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Down syndrome

What is Down syndrome?

Down syndrome is a common congenital condition affecting about one in every 700 babies in Canada. Congenital means the condition is present at birth. Down syndrome is due to a genetic variation and is not related to race, nationality, religion or socio-economic status.

While Down syndrome is associated with medical and developmental challenges, the features of the condition vary widely from one child to another. The presentation of the syndrome falls on a spectrum.

Children with Down syndrome attend school and participate in recreational activities just like other children. Many adults with Down syndrome hold jobs, live independently and contribute to their family, friends and community in many different and meaningful ways.

What causes Down syndrome?

Down syndrome is a genetic condition caused by having “extra” genetic material (or too many genes), of chromosome 21.

Trisomy 21

Each cell typically has 23 pairs of chromosomes for a total of 46 chromosomes. In children with Down syndrome, each cell in the body has 47 chromosomes because there is a third copy of chromosome 21. This is called trisomy 21, and affects approximately 94% of people with Down syndrome. This is most often a random genetic event and not caused by anything that either parent has done.

Trisomy 21 Down Syndrome

Other causes of Down syndrome

In a small number of Down syndrome cases, the extra chromosome 21 is the result of an unbalanced translocation. Translocation occurs when chromosome 21 attaches itself to another chromosome in the cell so a child has three copies of chromosome 21. Translocation Down syndrome can be inherited from an unaffected parent.

More information about Translocation Down Syndrome can be found here:

The least common type of Down syndrome is called mosaicism. It affects about 1% of patients with Down syndrome. In this situation only some of the cells in the body have an extra copy of chromosome 21.

More information about mosaicism can be found here:

What are the chances of having a baby with Down syndrome?

Women older than 35 years of age are at a greater risk to give birth to a child with Down syndrome, in comparison to women younger than 35. This risk increases with the mother’s age. However, because most babies in general are born to women who are younger than 35, most babies with Down syndrome (80%) are born to women younger than 35 years old.

The risk is also greater for parents who already have a child with Down syndrome, or for mothers or fathers who have a balanced translocation.

If you think you may be at risk, talk to your health-care professional.

Diagnosis of Down syndrome

Most babies born with Down syndrome are diagnosed with the condition after birth. However, there are several ways to test for Down syndrome before a baby is born. These include various blood tests along with an early fetal ultrasound to determine the chances that a baby might have trisomy 21.

These tests are sometimes referred to as integrated prenatal screening or first trimester screening. In recent years, non-invasive prenatal testing has been used. This is a very accurate blood test that helps determine if a fetus will have trisomy 21.

Other types of tests used to detect trisomy 21 in a fetus include chronic villus sampling and amniocentesis.

Although these tests may detect trisomy 21 before a baby is born, they are not able to predict how affected the child will be with regards to their development or medical issues.

Expectant parents should speak to their health-care providers for more information on diagnostic tests and procedures. A genetics counsellor can also provide more information, either prenatally or after delivery.

How does Down syndrome affect the body?

Babies with Down syndrome are more likely to be born prematurely. Their birth weight and length may be below average. Babies with Down syndrome are also more likely to have low muscle tone leading to floppiness (hypotonia).

In addition, there are several physical features that when taken all together are more often seen in children with Down syndrome. These features include: upward slanting eyes, flattened bridge of the nose, prominent tongue and low set ears.

Although children with Down syndrome share some common physical characteristics, they do not all look the same. A child with Down syndrome will look more like their parents, or other family members, than other children with the syndrome.

Children with Down syndrome also vary in personality and ability just like other children. They will all have intellectual impairment, delayed motor development, and speech problems. However, the level of impairment will be different for each individual. A child with Down syndrome may learn new skills slower than a child without Down syndrome. However, most children with Down syndrome should still be able to learn the same skills as other children, including walking, talking and being toilet trained.

There are several medical conditions that can affect children with Down syndrome. The most common medical conditions are hearing (75%) and vision problems (60%). About 40-50% of children with Down syndrome have heart defects. A smaller number of children (8-12%) have problems with their gastrointestinal tract at birth.

Children with Down syndrome are more likely to have certain infections, respiratory, blood and dental problems as well as thyroid and other medical conditions.

The effects of these conditions vary from child to child. They may be more serious in some children than in others. Some children with Down syndrome may have none of these medical conditions, while others will have several. With proper medical care most children and adults with Down syndrome can lead healthy lives.

The average life expectancy of individuals with Down syndrome is 60 years. Many people with Down syndrome will live into their sixties and seventies. In addition to some of the conditions mentioned above, adults with Down syndrome are more likely to have Alzheimer’s disease. Alzheimer's is a neurologic disease that causes problems with memory, thinking and behavior.

For more information please see Down syndrome: Medical conditions affecting children with the condition.

If you have any questions or concerns about any of these conditions, speak with your child’s doctor.

Treatment of Down syndrome

There is no cure for Down syndrome. However, there are many supportive treatments available to help target the associated medical and developmental challenges. Because children with Down syndrome can be affected differently, there are no standard medications required by all children with Down syndrome.

Medical problems for a child with Down syndrome often change with age. Your child’s doctor should be aware of these age-specific medical problems and organize the appropriate testing according to your child’s age. Health supervision guidelines for families are available online from the American Association of Pediatrics (AAP) at the following link:​

These guidelines highlight the common medical and developmental issues that should be monitored ona regular basis as well as the recommended tests that should be done on a yearly basis.

The full AAP guidelines for professionals are also available​.

Children with Down syndrome benefit from loving homes, early intervention, inclusive and accommodating education, appropriate medical care and positive public attitudes. An example of a typical program for a child with Down syndrome would include:

  • Early intervention services
  • Physiotherapy for gross motor skills
  • Occupational therapy for feeding, general development and fine motor skills
  • Speech and language therapy to work on communication skill
  • Collaboration between your child’s health-care professionals and daycares, schools, and other extra-curricular programs, to optimize your child’s care.

In adulthood, many people with Down syndrome hold jobs, live independently and enjoy recreational opportunities in their communities.

When to see a doctor

Babies and children with Down syndrome should be followed by a primary-care doctor. Your child’s primary-care doctor will care for them during illness and will see your child for annual health check-ups.

Some cities have multi-disciplinary clinics that offer expertise and help co-ordinate care for children with Down syndrome. Check with your regional children’s hospital to find out if these programs are available in your area.

Key points

  • Down syndrome is a genetic condition present at birth, and is due to the presence of extra genetic material from chromosome 21.
  • Down syndrome is a complex condition that affects the child’s health and development.
  • Children with Down syndrome can experience varying degrees of medical and developmental problems.
  • Individuals with Down syndrome benefit from loving homes, early intervention, inclusive and accommodating education and being connected to appropriate community resources throughout their lives.

Nirit Bernhard, MSc, MD, FRCPC

Priya Sayal, MD Candidate 2018, BHSc.​