Down syndrome

What is Down syndrome?

Down syndrome (also known as trisomy 21) is a

genetic condition

in which the person has an extra copy of chromosome 21.

Chromosomes are the blueprint for the body’s development. They are found in every cell in your body and determine your physical and mental characteristics. The usual number of chromosomes for human beings is 46 (arranged in 23 matched pairs). People with Down syndrome have an extra chromosome 21 in their genetic make-up.

Down syndrome is the most common chromosomal condition and occurs in all races and cultures at around the same rate. In Victoria, there are approximately 3500 people with Down syndrome and between 45 and 60 babies are born with Down syndrome each year.

People with Down syndrome have some level of intellectual disability, some characteristic physical features, increased risk of some health conditions (many of which are treatable), and some developmental delays

Types of Down syndrome

Although we know how Down syndrome occurs, we do not yet know why. There are three forms of Down syndrome:

Trisomy 2

1 – where every cell in the body has an extra chromosome 21. Most people with Down syndrome (about 95 per cent) have trisomy 21. It is a condition caused at conception and is not hereditary.

Mosaic Down syndrome

– where there is an extra chromosome 21 in some (but not all) of the cells, while the rest of the cells have the standard genetic composition. Mosaic Down syndrome occurs in one to two per cent of people with Down syndrome. It can result in a milder level of intellectual disability and less obvious physical characteristics than the other forms of Down syndrome.

Translocation Down syndrome

– where part of chromosome 21 is broken off and is then attached (translocated) onto another chromosome. This can occur before or at conception. This form of Down syndrome is uncommon, occurring in about three to four per cent of people with the condition. In about one third of these cases, the child has inherited the translocation from a parent. In such a case the family may be referred to a genetic counselling service.

Genetic tests can show what type of Down syndrome a baby has.

Down syndrome – capabilities and potential

People with Down syndrome lead inclusive, fulfilling lives. They will go to mainstream schools, get jobs, live independently, have relationships and get married.

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. People with Down syndrome demonstrate a wide range of capabilities. What happens after birth is far more important in shaping the outlook for a person with Down syndrome than the presence of an extra chromosome.

Children with Down syndrome attend childcare, kinder, primary and high school alongside other children of their age. Adults with Down syndrome attend post-school training, participate in the workforce and lead full lives as productive and valued members of the community. People with Down syndrome live independently, with some level of support, within the community.

People with Down syndrome often have their abilities and potential underestimated. A person with this condition will achieve in many areas when offered the opportunity and supported to do so.

Impacts of Down syndrome

Physical characteristics of Down syndrome

There are a number of physical characteristics associated with Down syndrome, although each person with Down syndrome may display only a few of these. The most common physical characteristics include:

slight upward slant of the eyes

– nearly all people with Down syndrome have a slight upward slant of the eyes. There can also be a small fold of skin on the inside of the eye (called an ‘epicanthic fold’) and small white patches on the edge of the iris of the eye (known as Brushfield spots)

characteristic facial shape

– the face of a person with Down syndrome is often rounded and tends to have a flat profile

smaller stature

– babies with Down syndrome are usually smaller and weigh less at birth than others. Children with Down syndrome tend to grow more slowly and are commonly smaller than other children their age. Adults with Down syndrome are commonly smaller than adults who do not have Down syndrome.

Despite some common physical characteristics, people with Down syndrome resemble other members of their family more than they resemble each other.

Down syndrome, intellectual disability and delayed development

Down syndrome is the most common cause of intellectual disability and every person with Down syndrome will have some level of intellectual disability. There will be some delay in development and some level of learning difficulty. Because everyone is unique, the level of delay will be different for each person.

Babies with Down syndrome reach the same developmental milestones (such as smiling, sitting up, crawling, walking, talking and toileting) as all babies, but with some degree of delay. Speech and language development is often the area of greatest delay.

People with Down syndrome generally need some level of support to achieve their potential – some will need very little support, while others may require a high level of support. However, people growing up with Down syndrome lead fulfilling lives and participate as valued members of their communities.

Down syndrome and Health & Wellbeing

There are some common health issues and some more serious medical conditions that are more likely to occur in people with Down syndrome than in other people. It is important to note that predisposition to a health issue does not mean that every person with Down syndrome will have that condition, however it does mean that early intervention through regular

GP (doctor)

check ups and screening is very important for people with Down syndrome to lead healthy lives. For more information go to:

DSA Health Screening

tool

External Link

Down Syndrome Australia - Health

Professionals

External Link

Diagnosis of Down syndrome

Down syndrome is usually recognisable at birth and confirmed by a blood test. A doctor can usually tell if a baby has Down syndrome from their physical appearance.

Prenatal tests

are available that can help to detect a high chance of Down syndrome and other conditions. Prenatal testing is not compulsory and is the choice of the family.

Prenatal screening tests can provide information about how likely it is that a baby might have a particular health problem, but cannot provide a definite answer.

Prenatal screening tests include:

ultrasound scans

maternal serum screening

non-invasive prenatal testing (NIPT)

Prenatal diagnostic test can provide more definite information about whether a condition is present.

Prenatal diagnostic tests include:

amniocentesis

chorionic villus sampling

Down syndrome

Down syndrome

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