Have you ever wondered what causes Down Syndrome? This genetic disorder is caused by an extra 21st chromosome and can affect around 1 in every 700 babies born in the United States. Despite physical, intellectual, and developmental challenges that often come with this condition, those with Down syndrome can lead happy lives if they receive proper care and support. So get ready to dive deep into learning more about this common chromosomal issue.
Types of Down Syndrome
Down syndrome is commonly divided into two distinct categories: Trisomy 21 (nondisjunction) and Translocation/Mosaicism (mutation). In nearly 95% of all cases, nondisjunction takes place when there’s an extra copy of chromosome 21 present in each cell. On the other hand, translocation/mosaicism happens if the additional copy only exists in some cells; otherwise, having a normal count of chromosomes. Whereas more rare circumstances may include supplementing from alternative sources, such as Robertsonian translocation from chromosome 13 or 14 to chromosome 21. All these types have similar characteristics but may vary depending on the type and amount of genetic material present in each individual case.
Who is at Risk for Down syndrome?
Annually, the Centers for Disease Control and Prevention (CDC) illuminates that approximately 6,000 babies are born with Down syndrome in the U.S., representing a chromosomal-based cause of mild to moderate intellectual disability among all racial and economic groups alike.
The cause of the extra full or partial chromosome is still unknown. Scientists around the globe may have identified several factors that may increase the likelihood of a child being born with Down Syndrome. And while there is still no definitive scientific research that indicates that Down syndrome is caused by environmental factors or the parents’ activities before or during pregnancy, some demographic characteristics in the United States appear to particularly raise this risk. These include geographical area, mother’s education level, marital status and Hispanic ethnicity. Furthermore, if either parent or another sibling possesses a chromosomal disorder or has already been born with Down syndrome, this also raises their chances of having an affected baby too.
As women age, the probability of having a baby with Down syndrome increases significantly due to an increased likelihood of extra chromosome 21 in the egg. While women over 35 comprise a small portion of births in America each year, almost half of the babies born with Down syndrome are from this same age group.
Is Down syndrome Screening Necessary?
Prenatal genetic screening offers parents the remarkable opportunity to identify any potential birth defects or severe hereditary risks before their baby is born. Noninvasive testing for Down syndrome has been developed, setting a new standard of accuracy compared with former tests used in past years.
Children with this extra chromosome have mental retardation and physical characteristics of Down syndrome, and about 40 percent will have serious heart problems. Today, screening tests used during pregnancy can determine the risk of having a child with a genetic disorder like Down syndrome as early as ten weeks gestation.
What Screening Tests tell You
Screening tests don’t diagnose the condition but inform parents about the likelihood or chance of having a child with a specific genetic disorder. Screening for Down syndrome can be performed as early as 11 to 14 weeks of pregnancy with a first-trimester ultrasound and blood test. Screening can also be performed between 15 and 20 weeks by a blood test referred to as the multiple marker serum screening test. Some women may elect to use a combination of first and second-trimester screening tests, known as the sequential screen.
These tests, which consider the mother’s age, blood test results, and fetal ultrasound measurements to give an adjusted risk of her having a baby with Down syndrome, are quite helpful. However, they cannot detect every case; their detection rates range from 80-90%.
Who should get a Screening Test?
Every mother during pregnancy can take a screening test for Down syndrome, and whether you decide to have one is entirely up to you. You may want to consider discussing with a genetic counselor if any of the following conditions apply: being at higher risk for delivering a child with trisomy 21 or other chromosomal disorders. Learning more about these risks can help you make an informed decision regarding your health at this special time.
35 or older when they deliver- a previous child or fetus with Down syndrome or a chromosome abnormality
- family history or parent with a chromosomal abnormality
- fetal anomalies detected on ultrasound
Regardless of the type of Down syndrome a person may have, all people with Down syndrome have an extra, critical portion of chromosome 21 present in all or some of their cells. People with Down syndrome can lead full lives if given proper care and support. We hope this blog post has helped you gain a better understanding of what causes down syndrome so you can help provide your loved ones with all they need to live healthy, happy lives!
References:
https://www.pennmedicine.org/updates/blogs/womens-health/2012/august/screening-for-down-syndrome
https://www.nichd.nih.gov/health/topics/down/conditioninfo/Risks#
https://kidshealth.org/en/parents/down-syndrome.html
https://www.webmd.com/children/understanding-down-syndrome-basics
