Genetic Screening – Answers About Your Genetic Health-image

Genetic Screening – Answers About Your Genetic Health

There are several reasons why you might want to have genetic screening when trying for a baby, and there are a couple of different ways to go about it. Genetic screening can be helpful if you are struggling to get pregnant, or are suffering recurrent miscarriages, or even if you have a genetic condition that runs in your family.  If you know that you have a genetic condition that runs in yours, or your partner’s family, you may want to do genetic screening to prevent passing it onto your children. This can be done by testing yourselves or testing your embryos. Firstly, it is important to understand how the genetics of the condition work to decide on the best way of genetic screening. So, quickly back to the classroom!  The birds and bees… genetics style Chromosomes We all have two sets of genetic material, one inherited from our mum and one from our dad. These sets are called chromosomes, and there are 23 chromosomes in each set. When your eggs are created, only one set of your chromosomes is left in the egg. This is ready to be paired with your partner’s genetic material, found in their sperm, to form the complete genetic makeup of your baby!  Chromosomal conditions Chromosomal disorders come about when there is the wrong number of chromosomes in your cells. This happens when cell divisions go wrong whilst making your eggs or sperm and results in your embryo having an extra chromosome, or a missing chromosome, causing conditions such as Down’s syndrome and Tuner’s syndrome.  There is only a small number of chromosomal abnormalities that are compatible with life, and most embryos with the wrong number of chromosomes will not cause pregnancy or will miscarry. Your risk of having a child with a chromosomal abnormality increase as you get older and your eggs decrease in quality, which is why screening for these conditions is highly recommended in Mum’s-to-be that are over 40.  Genes Now we have to look even closer at our genetics! Each chromosome is made up of thousands of genes, and each gene has different variations of itself, which is called an allele. Our alleles are what give us our traits, such as our eye colour, and makes us who we are! While most of our alleles just make us unique, some can go wrong and cause diseases.  Dominant genetic conditions Some genetic conditions only need one affected gene for the disease to present itself, and so only one of you needs the condition to pass it on your children. These are called dominant genetic diseases and include conditions such as Huntington’s disease and adult polycystic kidney disease. If this is relevant to you, you or your partner will display symptoms of the condition and you have a 50% chance of passing it on to your children. But don’t worry, if the condition runs in your family but you don’t have it, you can’t pass it on to your children either.  Recessive genetic conditions Other genetic conditions can be sneakier and may appear without you even knowing you carry an affected gene. These are called recessive genetic disorders, and they require two affected genes for the disease to present itself. Because of this, both you and your partner either need to have the condition or be a carrier of it to pass it on to your children. Being a carrier means that you have one copy of the affected allele and one healthy allele, and so you either display no symptoms, or only mild symptoms. We are all carriers of hundreds of recessive conditions, which is perfectly normal and will not affect your health in any way. This only becomes an issue when you are having a baby with a person who carries the same disease allele as you, as if you both pass on the affected allele, your baby will have the genetic condition.  Recessive genetic disorders tend to run within specific populations, and so the more genetically similar you and your partner are, the higher your chance of passing on a recessive genetic disorder. Although, this doesn’t mean that you have to be related to pass on a recessive genetic condition! In fact, sharing an ethnicity is enough of a similarity to put you at higher risk. For example, one in 29 Caucasians will carry the cystic fibrosis gene, but this only present in 1 in 90 Asians (Palomaki et al., 2004). Similarly, sickle cell is most prevalent in African American populations and Tay-Sachs is most common in people of eastern or central European Jewish decent. Taking a family history will help the specialists work out which recessive conditions are more at risk of having!  If both of you are carriers of the same recessive genetic condition, you have a 25% chance of having a baby which carries both affected alleles and so is affected by the disease. You will also have a 50% chance of your child being a carrier. If one of you is affected by the condition, and the other is a carrier, you have a 50% chance of passing on the condition, and 50% chance of your child being a carrier.  What are the different types of genetic screening? Genetic Carrier Screening Carrier testing is used to see which alleles you have that can cause a genetic disease to work out your chances of having an affected child. The genetic screening test is most commonly done by taking a blood sample. It can also be done with a saliva sample or from a swab of the inside of your cheek. The sample will be tested in the laboratory and you will be told whether you are positive or negative for the affected gene. If you do carry an affected allele, your partner will also need to be tested to see if they carry the same allele as you, and so if there is a chance you could have an affected child.  There are two types of carrier […]