Down syndrome is a broad-spectrum developmental disorder present at birth resulting from an abnormality in the number of inherited chromosomes.
Down syndrome, also known trisomy 21, was named after John Langdon Haydon Down, who first described the condition in 1866. In 1959, the French pediatrician Jerome Lejeune (1926–1994) discovered that the disorder is caused by a chromosomal abnormality. Ninety-five percent of individuals with Down syndrome have an extra chromosome in the twentyfirst pair (trisomy 21), giving them 47 chromosomes instead of the normal 46. Four percent of individuals with Down syndrome have translocation, a chromosomal abnormality where material from chromosome 21 breaks off and ends up attached to a different chromosome. About 1% of Down syndrome results from mosaicism, a condition in which the individual has both normal cells and cells with trisomy 21.
As a woman's age at time of conception increases, the risk of having an infant with Down syndrome increases significantly. For example, at younger ages, the risk is about one in 4,000. By the time a woman is age 35, the risk increases to one in 385; by age 40, the risk increases to one in 106; and by age 45, the risk becomes one in 30. Prenatal detection of Down syndrome is possible through amniocentesis and chorionic villus sampling.
Down syndrome is characterized by varying degrees of mental and motor retardation and distinct physical characteristics. Most people with the disorder are moderately to severely mentally handicapped. Individuals with Down syndrome have IQs ranging from 20–90, with the mean being 49. (An IQ of 100 is considered average.)
In addition to cognitive deficiencies, other types of defects often accompany Down syndrome. Between 40% and 50% of all children with Down syndrome have congenital heart defects. Malformations of the gastrointestinal tract are present in about 12% of children. Other medical conditions that occur in individuals with Down syndrome include an increased chance of developing infections, especially ear infections and pneumonia; seizures; certain kidney disorders; thyroid disease (especially low or hypothyroidism); hearing loss; vision impairment requiring glasses (corrective lenses); and a 20-times greater chance of developing leukemia (a blood cancer).
People with Down syndrome are widely perceived as having pleasant temperaments; they are generally cheerful, cooperative, affectionate, and relaxed. Their motor, speech, and sexual development are delayed, and their cognitive development may not peak until the age of 30 or 40. Good medical care, speech therapy, occupational therapy, and individualized learning can help individuals with this condition reach their full potential.
People with Down syndrome are capable of expressing complex feelings, developing richer personalities, and mastering higher degrees of learning using adaptive strategies such as computer-aided learning to teach reading and writing. Until the 1970s, Down syndrome children were often placed in institutions for lifelong care. Today, research shows that the best outlook for children with Down syndrome is a normal family life in their own home. This approach, however, requires careful support and education of the parents and siblings. Some community groups exist to help families deal with the emotional effects of the birth of a Down syndrome baby and to help plan for the infant's future. In the United States, schools are required to provide services for children with Down syndrome, sometimes in separate special education classrooms and sometimes in regular classrooms.Parents of children with Down syndrome may qualify for government-sponsored health care and supplemental security income (SSI). Many adults with mild to moderate Down syndrome are employable in jobs where tasks are regular and routine.
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March of Dimes Foundation, 1275 Mamaroneck Ave., White Plains, NY, 10605, (914) 997-4488, askus@ marchofdimes.com, http://www.marchofdimes.com .
National Down Syndrome Society, 666 Broadway, 8th Fl., New York, NY, 10012, (800) 221-4602, firstname.lastname@example.org, http://www.ndss.org .
The Arc—For People with Intellectual and Developmental Disabilities, 1825 K St. NW, Ste. 1200, Washington, DC, 20006, (202) 534-3700, (800) 433-5255, Fax: (202) 534-3731, email@example.com, www.thearc.org .