What is Down syndrome?

Down syndrome is a set of physical and mental traits caused by a gene problem that happens before birth. Children with Down syndrome tend to have certain features, such as a flat face and a short neck. They also have some degree of mental retardation. This varies from person to person, but in most cases it is mild to moderate.

Down syndrome is a lifelong condition. But with care and support, most children with Down syndrome can grow up to have healthy, happy, productive lives.

What causes Down syndrome?

Down syndrome is caused by problem with a baby’s chromosomes that happens long before the baby is born. Chromosomes are the part of your cells that contain your genetic material, or DNA. Normally, a baby has 46 chromosomes. But most people with Down syndrome have 47 chromosomes. In rare cases, other chromosome problems cause Down syndrome. Having extra or abnormal chromosomes changes the way the brain and body develop.

Experts don't really know what causes the chromosome problem. But some things are known to increase the chance that a baby will have Down syndrome. These things are called risk factors. They include having a:

• Mother who is over 35. The older the mother is, the higher her baby’s risk of Down syndrome. (But most babies with Down syndrome are born to mothers younger than 35, because younger women as a group have more babies than older women do.)
• Father who is over 40.
• Brother or sister with Down syndrome.

What are the symptoms?

Most children with Down syndrome have:

• Distinct facial features, such as a flat face, small ears, slanting eyes, and a small mouth.
• A short neck and short arms and legs.
• Weak muscles and loose joints. Muscle tone usually improves by late childhood.
• Below-average intelligence.

Many children with Down syndrome are also born with heart, intestine, ear, or breathing problems. These health conditions often lead to other problems, such as airway (respiratory) infections or hearing loss. Luckily, most of these problems can be treated.

How is Down syndrome diagnosed?

Your doctor may suggest that you have tests during pregnancy to find out if your baby has Down syndrome. A screening test can help show if the baby (fetus) is at risk for Down syndrome. But these tests sometimes give false-positive results, meaning they show a problem when there is none.

Screening tests include:

• A blood test and a fetal ultrasound late in the first trimester. The ultrasound looks for thickness in the back of the baby’s neck (nuchal fold), which can be a sign of Down syndrome. This kind of ultrasound is not available in many areas.
• A blood test called a maternal serum triple screen or quadruple screen in the second trimester. By measuring substances in your blood, these tests can estimate the chance that your baby has Down syndrome or other health problems.