Down Syndrome Information: What is Down Syndrome?

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 Mongolism, and later Down’s syndrome, the name 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.

The name “Down” comes from the surname of the first person to publish a paper about the syndrome, Dr. John Langdon Down. Dr. Down worked with children with mental retardation at the Earlswook Asylum in Surry, England. In his paper, published in 1866, he noted that several of the children he worked with had commonalities in their physical and behavioral characteristics. It was due to Dr. Down’s contention that the children he described were similar in appearance to people of the Mongolian race that the terms “Mongolism” and “Mongoloid” were applied to people with Down syndrome.

There are three different types of Down syndrome. Depending on the nature of the chromosomal anomaly that occurs either during or shortly after conception, people with Down syndrome will fall into one of these three subsets of the condition: non-disjunction, mosaicism, and translocation. These terms refer to the manner in which the extra copy of chromosome 21 occurs. Approximately 95% of people with Down syndrome have Down syndrome due to non-disjunction, which is also called Trisomy 21. Because of the overwhelming prevalence of non-disjunction as the cause, Down syndrome as a whole is often referred to as Trisomy 21, even though the term is inaccurate in approximately 5% of all cases.

For more specific information about Down syndrome, please see the articles below.

More Information about 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: Frequently Asked Questions
Down Syndrome Information: A Personal Account