Since learning I’m a balanced carrier, I’ve met with several genetics counselors to talk about what it all means. This is my layman’s explanation – always speak with a genetic counselor when you have questions about your specific karyotype and situation. Here’s a link to the website shared with me when I first learned I am a balanced carrier.
Translocation Down syndrome represents about 4% of all instances of Down syndrome. Most of the time, that translocation is random. Sometimes, the translocated chromosome is passed down from a parent who is known as a “balanced carrier.”
Typically, human beings have 46 chromosomes arranged in 23 pairs. (22 pairs of chromosomes and two sex chromosomes)
A balanced carrier has one “single” chromosome 21, and the other 21 is attached to another chromosome. In my examples here, I’ll be using my own karyotype: my 21st chromosome is attached to one of my 14th chromosomes. A carrier still has just two of each chromosome so there are no side effects other than what happens when a carrier conceives.
A balanced carrier can produce 6 types of eggs (or sperm – men can be carriers, too) which results in 6 possible combinations at conception.
It is possible for a balanced carrier to have a child with typical chromosomes, a child who is a carrier like themselves, or a child who has translocation Down syndrome. The other possible combinations are considered incompatible with life. (Trisomy 14, Monosomy 14, and Monosomy 21) Because of this, female carriers often have a higher rate of miscarriage than the typical population.
Learning that you are a balanced carrier may come as a surprise, and you might have unexpected feelings surrounding this news. Everything you are feeling is normal. It’s another thing to process as you learn more about Down syndrome itself.
Welcome to the family!