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Down syndrome is a common genetic disorder. It occurs in 1 out of 700-800 live births. Down syndrome causes birth defects, medical problems, and some degree of intellectual disability.

In fact, down syndrome is the most common genetic cause of mild to moderate intellectual disabilities.

Chromosomes contain the genetic makeup of your body. They occur in 23 pairs within the body. Down syndrome is a problem with chromosome pair 21. There is extra genetic material on the chromosome that may be caused by:

• An extra chromosome—This type is called Trisomy 21. This results from an error in cell division in the egg or sperm.
• Extra chromosomes in some cells—Called Mosaic Trisomy 21.
• Part of the chromosome has broken off and reattached to another chromosome—Called translocation trisomy. In about one third of individuals, the translocation is inherited from a parent.

Factors that increase the chance for Down syndrome include:

• Genetics: If either parent is a carrier of Translocation Down syndrome, there is an increased risk.
• Age: The chance of having a child with Down syndrome increases after a woman reaches age 35.
• Sex: More boys than girls are born with Down syndrome.
• History of a previous child with Down syndrome.

Infants born with Down syndrome may have some or all of the following physical features:

• Muscle hypotonia, low muscle tone
• Flat facial features, a somewhat depressed nasal bridge and a small nose
• Upward slanted eyes, small skin folds on the inner corner of the eyes
• Short neck
• Misshaped ears
• White spots on the colored part of the eye
• Single skin crease in the palm of the hand
• Excess flexibility in joints
• Heart defects
• Sight and hearing problems
• Large and protruding tongue
• Fifth finger has one flexion furrow instead of two
• Excessive space between large and second toe

The degree of medical problems and intellectual disability is different for each person. Talents, abilities, and pace of development will be different too. People with Down syndrome may be born with or develop:

• Vision problems
• Hearing loss
• Heart defects
• Increased incidence of acute leukemia
• Frequent ear infections and increased susceptibility to infection in general
• Gastrointestinal obstruction (imperforate anus and similar problems)
• Esophageal atresia or duodenal atresia
• Sleep problems (eg, blocked airways during sleep, daytime sleepiness, sleep anxiety, sleep walking)
• Increased incidence of dementia in older ages
• Instability of the back bones at the top of the neck, can result in compression injury of the spinal cord
• Urinary system defects
• High blood pressure in the lungs
• Seizures
• An under-active thyroid (hypothyroidism)
• Slow growth
• Late to sit, walk, toilet train
• Speech problems
• Obesity
• Emotional problems

Most of these health problems are treatable. The majority of people born with Down syndrome today have a life expectancy of about 55 years.

Doctors can usually identify a child born with Down syndrome at birth. When Down syndrome is suspected, a blood test will be done to confirm it.

Down syndrome may also be diagnosed before birth. There are screening tests and diagnostic tests to help identify chormosome abnormalities before birth.

Diagnostic Tests

Diagnostic tests will tell if the fetus actually has Down syndrome. These tests include:

• Chorionic villus sampling (CVS)—Usually done between 10 and 12 weeks
• Amniocentesis—Usually done between 12 and 20 weeks of gestation
• Percutaneous umbilical blood sampling (PUBS)—Usually done after 20 weeks

These tests are about 98%-99% accurate. Each test requires that a small piece of tissue be removed from the placenta or umbilical cord. This creates a small risk of miscarriage with these tests.

Amniocentesis

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There is no cure for Down syndrome.

Treatment may be needed for severe problems or to help with developmental delays. Living at home and receiving special therapy helps children with Down syndrome achieve their full potential. Most people with the condition can actively participate in the community. This includes activities at schools, jobs, and various leisure activities. Some people with Down syndrome live with family, some live with friends, and some live independently.

There are no guidelines for preventing Down syndrome. If you have concerns about having a child with Down syndrome, consider getting genetic counseling before becoming pregnant.