Down syndrome

Down syndrome (also known as trisomy 21) is a genetic condition in which a person has an extra copy of chromosome 21. Chromosomes are the blueprint for the body’s development. They are found in every cell and help determine our physical and mental characteristics.

Human beings usually have 46 chromosomes, arranged in 23 matched pairs. People with Down syndrome have an extra chromosome 21 in their genetic make-up. It is the most common chromosomal condition and occurs in all races and cultures at around the same rate.

People with Down syndrome have some level of intellectual disability, some characteristic physical features, an increased risk of certain health conditions (many of which are treatable), and some developmental delays. Although we understand how Down syndrome occurs, we do not yet know why.

Types of Down syndrome#

There are three forms of Down syndrome, and a genetic test can show which type a person has:

• Trisomy 21 – every cell in the body has an extra chromosome 21. About 95 per cent of people with Down syndrome have this form. It arises at conception and is not hereditary.
• Mosaic Down syndrome – an extra chromosome 21 is present in some, but not all, cells, while the rest have the usual genetic make-up. It occurs in one to two per cent of people with Down syndrome and can result in a milder level of intellectual disability and less obvious physical characteristics.
• Translocation Down syndrome – part of chromosome 21 breaks off and attaches (translocates) onto another chromosome, before or at conception. This form is uncommon, occurring in about three to four per cent of cases. In roughly one third of these, the child has inherited the translocation from a parent, and the family may be referred to a genetic counselling service.

Capabilities and potential#

People with Down syndrome lead inclusive, fulfilling lives. They attend mainstream schools, get jobs, live independently, have relationships and marry. Down syndrome affects a person’s development in certain ways, but it is not the most important influence on how that person develops and lives their life.

What happens after birth shapes a person’s outlook far more than the presence of an extra chromosome. Children with Down syndrome attend childcare and school alongside other children their age. Adults take part in further training and the workforce and live full lives as valued members of their community, with some level of support. Their abilities and potential are often underestimated, yet a person with Down syndrome can achieve in many areas when given the opportunity and the right support.

Physical characteristics#

Several physical features are associated with Down syndrome, although each person may show only a few of them. The most common include:

• a slight upward slant of the eyes
• a characteristic facial shape, often rounded with a flatter profile
• small white patches on the edge of the iris (known as Brushfield spots)
• smaller stature

Babies with Down syndrome are usually smaller and weigh less at birth than others, and children tend to grow more slowly and are commonly smaller than peers their age. Adults are also commonly smaller. Despite these shared features, people with Down syndrome resemble other members of their own family more than they resemble each other.

Intellectual disability and development#

Down syndrome is the most common cause of intellectual disability, and every person with Down syndrome will have some level of it, along with some delay in development and some learning difficulty. Because everyone is unique, the degree of delay differs from person to person.

Babies with Down syndrome reach the same developmental milestones as other babies — such as smiling, sitting up, crawling, walking, talking and toileting — but with some degree of delay. Speech and language development is often the area of greatest delay. Some people need very little support to reach their potential, while others need a high level of support.

Health and wellbeing#

Some common health issues and some more serious medical conditions are more likely to occur in people with Down syndrome than in others. Being predisposed to a health issue does not mean a person will develop it, but it does mean that early intervention through regular check-ups and screening is very important to help people with Down syndrome lead healthy lives.

Diagnosis#

Down syndrome is usually recognisable at birth and confirmed by a blood test; a doctor can often tell from a baby’s physical appearance. Tests are also available during pregnancy that can help detect a high chance of Down syndrome and other conditions. Prenatal testing is not compulsory and is the family’s choice.

Prenatal screening tests can indicate how likely it is that a baby has a particular condition, but cannot give a definite answer. They include:

• ultrasound scans
• maternal serum screening
• non-invasive prenatal testing (NIPT)
• amniocentesis
• chorionic villus sampling

Genetic counselling#

Genetic counselling may be helpful if screening suggests you may have a child with Down syndrome. Genetic counsellors are health professionals qualified in both counselling and genetics. As well as providing emotional support, they can help you understand Down syndrome, what causes it, and what a diagnosis means for your child’s health and development and for your family. They are trained to provide information and support that is sensitive to your family circumstances, culture and beliefs.

Support for people with Down syndrome and their families#

A range of supports is available for people with Down syndrome and their families. Community-based, not-for-profit associations advocate with and for people with Down syndrome so they can access the same opportunities, supports and community activities as everyone else, working within a human rights framework consistent with the United Nations Convention on the Rights of Persons with Disabilities.

These organisations provide information, training, general support, education support and services for people with Down syndrome, their families, professionals and the wider community. This often includes prenatal support and information for expectant parents and health professionals, telephone information and assistance, and peer support and social groups for families, teens and adults.

Key points#

• Down syndrome is the most common chromosomal condition and occurs in all races and cultures at around the same rate.
• Trisomy 21 arises at conception and is not hereditary.
• Translocation Down syndrome is uncommon, occurring in about three to four per cent of people with the condition.
• People with Down syndrome attend mainstream schools, get jobs, live independently, have relationships and marry.
• Children with Down syndrome attend childcare and school alongside other children their age.

Where to get help#