RMACT strives to bring awareness to various causes in the hopes to help educate and inform the community. Since March is Trisomy Awareness Month, we thought it would be a wonderful opportunity to have our very own geneticist, Jamie Speer, MS, shed some light on these conditions. Here, he provides insight into four of the most frequently asked questions he encounters on a daily basis about trisomies.
1. What Is Trisomy?
Trisomy refers to a condition where there is an extra chromosome, or an extra piece of a chromosome, in some or all cells of a person. Most commonly, people have 46 chromosomes, with 23 coming from the egg and 23 from the sperm. Those with a trisomy have 47 chromosomes instead of the typical 46.
2. How Do Trisomies Occur?
Most cases of trisomy are random or sporadic, occurring without any known family history. When the cells divide, sometimes an extra chromosome will result in an egg or sperm cell. There is an association with increasing age of the mother, but pregnancies with trisomies can occur at any age, and the extra chromosome can come from either the mother or the father. There are rare cases of trisomies which result from a parent having a rearrangement of their chromosomes, called a translocation, but this makes up a very small percentage.
3. What Are The Most Common Forms Of Trisomy?
Trisomy can occur with any of the 23 chromosomes, but only a very small number of them are seen in live-born babies, as most trisomies are associated with early pregnancy loss.
- Trisomy 21, more commonly known as Down syndrome, occurs in around 1 in 700 births. People with Down syndrome often have some characteristic facial differences, mild-to-moderate intellectual and developmental disability, and increased chances for other issues, including congenital heart problems.
- Trisomy 18, also known as Edward syndrome, occurs in around 1 in 5,000 births. Babies with Trisomy 18 often have serious birth defects of the heart and other organs, and their developmental disability tends to be more pronounced than what is seen with Down syndrome. Unfortunately, many babies with Trisomy 18 do not survive past their first birthday.
- Trisomy 13, also known as Patau syndrome, occurs in around 1 in 10,000 births. Babies with this condition also typically have serious birth defects, developmental disabilities, and increased chance of not surviving past the first year.
Some trisomies occur as “mosaics,” which means that there is a mixture of cells in the person, some with the typical number of chromosomes, and some with extra chromosomes. Some other trisomies result from certain sections of the chromosome being present in three copies, rather than three whole copies of the chromosome. The issues vary with the different types, but most have increased chances for physical birth defects and developmental disabilities.
4. Can Trisomies Be Detected Before Birth?
There are ways to look for the presence of trisomies before birth. For those couples pursuing in-vitro fertilization at a fertility clinic, Pre-Implantation Genetic Screening (PGS) is a test which can screen the chromosomes of embryos before they are transferred into the woman’s uterus.
There are also tests which can be considered during pregnancy, including amniocentesis and chorionic villi sampling (CVS). In addition, there are some blood tests which can screen for certain chromosome conditions early in pregnancy.
For more information on trisomies or if you are interested in speaking with Jamie, please call (203) 956-2265 to schedule an appointment.