Testing for Downs

Pre-Birth

To initiate finding out if a child has Trisomy 21, the history of the parents should be collected.  Medscape informs us that the following information should be collected:

When recording the history from the parents of a child with Down syndrome, the clinician should include the following:

• Parental concern about hearing, vision, developmental delay, respiratory infections, and other problems
• Feeding history to ensure adequate caloric intake
• Prenatal diagnosis of Down syndrome
• Vomiting secondary to gastrointestinal tract blockage by duodenal web or atresia
• Absence of stools secondary to Hirschsprung disease
• Delay in cognitive abilities, motor development, language development (specifically expressive skills), and social competence
• Arrhythmia, fainting episodes, palpitations, or chest pain secondary to a heart lesion
• Symptoms of sleep apnea, including snoring, restlessness during sleep, difficulty awaking, daytime somnolence, behavioral changes, and school problems

Once the history is collected, Medscape tells us that there are many physical notifiers that can tell us whether a child has Down Syndrome or not.

On physical examination, patients with trisomy 21 have characteristic craniofacial findings, such as the following:

• Flat occiput and a flattened facial appearance
• Brachycephaly
• Epicanthal folds
• Flat nasal bridge
• Upward-slanting palpebral fissures
• Brushfield spots
• Small nose and small mouth
• Protruding tongue
• Small and dysplastic ears
• Generous nuchal skin
• Diastasis recti
• Single transverse palmar crease
• Short fifth finger with clinodactyly
• A wide space between the first and second toes.

 During pregnancy there are 2 tests that can be done to test the presence of Trisomy 21. One of them is a screening test that looks at the risk of the baby having Down Syndrome, if the risk is high then the parent moves on to the next test, a diagnostic test. The diagnostic test tells you whether the baby has or does not have Down Syndrome. This second test can be done in 2 different ways, known as amniocentesis and chorionic villus sampling.

Amniocentesis tests the fluid around the baby in the pregnant belly. It is mainly performed in order to test for birth defects.

Chorionic villus sampling (CVS) takes samples of chorionic villi (finger-like growths within the placenta) from the placenta for a biopsy test to look for abnormal cells. Did you know that the chorionic villi and fetus cells contain the same genetic material?

Chorionic villus testing usually takes place between the 10th and 12th week of the pregnancy, whereas the amniocentesis tests are usually done between 15 and 20 weeks. Both tests are known to be about 98% accurate, so the results of the test are quite likely to be true. People typically do the CVS test when there is a genetic disorder that runs in their family, this is where family pedigrees come in handy!

You can click here to watch a video of a couple doing a pedigree to find out the likelihood of their child having Down Syndrome. There is a collection of videos with the different processes of the collection of data.

Post-Birth

Once a baby is born, doctors can do a Chromosome Analysis, also known as a Karyotype. This test finds the size, shape, and number of chromosomes in a sample of body cells. They typically will perform this test by drawing blood and testing the cells they pull from that. The performance of a Karyotype test typically occurs when the baby's appearance is abnormal (as stated in the previous blog post). The earlier Down Syndrome is diagnosed, the better the chances are that the child can have a higher quality of life and realize their potential abilities.

There are many programs in place for children with Down Syndrome to participate in activities in order to develop their sensory, motor, and cognitive skills. 

You may ask, "What kind of precautions can be taken to prevent Down Syndrome?" but there are no precautions you can take because it is a genetic disease. You can go to a genetic counsellor to talk about the risks of your baby having down syndrome and the pros and cons of being tested if there is a high concern that your baby may have trisomy of the 21st chromosome.

Trisomy 21 - Down Syndrome

Humans are born with chromosomal pairs, however, did you know that there are some babies born with sets of chromosomes containing 3 instead of just 2? When children have a set of chromosome 21, they are known to have Down Syndrome.

There are different types of Trisomy matches, the number that follows indicates which chromosome has a set of three chromosomes instead of just a pair of chromosomes. In the case of Down Syndrome, the chromosome that is tripled instead of just duplicated is chromosome 21, hence Trisomy 21. (http://www.stanfordchildrens.org/en/topic/default?id=down-syndrome-trisomy-21-90-P02356)

This post will be the first of a set of 3 blogs based on Down Syndrome so that we can learn more about it together. Please ask questions so I can hopefully address it in one of the later blog posts.

People with Down Syndrome generally have similar physical characteristics. The following diagram demonstrates the physical (inside and outside the body) characteristics associated with Trisomy 21. It also shows the chromosomal pairs that we have as humans while highlighting the set of chromosomes that differentiate people who have Down Syndrome from those who do not. Down Syndrome children typically develop slower than their peers who are without the syndrome.

Chromosomes become tripled during reproduction. Usually the father provides 23 single chromosomes and the mother provides the other half to total 23 pairs of chromosomes, 46 individual chromosomes. When Trisomy 21 occurs, the mother or father supply 2 chromosome 21 to pair with the individual chromosome 21 of their partners, thus resulting in 3 copies of chromosome 21. 

The likelihood of parents having a child with down syndrome increases as the mother ages. As demonstrated in the following chart, the frequency of live births of babies with Down Syndrome get significantly more likely each year a mother has a baby past 30 years old.

Age (years)	Frequency of Fetuses with Down Syndrome to Normal Fetuses at 16 weeks of pregnancy	Frequency of Live Births of Babies with Down Syndrome to Normal Births
15 - 19	----	1 / 1250
20 - 24	----	1 / 1400
25 - 29	----	1 / 1100
30 - 31	----	1 / 900
32	----	1 / 750
33	1 / 420	1 / 625
34	1 / 325	1 / 500
35	1 / 250	1 / 350
36	1 / 200	1 / 275
37	1 / 150	1 / 225
38	1 / 120	1 / 175
39	1 / 100	1 / 140
40	1 / 75	1 / 100
41	1 / 60	1 / 85
42	1 / 45	1 / 65
43	1 / 35	1 / 50
44	1 / 30	1 / 40
45 and older	1 / 20	1 / 25

This chart makes me question how many parents terminate their pregnancy, or have still-births, as they gain the knowledge about their Down Syndrome baby. I wonder this because the fetus' with Down Syndrome are more frequent than that of live births of babies with the syndrome. If we look at age 40, the likelihood of having a fetus with Down Syndrome is 1/75, but the births of baby's with Down Syndrome is 1/100. That shows that there are more fetus' with the syndrome than babies. Due to the personal decision of terminating pregnancies it is difficult to find out whether my opinion is correct or incorrect.

Other very informative sites for further information can be found by clicking the following links:

• Stanford Children's Health 
• Understanding Down Syndrome
• Just Like You - Down Syndrome
• WebMD

Keep your eyes open for the next post which will be focusing on the tests that can be done in regards to Down Syndrome. For instance, there is a test that can be done during pregnancy that determines whether their baby may or may not have Trisomy 21.