A chromosomal disorder caused by an error in cell division that results in an extra 21st chromosome.

Down syndrome occurs because of an abnormality characterized by an extra copy of genetic material on all or part of the 21st chromosome. Every cell in the body contains genes that are grouped along chromosomes in the cell's nucleus or center. There are normally 46 chromosomes in each cell, 23 inherited from your mother and 23 from your father. When some or all of a person's cells have an extra full or partial copy of chromosome 21, the result is Down syndrome.

Physical characteristics include: Eyes that have an upward slant, oblique fissures, epicanthic skin folds on the inner corner, and white spots on the iris Low muscle tone Small stature and short neck Flat nasal bridge Single, deep creases across the center of the palm Protruding tongue Large space between large and second toe A single flexion furrow of the fifth finger

Screening tests are used to estimate the risk that a fetus has Down syndrome, and diagnostic tests can tell whether the fetus actually has the condition. However, unlike diagnostic tests, screening tests cannot give definite answers as to whether the baby has Down syndrome. Diagnostic tests, which are 99% accurate in detecting Down syndrome and other problems, are usually performed inside the uterus and carry an extra risk of miscarriage, fetal injury, or preterm labor.

Nuchal translucency testing (at 11 to 14 weeks) - an ultrasound that measures clear space in folds of tissue behind the neck of a developing baby

Triple screen or quadruple screen (at 15 to 18 weeks) - measures the quantities of normal substances in the mother's blood

Integrated screen - combines first trimester screening tests (with or without nuchal translucency) and blood tests with second trimester quadruple screen

Genetic ultrasound (at 18 to 20 weeks) - Detailed ultrasound combined with blood test results

Chorionic villus sampling (at 8 to 12 weeks) - analysis of a tiny sample of placenta obtained from a needle inserted into the cervix or the abdomen

Amniocentesis (at 15 to 20 weeks) - analysis of a small amount of amniotic fluid obtained from a needle inserted into the abdomen

Percutaneous umbilical blood sampling (after 20 weeks) - analysis of a small sample of blood from the umbilical cord obtained from a needle inserted into the abdomen

It is very important to stimulate, encourage, and educate children with Down syndrome from infancy. Programs for young children with special needs are offered in many communities. Early intervention programs, including physical therapy, occupational therapy, and speech therapy can be very helpful.

Like all children, children with Down syndrome greatly benefit from being able to learn and explore in a safe and supportive environment. Being included in family, community, and preschool life will help a child with Down syndrome develop to his or her full potential.

While social development and social learning are often quite good, development in other areas such as motor skills, speech, and language are usually delayed. Many children with Down syndrome eventually reach most developmental milestones, but mild to severe learning difficulties will persist throughout life.

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kidshealth.org/parent/medical/genetic/down_syndrome.html

http://www.nlm.nih.gov/medlineplus/downsyndrome.html