Down syndrome is a chromosomal disorder when a person is born with three, rather than two, copies of the 21st chromosome. It happens in approximately 1 in 700 live births in Canada.
Normally there are 46 chromosomes (23 pairs), half of which are inherited from each parent. A person with Down syndrome, however, has cells that usually contain not 46, but 47 chromosomes, the extra one being a third chromosome 21. It is this extra genetic material that disrupts the child’s physical and cognitive development.
How is Down Syndrome Diagnosed?
Physicians may make a preliminary diagnosis of Down syndrome after careful examination of a newborn. Some common characteristics include
- Low muscle tone
- Low nasal bridge, small nose and ears
- Eye openings slanted upwards
- A ring of white dots in the iris of the eye
- Single deep crease across the center of the palm
- Excessive ability to extend the joints
- Fifth finger has one bending joint instead of two
- Small skin folds on the inner corners of the eyes
A blood test is necessary to verify the diagnosis.
Children with down syndrome continue to acquire physical and mental skills throughout their lives, even though their ability levels vary considerably. In general, the average rate of progress will be slower than the general population. Among the differences noted are delays in motor skills, language skills, and social adaptability and self-help skills.
Early intervention is important in facilitating learning for children with Down syndrome as in any other children. When given equal opportunities in every stage of their lives, people with Down syndrome will make a valuable contribution to society.
Prevention and Prenatal Testing
Although there is no way to prevent Down syndrome, the risk increases with a mother’s age, or a history of genetic defects in a family. For women over 35, the risk of having a child with Down syndrome is significantly increased to 1 in 350. At age 40 the risk increases to 1 in 100 births, and at age 45 the risk becomes approximately 1 in 25.
Genetic counselling, prenatal screening and diagnostic tests are important to assess the risk of the Down syndrome.