonsfoundation.org/index.php?option=com_mpower&task=disease&diseaseID=210)
- My46 Trait Profile (https://www.my46.org/trait-document?trait=Down%20syndrome&type=profile)
- National Genetics and Genomics Education Centre (UK) (http://www.geneticseducation.nhs.uk/genetic-conditions-54/649-down-syndrome-new)
- Orphanet: Down syndrome (http://www.orpha.net/consor/cgi-bin/OC_Exp.php?Lng=EN&Expert=870)
- The Merck Manual Home Health Handbook (http://www.merckmanuals.com/home/childrens_health_issues/chromosomal_and_genetic_abnormalities/down_syndrome_trisomy_21_trisomy_g.html)
- Your Genes Your Health from Cold Spring Harbor Laboratory (http://www.ygyh.org/ds/whatisit.htm)
Patient support - For patients and families
- Chromosome Disorder Outreach (http://www.chromodisorder.org/)
- Down Syndrome Cognition Research Lumind Foundation (https://lumindfoundation.org/)
- National Down Syndrome Congress (http://www.ndsccenter.org/)
- National Down Syndrome Society (http://www.ndss.org/)
- National Organization for Rare Disorders (https://www.rarediseases.org/rare-disease-information/rare-diseases/byID/34/viewAbstract)
- Research Down Syndrome (http://www.researchds.org/)
- Resource list from the University of Kansas Medical Center (http://www.kumc.edu/gec/support/down_syn.html)
You may also be interested in these resources, which are designed for healthcare professionals and researchers.
Genetic Testing Registry - Repository of genetic test information
- Genetic Testing Registry: Complete trisomy 21 syndrome (http://www.ncbi.nlm.nih.gov/gtr/conditions/C0013080)
- ClinicalTrials.gov - Linking patients to medical research (https://clinicaltrials.gov/ct2/results?cond=%22down%20syndrome%22)
- PubMed - Recent literature (http://www.ncbi.nlm.nih.gov/pubmed?term=%28Down%20Syndrome%5BMAJR%5D%29%20AND%20%28Down%20syndrome%5BTI%5D%29%20AND%20review%5Bpt%5D%20AND%20english%5Bla%5D%20AND%20human%5Bmh%5D%20AND%20%22last%201080%20days%22%5Bdp%5D)
- OMIM - Genetic disorder catalog (http://omim.org/entry/190685)
What other names do people use for Down syndrome?
- Down's syndrome
- trisomy 21
- trisomy G
For more information about naming genetic conditions, see the Genetics Home Reference
Condition Naming Guidelines (http://ghr.nlm.nih.gov/ConditionNameGuide)
How are genetic conditions and genes named? (http://ghr.nlm.nih.gov/handbook/mutationsanddisorders/naming) in the Handbook.
What if I still have specific questions about Down syndrome?
Ask the Genetic and Rare Diseases Information Center (http://rarediseases.info.nih.gov/gard).
What glossary definitions help with understanding Down syndrome?
cell division ;
gastroesophageal reflux ;
muscle tone ;
reproductive cells ;
You may find definitions for these and many other terms in the Genetics Home Reference
- Antonarakis SE, Lyle R, Dermitzakis ET, Reymond A, Deutsch S. Chromosome 21 and down syndrome: from genomics to pathophysiology. Nat Rev Genet. 2004 Oct;5(10):725-38. Review. (http://www.ncbi.nlm.nih.gov/pubmed/15510164?dopt=Abstract)
- Capone G, Goyal P, Ares W, Lannigan E. Neurobehavioral disorders in children, adolescents, and young adults with Down syndrome. Am J Med Genet C Semin Med Genet. 2006 Aug 15;142C(3):158-72. Review. (http://www.ncbi.nlm.nih.gov/pubmed/16838318?dopt=Abstract)
- Carter JC, Capone GT, Gray RM, Cox CS, Kaufmann WE. Autistic-spectrum disorders in Down syndrome: further delineation and distinction from other behavioral abnormalities. Am J Med Genet B Neuropsychiatr Genet. 2007 Jan 5;144B(1):87-94. (http://www.ncbi.nlm.nih.gov/pubmed/16958028?dopt=Abstract)
- Chapman RS, Hesketh LJ. Behavioral phenotype of individuals with Down syndrome. Ment Retard Dev Disabil Res Rev. 2000;6(2):84-95. Review. (http://www.ncbi.nlm.nih.gov/pubmed/10899801?dopt=Abstract)
- Cohen WI. Current dilemmas in Down syndrome clinical care: celiac disease, thyroid disorders, and atlanto-axial instability. Am J Med Genet C Semin Med Genet. 2006 Aug 15;142C(3):141-8. Review. (http://www.ncbi.nlm.nih.gov/pubmed/16838307?dopt=Abstract)
- Kumin L. Speech intelligibility and childhood verbal apraxia in children with Down syndrome. Downs Syndr Res Pract. 2006 Jul;10(1):10-22. (http://www.ncbi.nlm.nih.gov/pubmed/16869369?dopt=Abstract)
- Lott IT, Head E. Alzheimer disease and Down syndrome: factors in pathogenesis. Neurobiol Aging. 2005 Mar;26(3):383-9. Review. (http://www.ncbi.nlm.nih.gov/pubmed/15639317?dopt=Abstract)
- Lubec G, Engidawork E. The brain in Down syndrome (TRISOMY 21). J Neurol. 2002 Oct;249(10):1347-56. Review. (http://www.ncbi.nlm.nih.gov/pubmed/12382149?dopt=Abstract)
- Roizen NJ, Patterson D. Down's syndrome. Lancet. 2003 Apr 12;361(9365):1281-9. Review. (http://www.ncbi.nlm.nih.gov/pubmed/12699967?dopt=Abstract)
- Shapiro BL. Down syndrome and associated congenital malformations. J Neural Transm Suppl. 2003;(67):207-14. Review. (http://www.ncbi.nlm.nih.gov/pubmed/15068252?dopt=Abstract)
- Sherman SL, Allen EG, Bean LH, Freeman SB. Epidemiology of Down syndrome. Ment Retard Dev Disabil Res Rev. 2007;13(3):221-7. Review. (http://www.ncbi.nlm.nih.gov/pubmed/17910090?dopt=Abstract)
- Steingass KJ, Chicoine B, McGuire D, Roizen NJ. Developmental disabilities grown up: Down syndrome. J Dev Behav Pediatr. 2011 Sep;32(7):548-58. doi: 10.1097/DBP.0b013e31822182e0. Review. (http://www.ncbi.nlm.nih.gov/pubmed/21743353?dopt=Abstract)
- Zigman WB, Lott IT. Alzheimer's disease in Down syndrome: neurobiology and risk. Ment Retard Dev Disabil Res Rev. 2007;13(3):237-46. Review. (http://www.ncbi.nlm.nih.gov/pubmed/17910085?dopt=Abstract)
The resources on this site should not be used as a substitute for
professional medical care or advice. Users seeking information about
a personal genetic disease, syndrome, or condition should consult with a qualified
See How can I find a genetics professional in my area? (http://ghr.nlm.nih.gov/handbook/consult/findingprofessional) in the Handbook.