Healthcare Technology Featured Article

May 21, 2019

Microdeletions: What to Look for in A Non-Invasive Prenatal Test




Prenatal testing is now able to test for many potential chromosomal abnormalities even before the 10th week of pregnancy like certain trisomies, sex chromosome aneuploidies, and microdeletions in a fetus’s DNA. In most cases, a woman’s doctor will recommend non-invasive prenatal testing (NIPT) during her first or second prenatal appointment, which allows for her to plan any additional diagnostic testing necessary before the first trimester is over.

The increasing availability and prevalence of NIPT testing has led to a lot of questions about the potential genetic conditions that can arise in a fetus. Chromosomal abnormalities where a fetus inherits too many chromosomes (like Down syndrome), or extra genes on a chromosome (often associated with autism, heart defects, and more) are widely discussed among parents when starting a family, but microdeletions and their corresponding disorders remain less recognized by parents-to-be.  For example, what exactly is a microdeletion? And why is it important to test for them?

What is a Microdeletion?

Microdeletions are genomic disorders that occur when DNA is lost during the replication process.

Typically, human beings are born with 46 total chromosomes inherited from their parents-- 23 from their mother and 23 from their father. These chromosomes are the instructions for all of the cells in the human body, where they are continuously being copied to create new cells.

If a piece of a chromosome is “deleted,” or missing during the replication process, then it is called a “microdeletion.” Depending on the size and location of a chromosome’s microdeletion, a person will experience different symptoms with varying levels of severity.

Common Microdeletion Syndromes:

When a microdeletion occurs in an individual’s DNA, the individual is considered to have a type of genetic disorder called a microdeletion syndrome. The different kinds of genomic disorders, including microdeletion syndromes, are usually identified by their location on the chromosome and the symptoms experienced by the individual. Some of the most common microdeletion disorders and their symptoms are:

  • DiGeorge syndrome occurs when a portion of the 22nd chromosome is damaged or missing. Individuals with DiGeorge syndrome may be born with a heart murmur, cleft palate, and other problems associated with incomplete development of their internal body systems.
  • Angelman Syndrome occurs when all or a portion of the UBE3A gene on the 15th chromosome is damaged or missing. Individuals with Angelman syndrome may have developmental disabilities, intellectual disabilities, or seizures.
  • Cri-du-chat Syndrome occurs when a portion of the 5th chromosome is damaged or missing. Individuals with cri-du-chat often have developmental disabilities, intellectual disabilities, or smaller-than-average head size.
  • Prader-Willi Syndrome occurs when key portions of the 15th chromosome are damaged or missing. Individuals with Prader-Willi syndrome often experience developmental disabilities, intellectual disabilities, and problems associated with obesity later in life.
  • Jacobsen Syndrome occurs when a portion of the 11th chromosome is damaged or missing. Individuals with Jacobsen syndrome commonly experience development disabilities, intellectual disabilities, behavioral disorders, Paris-Trousseau syndrome, and heart defects.
  • Langer-Giedion Syndrome occurs when a portion of the 8th chromosome is damaged or missing. Individuals with Langer-Giedion syndrome may have bone abnormalities and additional developmental and intellectual disabilities.
  • Wolf-Hirschhorn Syndrome occurs when a portion of the 4th chromosome is damaged or missing. Individuals with Wolf-Hirschorn syndrome may experience developmental disabilities, intellectual disabilities, seizures, a cleft-palate, and a smaller-than-average head size.

Non-Invasive Prenatal Testing

NIPT testing is now able to test for all of the above microdeletion disorders in addition to many other chromosomal abnormalities. Before you meet with your doctor to decide on a non-invasive prenatal test, it’s important to make a list of your testing concerns-- what syndromes are you most interested in testing for, what your insurance plan covers/what you can afford, and any questions you have about the process. Your doctor will be able to better guide you through the options available and their resources.

Find out More

It’s important to keep in mind that most babies are born without chromosomal abnormalities or microdeletions, without any serious chromosomal abnormalities or microdeletions. However, if you have questions about microdeletions, other genetic disorders, or prenatal genetic testing, it’s important to speak to an expert. Your doctor should be able to help answer many of your questions and address any concerns, but they may refer you to a genetic counselor if you have additional genetic testing needs.

SOURCES:

  1. https://www.mayoclinic.org/diseases-conditions/digeorge-syndrome/symptoms-causes/syc-20353543
  2. https://ghr.nlm.nih.gov/condition/angelman-syndrome
  3. https://www.mayoclinic.org/diseases-conditions/angelman-syndrome/symptoms-causes/syc-20355621
  4. https://rarediseases.info.nih.gov/diseases/6213/cri-du-chat-syndrome
  5. https://ghr.nlm.nih.gov/condition/cri-du-chat-syndrome
  6. https://ghr.nlm.nih.gov/condition/prader-willi-syndrome#genes
  7. https://www.pwsausa.org/basic-facts/
  8. https://medlineplus.gov/praderwillisyndrome.html
  9. https://ghr.nlm.nih.gov/condition/jacobsen-syndrome
  10. https://www.healthline.com/health/jacobsen-syndrome
  11. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5006835/
  12. https://www.ncbi.nlm.nih.gov/gtr/conditions/C0023003/
  13. https://rarediseases.org/rare-diseases/trichorhinophalangeal-syndrome-type-ii/
  14. https://ghr.nlm.nih.gov/condition/wolf-hirschhorn-syndrome
  15. https://www.webmd.com/children/wolf-hirschorn-syndrome#1
  16. https://www.uptodate.com/contents/microdeletion-syndromes-chromosomes-1-to-11
  17. https://www.integratedgenetics.com/sites/ig2/files/Rep-1039-v2-0917.pdf
  18. https://www.merckmanuals.com/professional/pediatrics/chromosome-and-gene-anomalies/microdeletion-and-microduplication-syndromes
  19. https://www.whattoexpect.com/pregnancy/microdeletion/







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