Down syndrome is a genetic condition in which a person has 47 chromosomes instead of the usual 46.

In most cases, Down syndrome occurs when there is an extra copy of chromosome 21. This form of Down syndrome is called Trisomy 21. The extra chromosome causes problems with the way the body and brain develop.

Down syndrome is the most common single cause of human birth defects.

Down syndrome symptoms vary from person to person and can range from mild to severe. However, children with Down syndrome have a widely recognized characteristic appearance.

The head may be smaller than normal and abnormally shaped. For example, the head may be round with a flat area on the back. The inner corner of the eyes may be rounded instead of pointed.

Common physical signs include:

• Decreased muscle tone at birth
• Excessive skin at the nape of the neck
• Flattened nose
• Separated sutures (joints between the bones of the skull)
• Single crease in the palm of the hand
• Small ears
• Small mouth
• Upward slanting eyes
• Wide, short hands with short fingers
• White spots on the colored part of the eye (Brushfield spots)

Physical development is often slower than normal. Most children with Down syndrome never reach their average adult height. Children may also have delayed mental and social development. According to the National Institute of Child Health and Human Development, most persons with Down syndrome have mild to moderate mental retardation.

Many different medical conditions are seen in babies born with Down syndrome, including

• Birth defects involving the heart such as an atrial septal defect or ventricular septal defect
• Eye problems such as cataracts
• Gastrointestinal blockages such as esophageal atresia and duodenal atresia
• Hearing problems
• Hip dislocation
• Sleep apnea
• Underactive thyroid (hypothyroidism)

Children with Down syndrome also have a higher risk for acute lymphocytic leukemia.

A doctor can often make an initial diagnosis of Down syndrome at birth based on how the baby looks. The doctor may hear a heart murmur when listening to the chest with a stethoscope.

A blood test can be done to check for the extra chromosome and confirm the diagnosis. See: Chromosome studies

Other tests that may be done include:

• Echocardiogram
• ECG
• X-rays of the chest and gastrointestinal tract

Early and massive vomiting may be a sign of a gastrointestinal blockage. The blockage may also be discovered when a health care provider is unable to pass a tube from the nose into the stomach. See: Nasogastric or endotracheal intubation

There is no specific treatment for Down syndrome. A child born with a gastrointestinal blockage may need major surgery immediately after birth. Certain heart defects may also require surgery.

Special education and training is offered in most communities for children with delays in mental development. Speech therapy may help improve language skills. Physical therapy may be needed to teach movement skills.

Persons with Down syndrome need to be closely screened for eye problems, hearing loss, thyroid disease, and other medical conditions associated with the syndrome.

National Down Syndrome Society - www.ndss.org

National Down Syndrome Congress -- www.ndsccenter.org

Persons with Down syndrome are living longer than ever before. Many live independent and productive lives, well into adulthood.

About half of children with Down syndrome are born with heart problems, including atrial septal defect and ventricular septal defect. Heart problems may lead to early death.

Persons with Down syndrome have an increased risk for certain types of leukemia, which can also cause early death.

The level of mental retardation varies from patient to patient, but is usually moderate. Adults with Down syndrome have an increased risk for dementia.

• Airway blockage during sleep
• Compression injury of the spinal cord
• Eye problems
• Frequent ear infections and increased risk of other infections
• Hearing loss
• Heart problems
• Gastrointestinal blockage
• Weakness of the back bones at the top of the neck

A health care provider should be consulted to determine if the child needs special education and training. It is important for the child to have regular check ups with his or her doctor.

Experts recommend genetic counseling for persons with a family history of Down syndrome who wish to have a baby.

A woman's risk of having a child with Down syndrome increases as she gets older. The risk is significantly higher among women age 35 and older.

Couples who already have a baby with Down syndrome have an increased risk of having another baby with the condition.

Tests such as nuchal translucency ultrasound, amniocentesis, or chorionic villus sampling can be done on a fetus during the first few months of pregnancy to check for Down syndrome. The American College of Obstetricians and Gynecologists recommends offering Down syndrome screening tests to all pregnant women, regardless of age.

Ferri FF. Ferri’s Clinical Advisor 2007: Instant Diagnosis and Treatment. 9th ed. St. Louis, Mo: Mosby; 2007.

ACOG Committee on Practice Bulletins. ACOG Practice Bulletin No. 77: screening for fetal chromosomal abnormalities. Obstet Gynecol. 2007 Jan;109(1):217-27.

AAP Committee on Genetics. Health supervision for children with Down syndrome. Pediatrics. 2001 Feb;107(2):442-9.