What is Down Syndrome?
Down syndrome (sometimes called Down’s syndrome) is a condition in which a child is born with an extra copy of their 21st chromosome — hence its other name, trisomy 21. This causes physical and mental developmental delays and disabilities.
Many of the disabilities are lifelong, and they can also shorten life expectancy. However, people with Down syndrome can live healthy and fulfilling lives. Recent medical advances, as well as cultural and institutional support for people with Down syndrome and their families, provides many opportunities to help overcome the challenges of this condition.
Types of Down syndrome
There are three types of Down syndrome:
Trisomy 21 means there’s an extra copy of chromosome 21 in every cell. This is the most common form of Down syndrome.
Mosaicism occurs when a child is born with an extra chromosome in some but not all of their cells. People with mosaic Down syndrome tend to have fewer symptoms than those with trisomy 21.
In this type of Down syndrome, children have only an extra part of chromosome 21. There are 46 total chromosomes. However, one of them has an extra piece of chromosome 21 attached.
What causes Down syndrome?
Human cells normally contain 23 pairs of chromosomes. One chromosome in each pair comes from your father, the other from your mother.
Down syndrome results when abnormal cell division involving chromosome 21 occurs. These cell division abnormalities result in an extra partial or full chromosome 21. This extra genetic material is responsible for the characteristic features and developmental problems of Down syndrome. Any one of three genetic variations can cause Down syndrome:
- Trisomy 21. About 95 percent of the time, Down syndrome is caused by trisomy 21 — the person has three copies of chromosome 21, instead of the usual two copies, in all cells. This is caused by abnormal cell division during the development of the sperm cell or the egg cell.
- Mosaic Down syndrome. In this rare form of Down syndrome, a person has only some cells with an extra copy of chromosome 21. This mosaic of normal and abnormal cells is caused by abnormal cell division after fertilization.
- Translocation Down syndrome. Down syndrome can also occur when a portion of chromosome 21 becomes attached (translocated) onto another chromosome, before or at conception. These children have the usual two copies of chromosome 21, but they also have additional genetic material from chromosome 21 attached to another chromosome.
There are no known behavioral or environmental factors that cause Down syndrome.
Is it inherited?
Most of the time, Down syndrome isn’t inherited. It’s caused by a mistake in cell division during early development of the fetus.
Translocation Down syndrome can be passed from parent to child. However, only about 3 to 4 percent of children with Down syndrome have translocation and only some of them inherited it from one of their parents.
When balanced translocations are inherited, the mother or father has some rearranged genetic material from chromosome 21 on another chromosome, but no extra genetic material. This means he or she has no signs or symptoms of Down syndrome, but can pass an unbalanced translocation on to children, causing Down syndrome in the children.
What are the symptoms of Down syndrome?
Though the likelihood of carrying a baby with Down syndrome can be estimated by screening during pregnancy, you won’t experience any symptoms of carrying a child with Down syndrome.
At birth, babies with Down syndrome usually have certain characteristic signs, including:
- flat facial features
- small head and ears
- short neck
- bulging tongue
- eyes that slant upward
- atypically shaped ears
- poor muscle tone
An infant with Down syndrome can be born an average size, but will develop more slowly than a child without the condition.
People with Down syndrome usually have some degree of developmental disability, but it’s often mild to moderate. Mental and social development delays may mean that the child could have:
- impulsive behavior
- poor judgment
- short attention span
- slow learning capabilities
Medical complications often accompany Down syndrome. These may include:
- congenital heart defects
- hearing loss
- poor vision
- cataracts (clouded eyes)
- hip problems, such as dislocations
- chronic constipation
- sleep apnea (interrupted breathing during sleep)
- dementia (thought and memory problems)
- hypothyroidism (low thyroid function)
- late tooth growth, causing problems with chewing
- Alzheimer’s disease later in life
People with Down syndrome are also more prone to infection. They may struggle with respiratory infections, urinary tract infections, and skin infections.
Screening for Down syndrome during pregnancy
Screening for Down syndrome is offered as a routine part of prenatal care in the United States. If you’re a woman over 35, your baby’s father is over 40, or there’s a family history of Down syndrome, you may want to get an evaluation.
An ultrasound evaluation and blood tests can look for Down syndrome in your fetus. These tests have a higher false-positive rate than tests done at later pregnancy stages. If results aren’t normal, your doctor may follow up with an amniocentesis after your 15th week of pregnancy.
An ultrasound and quadruple marker screen (QMS) test can help identify Down syndrome and other defects in the brain and spinal cord. This test is done between 15 and 20 weeks of pregnancy.
If any of these tests aren’t normal, you’ll be considered at high risk for birth defects.
Additional prenatal tests
Your doctor may order additional tests to detect Down syndrome in your baby. These may include:
- Amniocentesis. Your doctor takes a sample of amniotic fluid to examine the number of chromosomes your baby has. The test is usually done after 15 weeks.
- Chorionic villus sampling (CVS). Your doctor will take cells from your placenta to analyze fetal chromosomes. This test is done between the 9th and 14th week of pregnancy. It can increase your risk of a miscarriage, but according to the Mayo Clinic, only by less than 1 percent.
- Percutaneous umbilical blood sampling (PUBS, or cordocentesis). Your doctor will take blood from the umbilical cord and examine it for chromosomal defects. It’s done after the 18th week of pregnancy. It has a higher risk of miscarriage, so it’s performed only if all other tests are uncertain.
Some women choose not to undergo these tests because of the risk of miscarriage. They’d rather have a child with Down syndrome than lose the pregnancy.
Tests at birth
At birth, your doctor will:
- perform a physical examination of your baby
- order a blood test called a karyotype to confirm Down syndrome
Does Down Syndrome Run in Families?
All 3 types of Down syndrome are genetic conditions (relating to the genes), but only 1% of all cases of Down syndrome have a hereditary component (passed from parent to child through the genes). Heredity is not a factor in trisomy 21 (nondisjunction) and mosaicism. However, in one-third of cases of Down syndrome resulting from translocation there is a hereditary component – accounting for about 1% of all cases of Down syndrome.
The age of the mother does not seem to be linked to the risk of translocation. Most cases are sporadic – chance – events. However, in about one-third of cases, one parent is a carrier of a translocated chromosome.
What Is the Likelihood of Having a Second Child with Down Syndrome?
Once a woman has given birth to a baby with trisomy 21 (nondisjunction) or translocation, it is estimated that her chances of having another baby with trisomy 21 is 1 in 100 up until age 40.
Life spans have increased dramatically for people with Down syndrome. Today, someone with Down syndrome can expect to live more than 60 years, depending on the severity of health problems.
There’s no way to prevent Down syndrome. If you’re at high risk of having a child with Down syndrome or you already have one child with Down syndrome, you may want to consult a genetic counselor before becoming pregnant.
A genetic counselor can help you understand your chances of having a child with Down syndrome. He or she can also explain the prenatal tests that are available and help explain the pros and cons of testing.
People with a higher chance of having a child with Down syndrome might receive screening and diagnostic tests.
Screening tests can estimate the probability of Down syndrome being present. Some diagnostic tests can definitively tell whether a baby will have the condition.
Women aged 30–35 years or above might receive genetic screening during pregnancy. This is because the chance of having a child with Down syndrome increases as women age.
Screening tests include:
- Nuchal translucency testing: At 11–14 weeks, an ultrasound can measure the clear space in folds of tissue behind the neck of a developing fetus.
- Triple screen or quadruple screen: At 15–18 weeks, this measures the quantities of various substances in the mother’s blood.
- Integrated screen: This combines results from first-trimester blood and screening tests, with or without nuchal translucency, with second-trimester quadruple screening results.
- Cell-free DNA: This is a blood test that analyzes fetal DNA present in the mother’s blood.
- Genetic ultrasound: At 18–20 weeks, doctors combine a detailed ultrasound with blood test results.
Screening is a cost-effective and less invasive way to determine whether more invasive diagnostic tests are needed.
However, unlike diagnostic tests, they cannot confirm whether Down syndrome is present.
Diagnostic tests are more accurate for detecting Down syndrome. A healthcare professional will usually perform such tests inside the uterus.
However, they increase the risk of miscarriage, fetal injury, and preterm labor.
Diagnostic tests include:
- Chorionic villus sampling: At 8–12 weeks, a doctor might obtain a tiny sample of placenta for analysis, using a needle inserted into the cervix or the abdomen.
- Amniocentesis: At 15–20 weeks, they may obtain a small amount of amniotic fluid for analysis, using a needle inserted into the abdomen.
- Percutaneous umbilical blood sampling: After 20 weeks, the doctor may take a small sample of blood from the umbilical cord for analysis, using a needle inserted into the abdomen.
A healthcare professional can also diagnose Down syndrome after a baby is born by inspecting their physical characteristics, blood, and tissue.
There is no specific treatment for Down syndrome. People who have the condition will receive care for any health problems, as other people do.
However, healthcare professionals may recommend additional health screening for issues common to the condition.
Early intervention can help a person maximize their potential and prepare them to take up an active role in the community.
Physicians, special educators, speech therapists, occupational therapists, and physical therapists, as well as social workers, can all help. The National Institute for Child Health and Human Development urge all specialists to provide stimulation and encouragement.
Children with specific learning and development difficulties may be eligible for educational support, either in a mainstream or specialized school.
In recent years, the tendency has been to attend mainstream schools, often with additional support to help them integrate and progress.
Some children will make use of an Individualized Education Program (IEP), which various specialists will support.
A person with Down syndrome can do many of the things that other people do. Children may take longer to acquire skills such as walking and talking, but with stimulation, they can acquire key life skills and attend school and, in some cases, college.
Depending on how the condition affects a person, it is often possible for someone to work and to live semi-independently with Down syndrome.
People with Down syndrome need friendships and relationships. Some will live with a partner or get married, and they will have an independent life.
It is worth noting that if one partner has Down syndrome, there is a 35–50 percent chance that their children will, too.
Average life expectancy is around 60 years, but many people with Down syndrome now live into their 70s.
Frequently Asked Questions About Down Syndrome
What is Down syndrome?
Down syndrome occurs when an individual has three, rather than two, copies of the 21st chromosome. This additional genetic material alters the course of development and causes the characteristics associated with Down syndrome.
Who gets Down syndrome?
- Down syndrome is the most commonly occurring chromosomal condition. One in every 733 babies is born with Down syndrome.
- There are more than 400,000 people living with Down syndrome in the United States.
- Down syndrome occurs in people of all races and economic levels.
- The incidence of births of children with Down syndrome increases with the age of the mother. But due to higher fertility rates in younger women, 80 percent of children with Down syndrome are born to women under 35 years of age.
How does Down syndrome affect your health?
- People with Down syndrome have an increased risk for certain medical conditions such as congenital heart defects, respiratory and hearing problems, Alzheimer’s disease, childhood leukemia, and thyroid conditions. Many of these conditions are now treatable, so most people with Down syndrome lead healthy lives.
- A few of the common physical traits of Down syndrome are low muscle tone, small stature, an upward slant to the eyes, and a single deep crease across the center of the palm. Every person with Down syndrome is a unique individual and may possess these characteristics to different degrees or not at all.
- Life expectancy for people with Down syndrome has increased dramatically in recent decades – from 25 in 1983 to 60 today.
What is it like to live with Down syndrome?
- People with Down syndrome attend school, work, participate in decisions that affect them, and contribute to society in many wonderful ways.
- All people with Down syndrome experience cognitive delays, but the effect is usually mild to moderate and is not indicative of the many strengths and talents that each individual possesses.
- Quality educational programs, a stimulating home environment, good health care, and positive support from family, friends and the community enable people with Down syndrome to develop their full potential and lead fulfilling lives.
- Researchers are making great strides in identifying the genes on Chromosome 21 that cause the characteristics of Down syndrome. Many feel strongly that it will be possible to improve, correct or prevent many of the problems associated with Down syndrome in the future.
Did I do anything wrong to cause my baby to be born with Down syndrome?
Nothing you did or thought caused your child to have Down syndrome. All individuals who have Down syndrome were born with extra chromosome material in their cells. This is a result of an error in cell division, in either the egg or sperm, prior to conception or very soon afterward. At this time it is not known why the extra genetic material causes Down syndrome.
Do I need a “special” pediatrician to care for my child with Down syndrome?
Your pediatrician for routine care does not need to be a “Down syndrome specialist”. It is more important for you to choose a doctor you are comfortable with and who is willing to learn with you. American Academy of Pediatricians site for Down syndrome.
What should I be doing to help my baby?
Soon after birth, early intervention specialists from Babies Can’t Wait, including physical, occupational, and speech therapists, will guide you in how to promote your baby’s progress. Make an appointment at the Emory Down Syndrome Clinic and talk to the multi-disciplinary staff there. Talk to other parents who live near you. They are often the best source of information for people and programs that can help maximize your child’s potential.
How do I explain Down syndrome to my other children?
We recommend a terrific book, We’ll Paint the Octopus Red, by Stephanie Stuve-Bodeen for preschool and early elementary aged children. The story is easy to understand and there is a question and answer section in the back that addresses many concerns that a young child may have. There are often sibling workshops offered for older brothers and sisters. The NDSC national convention each year includes a sibling track.
Are there special programs for children with Down syndrome?
There are programs available for people with Down syndrome in all stages of development. These include early intervention (Babies Can’t Wait, which starts at birth), preschool programs, free appropriate public education in the least restrictive environment, therapy, post-secondary school options, employment training, and a wide array of social and support programs.
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