Down syndrome is a chromosomal disorder caused by an additional (third) chromosome 21 or "trisomy 21." Down syndrome is associated with mental retardation, a characteristic facial appearance, and poor muscle tone (hypotonia).
How Common Is Down Syndrome?
Down syndrome occurs in one out of 800 live births, in all races and economic groups. Down syndrome is the most frequent genetic cause of mild to moderate mental retardation and associated medical problems.
The cause of Down syndrome is a genetic problem related to chromosome 21. While Down syndrome is genetic in that it involves an extra chromosome 21, it is not usually hereditary in the conventional sense. That is, Down syndrome is not inherited; it does not "run in families." Down syndrome is usually the result of a random event that occurs during the formation of reproductive cells (eggs and sperm). One exception is Down syndrome caused by a balanced translocation
(see Translocation and Down Syndrome).
As far as we know, Down syndrome is not caused by any behavioral activity of the parents or environmental factors.
Risk Factors for a Down Syndrome Baby
- Having a Down syndrome baby previously
- Increasing maternal age
- Carriers of a balanced translocation.
Characteristics of Down Syndrome
While Down syndrome is common, the symptoms an individual experiences can vary. Some people may have many
Down syndrome symptoms; others only a few. Some people will have very severe symptoms of Down syndrome, and others can have mild ones.
Common characteristics of Down syndrome include:
- A flat facial profile
- An upward slant to the eye
- A short neck
- Abnormally shaped ears
- White spots on the iris of the eye (called Brushfield spots)
- A single, deep transverse crease on the palm of the hand
- Smaller than average size
- Exaggerated space between the first and second toes
- Poor muscle tone (called hypotonia)
- Joint looseness
- Broad feet with short toes
- Learning disabilities.
Down Syndrome and Other Medical Conditions
Besides the physical characteristics, people with Down syndrome are also at increased risk of developing certain medical conditions that come with their own set of symptoms. Some of these conditions can include:
A
Down syndrome diagnosis can be made during prenatal testing. Diagnosing Down syndrome can also be done shortly after birth. In this case, the doctor may suspect that a baby has Down syndrome based on the presence of possible characteristics of the disorder. The diagnosis is confirmed with a special blood test.
Down syndrome treatment can include:
- Regular checkups and screening
- Medications
- Surgery
- Counseling and support.
Prognosis for Down Syndrome
Life expectancy for people with Down syndrome has increased substantially. In 1929, the average life span of a person with Down syndrome was nine years. Today, it is common for a person with Down syndrome to live to age 50 and beyond.
Other Names for Down Syndrome
Other names used by people for Down syndrome include:
- Down's syndrome
- Trisomy 21
- 47,XX,+21
- 47,XY,+21.
Down syndrome is named after John Langdon Down, the first physician to identify the condition in 1862.
In 1959, a group of geneticists lead by Jérôme Lejeune found that Down syndrome is a chromosomal irregularity. Lejeune and his colleagues found that people with Down syndrome had an additional 47th chromosome. The chromosomal irregularity was identified as trisomy 21.
Down syndrome is the accepted term in the United States, Canada, and other countries. The United Kingdom and other countries use Down's syndrome.
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