Down Syndrome
Also known as: Complete trisomy 21 · Trisomy 21
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In short
Down syndrome is a condition in which a person has an extra copy of chromosome 21, or an extra piece of it, which changes how a baby's body and brain develop. This condition usually happens by chance as an error during early fetal cell division, though the risk increases for mothers aged 35 and older. It can cause mild to moderate intellectual disabilities, delayed development, and physical signs such as a flat face, upward-slanting eyes, a short neck, and poor muscle tone. Associated health issues can include hearing loss, sleep apnea, congenital heart defects, and digestive problems.
Source: MedlinePlus, National Library of Medicine.
AI-generated summary of the sources cited on this page, checked automatically against them. Not reviewed by a clinician; not medical advice.
Codes
Description
What is Down syndrome?
Down syndrome is a condition in which a person has an extra chromosome or an extra piece of a chromosome. This extra copy changes how a baby's body and brain develop. It can cause both mental and physical challenges during their lifetime. Even though people with Down syndrome might act and look similar, each person has different abilities.
What causes Down syndrome?
Chromosomes are tiny "packages" in your cells that contain your genes. Genes carry information, called DNA, that controls what you look like and how your body works. People with Down syndrome have an extra copy of chromosome 21. In some cases, they may have an extra copy of part of the chromosome. Having an extra copy of a chromosome is called trisomy. So sometimes Down syndrome is also called trisomy 21.
Down syndrome is usually not inherited. It happens by chance, as an error when cells are dividing during early development of the fetus. It is not known for sure why Down syndrome occurs or how many different factors play a role.
One factor that increases the risk of having a baby with Down syndrome is the age of the mother. Women ages 35 and older are more likely to have a baby with Down syndrome.
What are the symptoms of Down syndrome?
The symptoms of Down syndrome are different in each person. And people with Down syndrome may have different problems at different times of their lives. They usually have mild to moderate intellectual disabilities. Their development is often delayed. For example, they may start talking later than other children.
Some of the common physical signs of Down syndrome include:
- A flat face
- Eyes that slant up
- A short neck
- Small hands and feet
- Poor muscle tone
- Loose joints
What other problems does Down syndrome cause?
Many people with Down syndrome have the common physical signs and have healthy lives. But some people with Down syndrome might have one or more birth defects or other health problems. Some of the more common ones include:
- Hearing loss
- Sleep apnea (a disorder that causes you to repeatedly stop breathing during sleep)
- Ear infections
- Eye diseases
- Congenital heart defects (heart defects that are present at birth)
- Digestive problems
- Problems with the upper part of the spine
- Obesity
How is Down syndrome diagnosed?
Health care providers can check for Down syndrome during pregnancy or after a child is born.
There are two basic types of tests that help find Down syndrome during pregnancy:
- Prenatal screening tests can show whether your unborn baby has a higher or lower chance of having Down syndrome. If a screening test shows that your baby could have Down syndrome, you'll need another test to find out for sure.
- Prenatal diagnostic tests can diagnose or rule out Down syndrome by checking the chromosomes in a sample of cells. These tests have a small risk of causing a miscarriage, so they're often done after a screening test shows that an unborn baby could have Down syndrome.
After a baby is born, the provider may make an initial diagnosis of Down syndrome based on the physical signs of the syndrome. The provider can use a karyotype genetic test to confirm the diagnosis. The test can check for extra chromosomes in a sample of the baby's blood.
What are the treatments for Down syndrome?
There is no single, standard treatment for Down syndrome. Treatments are based on each person's physical and intellectual needs, strengths, and limitations.
Services early in life focus on helping children with Down syndrome develop to their full potential. These services include speech, occupational, and physical therapies. They are typically offered through early intervention programs in each state. Children with Down syndrome may also need extra help or attention in school, although many children are included in regular classes.
Since people with Down syndrome can have birth defects and other health problems, they will need regular medical care. They may need to have certain extra health screenings to check for problems that happen more often in people with Down syndrome.
Centers for Disease Control and Prevention
Next to it in ICD-10
- Q37Cleft lip and palate
- Q61Polycystic and cystic kidney disease
- Q75Other congenital skull and face bone malformations
- Q96Turner Syndrome
- S02Skull and facial bone fractures
- S06Brain injury (including concussion)
Neighbouring codes in the classification, not a medical link.
External resources
Questions
What is the ICD-10 code for Down Syndrome?
Q90 (WHO, International Classification of Diseases, 10th Revision).
What is the ICD-11 code for Down Syndrome?
LD40.0: Complete trisomy 21 (WHO, ICD-11 for Mortality and Morbidity Statistics).
Sources and attribution
- ICD-11 for Mortality and Morbidity Statistics, © World Health Organization, licensed under CC BY-ND 3.0 IGO.
- Source: MedlinePlus, National Library of Medicine.
- Names other than the official source titles: Anpheros translations and plain-language names, made with AI assistance and checked automatically; the source names are in English.
- ICD-10 codes and titles © World Health Organization. Source: WHO, International Classification of Diseases, 10th Revision (2019).
Anpheros Search catalog 2026.10.5, published 17 October 2026. About the data →
About this page. This page brings together public information from official sources, each cited where it is used. It is not medical advice, it is not a diagnosis, and it does not tell you which treatment to take.
Treatments. Indications are quoted unchanged from official product information (European Medicines Agency, U.S. Food and Drug Administration). They describe what a medicine is approved for, not whether it is right for you. Approved uses can differ between countries. Always read the package leaflet and follow your doctor's or pharmacist's advice.
What people report. Figures marked "reported by Anpheros users" are anonymous counts from at least 20 people who agreed to share them. They show what people report, not what works, and they are not clinical evidence.
Links between terms. "May be associated with" means the link appears in a cited source. It does not mean you have that condition.
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