What causes Edwards syndrome (trisomy 18)?

What causes Edwards syndrome (trisomy 18)?

Having three copies of chromosome 18 instead of the typical two causes Edwards syndrome (trisomy 18).

All humans have 46 chromosomes that divide into 23 pairs. Chromosomes carry your DNA in cells, which tells your body how to form and function as its instruction manual. You receive one set of chromosomes from each of your parents.

When cells form, they start in reproductive organs as one fertilized cell (sperm in males and eggs in females). Cells divide (meiosis) to create pairs by copying themselves. The cell’s copy contains half the amount of DNA as the original cell, 23 chromosomes from 46, and each chromosome pair has a number.

During egg and sperm formation when chromosome pairs are supposed to divide, there’s a chance that a chromosome pair will not divide (as if they are too sticky) and both copies will be included in the egg or sperm. When fertilization happens, those two copies join one from the other parent so the result is three copies in total. The incorrect number of chromosomes is unpredictable and random and isn’t the result of something the parents did before or during pregnancy.

When a third copy of a cell joins a pair, a trisomy occurs. Trisomy means “three bodies.” If someone receives an Edwards syndrome diagnosis, they have a third copy of chromosome 18 in their cells.