Down Syndrome

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).

Color enhanced karyotype for a human female with Down syndrome. It is characterized by an extra copy of genetic material on the 21st chromosome. Karyotypes are an arrangement of chromosomes based on their appearance under a light microscope.

Color enhanced karyotype for a human female with Down syndrome. It is characterized by an extra copy of genetic material on the 21st chromosome. Karyotypes are an arrangement of chromosomes based on their appearance under a light microscope.
(© Biophoto Associates /Science Source Colorization by: Mary Martin)


This primary source contains a personal narrative published by WHO on the topic of life in the Russian Federation with Down syndrome.

Vlad Sanotsky is 29 years old. You might assume that a label of Down syndrome means limitation, but when he talks, you realize how rich life can be

My name is Vlad. I'm 29 years old, and I live with my mother. We go everywhere together. She doesn't allow me to go anywhere alone because she is afraid that someone will hurt or offend me. I play in a theatre and I am very good. I also like poetry and I know many poems by heart. I have music classes two times a week. I play the flute.

I am a champion swimmer – I have won many medals. But when I went to pre-school, the teacher told me I was too fast to be in her class. They couldn't catch me. In school in gym class they wouldn't let me play football. I mean the teacher and other kids. But I swam in competitions in Belgium, and the US - and won medals. When my mother and I were on vacation, and I was on the beach, other kids ignored me and laughed at me. Nobody wanted to talk to me. But after they saw me swimming, they started to say “hi” and talk to me. Unfortunately, I don't swim anymore, but I'd love to continue. I also like classical music and ballet.

SOURCE: “Personal Narratives: What's Disability to Me??” WHO.

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.



Hale, Natalie. Down Syndrome Parenting 101: Must-Have Advice for Making Your Life Easier. Bethesda, MD: Woodbine House, 2011.

Kumin, Libby. Early Communication Skills for Children with Down Syndrome: A Guide for Parents and Professionals. Bethesda, MD: Woodbine House, 2012.


Chen, Harold. “Down Syndrome.” Medscape Reference. (accessed July 24, 2015).

Mayo Clinic Staff. “Down Syndrome.” (accessed July 24, 2015).

National Down Syndrome Society. “Speech and Language Therapy for Children & Adolescents with Down Syndrome.”–Adolescents-withDown-Syndrome (accessed July 24, 2015).

National Library of Medicine. “Down Syndrome.” (accessed July 24, 2015).


March of Dimes Foundation, 1275 Mamaroneck Ave., White Plains, NY, 10605, (914) 997-4488, askus@, .

National Down Syndrome Society, 666 Broadway, 8th Fl., New York, NY, 10012, (800) 221-4602,, .

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,, .


The structures that carry genetic information. Chromosomes are located within every cell and are responsible for directing the development and functioning of all the cells in the body. The normal number is 46 (23 pairs).
Present at birth.
A term referring to a genetic condition, in which an individual's cells do not have the exact same composition of chromosomes. In individuals with Down syndrome some cells have a normal 46 chromosomes, and other cells have an abnormal 47 chromosomes.
A genetic term referring to a situation during cell division in which a piece of one chromosome breaks off and sticks to another chromosome.
The condition of having three identical chromosomes instead of the normal two.