Down Syndrome

1 What is Down Syndrome?

Down syndrome is a genetic disorder in which abnormal cell division leads to extra genetic material from chromosome 21.

This disorder leads to lifelong intellectual disability and dvelopmental delays and can cause health problems in some people.

It is one of the most common genetic disorder and may cause children to have learning disabilities.

The quality of life for people with Down syndrome can be improved by better understanding of this disorder and early inteventions.

2 Symptoms

The signs and symptoms of Down syndrome vary from individual to individual. Intellectual and developmental problems range from mild to severe. Some people may be healthy while others may have severe health problems such serious heart defects.

Children with Down syndrome have a distinct facial appearance. These may include:

  • Flattened facial features
  • Small head
  • Short neck
  • Protruding tongue
  • Upward slanting eyes, unusual for the child's ethnic group
  • 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 iris called Brushfield spots
  • Short height

Children with Down syndrome tend to grow slowly and may remain shorter than children of the same age, although they may have an average size. Developmental milestones, such as sitting and crawling, occur at about twice the age of children without impairment.

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3 Causes

Down syndrome is caused by abnormal cell division involving chromosome 21. Human cells normally contain 23 pairs of chromosomes. One chromosome in each pair comes from each parent. 

This leads to extra genetic material from chromosome 21. This extra chromosome is responsible for the characteristic features and developmental problems associated with Down syndrome.

Any one of three genetic variations can cause Down syndrome:

Trisomy 21

Occurs in  about 95 percent of cases of Down syndrome. It occurs when  the child 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

Is rare form of Down syndrome,  in which children have 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

Occurs when part of chromosome 21 becomes attached (translocated) onto another chromosome, before or at conception. Children with this type of Down syndrome have the usual two copies of chromosome 21, but they also have additional material from chromosome 21 attached to the translocated chromosome.

There are no known behavioral or environmental factors that cause Down syndrome. Most of the time, Down syndrome isn't inherited. It's caused by a mistake in cell division during the development of the egg, sperm or embryo.

Translocation Down syndrome is the only form of the disorder that can be inherited. However, only about 4 percent of children with Down syndrome have translocation. And only about one-third of these children inherited it from one of their parents. When translocations are inherited, the mother or father has some rearranged genetic material, but no extra genetic material — this means he or she is a balanced carrier.

A balanced carrier has no signs or symptoms of Down syndrome, but he or she can pass the translocation on to children, causing extra genetic material from chromosome 21. The chance of passing on the translocation depends on the sex of the parent who carries the rearranged chromosome 21. If the father is the carrier, the risk is about 3 percent. If the mother is the carrier, the risk is between 10 and 15 percent.

4 Making a Diagnosis

The American College of Obstetricians and Gynecologists recommends offering the option of screening tests and diagnostic tests for Down syndrome to all pregnant women.

Screening tests can indicate the likelihood a mother is carrying a baby with Down syndrome. Diagnostic tests can identify whether a baby has Down syndrome.

Screening tests for Down syndrome during pregnancy are offered as a routine part of prenatal care. Although screening tests aren't perfect, they can help a doctor to make decisions about more-specific diagnostic tests and the course of the pregnancy.

Various screening tests can help identify whether a woman has a high risk of carrying a baby with Down syndrome, but they can't identify whether the baby has Down syndrome.

Screening tests include

  • the first trimester combined test,
  • the integrated screening test
  • the cell-free fetal DNA analysis.

The first trimester combined test, which is done in two steps, includes:

1) Blood test

This blood test measures the levels of pregnancy-associated plasma protein-A (PAPP-A) and the pregnancy hormone known as human chorionic gonadotropin (HCG). Abnormal levels of PAPP-A and HCG may indicate a problem with the baby.

2) Ultrasound

Ultrasound is used to measure a specific area on the back of  the baby's neck. This is known as a nuchal translucency screening test. When abnormalities are present, more fluid than usual tends to collect in this neck tissue. Using the woman's age and the results of the blood test and the ultrasound, doctors can estimate the risk of having a baby with Down syndrome.

The integrated screening test is done in two parts during the first and second trimesters of pregnancy. The results are combined to estimate the risk that the baby has Down syndrome. This test can achieve the same level of detection as the first trimester combined test but with a lower false-positive rate, meaning that fewer women are incorrectly identified as carrying a baby with Down syndrome.

First trimester

Part one includes a blood test to measure PAPP-A and an ultrasound to measure nuchal translucency.

Second trimester

The quad screen measures the blood level of four pregnancy-associated substances: alpha fetoprotein, estriol, HCG and inhibin A. Cell-free fetal DNA analysis The cell-free fetal DNA test checks for fetal DNA circulating in the mother's blood. This test is usually recommended for women who have a higher risk of having a baby with Down syndrome or in response to risk detected by one of the previous tests.

The mother's blood can be tested during pregnancy after 10 weeks gestation. This test appears to be much more specific than other screening methods for Down syndrome. If this screening test indicates a high risk of Down syndrome, a more invasive diagnostic test may be used to determine whether  the  baby actually has Down syndrome.

Diagnostic tests during pregnancy

If the screening test results are positive or worrisome, or  a woman is at high risk of having a baby with Down syndrome, more tests might be needed to confirm the diagnosis. Diagnostic tests that can identify Down syndrome include:

Amniocentesis

A sample of the amniotic fluid surrounding the fetus is withdrawn through a needle inserted into the mother's uterus. This sample is then used to analyze the chromosomes of the fetus. Doctors usually perform this test in the second trimester, after 15 weeks of pregnancy. The test carries a slight risk of miscarriage, but risk increases if it's done before 15 weeks.

Chorionic villus sampling (CVS).

In CVS, cells are taken from the placenta and used to analyze the fetal chromosomes. Typically performed in the first trimester, after 10 weeks of pregnancy, this test appears to carry a somewhat higher risk of miscarriage than second trimester amniocentesis.

Cordocentesis

In this test, also known as percutaneous umbilical blood sampling or PUBS, fetal blood is taken from a vein in the umbilical cord and examined for chromosomal defects. Doctors can perform this test between 18 and 22 weeks of pregnancy. This test carries a significantly greater risk of miscarriage than does amniocentesis or CVS, so it's only offered when results of other tests are unclear and the desired information can't be obtained any other way.

Preimplantation genetic diagnosis is one option available for couples undergoing in vitro fertilization who are at increased risk of passing along certain genetic conditions.

The embryo is tested for genetic abnormalities before it is implanted in the womb. Diagnostic tests for newborns After birth, the initial diagnosis of Down syndrome is often based on the baby's appearance. But the features associated with Down syndrome can be found in babies without Down syndrome, therefore a doctor may order a test called a chromosomal karyotype. Using a sample of blood, this test analyzes a child's chromosomes. If there's an extra chromosome 21 present in all or some cells, the diagnosis is Down syndrome.

5 Treatment

When it comes to Down Syndrome, early intervention makes for the best possible treatment outcomes.

Early intervention for infants and children with Down syndrome can make a major difference in realizing their potential abilities and in their quality of life.

These programs offer children with Down syndrome stimulation at an early age with appropriate sensory, motor and cognitive activities.

Programs may vary, but they usually involve therapists and special educators whose goal is to help a baby develop

  • motor skills,
  • language,
  • social skills
  • self-help skills.

6 Prevention

There is no prevention for Down syndrome. Women who have a history of having a child with Down syndrome should consult a genetic specialist before becoming pregnant.

A genetic specialist may help a woman to understand the chances of having another child with Down syndrome.

7 Lifestyle and Coping

Lifestyle modifications are necessary for your children in order to cope with Down syndrome.

Having a child with Down syndrome can trigger a lot of emotions such as

  • anger,
  • fear,
  • worry,
  • sorrow
  • guilt.

Fear and worry can be overcome by knowing more about this disorder and by joining a support group.  Having a team of trusted professionals which may include health care providers, teachers and therapist can be beneficial for a child with Down syndrome.

It is important to expect a bright future since people with Down syndrome are capable of living fulfilling lives.

8 Risks and Complications

There are several risks and complications associated with Down syndrome.

Factors that may increase the risk of having a child with Down syndrome include:

  • Advancing maternal age. A woman's chances of giving birth to a child increases with age because older eggs have a risk of abnormal chromosome division. At 35 the risk of having a child with Down syndrome is 1 to 350, at 40 it is 1 to 100 and at 45 it is 1 gto 30. However children with Down syndrome may also be born to women younger than 35.
  • A history of having a child with  Down syndrome.
  • Being a carrier of the genetic translocation for Down syndrome.

Children with Down syndrome can have several health complications which tend to get worse with age.

Complications include:

  • Heart defects
  • Leukemia
  • Predisposition to infections due to a poor immune system
  • Dementia- the signs and symptoms usually occur after the age of 50
  • Sleep apnea due to obstruction of the airways as a result of soft tissue and skeletal changes
  • Obesity in future
  • Other health problems, such as:

The life expectancy of people with Down syndrome is 60 and above depending on the severity of health problems.

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