Down syndrome

Also known as trisomy 21

Down syndrome is a genetic disorder you are born with where you get an extra copy of chromosome 21.

On this page, you can find the following information:

Key points about Down syndrome

  1. Everyone with Down syndrome is unique and experiences different features and/or challenges.
  2. The chance of your baby having Down syndrome is 1 in 1000 and increases with the mother's age. Down syndrome does not run in the families in most cases.
  3. Down syndrome can be diagnosed antenatally (before birth) or postnatally (after birth). 
  4. There is no cure for Down syndrome. Treatment aims to monitor the condition and support people with Down syndrome to lead a normal life.
  5. Adults with Down’s syndrome lead longer, more healthy, fulfilling and varied lives than in the past.
  6. There are support groups available where you can listen to other people's stories and get support. 

Image credit: 123rf

What causes Down syndrome?

Each cell in the human body contains 46 chromosomes arranged in 23 pairs. One pair is inherited from the father and the other pair is inherited from the mother. Down syndrome is a condition where you have 3 copies of chromosome 21. There are 3 ways this can happen:

  • Trisomy 21 – you get an extra copy of chromosome 21 in all your body cells due to abnormal cell division. This accounts for 94% of Down syndrome cases.
  • Mosaic Down syndrome – only some of your body cells contain an extra copy of chromosome 21. This accounts for 1% of cases.
  • Translocation Down syndrome – the remaining cases are due to translocation, in which a portion of chromosome 21 becomes attached to another chromosome, resulting in the cells having 3 copies of chromosome 21. 

Image credit: 123rf

Who is most likely to have a baby with Down syndrome?

It’s not known exactly why these abnormal cell divisions happen. The chances of having a baby with Down syndrome increase with the mother's age. However because most women have children at a younger age, 70% of Down syndrome infants are born to mothers aged under 35 years. In most cases, Down syndrome does not run in the family. 

What are the features of Down syndrome?

Everyone with Down syndrome is different and not all people with Down syndrome have the same features or difficulties.

Typical physical features of Down syndrome include:

  • small head or flattened back of the head (occiput)
  • short neck
  • small nose and flattened nose bridge
  • flattened face
  • extra skin fold on the upper eyelid (epicanthal fold)
  • upward slanted eyes
  • protruding tongue
  • low-set or small ears
  • short height
  • single crease on the palm of the hand
  • broad, short hands
  • short fingers or inward curving of little finger
  • poor muscle tone
  • delayed and slow growth
  • large gap between the first and second toe.

Down syndrome can cause certain medical problems. These include:

  • congenital heart problems such as atrioventricular septal defect (a hole in the muscle that separates the heart chambers)
  • gastrointestinal problems such as duodenal atresia
  • vision problems such as cataracts, short-sightedness
  • ear infections and hearing problems 
  • teeth and bone developmental problems
  • cancer such as leukemia
  • underactive thyroid gland
  • diabetes
  • reduced fertility.

Children with Down syndrome will have some level of intellectual disability and behavioural problems. These range from mild to moderate or severe. Some common difficulties include:

  • delayed speech and language development
  • feeding difficulties
  • delayed motor development such as sitting, walking and crawling
  • low intellectual quotient (IQ).

How is Down syndrome diagnosed?

Down syndrome can be diagnosed antenatally (before birth) or postnatally (after birth). 

During pregnancy, Down syndrome can be diagnosed by screening and diagnostic tests. Screening tests for Down syndrome include a blood test (MSS1) and an ultrasound scan to check the fluid thickness behind your baby's neck. These are typically done if you are less than 14 weeks pregnant. If you are between 14 and 20 weeks pregnant, a screening blood test (MSS2) will be done. MSS stands for maternal serum screening (a blood test from the mother).

If the results of the screening tests show that your baby is at increased risk of having Down syndrome, diagnostic tests such as chorionic villus sampling or amniocentesis can be done, depending on the week of gestation. Read more about antenatal tests for Down syndrome and pregnancy screening for Down syndrome and other conditions.

After birth, Down syndrome is usually suspected if your baby has the typical facial features. It can be confirmed by genetic tests to look for the extra copy of chromosome 21. 

How is Down syndrome treated?

There is no cure for Down syndrome. Treatment aims to monitor the condition and support people with Down syndrome lead a normal life, including to manage the challenges associated with the condition. People living with Down syndrome also need regular follow-ups to monitor complications and get treated if needed. 

There are different types of healthcare providers that may be involved in your child's care. These include:

  • paediatricians
  • speech and language therapist
  • physiotherapists
  • dentists
  • GPs
  • occupational therapist
  • cardiologist.

In general, the earlier the treatment or support is provided, the better the long-term outcome for a person living with Down syndrome. 

How can I support my child with Down syndrome?

As your child grows, it is important to see the person first, not their condition. Children with Down syndrome develop at different rates and in different ways – they will have individual strengths, interests, talents and needs. It helps them to be socially included in their families, schools and communities. Their involvement brings rewards to those groups too.

Your child will develop by taking part in enjoyable opportunities for interacting, moving and playing in their first years of life. As they get older they will continue to progress in all areas. This development can be helped by early intervention, having their hearing and any other health needs met and, later, by being educated at school. The Down Syndrome Association has more advice and support for parents. 

What is the outlook for someone with Down syndrome?

With recent medical advances and earlier detection of Down syndrome, at least half of people with Down syndrome are able to lead a normal active life and live into their 50s and 60s. 

The most common causes of death for people living with Down syndrome are congenital heart problems. 

What support is available with Down syndrome?

It can be difficult to cope if you have a child with Down syndrome. There are support groups available where you can listen to other people's stories and get the support you need. If you are planning to have a baby and are concerned about the risk of having a baby with Down syndrome, talk to your GP and they may be able to refer you to a genetic counsellor. 

NZ Down Syndrome Association Freephone 0800 693 724
Find more support groups here.

Learn more

The following links provide further information about Down syndrome. Be aware that websites from other countries may have information that differs from New Zealand recommendations.

NZ Down Syndrome Association
Down syndrome
NHS Choices, UK
Down's syndrome Patient Info, UK


  1. Down syndrome Auckland Regional HealthPathways, NZ
  2. Down syndrome NHS Choices, UK
  3. Down's syndrome Patient Info, UK
  4. Children, families, and education Down Syndrome Association, UK

Reviewed by

Sarah Godsell is a registered nurse with a specialised degree in Child and Adolescent Public Health. She has experience and a special interest in mental and sexual health. 
Credits: Health Navigator Editorial Team. Reviewed By: Sarah Godsell, community nurse, Auckland DHB Last reviewed: 09 Jul 2020