What are translocations/chromosome rearrangements?

Translocation is a chromosome abnormality. It happens when a piece of a chromosome breaks off and reattaches to another chromosome. A balanced translocation means two pieces of chromosomes have switched places. Translocations can be harmless or they can cause serious health problems, depending on which sections of chromosomes get interchanged.

Many people have translocations and are not aware of this, because they have not had health issues. However, their egg or sperm cells can end up with extra genetic material or missing genetic material when the egg is fertilized by the sperm and starts to divide. In about four and a half percent of people with recurrent miscarriage, one or both partners have balanced translocations. Research has found that people with translocations are more likely to have miscarriages. A blood test known as a karyotype is used to detect whether either or both partners are carriers of translocations.

Many couples with recurrent miscarriage will eventually have a baby, but they will endure the emotional and physical pain of miscarriage a number of times before being successful. In some cases, couples can have IVF treatment with preimplantation genetic screening (PGS) to improve their chances of having a healthy baby. In IVF with PGS, the woman’s eggs are fertilized with the male partner’s sperm in the laboratory. The embryos are then tested to be sure they do not have an unbalanced translocation, known as aneuploidy, with too many or too few chromosomes. Only the healthiest embryos are then transferred to the woman’s uterus or frozen for use in the future.

Testing for translocations with PGS can increase your success rate at IVF by as much as 23 percent because healthier embryos are less likely to be miscarried. PGS can also detect Down syndrome, which is caused by an embryo having three copies of chromosome 21 instead of two, called trisomy 21. In most cases of Down syndrome trisomy 21 occurs spontaneously and is not due to translocation. In a few cases, down syndrome happens when part of chromosome 21 becomes translocated to another chromosome in the parent’s egg or sperm cells or very early in fetal development.