The Parent’s Guide to Down Syndrome
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What is Down syndrome?
Down syndrome is a genetic disorder caused when abnormal cell division results in an extra full or partial copy of chromosome 21. This additional genetic material causes the development changes and physical characteristics of Down syndrome. This extra copy of genetic material changes how the baby’s body and brain develop. So the effects of this additional genetic material can cause both physical and mental challenges for the baby.
The severity of down syndrome varies among individuals, causing lifelong intellectual disability and development delays. Down syndrome is the most common genetic disorder, and it can cause learning disabilities in children. Each year, about 6,000 babies born in the United States have Down syndrome, which means 1 in 600 babies. Down syndrome also can cause several other medical conditions, including heart and gastrointestinal disorders. Even though people with down syndrome might act and look very similar, each person has different abilities. People with down syndrome usually have an IQ in the mid to moderately low range and speak slower than other children.
Some common physical features of people with down syndrome are:
- A flattened face, especially the bridge of the nose
- Almond-shaped eyes that slant up
- A short neck
- Small ears
- A tongue that tends to stick out of the mouth
- Tiny white spots on the iris (coloured part) of the eye
- Small hands and feet
- A single line across the palm of the hand (palmar crease)
- Small pinky fingers that sometimes curve toward the thumb
- Poor muscle tone or loose joints
- Shorter in height as children and adults
What it's like to have Down's syndrome
People with Down’s syndrome will have some level of learning disability. This means they’ll have a range of abilities.
Some people will be more independent and do things like getting a job. Other people might need more regular care.
But, like everyone, people with Down’s syndrome have:
- their personalities
- things they like and dislike
- things that make them who they are
Having a baby with Down's syndrome
In almost all cases, Down’s syndrome does not run in families. Your chance of having a baby with Down’s syndrome increases as you get older, but anyone can have a baby with Down’s syndrome. Speak to a physician if you want to find out more. They may be able to refer you to a genetic counsellor.
If you’re pregnant, you’ll probably be offered a screening test to determine your chance of having a baby with Down’s syndrome. You can have the test at your dating scan (around 11 to 14 weeks). If you have a higher chance, you can have further tests.
Babies with Down’s syndrome are like any newborn babies. They’ll be eating, sleeping, crying, and needing love and cuddles just like all babies. Some babies with Down’s syndrome might need extra help. This could be with things like feeding.
What life will be like
No one can tell you what life will be like for your child. This is the same for children who do not have Down’s syndrome. Children with Down’s syndrome will have some level of learning disability – it’s not possible to know how this will affect them.
Like any child, they’ll:
- have their own personality
- learn at their own pace
- have things that are important and unique to them
Try not to think too far ahead and enjoy time with your baby.
What is a chromosome, and what is the role of chromosome 21?
Chromosomes are responsible for facilitating the proper cell division and replication. The primary function of the chromosomes is to fit the DNA inside the nucleus. Chromosomes also help in inheriting genes or DNA from parents to their offsprings. Furthermore, sex chromosomes decide the sex of the embryo. They also protect genes, protect DNA from damage, help in regulating gene expression, store and transfer genetic information.
Humans normally have 46 chromosomes in each cell, divided into 23 pairs of chromosomes. Two copies of chromosome 21, one copy inherited from each parent, form one of the pairs. Chromosome 21 is the smallest one of all human chromosomes, spanning about 48 million base pairs (the building blocks of DNA), representing 1.5 to 2 per cent of the total DNA in cells. The genome of chromosome 21 fully sequenced in 2000 as a result of the studies of the “Human Genome Project”.
There are several conditions associated with changes in the structure or number of copies of chromosome 21. Some of these changes are; Down syndrome, acute myeloid leukaemia, other chromosomal conditions like intellectual disability, delayed development, characteristic facial features and some different types of cancer.
Types of Down Syndrome
There are three types of Down syndrome. All three types’ physical and behavioural features are very similar, so it is usually impossible to tell the difference between them without analysing the chromosomes.
- Trisomy 21: About 95% of people with Down syndrome have Trisomy 21. With this type of Down syndrome, each cell in the body has three separate copies of chromosome 21 instead of the usual two copies.
- Translocation Down syndrome: This type accounts for a small percentage of people with Down syndrome (about 3%). This occurs when an extra part or a whole extra chromosome 21 is present, but it is attached or “trans-located” to a different chromosome rather than a separate chromosome 21.
- Mosaic Down syndrome: This type affects about 2% of people with Down syndrome. Mosaic means mixture or combination. For children with mosaic Down syndrome, some of their cells have three copies of chromosome 21, but other cells have the typical two copies of chromosome 21. Children with mosaic Down syndrome may have the same features as other children with Down syndrome. However, they may have fewer features of the condition due to some (or many) cells with a typical number of chromosomes.
Symptoms of Down Syndrome
Children and adults with Down syndrome have distinct facial features. Though not all people with Down syndrome have the same features, some of the more common features include:
- Flattened face
- Small head
- Short neck
- Protruding tongue
- Upward slanting eyelids (palpebral fissures)
- Unusually shaped or small ears
- Poor muscle tone
- Broad, short hands with a single crease in the palm
- Relatively short fingers and small hands and feet
- Excessive flexibility
- Tiny white spots on the coloured part (iris) of the eye called Brushfield’s spots.
- Short height
What Causes Down Syndrome?
The extra chromosome 21 leads to physical features and developmental challenges among people with Down syndrome. Researchers know that an extra chromosome causes down syndrome, but no one knows why Down syndrome occurs or how many different factors play a role.
One factor that increases the risk of having a baby with Down syndrome is the mother’s age. Women who are 35 years or older when they become pregnant are more likely to have a pregnancy affected by Down syndrome than women who become pregnant at a younger age. However, most babies with Down syndrome are born to mothers less than 35 years old because there are many more births among younger women.
Most of the time, Down syndrome isn’t inherited. It’s caused by a mistake in cell division during the early development of the fetus.
Translocation Down syndrome can be passed from parent to child. However, only about 3 to 4 per cent of children with Down syndrome have translocation, and only some of them inherited it from one of their parents.
What are the risk factors?
Some parents have a greater risk of having a baby with Down syndrome. Risk factors include:
- Advancing maternal age. A woman’s chances of giving birth to a child with Down syndrome increase with age because older eggs have a greater risk of improper chromosome division. A woman’s risk of conceiving a child with Down syndrome increases after 35 years of age. However, most children with Down syndrome are born to women under age 35 because younger women have far more babies.
- Being carriers of the genetic translocation for Down syndrome. Both men and women can pass the genetic translocation for Down syndrome on to their children.
- Having had one child with Down syndrome. Parents who have one child with Down syndrome and parents who have a translocation themselves are at an increased risk of having another child with Down syndrome. A genetic counsellor can help parents assess the risk of having a second child with Down syndrome.
There are two basic types of tests available to detect Down syndrome during pregnancy: screening tests and diagnostic tests. A screening test can tell a woman and her healthcare provider whether her pregnancy has a lower or higher chance of having Down syndrome. Screening tests do not provide a definitive diagnosis, but they are safer for the mother and the developing baby. Diagnostic tests can typically detect whether or not a baby will have Down syndrome, but they can be riskier for the mother and developing baby. Neither screening nor diagnostic tests can predict the full impact of Down syndrome on a baby; no one can predict this.
People with Down syndrome can have various complications, some of which become more prominent as they get older. These complications can include:
- Heart defects. About half the children with Down syndrome are born with some type of congenital heart defect. These heart problems can be life-threatening and may require surgery in early infancy.
- Gastrointestinal (GI) defects. GI abnormalities occur in some children with Down syndrome and may include abnormalities of the intestines, oesophagus, trachea and anus. The risk of developing digestive problems, such as GI blockage, heartburn (gastroesophageal reflux) or celiac disease, may be increased.
- Immune disorders. Because of abnormalities in their immune systems, people with Down syndrome are at increased risk of developing autoimmune disorders, some forms of cancer, and infectious diseases, such as pneumonia.
- Sleep apnea. Because of soft tissue and skeletal changes that lead to the obstruction of their airways, children and adults with Down syndrome are at greater risk of obstructive sleep apnea.
- Obesity. People with Down syndrome have a greater tendency to be obese compared with the general population.
- Spinal problems. Some people with Down syndrome may misalign the top two vertebrae in the neck (atlantoaxial instability). This condition puts them at risk of serious injury to the spinal cord from overextension of the neck.
- Leukaemia. Young children with Down syndrome have an increased risk of leukaemia.
- Dementia. People with Down syndrome have a significantly increased risk of dementia — signs and symptoms may begin around age 50. Having Down syndrome also increases the risk of developing Alzheimer’s disease.
- Other problems. Down syndrome may also be associated with other health conditions, including endocrine problems, dental problems, seizures, ear infections, and hearing and vision problems.
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 counsellor before becoming pregnant.
A genetic counsellor can help you understand your chances of having a child with Down syndrome. He or she can also explain the prenatal tests available and help explain the pros and cons of testing.
Screening tests often include a combination of a blood test, which measures the number of various substances in the mother’s blood (e.g., MS-AFP, Triple Screen, Quad-screen), and an ultrasound, which creates a picture of the baby. During an ultrasound, one of the technician’s things is the fluid behind the baby’s neck. Extra fluid in this region could indicate a genetic problem. These screening tests can help determine the baby’s risk of Down syndrome. Rarely, screening tests can give an abnormal result even when there is nothing wrong with the baby. Sometimes, the test results are normal, and yet they miss a problem that does exist.
There are three screening tests for Down syndrome: the combined first-trimester screening, the non-invasive prenatal testing (NIPT), and the second-trimester maternal serum screening.
Combined first-trimester screening
The combined first-trimester screening test is done between 9 weeks and 13 weeks (plus six days) into the pregnancy to calculate the chance of several abnormalities, including Down syndrome. It is safe for both mother and baby.
A computer is used to combine results from 2 tests:
- A blood test, done between 9 and 12 weeks into the pregnancy, looks for hormonal changes that suggest a problem with the baby’s chromosomes.
- An ultrasound scan, done at 12 to 13 weeks into the pregnancy, measures the thickness of fluid behind the baby’s neck, called the nuchal translucency. This is often larger in babies with Down syndrome.
These results, combined with the mother’s age, show the chance of Down syndrome. If the baby is at an increased chance, you will be offered a diagnostic test, which is optional, to confirm whether or not the baby has Down syndrome.
Non-invasive prenatal testing
The non-invasive prenatal test (or NIPT, and sometimes called by brand names such as Harmony or Percept) is a newer, very sensitive form of screening for Down syndrome. It involves a simple blood test that analyses DNA from the baby passed into the mother’s bloodstream. The test is done after ten weeks and is more than 99% accurate for Down syndrome.
Second-trimester maternal serum screening
Second-trimester screening sometimes called a maternal serum screen (MSS) or ‘triple test’, is done between 14 and 18 weeks into the pregnancy. It is usually offered to women who missed the combined first-trimester screening test or if it was not available where they were living.
It involves a blood test to look for hormones that indicate the baby has Down syndrome or a neural tube defect.
If your baby is at an increased chance, you will be offered a diagnostic test, which is optional, to confirm whether or not the baby has Down syndrome.
In addition to the MSS test, most pregnant women have a morphology scan (also known as an anomaly scan) at 18 to 22 weeks into the pregnancy to check on the baby’s growth and to see how the pregnancy is progressing. This can sometimes show signs of Down syndrome.
Diagnostic tests are usually performed after a positive screening test to confirm a Down syndrome diagnosis. Types of diagnostic tests include:
- Chorionic villus sampling (CVS). A needle, guided by ultrasound, is inserted through the mother’s abdomen to take a sample of cells from the placenta. These are tested for missing, extra or abnormal chromosomes. The procedure is done between 11 and 14 weeks of pregnancy. It is not painful and takes about 20 minutes. The risk of miscarriage is less than 1 in 100.
- Amniocentesis. A needle, guided by ultrasound, is inserted into the mother’s abdomen to take a sample of amniotic fluid. This is tested for missing, extra or abnormal chromosomes. This procedure is done between 15 and 18 weeks of pregnancy. It is not painful and takes about 20 minutes. The risk of miscarriage is also less than 1 in 100.
- Percutaneous umbilical blood sampling (PUBS). Percutaneous umbilical cord blood sampling (PUBS) is a diagnostic procedure in which a doctor extracts a sample of fetal blood from the vein in the umbilical cord. This blood can be analysed to detect chromosomal defects or other abnormalities. PUBS is also known as umbilical vein sampling, fetal blood sampling, and cordocentesis.
These tests look for changes in the chromosomes that would indicate a Down syndrome diagnosis.
There is no single, standard treatment for Down syndrome. Treatments are based on each individual’s physical and intellectual needs as well as his or her strengths and limitations. People with Down syndrome can receive proper care while living at home and in the community.
A child with Down syndrome likely will receive care from a team of health professionals, including, but not limited to, physicians, special educators, speech therapists, occupational therapists, physical therapists, and social workers. All professionals who interact with children with Down syndrome should provide stimulation and encouragement.
If you have a question or would like to share your experiences with other readers, you are welcome to join the conversation in the comments section.
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