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 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
• Excess skin at the nape of the neck
• Flattened nose
• Separated joints between the bones of the skull (sutures)
• 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. Common problems may include:

• Impulsive behavior
• Poor judgment
• Short attention span
• Slow learning

As children with Down syndrome grow and become aware of their limitations, they may also feel frustration and anger.

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
• Dementia, Alzheimer's type may be seen
• Eye problems, such as cataracts (most children with Down syndrome need glasses)
• Early and massive vomiting, which may be a sign of a gastrointestinal blockage, such as esophageal atresia and duodenal atresia
• Hearing problems, probably caused by regular ear infections
• Hip problems and risk of dislocation
• Long-term (chronic) constipation problems
• Sleep apnea (because the mouth, throat, and airway are narrowed in children with Down syndrome)
• Teeth that appear later than normal and in a location that may cause problems with chewing
• Underactive thyroid (hypothyroidism)

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 baby's 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 to check for heart defects (usually done soon after birth)
• ECG
• X-rays of the chest and gastrointestinal tract

Persons with Down syndrome need to be closely screened for certain medical conditions. They should have:

• Eye exam every year during infancy
• Hearing tests every 6 - 12 months, depending on age
• Dental exams every 6 months
• X-rays of the upper or cervical spine between ages 3 - 5 years
• Pap smears and pelvic exams beginning during puberty or by age 21

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.

When breast-feeding, the baby should be well supported and fully awake. The baby may have some leakage because of poor tongue control. However, many infants with Down syndrome can successfully breast-feed.

Obesity can become a problem for older children and adults. Getting plenty of activity and avoiding high-calorie foods are important. Before beginning sports activities, the child's neck and hips should be examined.

Behavioral training can help people with Down syndrome and their families deal with the frustration, anger, and compulsive behavior that often occur. Parents and caregivers should learn to help a person with Down syndrome deal with frustration. At the same time, it is important to encourage independence.

Adolescent females and women with Down syndrome are usually able to get pregnant. There is an increased risk of sexual abuse and other types of abuse in both males and females. It is important for those with Down syndrome to:

• Be taught about pregnancy and taking the proper precautions
• Learn to advocate for themselves in difficult situations
• Be in a safe environment

If the person has any heart defects or problems, check with the physician about the need for antibiotics to prevent heart infections called endocarditis.

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 teach movement skills. Occupational therapy may help with feeding and performing tasks. Mental health care can help both parents and the child manage mood or behavior problems. Special educators are also often needed.

National Down Syndrome Society - www.ndss.org

National Down Syndrome Congress -- www.ndsccenter.org

Persons with Down syndrome are living longer than ever before. Although many children have physical and mental limitations, they can 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
• Endocarditis
• 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.

ACOG Committee on Practice Bulletins. ACOG Practice Bulletin No. 77: screening for fetal chromosomal abnormalities. Obstet Gynecol. 2007 Jan;109(1):217-227.

AAP Committee on Genetics. Health supervision for children with Down syndrome. Pediatrics. 2001 Feb;107(2):442-449.

Davidson MA. Primary care for children and adolescents with Down syndrome. Pediatr Clin North Am. 2008;55:1099-1111.