ConditionChildren's health
Down Syndrome (Trisomy 21)
Down syndrome is a genetic condition caused by a full or partial extra copy of chromosome 21. It is the most common chromosomal condition, affecting about 1 in 700 babies born in the US. It causes characteristic facial features, low muscle tone and intellectual disability, usually mild to moderate, and raises the risk of certain health conditions, including heart defects, thyroid problems, hearing and vision issues, and early Alzheimer's disease. With modern health care and support, people with Down syndrome live into their 60s and beyond.
Also called: Trisomy 21, Down's syndrome
At a glance
- Cause
- An extra copy of chromosome 21 (trisomy 21 in about 95% of cases, translocation or mosaicism in the rest).
- How common
- About 1 in 700 US births. Risk rises with maternal age, but most babies are born to mothers under 35.
- Features
- Low muscle tone, upward-slanting eyes, flat nasal bridge, single palm crease, intellectual disability.
- Health risks
- Heart defects, hearing and vision problems, thyroid disease, sleep apnea, celiac disease, leukemia, early Alzheimer's.
- Support
- Early intervention, regular health screening, inclusive education and lifelong community support.
When to get help
Call 911 or go to the ER
- Neck pain, head tilt, new weakness, clumsiness, loss of bladder or bowel control, or change in walking (possible atlantoaxial instability compressing the spinal cord)
- A baby with blue color, breathing difficulty or poor feeding with sweating (possible heart defect)
- A newborn with vomiting, especially green vomit, or no stool passed (possible bowel blockage)
See a doctor within a day or two
- Unusual bruising, pale skin, frequent infections or fever without a cause (possible leukemia)
- Snoring with pauses in breathing, or daytime sleepiness
Book a routine appointment
- Changes in memory, behavior, skills or personality in an adult (possible dementia or depression)
- Weight gain, tiredness and constipation (check thyroid)
- Missed recommended screenings for hearing, vision, thyroid or celiac disease
Causes
Chromosomes carry genes. Most people have 46 chromosomes in 23 pairs. People with Down syndrome have extra chromosome 21 material, which changes development.
| Type | What happens | Share of cases |
|---|---|---|
| Trisomy 21 | Three full copies of chromosome 21 in every cell, from an error in egg or sperm formation | About 95% |
| Translocation | Extra chromosome 21 material attached to another chromosome. Can be inherited from a parent who carries a balanced translocation | About 3% to 4% |
| Mosaic | Only some cells have the extra chromosome, often milder features | About 1% to 2% |
The chance of trisomy 21 rises with the mother's age, especially after 35. Because younger women have more babies, most children with Down syndrome are born to mothers under 35. Nothing parents did before or during pregnancy causes Down syndrome.
Physical features
Features vary between individuals and do not predict abilities:
- low muscle tone (hypotonia), especially in infancy
- flattened face and nasal bridge
- upward-slanting eyes with skin folds at the inner corners
- small ears and small mouth with a tongue that may protrude
- a single crease across the palm
- small white spots on the colored part of the eye (Brushfield spots)
- short neck, short stature
- a wide gap between the first and second toes
- flexible joints
Development and learning
Most people with Down syndrome have mild to moderate intellectual disability. Children typically reach milestones later, especially speech. Visual learning is often a strength. Many people with Down syndrome learn to read, attend mainstream schools, work, form relationships and live semi-independently.
Associated health conditions
| Condition | Approximate frequency and notes |
|---|---|
| Congenital heart defects | About half, especially atrioventricular septal defects. Echocardiogram for all newborns |
| Hearing loss | Common, from glue ear and sensorineural causes |
| Vision problems | Refractive errors, squint, cataracts, keratoconus |
| Hypothyroidism | Common at all ages. Yearly thyroid tests |
| Obstructive sleep apnea | Common. Sleep study recommended by age 4 |
| Gut problems | Duodenal atresia, Hirschsprung disease, constipation, celiac disease |
| Blood conditions | Transient abnormal myelopoiesis in newborns, higher risk of leukemia in childhood |
| Atlantoaxial instability | Loose joint between top two neck bones. Rarely compresses the spinal cord |
| Alzheimer's disease | Very high lifetime risk, often from the 40s to 50s, because chromosome 21 carries the amyloid precursor protein gene |
| Other | Obesity, diabetes, skin conditions, early menopause, anxiety and depression |
Prenatal screening and diagnosis
ACOG recommends offering screening and diagnostic testing to all pregnant people, regardless of age.
- Screening tests estimate the chance: cell-free DNA (NIPT) blood test from 10 weeks, first-trimester combined screening, and second-trimester quad screen. A positive screen is not a diagnosis
- Diagnostic tests confirm: chorionic villus sampling (CVS) at 10 to 13 weeks or amniocentesis from 15 weeks
- After birth: a chromosome test (karyotype) confirms the diagnosis and type
Health care and support
The American Academy of Pediatrics publishes a health supervision schedule. Key elements:
- echocardiogram at birth
- hearing and vision checks at birth and regularly
- thyroid tests at birth, 6 and 12 months, then yearly
- blood counts in infancy and yearly
- sleep study by age 4
- celiac screening if symptoms
- awareness of neck instability symptoms
- growth monitoring on Down syndrome-specific charts
Adults need continued screening, with attention to thyroid, weight, hearing, vision, mental health and baseline cognitive assessment from around age 35 to 40.
Therapies and education
- early intervention from infancy: physical, speech and occupational therapy
- inclusive education with individualized plans
- social skills, vocational and independent living programs
- family support organizations
Outlook
Life expectancy has risen from about 25 years in 1983 to around 60 years today, thanks to heart surgery and better health care. Many adults with Down syndrome work, participate in their communities and report high life satisfaction.
Frequently asked questions
What causes Down syndrome?
Down syndrome is caused by extra chromosome 21 material, usually a full extra copy from an error when the egg or sperm forms. It is not caused by anything the parents did. The chance increases with the mother's age.
What are the common features of Down syndrome?
Common features include low muscle tone, a flattened face, upward-slanting eyes, small ears, a single palm crease, short stature and intellectual disability that is usually mild to moderate. Features vary widely between individuals.
What is the life expectancy for people with Down syndrome?
Life expectancy is now around 60 years and rising, compared with about 25 years in the early 1980s. Improved heart surgery, health screening and inclusion in society have driven the change.
Can Down syndrome be detected before birth?
Yes. Screening tests such as the cell-free DNA blood test estimate the likelihood, and diagnostic tests such as CVS or amniocentesis confirm it. ACOG recommends offering these options to all pregnant people.
What health problems are common with Down syndrome?
Heart defects, hearing and vision problems, thyroid disease, sleep apnea, celiac disease, gut malformations, leukemia and early-onset Alzheimer's disease are more common. Regular screening allows early treatment.
Sources
This guide was written from current patient and clinical guidance, including:
- American Academy of Pediatrics: Health supervision for children and adolescents with Down syndrome (2022)
- CDC: Facts about Down syndrome
- National Down Syndrome Society: About Down syndrome
- Global Down Syndrome Foundation: Medical care guidelines for adults with Down syndrome
- ACOG: Screening for fetal chromosomal abnormalities