Chromosome Inversions Information Leaflet - PDF document

Chromosome Inversions Information Leaflet Introduction This leaflet is written for individuals who have a chromosome inversion and for members of their family. It is intended to explain what a chromosome inversion is, what it means for the individual, for their wider family. What are genes and chromosomes? Genes are tiny 'packages' of vital information which influence our growth and development. Each person has approximately 20,000 pairs of genes, which work rather like special computer programmes, and determine features such as the colour of our eyes, how many fingers and toes we have, how tall and short we are, and so on. Genes are so small that they cannot be seen, even under a powerful microscope. They are arranged along little threadlike strands, rather like the way that beads are arranged along a string. These strands are called chromosomes, and are inside most of the cells in our body. Unlike genes, chromosomes can be seen under a microscope. A person usually has 46 chromosomes in each cell, arranged in 23 pairs. We inherit one of each pair of chromosomes from our mother and the other from our father. This is how we inherit characteristics from our parents. To help differentiate between chromosomes, each pair has been given a number. The number 1 chromosomes are the largest, the number two are the next largest and so on right down to the number 22 which are the smallest. The remaining pair (X and Y) are called the sex chromosomes and determine person is male (XY) or female (XX). What are chromosome inversions? Occasionally a chromosome will break in two places and the piece which is broken rejoins UP SIDE DOWN. Therefore, a person with a chromosome inversion will have one ‘normal’ chromosome and a chromosome with an inversion where the genes are in a different order compared to the other chromosome. People who have a chromosome inversion have no extra or missing genes and are expected to develop normally as it does not really matter which order the genes are in as long as they are all present. If a person has a chromosome inversion it can, however, cause problems when the individual comes to have children. Each person passes on half of their chromosomes to their children. At conception an egg (with 23 chromosomes) joins with a sperm (also with 23 chromosomes) to make an embryo. Usually, before each chromosome pair splits up to make and egg or sperm they line up closely together and sometimes exchange genes in a process called a crossover. To enable each of the genes to pair up with its partner on the opposite chromosome, one chromosome needs to form a loop. If there is a crossover between the chromosomes within the loop

, an imbalance in the number of genes will occur. Therefore, when chromosomes pair up before separating into an egg or sperm one of three things might happen: 1 - The parent with an inversion passes their ‘normal’ chromosome into the egg or sperm, so the baby will have the correct number of genes in the correct order. 2 - The parent with the inversion passes their chromosome with the piece which is inverted into the egg or sperm. The baby will inherit the inverted chromosome; however, as the correct amount of genetic material will be present the baby will not have any learning or developmental issues due to their parents chromosome inversion. 3 - If a loop and crossover has occurred whilst the egg or sperm were being formed, a baby could inherit a chromosome which is carrying an incorrect number of genes. This may result in an early miscarriage or problems with infertility. A child who has inherited either too much or too little genetic material will usually have physical and/or learning difficulties.
If we know a parent carries a chromosome inversion there are tests are available in pregnancy that enable us to check the chromosome pattern of the developing baby to determine if it is carrying the correct amount of genetic information. These tests are called amniocentesis and chronic villus sampling (CVS) and there are separate leaflets available which explains these tests in more detail. Some couples may be eligible for preimplantation genetic diagnosis (PGD). PGD involves checking the chromosomes of embryos created through IVF. Only embryos with the correct amount of genetic material are transferred into the womb with the hope it develops into a baby. How can someone find out if they carry a chromosome inversion? If you are aware someone in your family carriers a chromosome inversion you can request a referral into your local genetic service via your GP. Your genetic counsellor will arrange a blood test to look at your chromosome pattern If you need more advice about any aspect of chromosome inversions, you are welcome to contact: Cheshire and Merseyside Clinical Genetics Service Liverpool Women’s Hospital Crown Street L8 7SS Telephone 0151 802 5001 or 5002 Facsimile: 0151 702 4286 This leaflet can be made available in difference formats on request. If you would like to make any suggestions or comments about the content of this leaflet, then please contact the Patient Experience Team on 0151 702 4353 or by email at pals@lwh.nhs.uk Liverpool Women’s NHS Foundation Trust Crown Street Liverpool L8 7SS Tel: 0151 708 9988 Ref:Cli_2018-24 Issue Date: 01/05/2017 Review Date: 01/05/2020 © Liverpool Women’s NHS Foundation Trus