A translocation is the term used to describe a rearrangement of chromosome material between two or more chromosomes. There are two main types of translocations; reciprocal and Robertsonian translocations. In this blog piece, I will discuss reciprocal translocations.
In each of our body cells (excluding our egg or sperm cells) inside the nucleus we have 23 pairs of chromosomes. They are numbered 1 to 22 in descending order of size and the remaining pair of chromosomes are our sex chromosomes; XX for females and XY for males. A reciprocal translocation is where part of one chromosome breaks and exchanges with part of another chromosome, which has also broken off. Said another way, two chromosomes break and these broken pieces swap and join back together. When no genetic material is lost, this is said to be a balanced reciprocal translocation. Reciprocal translocations can involve any of the chromosomes.
Carriers of a balanced reciprocal translocation may not even be aware that they are carrying a chromosomal anomaly. Depending on the location of the break, if no interruption of the genetic information in the DNA code occurs, a carrier of a balanced translocation will have no symptoms and will not affect their development or health. However occasionally where the chromosomes break, if this is in the middle of an important gene, for example, the person may have some associated health issues. Most translocations are spontaneous, meaning, they occurred in the egg or the sperm that went on to create a person. However sometimes translocations can be inherited.
Balanced reciprocal translocation carriers are at risk of having chromosomes in their eggs or sperm with genetic material gained or lost and this could result in a pregnancy that has an unbalanced reciprocal translocation. Having extra or missing bits of chromosome can cause a wide variety of health problems including mild to severe health problems and developmental delay.
If someone is at risk of being a carrier of a balanced reciprocal translocation, they can have a genetic test examining their chromosomes. This test is called a karyotype and the scientists in the laboratory will be able to see if and where a translocation has occurred. A more detailed chromosome test called a microarray may also be ordered to see exactly where the breakpoints are and to see if any genetic material has been added or lost.
When a partner in a couple has a balanced translocation they may experience infertility or recurrent miscarriages. In some cases it may be possible to have Non Invasive Prenatal Testing (NIPT), which is a blood test on the pregnant mother from 10 weeks gestation, to see if the pregnancy has a translocation. In some cases NIPT is not possible. If this is the case, an invasive test during the pregnancy such as a chorionic villus sampling (CVS) or amniocentesis may be performed to examine the baby’s chromosomes.
Couples presenting for genetic counselling due to a reciprocal translocation can be challenging from a psychosocial point of view as well. Having long periods of infertility or miscarriage after miscarriage can be very taxing on couples. IVF is one technique that couples can utilize to increase their chances of having a baby. Other options would include donor egg, sperm or embryos or adoption.