Down Syndrome
(Down's Syndrome)
In this condition factsheet:
The Facts on Down Syndrome
Chromosomes are tiny structures found in every cell of our bodies. These structures hold the DNA genetic codes that dictate our natural traits and characteristics (e.g., hair and eye colour, height).
There are 23 pairs of chromosomes in each human cell (i.e., 46 individual chromosomes), including one pair of sex chromosomes. Down syndrome is a genetic condition caused by the presence of an extra whole chromosome, or part of a chromosome, specifically chromosome 21.
Although Down syndrome is a genetic condition, it is not inherited. In Canada, approximately 1 in 800 babies are born with Down syndrome. This risk increases with increasing maternal age.
Causes of Down Syndrome
According to the NDSS and the National Association for Down Syndrome (NADS), there is no connection between any type of Down syndrome and parents' activities before or during pregnancy. It is important to know that nothing the mother does during pregnancy could cause Down syndrome. However, we do know that the chance of having a baby with Down syndrome increases significantly with maternal age, and with teenage pregnancies. Since many couples are postponing pregnancy until later in life, the incidence of Down syndrome conceptions may increase. Therefore, genetic counselling for parents may become more important.
The most common type of Down syndrome is trisomy 21, which accounts for 95% of all cases. In this type of Down syndrome, abnormal cell division results in an extra chromosome 21 in each cell. Prior to or at conception, a pair of chromosomes 21 (in either the sperm or the egg) fails to separate. As the embryo develops, the extra chromosome is replicated in every cell of the body. At present, researchers are not sure what causes the presence of an extra chromosome 21. They do know that it can come from either the mother or the father. In a person with Down syndrome, each cell makes excess amounts of chemicals regulated by the chromosome 21 genes. This imbalance in part explains physical effects and biological changes noted in people with Down syndrome.
Other less common forms of Down syndrome result from other processes occurring during cell division, which result in an extra partial chromosome. 2% to 3% of people with Down syndrome have a type called translocation, and a very small portion of people with Down syndrome have a type called mosaicism.
Symptoms and Complications of Down Syndrome
There are several physical characteristics that are more common for babies with Down syndrome. These may include a flat facial profile, almond shaped eyes with an upward slant, unusual eyelids (known as epicanthic folds), a flat nasal bridge, a prominent tongue, small ears, single crease on the palms of the hands (known as a palmar crease), smaller limbs, smaller body frame, and a small head. Even though they may have these characteristics, babies and children with Down syndrome may still look much like other family members.
Health and development
Children with Down syndrome may have other health complications besides the usual childhood illnesses. No individual with Down syndrome will have all the health complications. However, every child needs supportive, preventative medical care. Early and proper health care can help people with Down syndrome better manage their condition.
Some health problems are less serious while others can be very problematic, such as malformations of the heart. Around the world, more than 40% of children born with Down syndrome have a congenital heart malformation. However, the diagnosis of a heart problem does not mean the baby is or will become seriously ill, and the extent of the heart problem varies from very mild to life-threatening. In addition, newborns with Down syndrome are at a higher risk of having a blockage in the intestines that requires surgery. Some degree of hearing loss (most often due to frequent ear infections) can affect children with Down syndrome.
Babies with Down syndrome can be breast-fed, and breast-feeding mothers may find it helpful to talk with their doctor or nurse to prepare for the process. Babies and children with Down syndrome also have an increased risk of developing hypothyroidism (low thyroid hormone), diabetes, leukemia, and seizure disorders. However, early detection and treatment can help manage these conditions.
Most children with Down syndrome will have speech delay, which can be further aggravated by hearing loss. In these cases, a speech therapist can play an important role in the child's learning and development. Visual problems (e.g., cataracts, crossed eyes, or far- or nearsightedness) are also more common for children with Down syndrome and occur in around 60% of cases. In some cases, corrective eyewear and medications may help to improve vision, while other children may require surgery to resolve visual problems. Due to poor muscle tone, babies with Down syndrome may have trouble rolling over, sitting up, and walking, and they may require regular physiotherapy.
For adults with Down syndrome, infertility is common for men. Pregnancies are possible for women with Down syndrome, although there is an increased risk of having a child with Down syndrome. Genetic counselling and family planning specialists are usually involved to educate and provide support where needed. Adults with Down syndrome also face an increased chance of developing early-onset Alzheimer's disease. They are also more likely to be obese in adulthood.
Learning and development
Levels of learning ability for people with Down syndrome can range from near-normal to severe disability. While most people with Down syndrome have mild-to-moderate learning impairment and developmental delays, the degree of impairment is not predictable either before or after birth. The extra chromosome means that your baby or child will likely be slower to reach developmental milestones and will have a certain degree of learning difficulty.
Like other children, most children with Down syndrome learn to walk and talk, ride a bicycle, read, and have a wide range of abilities and talents. If your child has Down syndrome, a base of good physical health and continued social support can help foster your child's ability to learn.
Effects on the family
Having a baby with Down syndrome may require a period of adjustment for the family. Parents may feel more pressure to focus on the development of their child with Down syndrome over their other children. Take time to get to know your child as part of the family, and keep in mind that he or she will have a unique personality and will require plenty of love and support from the parents, just like other children.
