The Basics of Genetic Testing
We are all the products of the genes we inherited from our parents and our many ancestors. We will pass those same genes on to our children. It is amazing with how complex our genetics are that most of the time billions of things work smoothly to create perfect babies.
Our bodies are made up of billions of cells. Within each cell is a nucleus, where our genetic material is stored. Within the nucleus there are chromosomes. Chromosomes are large packages of our genetic information. We should all have 46 chromosomes, we get 22 chromosomes and the sex chromosome X from Mom, and 22 chromosomes and either an X (girl) or Y (boy) from Dad.
When we count the number of chromosomes each person has, this is called a karyotype. Within each of these chromosome, there are genes. These are the discrete packages of information that tell our bodies how to grow and develop. Our DNA is the alphabet that actually makes up each of our genes.
You can use the encyclopedia analogy to consider the types of genetic material. All of your genetic material makes an encyclopedia set; each chromosome is like a book in that encyclopedia, so if one is missing or extra, it affects the completeness of your set. Within each book are chapters, which are like the genes. And the DNA is like the words that make up the chapters.
There are a number of reasons we may recommend genetic testing if you are planning to conceive or undergoing a fertility treatment.
Genetic screening- Many of us carry defective genes that can cause genetic diseases such as cystic fibrosis or sickle cell anemia. Luckily for most genetic diseases you have to have two abnormal genes (one from Mom and one from Dad) to have the genetic disease. This type of disease transmission is called autosomal recessive.
Most of us will carry one or more autosomal recessive gene mutations in our DNA. There are blood and saliva testing for these gene mutations. We recommend testing for the most common recessive genes such as cystic fibrosis, spinal muscular atrophy, and sickle cell anemia. Certain populations have higher rates of specific mutations so talk to your doctor about your race and ethnic heritage. If you have a common gene mutation we can then test your spouse to see if he or she also has that mutation.
Balanced translocation– Some men and women they have a chromosome that sticks to another chromosome. When the chromosomes line up to as the egg or sperm cells divide the double chromosome goes to one side or the other resulting in an egg or sperm with too many chromosomes, too few chromosomes, a normal number of chromosomes, or a balanced translocation carrier.
When someone has a balanced translocation they have high rates of miscarriages as their embryos often have too many or few chromosomes. If you go through IVF, we can biopsy the embryos and find out which embryos have a normal number or balanced translocation of embryos. These embryos can then be transferred which will drastically reduce the chance you will have a miscarriage.
Pre-implantation Genetic Diagnosis- If you have had a child with a previous genetic disease such as cystic fibrois or we know from genetic screening that both you and your partner are carriers for a recessive gene such as sickle cell anemia, then we can do pre-implantation genetic screening (PGS) to see which of your embryos carry the disease.
To do PGS we must do in vitro fertilization to make embryos and then the embryos are biopsied in the laboratory to check their DNA. Once we have the results of the DNA back, we can transfer the embryos that do not have the disease.