It is commonly known that the older a woman is at the time she conceives a child, the higher her risk is of giving birth to a child with Down syndrome. But did you know that 80 percent of children with Down syndrome are actually born to women under 35 years of age?
Down syndrome is a genetic condition that occurs in one out of every 691 births. It is the most commonly occurring chromosomal condition and is found in people of all races and economic levels. More than 400,000 people in the United States have Down syndrome, and about 6,000 babies with Down syndrome are born each year.
More and more Americans will interact with individuals with this genetic condition, which is increasing the need for widespread public education and acceptance.
There are no known behavioral or environmental factors that cause Down syndrome.
Instead, it occurs when an individual has three, rather than two copies of the 21st chromosome.
Typically, each human cell contains 23 pairs of different chromosomes. Each chromosome carries genes, which are needed for proper development and maintenance of the body. At conception, an individual inherits 23 chromosomes from the mother and 23 chromosomes from the father.
Sometimes, however, a person inherits an extra chromosome from one of the parents. In Down syndrome, an individual most often inherits two copies of chromosome 21 from the mother and one chromosome 21 from the father for a total of three chromosomes 21. Because Down syndrome is caused by the inheritance of three chromosomes 21, the disorder is also known as Trisomy 21. About 95% of individuals with Down syndrome inherit an entire extra chromosome 21.
In rarer instances, individuals with Down syndrome do not inherit an entire extra chromosome 21, but just some extra chromosome 21 genes, which are attached to another chromosome (usually chromosome 14). This is called a translocation and occurs in about 3% to 4% of individuals with Down syndrome.
In still rarer cases, or in about 2% to 4% of people with Down syndrome, additional genes from chromosome 21 are inherited, but not in every cell of the body. This is known as mosaic Down syndrome. For example, individuals may have inherited extra genes from chromosome 21 in the muscle cells, but not in any other type of cell.
Because the percentage of cells with extra genes from chromosome 21 varies in people with mosaic Down syndrome, they often do not have all the usual physical characteristics and may not be as severely intellectually impaired as people with full Trisomy 21.
While infants born with Down syndrome may be of average size, they typically grow slowly and remain shorter than other children of the same age.
Most often setting those children with Down syndrome apart from their peers are their distinct facial appearances. While not all children with Down syndrome have the same features, some of the common ones include:
- Flattened facial features
- Protruding tongue
- Small head
- Upward slanting eyes, unusual for the child's ethnic group
- Unusually shaped ears
Children with Down syndrome may also have:
- Poor muscle tone
- Broad, short hands with a single crease in the palm
- Relatively short fingers
- Excessive flexibility
Down syndrome is the leading cause of cognitive impairment. It is associated with mild to moderate learning disabilities and developmental delays. The symptoms of Down syndrome range from mild to severe.
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