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Down Syndrome also known as Down syndrome or trisomy 21, is a genetic condition that typically causes some level of learning disability and certain physical characteristics.


  • Down syndrome occurs when an individual has a full or partial extra copy of chromosome 21. This additional genetic material alters the course of development and causes the characteristics associated with Down syndrome

  • There are three types of Down syndrome: trisomy 21 (nondisjunction) accounts for 95% of cases, translocation accounts for about 4%, and mosaicism accounts for about 1%

  • Down syndrome is the most commonly occurring chromosomal condition. 

  • Down syndrome occurs in people of all races and economic levels.

  • The incidence of births of children with Down syndrome increases with the age of the mother. But due to higher fertility rates in younger women, 80% of children with Down syndrome are born to women under 35 years of age.

  • People with Down syndrome have an increased risk for certain medical conditions such as congenital heart defects, respiratory and hearing problems, Alzheimer’s disease, childhood leukemia and thyroid conditions. Many of these conditions are now treatable, so most people with Down syndrome lead healthy lives

  • A few of the common physical traits of Down syndrome are: low muscle tone, small stature, an upward slant to the eyes, and a single deep crease across the center of the palm. Every person with Down syndrome is a unique individual and may possess these characteristics to different degrees or not at all

  • Life expectancy for people with Down syndrome has increased dramatically in recent decades – from 25 in 1983 to 60 today.

  • All people with Down syndrome experience cognitive delays, but the effect is usually mild to moderate and is not indicative of the many strengths and talents that each individual possesses.

  • Quality educational programs, a stimulating home environment, good health care and positive support from family, friends and the community enable people with Down syndrome to lead fulfilling and productive lives


Characteristics of Down's syndrome

Most babies born with Down's Syndrome are diagnosed soon after birth and may have:

  • floppiness (hypotonia)

  • eyes that slant upwards and outwards

  • a small mouth with a tongue that may stick out

  • a flat back of the head

  • below-average weight and length at birth

  • their palm may have only one crease across it


Although children with Down's syndrome share some common physical characteristics, they don't all look the same. A child with Down's will look more like their family members than other children who have the syndrome.


People with Down's syndrome will also have different personalities and abilities. Everyone born with Down's syndrome will have some degree of learning disability, but this will be different for each person.


Screening for Down's syndrome

Sometimes parents find out their baby has Down's syndrome during pregnancy because of screening tests. All pregnant women are offered screening tests for Down's syndrome.

Screening tests can't tell you for certain if your baby has Down's syndrome, but they can tell you how likely it is.

If screening tests show there's a chance your baby has Down's, more tests can be done during pregnancy to confirm it.


These include:

  • chorionic villus sampling (CVS) – a small sample of the placenta is tested, usually during weeks 11-14 of pregnancy

  • amniocentesis – a sample of amniotic fluid is tested, usually during weeks 15-20 of pregnancy


If these tests show that your baby has Down's syndrome, you and your baby's other parent will be offered counselling so you can talk about the impact of the diagnosis.


You may also be offered an appointment to meet a doctor or other health professional who works with children with Down's syndrome. They can tell you more about the condition and answer any questions you have.

See more about screening for Down's syndrome


Causes of Down's syndrome

Down's syndrome is usually caused by an extra chromosome in a baby's cells. In most cases, this isn't inherited – it's simply the result of a one-off genetic change in the sperm or egg.


There's a small chance of having a child with Down's syndrome with any pregnancy, but the likelihood increases with the age of the mother.


For example, a woman who is 20 has about a 1 in 1,500 chance of having a baby with Down's, while a woman who is 40 has a 1 in 100 chance.


There's no evidence that anything done before or during pregnancy increases or decreases the chance of having a child with Down's syndrome.


Living with Down's syndrome

Although there's no "cure" for Down's syndrome, there is support available to help children with the condition lead healthy, fulfilling lives.


This includes:

  • access to good healthcare – including a range of different specialists

  • support for your child's development – this may include speech and language therapy, physiotherapy, and home teaching 

  • support groups – such as the Down's Syndrome Association, who can put you in touch with other families who have a child with Down's syndrome


Lots of people with Down's syndrome are able to leave home, have relationships, work, and lead largely independent lives.


People with Down's syndrome are more likely to have certain health problems, including:

  • heart disorders, such as congenital heart disease

  • hearing and vision problems

  • thyroid problems, such as an underactive thyroid gland (hypothyroidism)

  • recurrent infections, such as pneumonia


Your child may be checked by a paediatrician more often than other children to pick up problems as early as possible. 

If you have any concerns about your child's health, talk to your GP, health visitor or paediatrician.

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