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Thursday, November 20, 2014
Inherited Disorders and Birth Defects
A friend of my had a miscarriage last year. She went to the Doctors to get some blood work done. Result was she has Balanced Translocation (46,XX,t(15;19)(q21;p13.3). Will she be able to have a healthy baby.
Chromosomal translocations can be somewhat tricky to understand. A balanced translocation occurs when two pieces of chromosomes break off and switch places with each other. If all the chromosomal material is present, just rearranged – that is, switched places (translocated) - this person should have no health problems since all the chromosomal material needed is present and functioning properly. This is called a balanced translocation. There is no way to tell whether or not a person has one of these rearrangements unless you look at his or her blood to examine the chromosomes - such as the case for your friend.
However, there can be problems if some of the chromosomal material that was switched is lost or duplicated when the chromosomes broke and the switch took place – then there is extra and / or missing information that can lead to birth defects and cognitive problems such as mental retardation. This is an unbalanced translocation.
The chance of having an egg that has the unbalanced translocation vs. the normal or balanced rearrangement depends on how the chromosomes line up, divide and segregate – that is how the chromosomes divide into two daughter cells. In theory, there is a 25% chance that the gametes (eggs or sperm) that the mom or dad produces – will have a normal chromosome complement, a 25% chance that the egg or sperm will have the balanced translocation and a 50% chance that the egg or sperm would produce an unbalanced chromosome complement. Usually the eggs or sperm that produce an unbalanced complement are miscarried because they are not viable (capable of producing a live born child). So most of the time, a woman who is a carrier of a balanced chromosomal translocation will have children with normal chromosomes or will miscarry.
While most pregnancies that have an unbalanced chromosomal rearrangement are miscarried, of those that make it to term - the abnormalities seen range from mild to severe. If the abnormalities are severe, there is a greater chance that the child may die in infancy or early childhood. Life span is usually shortened in children with chromosome abnormalities, but not always. Mental retardation is almost always a part of the picture for children with chromosome abnormalities.
If she as not already done so, I would suggest that your friend speak to the genetic counselor or a geneticist to discuss the specific chromosomal translocation that she has.
Anne Matthews, RN, PhD
Associate Professor of Genetics
School of Medicine
Case Western Reserve University