Down Syndrome Information: Frequently Asked Questions (FAQ)

A:Down syndrome, known commonly (although not always) as Trisomy 21, is a chromosomal disorder that is believed to occur at conception. As the result of and extra, or "copied" chromosome that the developing fetus possesses, the child with Down syndrome is born with a combination of physical, medical, and cognitive disorders which vary in severity from case to case. Included in these congenital anomalies are differences in stature, facial characteristics, and muscle tone as physical traits; increased incidence of heart defects, gastrointestinal problems, immunodeficiency problems, and vision and hearing problems are common medical problems; and mental retardation ranging from almost undetectable to profound is the result of the cognitive impairment associated with the syndrome.

Once known as Mongoloidism, and later Down's syndrome, the name of the condition was changed in the 1970s to remove the possessive quality of the condition's moniker. The name Down's syndrome, however, is still used in the United Kingdom, and in some other countries in Europe. People searching for complete information about Down syndrome may want to search under both names.

Q: Why does Down syndrome occur?

A: Down syndrome is the result of an extra copy of chromosome 21. There are 23 sets of chromosomes in the average, healthy, "normal" person, with two chromosomes present per set. Therefore, people with Down syndrome have three chromosomes 21, and forty-seven chromosomes in total, as opposed to the forty-six found in most people.

This extra, or "copied" chromosome in people with Down syndrome is caused by one of three chromosomal phenomenon. These abnormalities are called non-disjunction, mosaicism, and translocation. Depending on the type of Down syndrome a person has, the extra chromosome may be found in all of his or her cells, or only in some, however all people with Down syndrome will have some occurrence of the extra chromosome 21.

Q: My child has Down syndrome. Was there something I did to cause it?

A: Down syndrome is not the result of any habit or behavior on the part of the parents. Down syndrome is the result of a chromosomal anomaly, and is not the result of eating patterns, lifestyle, or overall health of the parents. It is not linked to pre-conceptional or gestational drug or alcohol use by the parents.

There is a strong correlation between Down syndrome and the age of the parent, most particularly the mother, at the time of conception and gestation. However, due to the fact that the reproduction rate drops dramatically as women age, the overwhelming majority of Down syndrome children are born to mothers under the age of thirty-five.

Q: Is Down syndrome hereditary?

A: In approximately 3% of cases, Down syndrome is thought to be hereditary. Generally, the children with hereditary Down syndrome are the product of a chromosomal anomaly called translocation (one of the three causes of Down syndrome). In translocation, the age of the mother is not considered to be a factor. Rather, there seems to be a genetic factor that is carried in one of the parents. Because of this, parents with a child with Down syndrome due to translocation run a greater risk of having a second child with the condition than those with a child born with it due to non-disjunction or mosaicism.

Q: I already have a child with Down syndrome. How likely is it that my next child will have the condition?

A: Very unlikely. For parents with a child with Down syndrome due to non-disjunction or mosaicism, the chances of having another child with the condition is the same as it was before they had their child with Down. Parents of children with Down syndrome due to translocation run a slightly higher chance of the condition repeating itself. As noted above, this chance is approximately 3%.

Q: What, specifically, are the causes Down syndrome?

A: Down syndrome is the result of an extra copy of chromosome 21. There are 23 sets of chromosomes in the average, healthy, "normal" person, with two chromosomes present per set. Therefore, people with Down syndrome have three chromosomes 21, and forty-seven chromosomes in total, as opposed to the forty-six found in most people.

This extra, or "copied" chromosome in people with Down syndrome is caused by one of three chromosomal phenomenon. These abnormalities are called non-disjunction, mosaicism, and translocation. Depending on the type of Down syndrome a person has, the extra chromosome may be found in all of his or her cells, or only in some, however all people with Down syndrome will have some occurrence of the extra chromosome 21.

Q: How many types of Down syndrome are there?

A: There are three identified types of Down syndrome: Down syndrome due to non-disjunction, mosaicism, and translocation. All three types are caused by anomalies in the pairing of chromosome 21. In non-disjunction and mosaicism, there is an extra copy of the chromosome, and in translocation, a piece of one of the original chromosome 21s breaks off and attaches itself to another chromosome.

By far, the most prevalent type of Down syndrome is due to non-disjunction, which accounts for approximately 95% of the incidence of the syndrome. This condition is also known as Trisomy 21. Because such a high percentage of people with Down syndrome are the result of non-disjunction, all people with the condition are commonly identified as having Trisomy 21, even though this is inaccurate about 5% of the time

Q: How often does Down syndrome occur?

A: Down syndrome occurs in approximately 1 out of 800 live births.

Q: Where can I get more information about Down syndrome?

A: There is a lot of information available about Down syndrome. For web based searches, I recommend the websites for the National Down Syndrome Society http://www.ndss.org/content.cfm?fuseaction=InfoRes.Generalarticle&article=30 and the National Association for Down Syndrome. http://www.nads.org/

There is, however, a wealth of information available on line about Down syndrome. For a fairly comprehensive list of Down syndrome resources on the Internet, check out this page of the site Down Syndrome dot com. http://www.downsyndrome.com/

More Information about Down Syndrome
Down Syndrome Information: What is Down Syndrome?
Down Syndrome Information: Diagnosis of Down Syndrome
Down Syndrome Information: Causes of Down Syndrome
Down Syndrome Information: Characteristics of Down Syndrome
Down Syndrome Information: What Special Care do People with Down Syndrome Need?
Down Syndrome Information: A Personal Account