What are genes and chromosomes?
The human body is made up of billions of cells. A person usually has 46 chromosomes in each cell (arranged in 23 pairs). A pair of chromosomes that are basically identical in structure are called homologous chromosomes. One of each pair of chromosomes is inherited from the mother, and one from the father. Most chromosomes carry hundreds to thousands of genes that provide instructions to determine an individual's physical traits and help the body to grow and function properly. It is important to have the correct amount of chromosomal material for normal development.
What is reciprocal translocation?
Chromosome translocation is an unusual arrangement of the chromosomes in the cell. Reciprocal translocation is an exchange of genetic material between the two non-homologous chromosomes, where parts of two chromosomes have broken off and 'swapped' places to produce the new chromosomal arrangement. It can occur in any chromosome randomly and with an equal chance. About 1 in 500 people has a reciprocal translocation.
Most people with a reciprocal translocation have the correct amount of genetic material but it is arranged in an unusual pattern. If the chromosome material has been rearranged with no loss or gain, it is known as a balanced reciprocal translocation.
The picture below shows how a balanced reciprocal translocation happens: A piece of chromosome A has swapped with chromosome B
Does a reciprocal translocation affect health?
People who carry the chromosome with balanced reciprocal translocation (a carrier) usually have no health or developmental problems, but it may become important when they come to have children as there is a possibility a fetus/baby can inherit an unbalanced translocation with missing or extra genetic material. An unbalanced translocation may end in miscarriage or the birth of a child with congenital abnormalities and/or learning difficulties.
Can a balanced reciprocal translocation carrier have children?
Although the carrier of balanced reciprocal translocation has an increased risk for infertility, recurrent miscarriages, or having children with congenital abnormalities, most men and women with a balanced reciprocal translocation can have children. There are usually four possible outcomes if one parent is a carrier of balanced reciprocal translocation:
Gene Map of Reciprocal Translocation:
A balanced reciprocal Translocation carrier will produce either normal or abnormal gametes. If one of the parent is balanced reciprocal Translocation carrier, for each pregnancy, it may produce an offspring who
How to detect chromosome translocations?
Chromosome translocations can be detected by a genetic test called karyotyping. It is a simple test that examines the chromosomes inside the cells from the blood or other specimens (like amniotic fluid) to look at any unusual chromosomal arrangement. The test can be performed to detect the karyotype of an individual or fetus.
Balanced reciprocal translocation carriers do not have any physical signs or symptoms, so most of the carriers are unaware of their conditions until parental karyotyping or karyotyping of either aborted fetus or affected newborn is performed. Because balanced reciprocal translocation carriers are at higher risk of recurrent miscarriage, therefore, karyotyping is recommended for couples who have had three or more pregnancy losses to detect whether they are carriers of balanced reciprocal translocation.
What can be done if you have a balanced reciprocal translocation?
Although a balanced reciprocal translocation cannot be corrected and does NOT affect the health of the carriers, genetic counselling is recommended for the carriers when planning for a pregnancy. The results of genetic testing may help to clarify the risks and the options for the next pregnancy.
Depending on the genetic test results, the couples may consider:
Should I tell other family members if I am a carrier?
As reciprocal translocation is a genetic condition, other family members may have inherited the same condition. They may benefit from knowing whether they have a balanced reciprocal translocation, particularly if they are likely to have children in the future. In this instance, it is recommended for them to seek medical advice from healthcare professionals.
For further enquires, you may contact us.
Department of Clinical Genetics
Address: Specialist Outpatient Clinic, 1/F, Tower B, Hong Kong Children's Hospital, 1 Shing Cheong Road, Kowloon Bay, Kowloon, Hong Kong
Office Tel: 5741 3186
DCG - Reciprocal Translocation
JUNE 2024